What are typical minimal usable bellows extensions?

[Leonard Evens]

I am in the process of compiling an article about view camera geometry. Some of my calculations seem to require making an assumption about minimal usable bellows extension. Various factors, such as the stiffness of the bellows, the construction of the camera, limits of rise/fall or shift, and the rear depth of the lens beyond the lensboard will play a role. And generally speaking, one can't get much less than the focal length of the lens.

What are typical minimal bellows extensions?

Are there any factors I haven't listed which might affect that? For example, does the optics really work properly if the back of the lens is within a few mm of the gg, even if the focal length would theoretically allow it?

[robert fallis]

My portrait camera has a minimum, I suppose it's compression not extention.of 24cm,
but it's one I made and the bellows are to thick so I'm in the process of making some thinner ones
bob

[Joanna Carter]

Well, according to the Ebony specs, the minimum extension on my SV45Te is 55mm and I have no problem covering the GG with a 72mm SuperAngulon XL.

[Ole Tjugen]

Two of my cameras compress to below 30mm. The others don't, but since I rarely use a 47mm lens on anything larger than 4x5" it's not a problem. If I need REALLY wide, I'd have to look for a Hypergon to use on the 9.5x12" camera - which incidentally also compresses down to less than 30mm from lens board to GG.

For example, does the optics really work properly if the back of the lens is within a few mm of the gg, even if the focal length would theoretically allow it?

Of course it does. If the rear element of a lens is pressed against the ground glass / film when focussed at infinity, then that's the way the maker has designed it. There are even lenses (rare photogrammetry ones, mostly) which are designed for the film to be in contact with the rear element.

[Nick_3536]

My Shen FCL-810 with the bag bellows is riduculos. I think it's similar in design to the Phillips. Even with the stock bellows it'll do 90mm on a flat board. Which isn't bad for an 8x10.

[Dan Fromm]

Leonard, here are Graphic (Anny on, Super Graphic excepted) minimum flange-to-film distances pasted in from a spreadsheet. I apologize in advance for formatting problems.

Minimum Flange-to-Film Distances
For Selected Graphic Cameras
Distance
Size & Model (inches) (mm)

2 1/4 x 3 1/4

Miniature Speed 2 5/16 58.7
Pacemaker Speed 2 7/16 61.9
Pacemaker Crown 1 3/8 34.9
Century 1 3/8 34.9

3 1/4 x 4 1/4

Anniversary 2 1/2 63.5
Pacemaker Speed 2 5/8 66.7
Pacemaker Crown 1 5/8 41.3

4 x 5

Anniversary 2 9/16 65.1
Pacemaker Speed 2 5/8 66.7
Pacemaker Crown 2 1/16 52.4

From Graphic Graflex Photography, 10th Edition

I don't know what you intend to say in your article. I'm sure you've thought of it, but that won't stop me from suggesting that you consider discussing back focus (rear of lens to film plane at infinity) too. Modern w/a lenses have flange to film distances at infinity (what the French call tirage mechanique) much greater than back focus (tirage optique), so can be used on cameras with longer tirage mechanique than one would expect given the focal length and the camera's minimum flange-to-film distance. As for example Grandagons, Super Angulons, ...

[Leonard Evens]

I've studied the problem some more, and I realized that I also need the image circle to include the frame. That coverage anlge with limitations on rise/fall or shift, as well as the focal length should set some lower bound. Also, I am not interested in the bellows extension itself, but where the rear principal plane is in relation the film. If the standards are parallel, then there is no point in worrying about anything closer than the focal length, but it gets a bit confusing when you consider tilted lens plane. I am trying to see in that case whether it is possible to get closer than the focal length. The geometry is a bit complicated and it looks like there may be some messy trigonometry in figuring it out, but I think I can do it now.

[BOB BERESFORD]

Two of my cameras compress to below 30mm. The others don't, but since I rarely use a 47mm lens on anything larger than 4x5" it's not a problem. If I need REALLY wide, I'd have to look for a Hypergon to use on the 9.5x12" camera - which incidentally also compresses down to less than 30mm from lens board to GG.



Of course it does. If the rear element of a lens is pressed against the ground glass / film when focussed at infinity, then that's the way the maker has designed it. There are even lenses (rare photogrammetry ones, mostly) which are designed for the film to be in contact with the rear element.

Hi Ole

That's highly interesting.....I was under the illusion that only a Sinar F would get to 30 or below without radical custom jobs - similar to what I've done on a simple old Linhof mono ( much grinding and chopping ) and am planning on a Toyo G ( less violently ) .

[Ole Tjugen]

Bob,

My "main" 4x5" camera is a Carbon Infinity, which tends not to show up on lists of common view cameras as there were only about 80 of them made.

The 9.5x12" camera is a German tailboard-focussing plate camera from the early days of the 20th century - also not among the most common cameras.

[Nathan Potter]

Leonard, light falloff over the film would seem to be a big factor for a rear element very close to the film/GG. In the case of a tilted lens plane and the lens very close to the film plane the light falloff over the format would seem to be radially very non-uniform. I wonder if one could come up with a general expression for the radially non-uniform case.

Nate Potter