canon rumors FORUM

Gear Talk => Lenses => Topic started by: carlc on June 02, 2012, 08:34:03 PM

Title: Can a UV filter affect IQ (sharpness) on a lens?
Post by: carlc on June 02, 2012, 08:34:03 PM
Using a 7D, ef-s 17-55mm and a Hoya HMC SUPER UV(0) and without the filter my results seem more precise at the intended focus point (usually center spot).  I don't understand and I have never experienced this before.  I have used this filter on my 70-200 f2.8 MkII and never noticed any loss in IQ.

Is this an issue with the 17-55 lens?  I just purchased this lens 30 days ago and without the filter the lens performs flawlessly and I love the results.  At first I thought I might have a slight front focus issue and then I tried the lens without the filter, bingo, much better.

Thanks for any help or suggestions.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: pdirestajr on June 02, 2012, 10:44:36 PM
So then why not just keep the "filter" off? All it really offers is protection- so instead, you can always just add a lens hood for protection... Unless you are in an extreme environment, or running through the woods where a branch can jump out and attack your lens, you should be fine.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Random Orbits on June 02, 2012, 11:24:59 PM
Used a Canon and a B+W filter on my 17-55 and never had an issue with either of them.  I'd suggest trying another filter brand (at a camera store or a friend's) just to see if it is a lens issue or not.  Tolerance stack ups vary from lens to lens, so yours might be more sensitive naturally to filter variation.  Another consideration is that longer lenses have longer focal lengths which may lessen the impact of bad filter.  There are many videos showing that lenses with slightly damaged front elements don't perform noticeably different than those with perfect front elements.  However, at the shortest focal lengths (i.e. fisheyes), dirt on the front element can be visible.  You might be able to test this hypothesis by seeing if the image IQ hit is worse at the wide end than the tele end, but in any case, I'd suggest trying another filter.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Tcapp on June 02, 2012, 11:34:46 PM
Used a Canon and a B+W filter on my 17-55 and never had an issue with either of them.  I'd suggest trying another filter brand (at a camera store or a friend's) just to see if it is a lens issue or not.  Tolerance stack ups vary from lens to lens, so yours might be more sensitive naturally to filter variation.  Another consideration is that longer lenses have longer focal lengths which may lessen the impact of bad filter.  There are many videos showing that lenses with slightly damaged front elements don't perform noticeably different than those with perfect front elements.  However, at the shortest focal lengths (i.e. fisheyes), dirt on the front element can be visible.  You might be able to test this hypothesis by seeing if the image IQ hit is worse at the wide end than the tele end, but in any case, I'd suggest trying another filter.

+1.

Whenever you use a filter, it is going to affect you image quality. Fact of life. I keep filters on most of my lenses, unless it has a recessed front element like the 50 1.4. I like not having to worry about fussing with lens caps when i need to switch lenses real fast at a wedding. UV filters let me not worry about it.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Dylan777 on June 03, 2012, 03:29:02 AM

Not when you use this filter:

http://www.bhphotovideo.com/c/product/756818-REG/B_W_66_1066111_77mm_XS_Pro_NANO_Clear.html

All my lenses are protected by B&W Clear...no problem at all
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Quasimodo on June 03, 2012, 04:14:17 AM

[/quote]

+1.

Whenever you use a filter, it is going to affect you image quality. Fact of life. I keep filters on most of my lenses, unless it has a recessed front element like the 50 1.4. I like not having to worry about fussing with lens caps when i need to switch lenses real fast at a wedding. UV filters let me not worry about it.
[/quote]

What do you mean with a recessed front element? Also, I have always used a Kenko Pro 1 W filter on my 50 1.4, and have never had any issues. Are you saying that the IQ will be better if I remove it? (so far I have had nothing but good thing to say about this particular lens).
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Tcapp on June 03, 2012, 04:24:59 AM


+1.

Whenever you use a filter, it is going to affect you image quality. Fact of life. I keep filters on most of my lenses, unless it has a recessed front element like the 50 1.4. I like not having to worry about fussing with lens caps when i need to switch lenses real fast at a wedding. UV filters let me not worry about it.
[/quote]


What do you mean with a recessed front element? Also, I have always used a Kenko Pro 1 W filter on my 50 1.4, and have never had any issues. Are you saying that the IQ will be better if I remove it? (so far I have had nothing but good thing to say about this particular lens).
[/quote]

Good quality filters will have a very small effect on IQ. But one danger of filters is creating reflections from certain light sources. Example:
http://www.flickr.com/photos/chris28mm/4446223418/# (http://www.flickr.com/photos/chris28mm/4446223418/#)


When I say recessed front element, i mean that the front lens is set back in the lens, rather than flush with the filter thread. Example of recessed: http://i468.photobucket.com/albums/rr48/bullitt411/Siggy%2010-20/Tokina/DED_3739.jpg (http://i468.photobucket.com/albums/rr48/bullitt411/Siggy%2010-20/Tokina/DED_3739.jpg)

Not recessed: http://www.yacart.com/blog/wp-content/uploads/2011/12/canon_ef_70_200mm_f2.8_l_is_usm_lens.jpg (http://www.yacart.com/blog/wp-content/uploads/2011/12/canon_ef_70_200mm_f2.8_l_is_usm_lens.jpg)


When the lens element is set farther back in the body of the lens, it is more protected and unlikely to be damaged.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Quasimodo on June 03, 2012, 04:52:48 AM


+1.

Whenever you use a filter, it is going to affect you image quality. Fact of life. I keep filters on most of my lenses, unless it has a recessed front element like the 50 1.4. I like not having to worry about fussing with lens caps when i need to switch lenses real fast at a wedding. UV filters let me not worry about it.


