Film Holder as Reducing Back

[William Marderness]

Does anyone know of an 8x10 sized film holder that accepts 4x5 film? Such a film holder would serve as an inexpensive and universal reducing back. Can a film ho lder be modified to accept smaller film?

[George Losse]

I modified a couple of 8x10 holders to 4x10 buy gluing down small pieces of plastic inside the holder onto the septum of the 8x10 holder. Do under stand that this made the holder unusable for 8x10.

[Robert A. Zeichner]

There is an inherent problem in doing this sort of thing. The depth tolerance for 5x7 and 8x10 is progressively looser than it is for 4x5. It is therefore possible that an 8x10 holder would suspend the film within the specified location for acceptable focus on 8x10 film, but clearly out of the specified location for equally acceptable results on 4x5 film.

[Robert A. Zeichner]

I checked my data files for the specifics in case you're curious. The ANSI spec for photographic film holders (Z38.1.51-1951) states that the depth for a 4x5 holder is 0.197" +/- 0.007". For a 5x7 holder it's 0.228" +/- 0.010". For 8x10 it's 0.260" +/- 0.016". As you can see, unless whatever device used for holding 4x5 sheet film in a larger holder also moved the film closer to the lens, your results would most likely be noticeably out of focus!

[Jonthan Borden]

Not necessarily true. The 8x10 ground glass in the 8x10 back is still calibrated for the 8x10 film depth and hence this will work although the tolerance for error is greater.

[Robert A. Zeichner]

Assuming the groundglass is dead nuts perfect (they seldom are) and that the film holder depth is centered within the specified tolerance, you might get acceptable results. The chances of this are slim. Using a film holder as a reducing back is crude at best. I've seen too many cameras with gg's out of alignment to a degree that use of film holders of the correct size yields less than perfect results. Let's get serious here. If you're working in 8x10, isn't it a safe assumption that you can afford 8x10 film? And if you can afford that why not just get a reducing back made for the camera? If no such back is made, perhaps a reducing back for another type of camera could be adapted. At least this way there is some chance of the gg being in proper alignment with the average film holder.

[William Marderness]

Actually, I can afford 8x10 film (B+W), but not for the testing I am doing. I found a reducing film holder on ebay, and will use it with 4x5 film to make density tests. I do not want to buy a $400 reducing back, nor do I want to carry it around. If the reducing film holder works okay, I will use it for color film, since I cannot afford 8x10 color film.

[Robert A. Zeichner]

OK, I see your point. Do you have access to a collimator? If you can get the use of one for an hour or two, you can "calibrate" an 8x10 holder for use with 4x5 film. What you need to do is determine the difference in optical depth between your ground glass and the surface of the plenum in the holder you select for modification. This will tell you how much you would have to "build out" the plenum depth to hold the film in the proper plane. Mylar shim stock is what I would recommend to do this in that it should be dimensionally stable. Keep in mind the 0.007" thickness of the filmstock (TMX/TMY) If you're using Tech Pan or something different, use that film's thickness as your basis for determining depth. To create the film holder, you might cut a piece of Mylar to a dimension of about 1/4" larger than 4x5 film and fold over about 1/8" along three edges. Trim the ends to create an easy to insert pocket for the film. Make certain you use a holder that is on the deep side of tolerance and build out with Mylar otherwise the 4x5 sheet will be too close to the lens. If you do this, let us know how you make out.

[William Marderness]

Robert, thanks for understanding. As you can see from another thread, I spent $100 on film just test Xtol, and ended up with nothing, that is, no consistent development time. I wish I had spend $30 on 4x5 film instead.

[Mark_437]

William - I gather from your comments that you're mainly interested in this for doing testing (development times, etc.). If so, a quick and dirty fix is simply to tape one (or two) pieces of 4x5 film directly onto the septum of an 8x10 holder, then fire away. I believe I first heard of this from Fred Picker's writings, but I'll bet it's been done for ages. I'd use small pieces of low-tack drafting tape in the corners. Obviously, you're not going to make any "real" photos this way, but it will reduce your cost for film testing by a factor of four.

Cheers!

[Alan Gibson]

You might be able to create darkslides that only expose a quarter of the sheet at a time. Not a perfect solution, of course, because you have to fiddle with the lens for each of the 4 shots, and they each have to receive the same development.