7x17 and 12x20 questions

Ales' · Mar 1, 2025

Hi, im planing to build an 7x17 sliding box camera to use with 360mm sitonar only to make one type of shot: full body portrait. The reason is that my studio is very small so i have 1.36m backdrop; narrow for 8x10… so when i contact print on platinum i tend do crop a lot. My assumotion is if 360mm is okay for 8x10 full width shot it shoud be fine on 7inch wide film. My question is woud i get streched head and legs considering that verticaly 360 is kind of wide? Magnifcication for small kids 1:3, average person woud be 1:4.5.

Now About 12x20. When ill have the money for 450mm nikkor im planing to order a back with bellows from an european camera maker.
He manufactures them for sinar but i came up with an idea: is it possibile to machine mounting plate for 12x20 back that coud slide into arca swiss base rail? My idea is that by avoiding carrier and og rail all’ toghether its possibile to lower enought the back to the base of the rail to maintain enought rise. Question is coud i achive indirect back tilt and swing by tilting and rotating camera and then adjusting the front standard? Where I can get fresnel lens for 12x20? Do adox still cut the film in this size?

Ales' · Mar 1, 2025

P.s. Accept advices on developing tank that woud fit both formats, and a source for negative sleeves in these sizes in europe.

Dan Fromm · Mar 1, 2025

Sitonar? Are you thinking of Rodenstock's Sironar? If so, the Apo-Sironar S should just cover 7x17. If you have the lens, ask it whether it will do what you need.

Ales' · Mar 9, 2025

Dan Fromm said:
Sitonar? Are you thinking of Rodenstock's Sironar? If so, the Apo-Sironar S should just cover 7x17. If you have the lens, ask it whether it will do what you need.

Sironar, my question is not about coverage but about stretching of the extremes of the negative.

Michael Mutmansky · Mar 12, 2025

What other camera systems do you have that you can test the concept of coverage with? Do you have a 35mm digital or a Fujifilm GFX? You can translate the focal lengths down to a smaller format because focal lengths and angle of coverage exhibit similitude amongst formats when you convert by the linear dimensional size differences between them (NOT the area, but the linear dimensions).

In the case of a banquet format, you need to take the long dimension and compare it to the long dimension on the other format, so for the 7x17, look at the ratio of 17" to the 10" length on an 8x10 for example. Disregard the short side because that isn't your constraining variable.

So an 8x20 is exactly 2x an 8x10 format, so the "effective" focal length in terms of an 8x10 lens will be the inverse ratio (1/2), so a 360mm will effectively have the angle of coverage (on the long dimension) of a 180mm on 8x10. That's getting pretty wide and you will likely have some visible "pulling" distortion getting near the edges of the top/bottom of a vertical shot.

For 35mm lenses, the ratio between 7x17 and 24x36mm is 12 (convert to mm and then do the ratio). So a 360mm lens is equivalent to about a 30mm lens on a 35mm camera. If you have a zoom that covers this focal length, you can test it a bit in the studio and see how things look at the top/bottom. But don't look into the corners, you have to take the 35mm shot and crop the center into the 7x17 ratio first. By far, the worst pulling will be cropped away.

a 30mm lens isn't hugely wide, but it will show some pulling towards the edges.

One thing you have going for you is that the shot will be in a semi-macro condition and that means the angle of coverage decreases slightly, so maybe you won't really find the pulling to be objectionable.

The reason this occurs is what happens when the lens is shooting close up. Imagine a lens focused at infinity, it will have a coverage on the film that can be expressed in degrees and it creates a cone of light that the film is placed within to create the image. When you refocus to 1:1 with the same lens, the cone of light remains the same, but the lens will be 2x farther back from the film, so the actual circle of light will be 2x larger and that means the film will actually only receive light from 1/2 the angular coverage that it will when shooting at infinity. This is why when shooting at 1:1 you need to add two stops to exposure calculations as well, by the way, since the film is only getting 1/4 of the light that was originally calculated for the film in an infinity condition (1/2 in each dimension times 1/2 in the other dimension equals 1/4, or two stops).

Your full-height portrait on a 7x17 isn't anywhere close to 1:1, but it isn't at infinity either, so you will essentially have a lower angle of coverage when shooting close up than you might think and this might help you out.

Ales' · Mar 12, 2025

Michael Mutmansky said:
What other camera systems do you have that you can test the concept of coverage with? Do you have a 35mm digital or a Fujifilm GFX? You can translate the focal lengths down to a smaller format because focal lengths and angle of coverage exhibit similitude amongst formats when you convert by the linear dimensional size differences between them (NOT the area, but the linear dimensions).

In the case of a banquet format, you need to take the long dimension and compare it to the long dimension on the other format, so for the 7x17, look at the ratio of 17" to the 10" length on an 8x10 for example. Disregard the short side because that isn't your constraining variable.

So an 8x20 is exactly 2x an 8x10 format, so the "effective" focal length in terms of an 8x10 lens will be the inverse ratio (1/2), so a 360mm will effectively have the angle of coverage (on the long dimension) of a 180mm on 8x10. That's getting pretty wide and you will likely have some visible "pulling" distortion getting near the edges of the top/bottom of a vertical shot.

For 35mm lenses, the ratio between 7x17 and 24x36mm is 12 (convert to mm and then do the ratio). So a 360mm lens is equivalent to about a 30mm lens on a 35mm camera. If you have a zoom that covers this focal length, you can test it a bit in the studio and see how things look at the top/bottom. But don't look into the corners, you have to take the 35mm shot and crop the center into the 7x17 ratio first. By far, the worst pulling will be cropped away.

a 30mm lens isn't hugely wide, but it will show some pulling towards the edges.

One thing you have going for you is that the shot will be in a semi-macro condition and that means the angle of coverage decreases slightly, so maybe you won't really find the pulling to be objectionable.

