View Full Version : Determining maximum focal length for a given bellows extension

Sean Galbraith
21-Dec-2010, 11:43
I'm going to be shopping for a new 4x5 camera soon, and wanted to know if there is a formula for determining the longest focal length a camera can use based on a given maximum bellows extension? This is probably a supernoob question.

21-Dec-2010, 12:10
if the camera specs say 450mm of extension then you can use a 450mm lens on it focussed @ infinity, anything closer and you need longer bellows.

Louis Pacilla
21-Dec-2010, 12:10
Hi Sean

It depends on how close you intend to focus your longest lens. If your bellows stretch to 15" , Then the longest lens you can focus to infinity is a 15" focal length. If your bellows are say, 22" then 22" lens to infinity . See what I mean. If your bellows are 15" the longest lens would want to use in practical terms might be say,14" lens. This leave you some extra bellows for closer than infinity focus.

Hope this makes sense & does not simply confuse you.

Sean Galbraith
21-Dec-2010, 12:12
That's easy enough. Thanks!

Bob McCarthy
21-Dec-2010, 12:13
Realistically, unless your doing macro work, lenses up to 70% of bellows entension work great for ordinary photography. If you need to get closer, use a shorter lense.

Most 4x5 camera will work fine with up to 300mm lenses, unless the camera is specifically designed to work with shorter lenses.


Len Middleton
21-Dec-2010, 12:22

If you want to put some real world numbers to it, my 4x5 has about a 16" bellows which restricts my 355mm (around 14") process lens (non-telephoto design) on a flat board to focusing no closer than about 10 feet.

You will note I added some additional information. You can get telephoto designs that can have a shorter flange to ground glass distance at infinity, and you can mount lenses onto "top hat" lensboards (for long lenses) or recessed lensboards (for wide angle lenses), as well as flat lensboards.

Hope that is helpful and does not create additional confusion,


Sean Galbraith
21-Dec-2010, 12:28
I think I understand what you're saying :-)

21-Dec-2010, 15:53
Bellows extension = Focal length to focus at infinity.
Bellows extension = Focal length x 2 to focus 1:1 macro

Most of your work will be between those two extremes.