ULF > Macro options?

[drew.saunders]

Many of your equations are here: https://www.kennethleegallery.com/html/tech/bellows.php

So, with 40x50", a 4x life size image will give you a subject size of 1/4 your plate size, or 12.5x10", which would be a pretty good tight head shot not unlike the example in your first post.

Let's stick with inches to make life easier. You've had a 24" (600mm) and 36" (900mm) lens recommended, so we'll do the math with either of them. Common lenses in those focal lengths are Tessar formulas, where the image circle is just a bit larger than the distance of the lens to the image plane, so we'll stick with that math. I.e.: A 24" lens focused at infinity will have a 24" image circle, and you need a 64" image circle, so that won't work.

OK, 4x life size:
M = (B-F) / F
where M = magnification ratio, B = bellows extension, F = focal length

4 = (B-24)/24, solve for B. That's 72" of bellows extension, giving about a 72" image circle (and many stops less light), so a 24" lens would work just fine. 72" is 1.83m for most of the world!
4 = (B-26)/36, that's 108" of bellows draw. That's a pretty large camera, if you want to work with a 900mm/36" lens!

What's your working distance with a 24" lens and 72" of bellows, or a 36" lens with 108" of bellows?

1/F = 1/D + 1/B
where F = focal length, D = distance, B = Bellows Draw

1/24 = 1/D + 1/72, D is 36" (just under a meter in the modern world). That may be a bit close to your subject, or not, that's for you to decide.
1/36 = 1/D + 1/108, D is 54".

Maybe try to find a 800mm or 900mm lens? Good luck!

[cpjfox]

I bought that book on Dan's advice years ago

I suggest you first try it on tiny format 8X10…

I’m embarrassed to say i’ll probably start on 4x5

Many of your equations are here: https://www.kennethleegallery.com/html/tech/bellows.php
…
… Maybe try to find a 800mm or 900mm lens? Good luck!

Thankyou for taking the time to help show the algebra behind it, it will save me some time and misery no doubt as i plan the next phase.

With any lens, the maximum magnification is infinity…

Thankyou for sharing also, foolishly i’m self taught without regard to youtube or books, so a lot of what seems pretty common knowledge is still mysterious for me.

No, at 1:1 the film plane-to-subject distance is 4 focal lengths. And at 1:1, the front node-to-subject distance and rear node-to-film plane distance are 2 focal lengths…

Please stop seeking enlightenment via question and answer sessions on a bulletin board…

Thanks Dan for providing me with the means to gain enlightenment, I will be buying a copy of the book this week and I will study it in earnest. I am sorry for overstepping the bounds of what this forum is for.

If you work out how much magnification you want, and what the distance will be from the lens to your plate, the math to determine the needed focal length is a simple algebraic equation.
Average human head is around 9" from chin to top of head, how big do you want that on your 40x50 plate?
What will the distance be from your lens to your plate?

Hi Tracy, firstly wow, 20x24 polaroid, thats on my bucket list, before I die I hope to travel to america and use one of those mammoth cameras, thankyou for keeping the cameras and my dream alive. To answer your question I want the head to be most of the plate, nominally ~40” I’ll sit down and do some maths about the distance from lens to plate, I will make the camera as big as I have to, it’s basically going to be an oversized “Big Shot” for this project.

[Dan Fromm]

I am sorry for overstepping the bounds of what this forum is for.

There are few bounds here, and they are enforced by the moderators. You didn't overstep the bounds, you made the common beginner's mistake of asking an apparently simple question that required a book-length answer. The bulletin board medium is useful, but the helpful people who post on bulletin boards can't be expected to put books up on them.

Good luck, have fun. Never forget that there's much to be said for the joy of tinkering.