Using filters on rear element of LF lenses

[ed_brock2]

I am noticing the rear element of my lenses is much smaller in

diameter than the front. I am thinking about adapting my screw-in

glass filters to that smaller size. It would seem that I could get

by with much smaller filters - especially for wide angle lenses. Or

is this not true? There must be other considerations or everyone

would be doing this?

[bruce_watson1]

Putting the filter on the rear element hrows your focus off by, IIRC, 1/3 the thickness of the filter. So after you do your initial setup, you add the aditional steps of pulling the lens, screwing in the filter, going back under the dark cloth, and touching up critical focus (a real treat depending on the filter and the light). There's enough going on that most people, including me, would rather spend the money on larger filters and simplify the workflow.

 

I've done it both ways, and tossed a number of slightly out of focus negatives because I forgot to re-focus after putting on the filter. IMHO, a filter on the front is *much* nicer. Of course, YMMV.

[dave_moeller]

Bruce is quite right regarding the focus shift caused by mounting filters behind the lens. If you're going to do this, it's best to do it with thin filters (gel or polyester), as the focus shift will be so small as to make no difference.

 

The other option is to focus with the filter in place; depending on the filter and the light, this can be a simple answer or a real pain. With a yellow filter you probably won't have any trouble, but with a dark ND you'll likely go crazy trying to focus with the filter in place.

 

I finally opted for thin filters. It's worked fine for me so far (although you still have to remove the lens to put the filter in place).

[scott_walton2]

Calumet makes a gel holder for the rear and with the thin gels, I have never seen any issues with focus or anything else for that matter. It is, a bit more problematic as far as focusing through the filter due to it's darkness but with the help of a bright screen it is tolerable.

[danny_wong2]

I used to use behind the lens mount of gel filter to balance my lights using the cc filters. This way I use 3X3 as opposed to harder to get and expensive 4X4 in front of the lens. ALso due to being protected by the bellows and the set cannot be disturbed until we get final Ok for the tranny rear mounting gel filters make them last longer and less prone to dust pickup.

 

Due to focus plane shift I never tried using glass filters behind the rear elements

 

HTH

DW

[Aoresteen]

I mount filters behind my 15mm CV Heliar with a custom SK Grimes adapter and use it on my Leica IF. Since the depth of field/focus is so great with the 15mm I have not had a problem.

[andy_shand1]

it makes sense also to put the first one on the back (focus with it in place)and if you need a second then put it on the front. With a rear mount the shadeing issue is much less. Two together is a real no no with bright lights/sun in the scene ...you see having two flat layers right opposite to each other which are reflective (gels are reflective and probably the others too) will act as mirrors between each other causing unwanted ghosting and flare. The closer they are the more obvious this problem gets. Bearing in mind the lens itself is curved and hopefully coated then this problem falls away if its one flat filter against the lens. ie one on the front if you have to and one on the back....the back being the first if possible. I found this out the hard way.