What do you mean with a recessed front element? Also, I have always used a Kenko Pro 1 W filter on my 50 1.4, and have never had any issues. Are you saying that the IQ will be better if I remove it? (so far I have had nothing but good thing to say about this particular lens).
[/quote]

Good quality filters will have a very small effect on IQ. But one danger of filters is creating reflections from certain light sources. Example:
http://www.flickr.com/photos/chris28mm/4446223418/# (http://www.flickr.com/photos/chris28mm/4446223418/#)


When I say recessed front element, i mean that the front lens is set back in the lens, rather than flush with the filter thread. Example of recessed: http://i468.photobucket.com/albums/rr48/bullitt411/Siggy%2010-20/Tokina/DED_3739.jpg (http://i468.photobucket.com/albums/rr48/bullitt411/Siggy%2010-20/Tokina/DED_3739.jpg)

Not recessed: http://www.yacart.com/blog/wp-content/uploads/2011/12/canon_ef_70_200mm_f2.8_l_is_usm_lens.jpg (http://www.yacart.com/blog/wp-content/uploads/2011/12/canon_ef_70_200mm_f2.8_l_is_usm_lens.jpg)


When the lens element is set farther back in the body of the lens, it is more protected and unlikely to be damaged.
[/quote]

Ok, thanks :)
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: 7enderbender on June 03, 2012, 08:47:09 AM
I leave clear filters on all of my lenses except the 50 1.4. On the latter I always (!) leave the lens hood on because the little motor and/or clutch in that lens can break from mechanical strain coming from the moving front element.

I personally can't see ANY difference in image quality and can't really imagine where it would be coming form.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Dylan777 on June 03, 2012, 12:32:55 PM
I leave clear filters on all of my lenses except the 50 1.4. On the latter I always (!) leave the lens hood on because the little motor and/or clutch in that lens can break from mechanical strain coming from the moving front element.I personally can't see ANY difference in image quality and can't really imagine where it would be coming form.

+1...same here
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: jebrady03 on June 03, 2012, 01:27:03 PM
I bookmarked this thread last year as a reference for myself and thought it may be useful here: http://forums.dpreview.com/forums/read.asp?forum=1002&message=37394169 (http://forums.dpreview.com/forums/read.asp?forum=1002&message=37394169)

The initial post is very common-sense-like and often pretty funny.  Worth the read whether you agree or not :)
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Dylan777 on June 04, 2012, 01:06:11 AM
I bookmarked this thread last year as a reference for myself and thought it may be useful here: http://forums.dpreview.com/forums/read.asp?forum=1002&message=37394169 (http://forums.dpreview.com/forums/read.asp?forum=1002&message=37394169)

The initial post is very common-sense-like and often pretty funny.  Worth the read whether you agree or not :)

I can't stand dpreview  :( :(
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Tcapp on June 04, 2012, 01:41:27 AM
I bookmarked this thread last year as a reference for myself and thought it may be useful here: http://forums.dpreview.com/forums/read.asp?forum=1002&message=37394169 (http://forums.dpreview.com/forums/read.asp?forum=1002&message=37394169)

The initial post is very common-sense-like and often pretty funny.  Worth the read whether you agree or not :)

I can't stand dpreview  :( :(

Ditto.

2 good reasons to use a filter:

1. Weather sealing. A lot of L glass needs a filter to complete the seal.

2. Its nice not having to mess with lens caps at an event when you need to change lenses quickly.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: neuroanatomist on June 04, 2012, 06:34:24 AM
3. Ease of cleaning.  A B+W MRC or Hoya HD filter is much easier to clean than the front element of most lenses.  There's a reason Canon is now putting a fluorine coating on the front/rear elements of the newest lenses.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: jebrady03 on June 04, 2012, 08:06:51 AM
I can't stand dpreview  :( :(

Just because you can't stand that site, doesn't mean there's not good info/posts there.  I can't stand politicians but occasionally they... okay... bad example.  But I think you know what I mean :)

1. Weather sealing. A lot of L glass needs a filter to complete the seal.

Says who?  Canon?  If Canon says it's weather sealed, shouldn't that mean it's weather sealed without a filter?  I'm not doubting you, just requesting a reference.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: RC on June 04, 2012, 09:19:03 AM

1. Weather sealing. A lot of L glass needs a filter to complete the seal.

Says who?  Canon?  If Canon says it's weather sealed, shouldn't that mean it's weather sealed without a filter?  I'm not doubting you, just requesting a reference.

Several Canon lens require a filter to "complete" (the key word being complete) the weather sealing.   Example, 16-35, page 7. 
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: jm345 on June 04, 2012, 09:25:56 AM

1. Weather sealing. A lot of L glass needs a filter to complete the seal.

Says who?  Canon?  If Canon says it's weather sealed, shouldn't that mean it's weather sealed without a filter?  I'm not doubting you, just requesting a reference.

Several Canon lens require a filter to "complete" (the key word being complete) the weather sealing.   Example, 16-35, page 7.

Is there a list anywhere for the Canon lenses that require a front filter for complete weather sealing?
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: SambalOelek on June 04, 2012, 09:35:59 AM

1. Weather sealing. A lot of L glass needs a filter to complete the seal.

Says who?  Canon?  If Canon says it's weather sealed, shouldn't that mean it's weather sealed without a filter?  I'm not doubting you, just requesting a reference.

Several Canon lens require a filter to "complete" (the key word being complete) the weather sealing.   Example, 16-35, page 7.

Is there a list anywhere for the Canon lenses that require a front filter for complete weather sealing?

EF 16-35mm f/2.8 L USM 
EF 16-35mm f/2.8 L II USM 
EF 17-40mm f/4 L USM
EF 50mm f/1.2 L USM
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: RC on June 04, 2012, 09:45:29 AM

1. Weather sealing. A lot of L glass needs a filter to complete the seal.

Says who?  Canon?  If Canon says it's weather sealed, shouldn't that mean it's weather sealed without a filter?  I'm not doubting you, just requesting a reference.

Several Canon lens require a filter to "complete" (the key word being complete) the weather sealing.   Example, 16-35, page 7.

Is there a list anywhere for the Canon lenses that require a front filter for complete weather sealing?

