FOV question?

[rbiemer]

This fall/winter I am building myself a 6 x 9 (on 120 film) pinhole camera and would appreciate it if you folks would help me out a bit.
I want to make this one with multiple focal lengths and I think I'll be able to use my FSU turret finder if I have the correct equivalent focal lengths?
So, 6 x 9 is 2.5 times as large as 24 x 36 and if I'm correct, I should be able to use:
28mm for 70mm
35mm for (aprox)87mm
50mm for 125mm
85mm for (aprox) 212mm
135mm for (aprox) 337mm

Do these seem like reasonable approximations to you folks?

I will likely not use all five but will probably go for three: wide, "normal", and short tele or 70, 125, and 337.
Not sure if I'll be attempting to make a bellows for this or--more likely but I've not settled this in my head yet--something like a set of nested boxes.

I have some old cameras I'll use for some of the winding mechanism, cold shoe, and red window.

Thanks, all!
Rob

 

[pvdhaar]

The ratio is not exactly 2.5, that because the actual 6x9 frame is 55.6mmx85.6mm.

But it's close enough according to an angle of view calculator:

70mm on 6x9 is ca. 72.2 degrees; 28mm on 35mm is ca. 75.4 degrees
87mm on 6x9 is ca. 60.8 degrees; 35mm on 35mm is ca. 63.4 degrees
125mm on 6x9 is ca. 44.4 degrees; 50mm on 35mm is ca. 46.8 degrees
212mm on 6x9 is ca. 27.1 degrees; 85mm on 35mm is ca. 28.6 degrees
337mm on 6x9 is ca. 17.2 degrees; 135mm on 35mm is ca. 18.2 degrees

Hope this helps..

 

[rbiemer]

Very helpful, indeed. Thanks!
And you reminded me of the Pinhole Designer software so I have got that again (see here for it: http://www.pinhole.cz/en/pinholedesigner/ )
And since I'm building this camera, I can decide my own film gate size. Which will be as close to 56 x 90 as I can get.
Thanks!
Rob

The ratio is not exactly 2.5, that because the actual 6x9 frame is 55.6mmx85.6mm.

But it's close enough according to an angle of view calculator:

70mm on 6x9 is ca. 72.2 degrees; 28mm on 35mm is ca. 75.4 degrees
87mm on 6x9 is ca. 60.8 degrees; 35mm on 35mm is ca. 63.4 degrees
125mm on 6x9 is ca. 44.4 degrees; 50mm on 35mm is ca. 46.8 degrees
212mm on 6x9 is ca. 27.1 degrees; 85mm on 35mm is ca. 28.6 degrees
337mm on 6x9 is ca. 17.2 degrees; 135mm on 35mm is ca. 18.2 degrees

Hope this helps..