Mounting gels behind the lens, 4x5

[Ulophot]

In pursuit of a Wratten 47 gel for enlarging, I picked up a set including 6 other gels as well -- red, yellow, and green -- nearly all mounted in black metal frames, for $10. Made my day. Anyway, I'm inclined to keep my stack of screw-ons for my MF kit and use these for LF. Adams wrote about rear mounting to keep flare down. Since I have no matte box, it makes sense to me to mount the filters aft of the lens. My camera takes the Linhof lens board. So, two questions.

1. Do I need to make a holder for these that attaches, permanently or otherwise, to my two lenses' (210, 135) boards ?

2. If so, would you recommend keeping the filters in the frames or not?

I suppose a holder could be as simple as a little arm that clips the top corner of the gel above the lens, but then tilt could be an issue. Design thoughts or illustrations?

Thanks.

[j.e.simmons]

Fred Picker made a little U-shaped piece from spring steel. It extended a bit farther back than the rear lens element. He used a magnet to hold the filter gel in place behind the lens.

[Bob Salomon]

Fred Picker made a little U-shaped piece from spring steel. It extended a bit farther back than the rear lens element. He used a magnet to hold the filter gel in place behind the lens.

To aluminum boards and non ferrous lens barrels?

[j.e.simmons]

He glued (I think) the adapter to the back of the lensboard above the lens.

[Ulophot]

John, thanks. I'm the world's worst builder. Can you offer a drawing of the design? I can imagine something, but I'd do it wrong.

I can, however, imagine gluing vertical pieces of stiff black matte plastic or metal on either side of the lens boards' rear surfaces, acting as slots into which the other part could be easily inserted for use, so that one could be switched quickly between lens boards.

[Ulophot]

Hey, folks, I just OCR'd my PDF of the complete Zone VI newsletters and found Fred P's complete description. It in Dec. 1977. If anyone's interested, I'll transcribe it.

[j.e.simmons]

I can, however, imagine gluing vertical pieces of stiff black matte plastic or metal on either side of the lens boards' rear surfaces, acting as slots into which the other part could be easily inserted for use, so that one could be switched quickly between lens boards.
I did that using small pieces of wood. It worked just fine. Glad you found Fred’s instructions. - my drawing ability is not very good.

[Conrad . Marvin]

Gels are fragile but I never figured that I’d be using the corners so I taped them to the LB or the bellows.

[Drew Wiley]

Expect a bit of inevitable image degradation if gels are used behind the lens. This has been argued back and forth forever; but regardless of the optical theory, it's almost impossible to keep gels dirt, smudge, and crinkle free. But if ya gotta do it, there were little spring-clip devices once commercially made for that. B&H still offers the Lee metal version, which could easily be thread-adapted by epoxying on a step ring. Otherwise, improvise. It's actually easy to make a thread adapter for the front end of the lens, just like I just described. But I've bought those outright too. I never use gels for image-forming purposes unless there is no other option, or unless I'm just testing for effect prior to acquiring an equivalent real glass filter. They do need to be pampered.

[Alan9940]

I don't use gels behind the lens anymore, but back when I did, I made a simple Z thingy out of some sheet steel with a depth slightly more than the rear lens element, glued it to the back of the lens board (both wood and metal boards), then used a small magnet to hold the gel in place. As already shared, gels are a bit of a pain because they attack dust easily, scratch easily, kink easily and, yeah, can't tell ya how many times the thing blew off the back of the lens before I could get it into the camera. ;)

[Drew Wiley]

They last a lot better in the lab or studio than in the field. But ya still gotta be careful. Keep around some alcohol wipes for your fingers. And some colors are more susceptible to fading than others, which is one reason I never buy used or even old gels unless I'm certain of their storage conditions. The old Kodak Wratten handbook is excellent, with all its spectrograms, transmission characteristic, fade rating, etc.

[Tin Can]

Horsemen Camera offered a behind the lens mount

I once got a DIY Horseman glue up emulation

Never tried it, seemed a poor idea

[B.S.Kumar]

The Horseman BTL filter holder looks like this:

https://i.postimg.cc/v8ScFCbk/Horseman-BTLLens-Board-01.jpg

https://i.postimg.cc/4yMd6HWs/Horseman-BTLLens-Board-02.jpg

https://i.postimg.cc/8CDCmSmJ/Horseman-BTLLens-Board-03.jpg

The filter holder can be detached, but it is too large to fit a camera that takes Linhof Technika boards.

Kumar

[Ulophot]

Kumar, that's quite an apparatus, a testament to the extensive thoughtfulness that went into professional design in an economy that valued industrial quality and innovation.

[brian mcweeney]

I'm sure a lot of people will frown on this idea but ... in my early days of commercial photography we almost always used CC wratten filters behind the lens. We simply rolled a piece of black/photo masking tape backwards along the rear lens edge. This made a sticky place for the very lightweight wratten filter to attach itself to.

[Drew Wiley]

Yep- There's nothing like trying to get old masking tape and its residue off of equipment. The labs and studios used miles of it. That horrible custom only ended when duct tape got popular instead - even worse.

[Tin Can]

Lee Gelsnap Filter Holder will fit on rear

https://www.leefilters.com/index.php/camera-directory/camera-dir-list/category/gelsnap-filter-holder