EF 16-35mm f/2.8 L USM 
EF 16-35mm f/2.8 L II USM 
EF 17-40mm f/4 L USM
EF 50mm f/1.2 L USM

Another way to look at this is those lens which are vented and can (theoretically) suck in dust.  It's probably wise to put a filter on the non WS, non L, 17-55 since it has been known to pick up dust.  (actually I don't know where the vent is on this specific lens but you get the point).
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: bycostello on June 04, 2012, 10:16:09 AM
yes
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: preppyak on June 04, 2012, 10:23:31 AM
Says who?  Canon?  If Canon says it's weather sealed, shouldn't that mean it's weather sealed without a filter?  I'm not doubting you, just requesting a reference.
Canon themselves in the user manual for the lenses that need it (it's mostly the wide-angles I believe)

The-Digital-Picture sums it up
Quote
...the 16-35 L II is fully weather sealed to protect against dust and moisture only when a filter (typically a UV Filter) is in place like all of the other current-at-this-time sealed non-super telephoto lenses). Even though the extending inside portion of the lens barrel is gasketed, This filter is necessary to fully seal the lens. The lens does not change in overall size, but the inner barrel extends to its maximum near 28mm from its minimum at 16mm. A filter completely encloses this movement - and does not rotate. Mouse over the pic below to see the limits of movement.
It's the paragraph early on right above the picture of the front lens element

http://www.the-digital-picture.com/Reviews/Canon-EF-16-35mm-f-2.8-L-II-USM-Lens-Review.aspx (http://www.the-digital-picture.com/Reviews/Canon-EF-16-35mm-f-2.8-L-II-USM-Lens-Review.aspx)
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Dylan777 on June 04, 2012, 10:40:38 AM
I can't stand dpreview  :( :(

Just because you can't stand that site, doesn't mean there's not good info/posts there.  I can't stand politicians but occasionally they... okay... bad example.  But I think you know what I mean :)

 ;D ;D ;D
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: bkorcel on June 04, 2012, 11:34:01 AM
The only filter that makes sense would be a polarizer and that's due to it's special purpose.  Any additional glass in the path will affect IQ.  It becomes especially apparent using longer focal lengths and lenses that are already as sharp as the Hubble Space Telecope.  In addition, the flat surfaces also tend to cause more internal reflections and ghosting, even ones that are multicoated.  Many of Canons lenses use meniscus front lenses that are slightly curved to reduce this effect.  Adding a filter on the front just defeats the engineering.

Never use a filter unless you have a specific need for it and are willing to accept some loss of IQ.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: neuroanatomist on June 04, 2012, 12:53:55 PM
EF 16-35mm f/2.8 L USM 
EF 16-35mm f/2.8 L II USM 
EF 17-40mm f/4 L USM
EF 50mm f/1.2 L USM

Yes, these lenses state the requirement in the manual - all have either an 'extending' zoom or front focus mechanism that moves within the barrel and behind the plane of the filter threads. 

In addition, in an email exchange with Chuck Westfall, he recommended using a filter on any 'sealed' L-series which accepts a filter if the lens is to be used in wet conditions.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: npc2396 on June 04, 2012, 01:52:19 PM
I did an aperature sharpness test using Focal and every UV filter I tested showed a 8-15% reduction in the Focal focus scores.  The better filters affected the number less but I was amazed that they all showed atleast a 8-10% reduction in the scores.  I figured a UV filter would degrade image quality but it was nice to put an actual number on it.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: npc2396 on June 04, 2012, 02:46:02 PM
Here's a Focal report on a 70-200 version one with and without the filter.  It's a friends lens so I'll find out the exact filter.

This one was a good bit more then 10%

f/8.0 no filter 835.7
f/8.0 with filter 648.7

Just for kicks I put on my 70-200 II with no filter at f/8.0 and got 1246.5 so my II was significantly sharper than his I.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Tymo93 on June 04, 2012, 02:48:48 PM
My 50mm 1.4 believe it or not is sharper with the UV filter... :))
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: RLPhoto on June 04, 2012, 02:51:28 PM
Here's a Focal report on a 70-200 version one with and without the filter.  It's a friends lens so I'll find out the exact filter.

This one was a good bit more then 10%

f/8.0 no filter 835.7
f/8.0 with filter 648.7

Just for kicks I put on my 70-200 II with no filter at f/8.0 and got 1246.5 so my II was significantly sharper than his I.

Interesting, There is a slight degradation but the original 70-200MM wasn't that great of a lens anyway. Plus It could be a terrible uncoated filter with horrid glass.

Can you tell me if I used a UV filter here? (The answer should be obvious  ;D)
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: npc2396 on June 04, 2012, 03:03:43 PM
My 50mm 1.4 believe it or not is sharper with the UV filter... :))

Interestingly he had a 1.4 that did fair better.  Some aperatures the filtered lens was sharper but overall the unfiltered lens performed better.  I contributed this to the focus consistansty of the 1.4 it's good but a variation of 10% seems common. 

Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: neuroanatomist on June 04, 2012, 03:54:09 PM
f/8.0 no filter 835.7
f/8.0 with filter 648.7

How many times did you run the test for each condition?
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Tcapp on June 04, 2012, 04:12:27 PM
Here's a Focal report on a 70-200 version one with and without the filter.  It's a friends lens so I'll find out the exact filter.

This one was a good bit more then 10%

f/8.0 no filter 835.7
f/8.0 with filter 648.7

Just for kicks I put on my 70-200 II with no filter at f/8.0 and got 1246.5 so my II was significantly sharper than his I.

Interesting, There is a slight degradation but the original 70-200MM wasn't that great of a lens anyway. Plus It could be a terrible uncoated filter with horrid glass.

Can you tell me if I used a UV filter here? (The answer should be obvious  ;D)

Of course you did, otherwise you lens would have exploded!

Seriously, since its a nice sharp image I'm assuming you didn't use a filter and are trying to prove a point. So you think that kind of sharpness is impossible with a filter? Tell that to all the landscape shooters who use ND filters for a nice exposure. Landscape is more sharpness demanding than portraiture.

