Can a UV filter affect IQ (sharpness) on a lens?

[Tcapp]

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  )

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.

[Mr Simpleton]

Guess the verdict is out!!
http://www.lensrentals.com/blog/2011/06/good-times-with-bad-filters#more-2103

[RLPhoto]

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  )

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.

[Tcapp]

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  )

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!

[Razor2012]

Yep. love my B+W's.  I buy the XS-Pro Nanos now.

[SambalOelek]

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.

[npc2396]

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. 

[helpful]

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.

[DB]

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

[avatar13]

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.

[RC]

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

[neuroanatomist]

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.

[Mt Spokane Photography]

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.

[helpful]

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.

[neuroanatomist]

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.