Back focal distance of large format camera

[Ho Pei Jiun]

Dear Sir/Madam,

I am a beginner to large format cameras.

May i know what is the standard rear focal distance of large format camera? And what does rear focal distance means?

Please kindly advise me. Thanks.

Regards,
Ho Pei Jiun

[Robert McClure]

Hello Mr. Ho Pei Jiun,

This may help:

"Back focal distance, meaning the distance (length) from the tip of the lens's furthest rear surface to the film surface where the image is focused."

see: http://www.nikon.co.jp/main/eng/society/nikkor/nwords-e.htm (http://www.nikon.co.jp/main/eng/society/nikkor/nwords-e.htm)

This distance would change according to what lens was being used, obviously. Further, it would have to change depending on whether the lens was focused at infinity or at, say, 1:1 (which would imply a greater-than-focal-length distance of lens from film).

Perhaps some of the more knowlegeable folks out there could comment. I'm guessing that your
" BFD" is always relative to what the lens is focused on and what specific portion of the film happens to be in focus.

Robert McClure - Atlanta

[Bob Salomon]

" what is the standard rear focal distance of large format camera"

There is no standard. Even the same focal length lenses from the same company can have different flange focal length distances.
For instance the flange focal length distance for the 150mm Apo Sironar N is 142mm while it is 147mm for the 150mm Apo Sironar S and was 141mm for the 150mm Apo Sironar W. For a 155mm Grandagon it was 169mm, for a 150mm Apo Sironar Digital it is 147mm.

No standard whatsoever.

[Peter Hruby]

Hi all,

Is it important to know that or not? What would be the reason to know it? Because of camera bellows contractions?

Peter.

[Ralph Barker]

Knowing the flange focal distance, or "back focus distance", can be useful when considering a lens of a focal length near either of the limits of the camera's bellows-extension specs (minimum or maximum extension).

[Alan Davenport]

Cameras don't have focal lengths, lenses do. There is a back focus distance, which is as one focal length measured from the rear nodal point when the lens is focused at infinity. There is also a flange focal distance, measured from the lensboard to the film plane (with the lens focused at infinity.)

Where this relates to the camera is the bellows length -- the maximum extension available. The camera must have at least as much bellows extension, as the flange focal distance of a lens for that lens to be usable.