The reason this occurs is what happens when the lens is shooting close up. Imagine a lens focused at infinity, it will have a coverage on the film that can be expressed in degrees and it creates a cone of light that the film is placed within to create the image. When you refocus to 1:1 with the same lens, the cone of light remains the same, but the lens will be 2x farther back from the film, so the actual circle of light will be 2x larger and that means the film will actually only receive light from 1/2 the angular coverage that it will when shooting at infinity. This is why when shooting at 1:1 you need to add two stops to exposure calculations as well, by the way, since the film is only getting 1/4 of the light that was originally calculated for the film in an infinity condition (1/2 in each dimension times 1/2 in the other dimension equals 1/4, or two stops).

Your full-height portrait on a 7x17 isn't anywhere close to 1:1, but it isn't at infinity either, so you will essentially have a lower angle of coverage when shooting close up than you might think and this might help you out.

I have made some shots in past with wider angle say 38mm on 6x6 but that was “flat field” lens. On my gfx shortest is 35mm 28mm equivalent so full body shots are still okay.
I ask because my Fuji 250mm on 8x10 distorts extremes (picture attached) with full rise.
If I have to use a longer lens ill just buy it and make camera longer.
I stated intended magnification 1:4-1:5

Michael Mutmansky · Mar 13, 2025

I'm not sure the coverage angle of the lenses you have, but I suspect it is 64 degrees +/-? That is equivalent to the coverage of a 35mm lens on a 35mm camera so when you use lots of rise or shift and get close to the edges of coverage, you will have pulling similar to that of the far corners in a 35mm lens on 35mm.

However, it won't feel as strong because you don't have a wide format horizontally (if shooting 7x17 vertically) and therefore the corners on the frame won't be pulling away from each other too strongly side to side. Add to that, the fact that you are shooting at less than infinity and I suspect you'd feel OK with it, but you should be able to test it by shooting a 35mm lens on a 35mm camera or a 45mm lens on the GFX (both vertically) and then crop the images to the 7x17 proportions and then look carefully at them and you will have your answer.

One thing though, if you are shooting a full height shot with a lens that doesn't have extra coverage, you will have the camera at about waist level, so shooting up the person's nose a bit. It might make sense to look into a longer lens so you can have the camera a little higher up and then apply some fall in the shot to include the feet. It might feel a bit more natural.

this site:

https://nielspn.dk/files/apo-sironar-n.pdf

...says the IC of the 360mm is 435mm at infinity. You need about 465mm for 7x17. I am guessing the official number is a little conservative and since you are not at infinity, you may not have a problem, but I think I'd be looking at a 450mm lens for this to give you more room for movements and to also address the potential pulling issue.

One thing I can suggest, because I did this at least a few times in the past... Make a mockup of the camera out of cardboard and use a piece of vellum for the GG and you can see how the coverage works with the lens, and you can also see how much it pulls in those conditions.

grain elevator · Mar 13, 2025

Isn't the basic concept here that a natural perspective without unpleasant distortion will result from a natural distance? A full body portrait taken from an uncomfortably close distance will look uncomfortable. This can be exploited for effect, but if you want natural and pleasant looking pictures, they'll have to be take from a comfortable distance from which you'd look at a stranger's body. You can't get around that with cameras and lenses, it's geometry. And you unfortunately just need the space for it. In your position, I'd ask a model to pose for me and work with a digital camera or an improvised director's viewfinder / frame to figure out what distance/perspective I want. Then chose camera/lens combination that gives you that.

Ales' · Mar 13, 2025

grain elevator said:
Isn't the basic concept here that a natural perspective without unpleasant distortion will result from a natural distance? A full body portrait taken from an uncomfortably close distance will look uncomfortable. This can be exploited for effect, but if you want natural and pleasant looking pictures, they'll have to be take from a comfortable distance from which you'd look at a stranger's body. You can't get around that with cameras and lenses, it's geometry. And you unfortunately just need the space for it. In your position, I'd ask a model to pose for me and work with a digital camera or an improvised director's viewfinder / frame to figure out what distance/perspective I want. Then chose camera/lens combination that gives you that.

Negative is shorter in horizontal than an 8x10, so the distance is greater with 7x17 If I take “full person width” portrait than on 8x10 , just more legs, with same focal legth, already figured that out. Result I want is “Avedon” style shot but with less space blank space on sides and full legs, he used 360mm, but Thanks for suggestion, I already done a bit of portfolio shots for clients in my studio and only problem was photoshoping backdrop to make it larger( dont like shots that include grear around backdrop).

_T_ · Mar 25, 2025

For a full body portrait on 8x20 with a 360mm Sironar you would have to place the camera ≈1.77m from the subject which would give you a bellows extension of ≈427mm and a circle of coverage at f/11 of ≈532mm which is not quite enough to cover 8x20. If you stop down to f/22 you will have a circle of coverage of ≈558mm and it will be able to cover the frame.

If you don’t mind shooting stopped down so far it should work okay. Although you would need lights about twice as bright as the sun to be able to shoot on ISO 100 film so it could become unpleasant to be the subject, especially if you shoot slower film.

I don’t see a problem with the subject distance. The range of 1.5-2m looks pretty normal to my eyes, but you would have to judge for yourself. It’s a pretty personal thing deciding which kind of distortion looks best.

Unfortunately if these limitations are not acceptable to you, moving up a focal length to the 480mm sironar wouldn’t really help as it’s got a smaller angle of coverage and you’ll hit the same limitations only the camera will be a little further from the subject.

You would have to spend quite a bit more on the 360mm sironar s to be able to shoot at wider apertures. I see a few listings priced in the $3,000-$4,000 range.

7x17 and 12x20 questions

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