Incense

by Bart Arondson

submit your photo


Hall of Fame
View past winners from this year

Please participate in Meta
and help us grow.

Take the 2-minute tour ×
Photography Stack Exchange is a question and answer site for professional, enthusiast and amateur photographers. It's 100% free, no registration required.

Lenses such as the Canon EF 17-40mm f/4 L USM offer rear gelatin filter holders, but also accept front filters via a 77mm screw on type. If I was using a circular polarizer, I would need to put it on the front element to manipulate it. But if I was adding a solid ND filter or a color filter, what are the reasons to use or not to use the rear gelatin filter over the front screw on type?

This is the Canon EF 17-40mm f/4 L USM lens rear element. You can see the outline for the gelatin filter holder if you look closely. It is noted by the white square around the glass: enter image description here

share|improve this question
    
I do want other people to answer this since I am not an expert. I just answered it myself since I had a few ideas. –  dpollitt May 20 '13 at 1:40
1  
Holy crap, I didn't even know that my 17-40 accepted rear filters. How did I miss that... –  AJ Henderson May 20 '13 at 3:58
    
@AJHenderson, I would recommend reading all of your equipment manuals. The can tell you quite a bit. –  Evan Pak May 20 '13 at 12:38
    
@EvanPak - that's the scary part... I do! (Typically before the device is even in my possession.) I still missed it somehow. Or perhaps forgot it because I didn't care at the time. –  AJ Henderson May 20 '13 at 12:49
    
@AJHenderson, I'm sure that I've done the same thing with my cameras. –  Evan Pak May 20 '13 at 16:17

2 Answers 2

Gels aren't generally available as screw-on type filters. To place a gel on the front of the lens requires a holder of some kind and a much larger quantity of the filter media. Many "sample" sets of various color gels come in sizes that allow for trimming to fit a rear filter holder but not large enough to fill a front sized filter holder. Due to the less durable materials a gel filter is made of, it is protected from potential damage when inserted in a rear holder.

share|improve this answer
2  
The sample swatches are almost always of lighting filters ("cine gels"), which are not the sort of thing one would ordinarily use in the optical path when creating an image. Imaging gels are usually small, delicate (traditionally, actual gelatin), optically flat and relatively expensive. –  user2719 May 20 '13 at 3:12
    
@StanRogers - Interesting. I've never come across any type of gels other than the "cine gel" type. I've searched the B&H and a couple of other photo supply houses websites trying to find "Imaging gels" without success. Could you point me in the direction of somewhere that offers them? –  Michael Clark May 20 '13 at 10:08
1  
They're not particularly common anymore, since their main uses (colour correction and B&W contrast) have largely become the province of post-processing. The main supplier was, at one time, Kodak (the brand to search for is Wratten). B&H still sells them. –  user2719 May 20 '13 at 10:28
1  
Thanks! So for use in a lens like the EF 17-40 f/4L you would still need to purchase a larger size of the material and trim to fit the holder at the rear of the lens? Do you know if more than one thickness of the ND gelatin would fit in the internal holder? I could also see using the ND material to create an internal graduated filter by trimming it smaller than the holder size in the vertical dimension. –  Michael Clark May 20 '13 at 12:34
1  
The gels (real gelatin gels, at least) are really, really thin, so yes, you could fit multiples. The problem is that they'll stick together when it's humid and warm, and Newton's rings aren't an unknown side effect of stacking if the filters are warped/rippled. They're also really easy to tear, snap and permanently fingerprint (hey, they are gelatin after all). They're optically much better than glass, but such a royal pain — there's no getting around the fact that they're expensive disposables, so if you're not making money with 'em... –  user2719 May 20 '13 at 19:27

This isn't meant to be an exhaustive list or answer as I have very little experience with this but wanted to point out of the obvious reasons:

Cons of rear filters

  • Having to remove the lens each time to add or remove a filter
  • Does not allow filters requiring manipulation(vari-ND or circular polarizers for example)

Pros of rear filters

  • Allows filters to be used when screw on isn't an option(fisheye lenses)
  • No chance of vignetting from rear filter
  • Ability to stack even more filters with less potential for vignetting
  • Smaller size might cost less
  • Less chance of scratching filter
  • Smaller size to carry and travel with

Unknown as pro or con off rear filters

  • Cost
  • Optical quality
  • Availability
share|improve this answer
    
Note that many lenses need not be removed to change a gel filter. You only slip out the holder change filters, slide it back in and lock. –  Itai May 20 '13 at 1:52
    
Yeah good point itai. I've never owned one of those so I always forget about them. –  dpollitt May 20 '13 at 2:03

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.