Beginner-Bellows Question Small and Medium Format Macro

I just picked up a new set of bellows. I have a lot of reading to do. There seems to be a good bit of math and measurement ahead of me

on this. While playing around with the bellows, I bayonetted on a 80~160 zoom, and I think I figured this out:

A. Lens to subject distance drives focal length choice.

B. Extension drives magnification

C. Lens helical focus ring acts as a fine focus

D. Film plane to subject distance drives overall focus.

E. In-focus fields can be found in cycles that are based on division problems related to the four factors above.

Am I on the right track? Is this true? I ask because there are about a two hundred entries in this focal length and focus chart built into the

back pages of this bellows user manual. Any thoughts or verification would be appreciated. I think using these principles might simplify

my future bellows setups. Thanks, J.

My 2 cents

A. Lens to subject distance drives focal length choice.

Not exactly. It is only one of the many parameters. One can select focal length based on magnifications, back

grounds renditions, available light and/or tripod and etc. With some zoom lens, it can also be use as a mean to

focus macro distant.

B. Extension drives magnification

Change extension can change magnification but it also change effective aperture. Changing focal length with an

given extension also change magnification.

C. Lens helical focus ring acts as a fine focus

At macro distant with most lens (unless it is a rare telecentric design) it is hardly focus. One use a focus rail to

focus. Some Bellow has one built-in.

D. Film plane to subject distance drives overall focus.

Drive? Isn't it by definition a contant when it is in focus? I did heard some rare lens design that can have two film to

subject distants at two different magnifications. More like an exception than rule.

E. In-focus fields can be found in cycles that are based on division problems related to the four factors above

This one is way beyond me.

A good book to read is The manaul of Close-Up Photography By Lefkowitz

John- You are on the right track and the track can be long. Also know that degree of magnification using a bellows also dictates

exposure. Think of it like this: from the film's or sensor's point of view, the light source gets farther away (and dimmer) when you stretch

out the bellows, making the image bigger. It's something large format photographers have to deal with every day. And knowing about all

these rules does make your work easier. Good luck.

Thanks to you both for your feedback. Y'all brought out several of the points I had been noticing, but had not yet been

quite able to articulate. I will find a copy of that book soon; it just doesn't happen to be in my local public library's

collection. Thanks for your time. J.