Nice shot by the way.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Mr Simpleton on June 04, 2012, 04:18:44 PM
Guess the verdict is out!!
http://www.lensrentals.com/blog/2011/06/good-times-with-bad-filters#more-2103 (http://www.lensrentals.com/blog/2011/06/good-times-with-bad-filters#more-2103)

Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: RLPhoto on June 04, 2012, 04:23:07 PM
Here's a Focal report on a 70-200 version one with and without the filter.  It's a friends lens so I'll find out the exact filter.

This one was a good bit more then 10%

f/8.0 no filter 835.7
f/8.0 with filter 648.7

Just for kicks I put on my 70-200 II with no filter at f/8.0 and got 1246.5 so my II was significantly sharper than his I.

Interesting, There is a slight degradation but the original 70-200MM wasn't that great of a lens anyway. Plus It could be a terrible uncoated filter with horrid glass.

Can you tell me if I used a UV filter here? (The answer should be obvious  ;D)

Of course you did, otherwise you lens would have exploded!

Seriously, since its a nice sharp image I'm assuming you didn't use a filter and are trying to prove a point. So you think that kind of sharpness is impossible with a filter? Tell that to all the landscape shooters who use ND filters for a nice exposure. Landscape is more sharpness demanding than portraiture.

Nice shot by the way.

Thanks Broskie, I have a Filter to seal my 50mm 1.2L. There was massive amounts of water hitting my 7D that day and I was soaked but everything was tip-top.

I agree with you all the way, I was trying to prove that excellent filters wont degrade your photos. Landscapers will appreciate the excellent quality filters from B&W and Schneider Optics because they have null effect on real-life IQ.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Tcapp on June 04, 2012, 04:53:25 PM
Here's a Focal report on a 70-200 version one with and without the filter.  It's a friends lens so I'll find out the exact filter.

This one was a good bit more then 10%

f/8.0 no filter 835.7
f/8.0 with filter 648.7

Just for kicks I put on my 70-200 II with no filter at f/8.0 and got 1246.5 so my II was significantly sharper than his I.

Interesting, There is a slight degradation but the original 70-200MM wasn't that great of a lens anyway. Plus It could be a terrible uncoated filter with horrid glass.

Can you tell me if I used a UV filter here? (The answer should be obvious  ;D)

Of course you did, otherwise you lens would have exploded!

Seriously, since its a nice sharp image I'm assuming you didn't use a filter and are trying to prove a point. So you think that kind of sharpness is impossible with a filter? Tell that to all the landscape shooters who use ND filters for a nice exposure. Landscape is more sharpness demanding than portraiture.

Nice shot by the way.

Thanks Broskie, I have a Filter to seal my 50mm 1.2L. There was massive amounts of water hitting my 7D that day and I was soaked but everything was tip-top.

I agree with you all the way, I was trying to prove that excellent filters wont degrade your photos. Landscapers will appreciate the excellent quality filters from B&W and Schneider Optics because they have null effect on real-life IQ.

B&W are expensive, but they are awesome. I have a 10 stop ND from them. That is a crazy filter. Good times!
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Razor2012 on June 04, 2012, 05:04:21 PM
Yep. love my B+W's.  I buy the XS-Pro Nanos now.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: SambalOelek on June 05, 2012, 07:45:35 AM

Is there a list anywhere for the Canon lenses that require a front filter for complete weather sealing?

EF 16-35mm f/2.8 L USM 
EF 16-35mm f/2.8 L II USM 
EF 17-40mm f/4 L USM
EF 50mm f/1.2 L USM

Another way to look at this is those lens which are vented and can (theoretically) suck in dust.  It's probably wise to put a filter on the non WS, non L, 17-55 since it has been known to pick up dust.  (actually I don't know where the vent is on this specific lens but you get the point).

There are vents around the front element, but dust may accumulate over time even if a filter is used. If necessary, however, it is very easy to remove the front element and get rid of the dust. The entire operation takes less than five minutes.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: npc2396 on June 05, 2012, 09:31:52 AM
f/8.0 no filter 835.7
f/8.0 with filter 648.7

How many times did you run the test for each condition?

I ran through the aperature sharpness test twice with and without the filter with similiar results. 
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: helpful on June 05, 2012, 12:36:33 PM
Disclaimer: I have not read through all the answers yet. But I do have a strong opinion on this subject, based I believe on experience and accurate measurements.

A UV filter always affects image quality, including sharpness. It lowers performance in sharpness, contrast, transmission, etc., by at least 5%. For some filters, more than 10%. That's doesn't sound bad considering that the Sony SLT cameras absorb 33% of light (transmission only), but here we are talking about a 5% or more reduction in every optical characteristic of the lens, not just transmission.

It gets worse the larger the area of the filter. So for 18-55mm lenses it's not really important. But for a 300mm f/2.8 lens, it would be ridiculous.

A 5% reduction across the board is enough to take away the $5000 benefit of owning exotic glass.

I never use UV filters (unless I am taking photos directly in the face of flying rocks or other objects--I do own filters for that purpose, and of course other filters that have actual purposes). There are clueless photographers who won't buy used lenses from me as a result, and they are the same people who set lenses on their side rolling all over the place because they are afraid to set them face down the way they were designed.

Also, I clean my lenses very sparingly. More damage is done by excessive cleaning than by any dust or dirt on the lens. I have had dirt cascade into the front hood of my 300mm and get on the lens, and it was barely noticeable in the images. Take note that the dirt doesn't reflect light very well, so the image quality degradation was only in proportion to the actual square inches of the grains of dirt that were on the lens. It was a much smaller effect than caused by a UV filter. Dirt has great anti-reflective characteristics, I have observed. So by putting a UV filter on your lens, you are basically doing worse than covering it with a light coating of dirt.

And my lens was fine. Just a brush off and it was indistinguishable from the day I purchased it.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: DB on June 05, 2012, 12:37:43 PM
I leave clear filters on all of my lenses except the 50 1.4. On the latter I always (!) leave the lens hood on because the little motor and/or clutch in that lens can break from mechanical strain coming from the moving front element.I personally can't see ANY difference in image quality and can't really imagine where it would be coming form.

