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

[RC]

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. 

[jm345]

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?

[SambalOelek]

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

[RC]

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).

[bycostello]

yes

[preppyak]

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

...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

[Dylan777]

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

 

[bkorcel]

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.

[neuroanatomist]

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.

[npc2396]

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.

[npc2396]

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.

[Tymo93]

My 50mm 1.4 believe it or not is sharper with the UV filter...

[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  )

[npc2396]

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. 

[neuroanatomist]

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?