basic question

[Barbara Jaffe]

Need to know tonight. I know that exposure for large format photography requires bellows extension factors because the lens is further away from the film when focused on other than infinity. My question is really basic - in 35mm is the principle the same?

[Oren Grad]

Yes, the principle is the same.

[Vaughn]

The square of the bellows extension divided by the square of the focal length of the lens equals the bellows extension factor. bellows out 10" with an 180mm (7") lens is 10x10/7x7 = 100/47 = 2 (or one stop)

The problem with 35mm is that the distances are smaller, thus if you are not measuring from the right places, you numbers may not come out too close. But then, if the 35mm camera has a meter, just read the meter as it corrects for all that automatically -- just like with filters.

[Barbara Jaffe]

The changes are often minimal, right, unless the lens is a very long lens? With normal lens on 35 it wouldn't be that noticeable.

[Eric James]

Vaughn's point about metering through the lens may be all you need to know for tonight's project, but there's more help here:

From the LF home page:
http://www.largeformatphotography.info/bellows-factor.html

A helpful tool:
http://www.salzgeber.at/disc/index.html

[Oren Grad]

Most late-model 35mm cameras have through-the-lens metering, so most users have never had to think about it. The latitude of print film will also mask fairly large exposure errors.

For practical purposes, it's rarely an issue other than in macro work with a camera that's either meterless or can't meter stopped-down when using bellows or non-meter-coupled lenses or extension tubes. And that scenario is extremely uncommon these days.

[Walter Calahan]

Yep, in fact most micro/macro 35 mm format lenses self-adjust its aperture to factor in bellows draw. Nikon and Canon do not blow off proper exposure with their macro lenses.