+1...same here

+1 too.... when I got my 24-70mm L lens i wanted a really good filter solely for protection so I did a bit of online research and opted for a clear Hoya HD (even watched the Youtube video of steel ball-bearings being dropped on it from a height!). It works great. Tested with vs w/o, no difference

http://www.ebay.ie/itm/HOYA-77mm-Protector-HD-High-Definition-Filter-77-New-UK-/120901742208?pt=UK_CamerasPhoto_CameraAccessories_CameraLensesFilters_JN&hash=item1c264e2e80#ht_3303wt_904 (http://www.ebay.ie/itm/HOYA-77mm-Protector-HD-High-Definition-Filter-77-New-UK-/120901742208?pt=UK_CamerasPhoto_CameraAccessories_CameraLensesFilters_JN&hash=item1c264e2e80#ht_3303wt_904)
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: avatar13 on June 05, 2012, 03:32:18 PM

Is there a list anywhere for the Canon lenses that require a front filter for complete weather sealing?

EF 16-35mm f/2.8 L USM 
EF 16-35mm f/2.8 L II USM 
EF 17-40mm f/4 L USM
EF 50mm f/1.2 L USM

Another way to look at this is those lens which are vented and can (theoretically) suck in dust.  It's probably wise to put a filter on the non WS, non L, 17-55 since it has been known to pick up dust.  (actually I don't know where the vent is on this specific lens but you get the point).

There are vents around the front element, but dust may accumulate over time even if a filter is used. If necessary, however, it is very easy to remove the front element and get rid of the dust. The entire operation takes less than five minutes.

I have a 17-55 IS and use it with a B+W MRC UV Filter which is always on.  I still tend to get dust particles inside, this lens is notorious for this.  I had it sent to Canon one time for cleaning (and to replace the IS motor, total was like $130).  There are some small dust particles again inside but it never shows up in the pictures.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: RC on June 05, 2012, 03:54:02 PM
I have a 17-55 IS and use it with a B+W MRC UV Filter which is always on.  I still tend to get dust particles inside, this lens is notorious for this.  I had it sent to Canon one time for cleaning (and to replace the IS motor, total was like $130).  There are some small dust particles again inside but it never shows up in the pictures.

Interesting.  I sure would like to know what the differences are for those who get lots of dust and those who get none.

- environment, wind, dust, humidity, geography
- filters, lens caps off
- amount of zooming
- amount of use
- manufacturing, serial numbers

Obviously too many variables to really know
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: neuroanatomist on June 05, 2012, 06:53:24 PM
A UV filter always affects image quality, including sharpness. It lowers performance in sharpness, contrast, transmission, etc., by at least 5%. For some filters, more than 10%. That's doesn't sound bad considering that the Sony SLT cameras absorb 33% of light (transmission only), but here we are talking about a 5% or more reduction in every optical characteristic of the lens, not just transmission.

It gets worse the larger the area of the filter. So for 18-55mm lenses it's not really important. But for a 300mm f/2.8 lens, it would be ridiculous.

I will respectfully disagree.  I've shot with/without tests using a B+W MRC UV filters and an ISO 12233-based test chart which costs more than some L-series lenses, and detected no difference in sharpness.  Granted, that was under ideal lighting conditions.  I have also tested the effect on flare, and there is an increase.  Although my flare testing was a 'worst case scenario' - very bright light in the extreme corner of the image, in an otherwise dark room (literally, a darkroom) - the increased flare is sufficient to reduce contrast.  Reduced contrast will manifest as a reduction in sharpness, so in that sense, with side lighting or backlighting, a filter may cause a reduction in sharpness.  I'd think it will fall short of a 5% loss in most cases.

Of course, as you know the 300/2.8 does not take a front filter, only a drop-in 52mm filter.  Interestingly, while you can choose to leave off a front filter, the supertele lenses actually require a filter.   Canon states you should keep a clear glass filter in that drop-in holder (check the manual) because the optical design of the lens incorporates a filter in the holder.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Mt Spokane Photography on June 05, 2012, 07:02:03 PM
Filters always affect IQ, even air affects IQ, its just a matter of how much.  Although I have plenty of B&W and Heliopan filters, I avoid using them unless its dusty, or likely to get damage, water, salt spray, etc on the lens.
 
I always kept a filter on my 17-55 and after 3 years had no internal dust.  That was the one exception to my occasional use of filters.
 
I have very few cases where the difference in sharpness would be noticible except by obsessing ofer a 100% view of the image.  For a wide angle lendscape where I need all the detail I can get, I'd remove any UV filter.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: helpful on June 07, 2012, 09:05:20 PM
A UV filter always affects image quality, including sharpness. It lowers performance in sharpness, contrast, transmission, etc., by at least 5%. For some filters, more than 10%. That's doesn't sound bad considering that the Sony SLT cameras absorb 33% of light (transmission only), but here we are talking about a 5% or more reduction in every optical characteristic of the lens, not just transmission.

It gets worse the larger the area of the filter. So for 18-55mm lenses it's not really important. But for a 300mm f/2.8 lens, it would be ridiculous.

I will respectfully disagree.  I've shot with/without tests using a B+W MRC UV filters and an ISO 12233-based test chart which costs more than some L-series lenses, and detected no difference in sharpness.  Granted, that was under ideal lighting conditions.  I have also tested the effect on flare, and there is an increase.  Although my flare testing was a 'worst case scenario' - very bright light in the extreme corner of the image, in an otherwise dark room (literally, a darkroom) - the increased flare is sufficient to reduce contrast.  Reduced contrast will manifest as a reduction in sharpness, so in that sense, with side lighting or backlighting, a filter may cause a reduction in sharpness.  I'd think it will fall short of a 5% loss in most cases.

Of course, as you know the 300/2.8 does not take a front filter, only a drop-in 52mm filter.  Interestingly, while you can choose to leave off a front filter, the supertele lenses actually require a filter.   Canon states you should keep a clear glass filter in that drop-in holder (check the manual) because the optical design of the lens incorporates a filter in the holder.

