# Help Request For How To Clean Gelatin Rear Filters



## Bruce Photography (May 21, 2011)

I recently purchased my first and only Canon Supertele the 500mm. I've been using the lens some now and it is time to clean the rear drop in filter. The surface is open to the back and does protect the other back lens elements. However it has been called a gelatin filter. Is it? It looks like very thin and delicate glass. The Canon documentation seems to indicate that it is a UV filter. Is that true or is it just clear. Can I clean it like any other lens glass or do I need a special fine cloth. Can I use liquid lens cleaner on both surfaces.

By the way, it seem to go into the slot either way. By facing the back of the lens, I assume that you want to see the Canon lettering toward you (facing toward the back lens cap). Am I correct? This may make no difference or might make a difference with a polarizer.

This is my first lens with a rear filter. I'd appreciate your help. Bruce


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## J. McCabe (May 22, 2011)

Why would one want to use a rear mounted UV filter with a DSLR ?

The sensor (in contrast to film) does not gain from it, and mounted in the back it can't protect the front element.


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## Bruce Photography (May 22, 2011)

You probably would need to ask a Canon designer, but ALL Canon Super Telephoto lenses use a rear drop in filter of 52mm as well as many other Large front element lenses whose diameter is much larger than current round filters would allow for. Some examples include the 300 and 400mm F2.8 lenses, Supers, and the F2 200mm. Take a look at online. Any lens over $3000 uses this rear drop in filter which I think are all 52mm in size.


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## Edwin Herdman (May 22, 2011)

I don't have a supertele or any experience with them, but it sounds as if the rear filter holder is currently occupied by a UV filter. As McCabe suggests, it probably isn't critical to have a UV filter in there, most of the time. A circular polarizer might be more useful back there.

Too bad I don't have a 500mm lens..! Enjoy.

By the way, here's a comparison of shots taken with the 500mm f/4 with and without the drop-in circular polarizer.


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## John Smith (May 22, 2011)

Bruce Photography said:


> You probably would need to ask a Canon designer, but ALL Canon Super Telephoto lenses use a rear drop in filter of 52mm as well as many other Large front element lenses whose diameter is much larger than current round filters would allow for. Some examples include the 300 and 400mm F2.8 lenses, Supers, and the F2 200mm. Take a look at online. Any lens over $3000 uses this rear drop in filter which I think are all 52mm in size.



I'm uncertain whether this is addressed to me. I know some lenses use read gelatin filter due to very curved front element, e.g. EF 15mm fisheye, or large front element.

What I'm uncertain about is what benefit would a UV filter have when such a lens is mounted on a DSLR. AFAIK it would just hurt IQ.


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## Admin US West (May 22, 2011)

The included rear glass filter on the Canon supertelephoto lenses is a clear filter, not a UV. It certainly DOES need to be there if you want the best quality photos. The lens is designed to use it.

Read page 16 of the manual.

http://pdisp01.c-wss.com/gdl/WWUFORedirectTarget.do?id=MDMwMDAwMzQ3MDAx&cmp=ABR&lang=EN


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## Bruce Photography (May 22, 2011)

ScalesUSA: Thank you for your help. Of all the Canon lenses I have the 500mm is the only one that I don't have a manual for. I printed it out and found just my answers on page 16 as you said. The manual was printed in 1999 when the lens first came out and it did say it was glass but I thought I read somewhere that it was UV. Perhaps they have updated from glass to UV. For this kind of money, it sure should be UV. 

Some replies to this thread say that Digital cameras don't need UV filters. That is not what I've seen it taking distance photos. In fact the 415 UV cut filters that I have mounted on my 70-200 F4 IS lens do an amazing job of cutting through UV haze better than any other UV filters that I have tried. I've done shots with and without. UV does work well with digital. That is just my opinion based upon my testing.


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