Exposure question

[MacCaulay]

Does racking out the bellows when focusing alter the amount of light hitting the film?

 

[Colin Graham]

Very much so. There are some factor calculation formulas here

 

[Roger Hicks]

Does racking out the bellows when focusing alter the amount of light hitting the film?

Yes, but not significantly down to about 1/10 life size.

Cheers,

Roger (www.rogerandfrances.com)

 

[MacCaulay]

Thanks for the help. Does that mean that I need not worry about exposure compensation when using the Crown Graphic for, say, landscape?

 

[Roger Hicks]

Thanks for the help. Does that mean that I need not worry about exposure compensation when using the Crown Graphic for, say, landscape?

Dear Jenni,

Dead right. Or even portraits. When a full head is two inches high on 4x5 inch, you are running at about 1/7 life size and even this requires only about 1/4 stop compensation (very rough figures) so it ain't a major problem.

Cheers,

R.

 

[seadrive]

Bellows extension factors work the same as f/stops. If you're using an eight-inch lens (about 210mm), and you rack it out from eight inches to eleven inches, you've halved the amount of light reaching the film, the same as stopping down from f/8 to f/11.

So, to compensate, you'd open up one stop, or double the exposure time.

Hope this helps...

 

[raucousimages]

I drew a ruler and bellows data for all of my lenses on the white side of my dark cloth. It is a simple way to keep the info handy.

 

[Campbell]

Thanks for the help. Does that mean that I need not worry about exposure compensation when using the Crown Graphic for, say, landscape?

Not necessarily. It depends on how close the object on which you're focusing is from the lens. Sometimes we include objects that are fairly close to us in landscape photography. If the object on which you end up focusing is closer than 10 times the focal length of the lens (or some people say 8 times but using 10 not only is more conservative, it makes the math easier) then you should consider compensating for bellows extension.

 

[BrianShaw]

I'm with Roger on this one. I've never experienced a situation in landscape or portraiture (full-length thru head-and-shoulder) where there was any practical need to compensate exposure for bellows draw.

 

[MacCaulay]

Thanks everybody. You are most helpful.
Large format can be a bit confusing, but I've got hold of The Ansel Adams Guide vol 1, hoping it might explain a few things. However, being able to ask a question directly, and to receive answers from people experienced in the field, is invaluable.