Neuro, 5% is a very small amount, but that is an old literature value for least possible amount of image quality reduction on light rays passing through an optical system (one element or a group of elements without any intervening air to glass interfaces). I tried to look that number up again, and was unable to. However, I talked to one of my best friends today, who was responsible for designing the most expensive lens system ever created at that time for the Voyager I and Voyager II space probes (an f/0.7 lens design that used a single block of beryllium valued at over $2 million, the largest one ever manufactured). He gave me his professional opinion that with current technology (coatings, etc.) the minimum effect on image quality per air to glass interface is 3%. Filters have a bigger effect on image quality than any other element in an optical system because both sides are a flat air-to-glass interface. So the image quality would be 97% of it's original quality when passing inside of the filter, and then (97%) times (97%) when passing through the other side into the lens. That leaves the image at about 94% of it's original quality.

Looking at the resulting image, it's almost impossible to say "This image looks like 94% of perfect," because the lighting conditions in the picture, etc., can all affect the image quality (clear day vs. hazy day for example).

One time there was a salesman saying that an oven was so good that the heat would never escape. That's impossible, and so is the idea that a filter doesn't affect the image.

Search the internet for some photos of top quality filters stacked on top of each other. You can clearly see from a photo looking through the stack of filters that the rims of the filters become less and less well defined as the number of filter layers increased.

For example, after 10 filters there would be 73.7% transmission with an optically perfect set of filters (.97)^10 = 73.7%.

Depending on the angle of the light ray passing through the filter, the abberations / MTF deficiency will vary, but once again, 3% is basically a minimum level of effect.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: neuroanatomist on June 07, 2012, 09:40:26 PM
However, I talked to one of my best friends today...He gave me his professional opinion that with current technology (coatings, etc.) the minimum effect on image quality per air to glass interface is 3%.

For example, after 10 filters there would be 73.7% transmission with an optically perfect set of filters (.97)^10 = 73.7%.

Depending on the angle of the light ray passing through the filter, the abberations / MTF deficiency will vary, but once again, 3% is basically a minimum level of effect.

Sorry, going to disagree again. First off, I'm not sure you're distinguishing between transmission loss and IQ decrement. Transmission loss with modern lens coatings is much less than 1% per interface.

Now, take your friend's value of 3% IQ loss per interface leading to a 6% loss of IQ from a filter.  Roger Cicala's (lensrentals.com) tests of large filter stacks refutes that.  Moreover, optically there's no difference between a curved glass-air interface and a flat one - the magnitude of refraction and reflection is the same, only the vector direction differs.  So, let's look at the 70-200mm f/2.8L IS II - arguably the best zoom lens in existence. It has 19 groups, meaning 38 glass-air interfaces. At 3% loss per interface, that means absolutely no light hitting the sensor if you mean transmission, or over 100% IQ loss if you don't mean transmission. I don't think either is even close to true.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Random Orbits on June 07, 2012, 10:26:35 PM
However, I talked to one of my best friends today...He gave me his professional opinion that with current technology (coatings, etc.) the minimum effect on image quality per air to glass interface is 3%.

For example, after 10 filters there would be 73.7% transmission with an optically perfect set of filters (.97)^10 = 73.7%.

Depending on the angle of the light ray passing through the filter, the abberations / MTF deficiency will vary, but once again, 3% is basically a minimum level of effect.

Sorry, going to disagree again. First off, I'm not sure you're distinguishing between transmission loss and IQ decrement. Transmission loss with modern lens coatings is much less than 1% per interface.

Now, take your friend's value of 3% IQ loss per interface leading to a 6% loss of IQ from a filter.  Roger Cicala's (lensrentals.com) tests of large filter stacks refutes that.  Moreover, optically there's no difference between a curved glass-air interface and a flat one - the magnitude of refraction and reflection is the same, only the vector direction differs.  So, let's look at the 70-200mm f/2.8L IS II - arguably the best zoom lens in existence. It has 19 groups, meaning 38 glass-air interfaces. At 3% loss per interface, that means absolutely no light hitting the sensor if you mean transmission, or over 100% IQ loss if you don't mean transmission. I don't think either is even close to true.

The lensrental page below cites that "a modern coating that is 99.9% effective, and total reflection changes to less than 2% for the simple lens and just over 3% for the complex lens." and that "Without coatings each interface would reflect about 4% of the light that reaches it."

http://www.lensrentals.com/blog/2011/12/reflections-on-reflections-the-most-important-part-of-your-lens (http://www.lensrentals.com/blog/2011/12/reflections-on-reflections-the-most-important-part-of-your-lens)
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: RLPhoto on June 07, 2012, 10:35:35 PM
However, I talked to one of my best friends today...He gave me his professional opinion that with current technology (coatings, etc.) the minimum effect on image quality per air to glass interface is 3%.

For example, after 10 filters there would be 73.7% transmission with an optically perfect set of filters (.97)^10 = 73.7%.

Depending on the angle of the light ray passing through the filter, the abberations / MTF deficiency will vary, but once again, 3% is basically a minimum level of effect.

Sorry, going to disagree again. First off, I'm not sure you're distinguishing between transmission loss and IQ decrement. Transmission loss with modern lens coatings is much less than 1% per interface.

Now, take your friend's value of 3% IQ loss per interface leading to a 6% loss of IQ from a filter.  Roger Cicala's (lensrentals.com) tests of large filter stacks refutes that.  Moreover, optically there's no difference between a curved glass-air interface and a flat one - the magnitude of refraction and reflection is the same, only the vector direction differs.  So, let's look at the 70-200mm f/2.8L IS II - arguably the best zoom lens in existence. It has 19 groups, meaning 38 glass-air interfaces. At 3% loss per interface, that means absolutely no light hitting the sensor if you mean transmission, or over 100% IQ loss if you don't mean transmission. I don't think either is even close to true.

