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About 20 years ago when I was just starting out in photography, I was at a portrait photographer's studio. He was showing me some of his equipment. One thing that I found interesting was a set of square filters he used. They were made of solid glass, about 1/8" to 1/4" thick and appeared to have metal flakes at different depths in the glass. What was odd was that the filters were inserted between the lens and the camera body rather than being mounted to the front of the lens. If I recall correctly, they gave a glowy, softening effect that I've heard videographers refer to as the "Barbara Walters" effect.

What are these filters called? I've never seen anything similar since then, though I don't do much portrait photography.

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  • \$\begingroup\$ Any gelatin filter that was left lying nearby while one drilled, filed, or sanded something while tinkering with eg lens mount or tripod mechanics.... \$\endgroup\$
    – rackandboneman
    Feb 3, 2019 at 9:10
  • \$\begingroup\$ @rackandboneman gels are not likely to be mistaken for "solid glass 1/8" to 1/4" thick." \$\endgroup\$
    – Michael C
    Feb 3, 2019 at 14:50

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Although not as common as they used to be, there are lenses made with gelatin filter holders on the back of the lens. Probably two of the most common ones still in current catalogs are Canon's EF 17-40mm f/4 L and EF 14mm f/2.8 L.

enter image description here

Most lenses with such filters are wider angle lenses that make it problematic to place a filter in front of the lens, due to either bulbous front elements or issues with vignetting due to the lens' wide angles of view.

Going back even further, square glass filters behind the lens were much more common with large format view cameras than they are with smaller format cameras such as FF and smaller digital cameras. They were common enough that everyone familiar with large format cameras seems to know that inserting a glass filter behind the lens will alter the focus distance to the film by 1/3 the thickness of the filter. Thus the camera should always be focused after the filter is in place.

Related:
Why would I use a rear gelatin filter over a front filter?
How do rear gelatine filters compare optically with "regular" front-mounted filters? Where to buy them? How to cut them?

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  • \$\begingroup\$ This certainly sounds like what I think I remember seeing. Would you know of any brands of such filters? (Or model numbers?) I'm just curious to know more about them. \$\endgroup\$
    – user1118321
    Feb 3, 2019 at 4:51
  • \$\begingroup\$ There are a few links in the linked related questions and their answers, as well as a discussion on how to find them in this answer. \$\endgroup\$
    – Michael C
    Feb 3, 2019 at 14:48
  • \$\begingroup\$ Very interesting! Thank you for your help. It's entirely possible that he was only using gels between the lens and body and the other filters went on the front, and I just don't remember that part. \$\endgroup\$
    – user1118321
    Feb 3, 2019 at 19:00
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As far as I'm aware, most square/rectangular filters go in front of the lens in a holder. Some lenses are designed to take filters behind the rear element, but the ones I've seen are round. Thick glass would also be expected to affect focus. So the lens and filter would have to have been designed specifically to work together.

  • A teleconverter with multiple elements might appear to be thick glass and would fit between the lens and body. A poor-quality one could give images a "glow" or soft-focus look.

  • Michael C states "square glass filters behind the lens were much more common with large format view cameras". Are you able to recall whether the photographer was using a large-format view camera?

Here are some other possibilities, though none fit your description exactly:

  • There is a glimmerglass filter, which Tiffen describes as having 'a distinct silver 'sparkle'".

  • Some diffusion or soft-focus filters have a mesh within them that you might have thought were metal flakes.

  • Maybe it was a DIY filter with something sandwiched between two pieces of filter glass.

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  • \$\begingroup\$ Thanks! My memory is definitely not great. The glimmerglass and smoque filters look like the effect that was produced. The filter was definitely not a teleconverter, though, as I had him scan one with a flatbed scanner and give me the resulting image file. (Alas, I no longer have the file.) But this is definitely in the right direction. Thank you! If it helps, I'm pretty sure they were rectangular and not round. The DIY aspect is an interesting thought. I don't think he made them himself, but it's possible. \$\endgroup\$
    – user1118321
    Feb 3, 2019 at 2:47

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