The lensrental page below cites that "a modern coating that is 99.9% effective, and total reflection changes to less than 2% for the simple lens and just over 3% for the complex lens." and that "Without coatings each interface would reflect about 4% of the light that reaches it."

http://www.lensrentals.com/blog/2011/12/reflections-on-reflections-the-most-important-part-of-your-lens (http://www.lensrentals.com/blog/2011/12/reflections-on-reflections-the-most-important-part-of-your-lens)

A excellent filter will not affect IQ enough for anyone to notice. NOT anyone, even fellow pro's won't be able to say "hey this photo had a Uv filter on it!"
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: helpful on June 08, 2012, 12:50:37 AM
However, I talked to one of my best friends today...He gave me his professional opinion that with current technology (coatings, etc.) the minimum effect on image quality per air to glass interface is 3%.

For example, after 10 filters there would be 73.7% transmission with an optically perfect set of filters (.97)^10 = 73.7%.

Depending on the angle of the light ray passing through the filter, the abberations / MTF deficiency will vary, but once again, 3% is basically a minimum level of effect.

Sorry, going to disagree again. First off, I'm not sure you're distinguishing between transmission loss and IQ decrement. Transmission loss with modern lens coatings is much less than 1% per interface.

Now, take your friend's value of 3% IQ loss per interface leading to a 6% loss of IQ from a filter.  Roger Cicala's (lensrentals.com) tests of large filter stacks refutes that.  Moreover, optically there's no difference between a curved glass-air interface and a flat one - the magnitude of refraction and reflection is the same, only the vector direction differs.  So, let's look at the 70-200mm f/2.8L IS II - arguably the best zoom lens in existence. It has 19 groups, meaning 38 glass-air interfaces. At 3% loss per interface, that means absolutely no light hitting the sensor if you mean transmission, or over 100% IQ loss if you don't mean transmission. I don't think either is even close to true.

You are confusing transmittance vs. absorbance.

Let's say I take a one-inch pane of glass. I cut it in half so that it is 1/2 inch thick. I have doubled something as a result. Perhaps the amount of light that gets through??? Then I cut it in half again, so now I have doubled something again. 2*2 = 4. Does that mean that four times as much light gets through? So I could clearly get a large amount of light through if I kept on doubling the transmission, doubling the transmission, and on and on., and I guess it would be infinitely bright light when I ran out of glass to cut in half... Wrong.

But that's the mistake you are making by saying that 100% IQ loss would occur based on the 23 elements / 19 groups in the 70-200mm II lens.

You are adding the 5% 23 times and getting more than 100%, right?

The correct way to compute it is not by subtraction but my multiplication. As I did above, if there are 10 surfaces, then there is about 73% transmittance.

That is only for flat air to glass transitions.

With binoculars they have nitrogen filled optical designs, and there are similar tricks for lenses.

And another thing is that optical groups (lenses directly combined with other lenses) count as a single element.

The answer to your question is to look at the Tstop value for the 70-200mm lens.

This Tstop value is 3.4.

Calculate the number of stops lost: log_2((3.4)^2/(2.8 )^2) = .5602 stops

This translates into a 47% loss of light vs. a hollow tube of the same diameter as the lens.

We can find the amount of light lost at each of the 19 groups as follows:

1 - .47 = (1 - x) ^ 19
.53 = (1-x)^19
.53^(1/19) = 1-x
x = 1 - .53^(1/19)
x = 3.286%.

That's almost exactly what my expert friend quoted.

You can't beat someone who works for NASA, and designed lenses for the space program at age 23 back in the 1970s.

Have a great day!
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: bycostello on November 01, 2012, 08:56:56 PM
of course, it is another piece of glass in front of the lens!
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: symmar22 on November 01, 2012, 09:56:30 PM
The only filter that makes sense would be a polarizer and that's due to it's special purpose.  Any additional glass in the path will affect IQ.  It becomes especially apparent using longer focal lengths and lenses that are already as sharp as the Hubble Space Telecope.  In addition, the flat surfaces also tend to cause more internal reflections and ghosting, even ones that are multicoated.  Many of Canons lenses use meniscus front lenses that are slightly curved to reduce this effect.  Adding a filter on the front just defeats the engineering.

Never use a filter unless you have a specific need for it and are willing to accept some loss of IQ.

+1

Always found strange that people invest 2000$ to get the best IQ from a lens and ruin it with a 25$ piece of cheap glass....
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: tron on November 01, 2012, 10:18:39 PM
Just because you can't stand that site, doesn't mean there's not good info/posts there.  I can't stand politicians but occasionally they... okay... bad example.  But I think you know what I mean :)
  ;D  ;D   ;D
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Invertalon on November 01, 2012, 11:35:04 PM
I just ran my 70-200 II at 70mm through Focal with and without the Hoya HD filter I use regularly.

I ran it six times total. I used live-view focus before the first shot so AF would have NO factor in these results as it stayed the same between all the tests. Three tests with filter and three without back to back to directly compare.

My three best shot results WITHOUT a filter... 2091, 2092 and 2065.

My three best shot results WITH a filter... 2010, 2045 and 2053.

Filter OFF Average: 2082.66
Filter ON Average: 2036

Difference of around 2.24% using this testing method. Would you see that in real world shooting? Probably not. But if you want to maximize IQ than filter off.

Note, even running the same test back to back shows some difference in final results... Without moving anything at all or letting the camera AF. Most likely a slightly tolerance in the analysis software. However, the results are still consistent between them.

Another side note, there is quite a noticeable reduction in light hitting the sensor with the filter on. Afterward, I did 2 set's of comparison shots with and without a filter, same exposure, WB, etc... The shot with the filter was always a hair more underexposed. I did not expect it to be as noticeable as it was. In Lightroom, both images came out to about a 8% difference in exposure with the filter (.08 slider adjustment to match the exposures).
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: weixing on November 01, 2012, 11:46:28 PM
The only filter that makes sense would be a polarizer and that's due to it's special purpose.  Any additional glass in the path will affect IQ.  It becomes especially apparent using longer focal lengths and lenses that are already as sharp as the Hubble Space Telecope.  In addition, the flat surfaces also tend to cause more internal reflections and ghosting, even ones that are multicoated.  Many of Canons lenses use meniscus front lenses that are slightly curved to reduce this effect.  Adding a filter on the front just defeats the engineering.

Never use a filter unless you have a specific need for it and are willing to accept some loss of IQ.

+1

Always found strange that people invest 2000$ to get the best IQ from a lens and ruin it with a 25$ piece of cheap glass....
   +1. I also found that the case and they seem to forget that the IQ of the lens will only be as good as the quality of the worst element in the optical train and the filter is part of that when added.

  Anyway, the below is a link about Canon coating technology:
http://www.canon.com/technology/s_labo/light/003/03.html (http://www.canon.com/technology/s_labo/light/003/03.html)

  Have a nice day.
   
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Zv on November 02, 2012, 01:41:45 AM
I want to know more about these flourine coatings by Canon. Neuro can you explain what that does? Does it mean we no longer need clear filters?
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: ZoeEnPhos on November 02, 2012, 07:35:16 AM
The only filter that makes sense would be a polarizer and that's due to it's special purpose.  Any additional glass in the path will affect IQ.  It becomes especially apparent using longer focal lengths and lenses that are already as sharp as the Hubble Space Telecope.  In addition, the flat surfaces also tend to cause more internal reflections and ghosting, even ones that are multicoated.  Many of Canons lenses use meniscus front lenses that are slightly curved to reduce this effect.  Adding a filter on the front just defeats the engineering.

Never use a filter unless you have a specific need for it and are willing to accept some loss of IQ.

+1

Always found strange that people invest 2000$ to get the best IQ from a lens and ruin it with a 25$ piece of cheap glass....

Just wish to add my personal experience - I purchase an almost brand new Canon EF 300mm f/4L IS USM and the former owner was "generous" by adding with the lens a 77mm "un-common-cheap-brand-UV-filter".
In the beginning I made the very mistake to place this filter in the end of the lens-barrel and I noticed a problem with FLARE and lack of decent contrast and somehow less colours....I then decided to NOT use any filter of any kind to this tele-lens with decent hood and saw an immediate effect of a better overall IQ in post processing when carefully examine my .CR2 RAW files before and after removing the cheap-junk-filter.

I have not attached any filter to this lens today and I am carefully using the built-in retractable lens hood with the convenience of quickly sliding the hood out/in for use/storage.

(However I am considering to buy a Nano-based slim-filter of 82mm to my Canon TS-E 24mm f/3.5L II that I am still using without any filter so far. By the way, do anyone have a suggest what would be the best choice in order to protect the wide-angel-front-lens to this quite expensive TS-E lens?)
Wishing you a wonderful coming Week-end!
/Charl
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: neuroanatomist on November 02, 2012, 08:12:31 AM
I want to know more about these flourine coatings by Canon. Neuro can you explain what that does? Does it mean we no longer need clear filters?

The fluorine coating makes cleaning the front and rear elements easier - it's the same stuff they use on the walls in urban centers, to make graffiti removal easier.  There is no protection against scratches, etc.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Zv on November 02, 2012, 09:25:05 AM
I want to know more about these flourine coatings by Canon. Neuro can you explain what that does? Does it mean we no longer need clear filters?

The fluorine coating makes cleaning the front and rear elements easier - it's the same stuff they use on the walls in urban centers, to make graffiti removal easier.  There is no protection against scratches, etc.

Thanks!
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: FTb-n on November 02, 2012, 03:28:49 PM
The Hoya HMC will degrade image quality.  That's why I switched to the Hoya HD Clear filters.  They are tough and very easy to clean.  Given the cost of the filter, I wanted to know if it was worth it.  I did some testing with and without it and I don't see any degredation of IQ.  My 70-200 f2.8L II can be glare-prone (but not as bad as the Mark I), but the filter doesn't add any glare of it's own.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: tron on November 02, 2012, 03:37:02 PM
The Hoya HMC will degrade image quality.
Interesting. Have you used HMC Super?
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: Mika on November 05, 2012, 06:42:41 PM
The UV filter will not only affect the sharpness of a lens, but also the whole performance, including bokeh. This is specifically true for telephoto lenses, following are shots taken with Sigma 120-400 immediately after buying it (sorry, I had to resize to 70 % of the original due to attachment size limit).

I wondered about the performance of the lens as I thought it really should be better than what I got, and contacted the importer. It turned out that the cause for image quality degradation was a comparatively bad UV filter.

I actually do have some interferograms of the filter; the filter shape error can be determined from bokeh outline (diagonal lines). Without the UV filter, the lens worked much better. I still use UV filters in front of normal and short telephoto lenses, but not in the 120-400. The only reason why I still keep them on is mainly the ease of cleaning a separable glass plate.
Title: Re: Can a UV filter affect IQ (sharpness) on a lens?
Post by: NormanBates on November 06, 2012, 03:28:44 AM
I needed a filter ring with no glass for a DIY project, so I bought a $3 UV filter from ebay and cracked the glass. Before doing so, just out of curiosity, I tested it against my "one dollar resolution chart".

These are the 100% crops from the Canon 500D that I had at the time:

no filter:
(http://www.similaar.com/foto/lenstests/nd/cheapuv/uv_without.jpg)

with $3 UV filter:
(http://www.similaar.com/foto/lenstests/nd/cheapuv/uv_with.jpg)

if you stack a bunch of these you'll start seeing some effect (http://www.lensrentals.com/blog/2011/06/good-times-with-bad-filters (http://www.lensrentals.com/blog/2011/06/good-times-with-bad-filters)), but for just one filter... you're pretty safe, even if it's a shitty $3 filter from ebay


edit: other filters will definitely have an effect on sharpness; for example, cheap resin NDs, or fader NDs: http://www.similaar.com/foto/lenstests/lenstestsn.html (http://www.similaar.com/foto/lenstests/lenstestsn.html)