Exposure question.

[jeff bishop]

Please bear with me because I'm new at this! I have a 1937 Zeca

9x12 camera. I'm familiar with my 35mm and TLR's, where I can

utilize the sunny 16 rule for exposure. I'm looking at this bellows

and wondering if the light drops off because of distance, and if I

can use the sunny 16 rule with this camera as well. Also, if the

bellows extension comes into play for exposure, at what distance or

extension does this occur at? Is there a simple method (such as the

sunny 16 rule) that will get me close with exposure?

 

Thanks in advance!

Jeff Bishop

[www.graemehird.com]

At normal focusing distances, you won't need to worry about bellows extension factor. When you start doing photos where you need to extend the bellows more than ~30% of its infinity distance, you'll start experiencing some drop of exposure on the film.

 

Since you're estimating anyway, just double your exposure when you add 50% to your bellows length due to close focusing.

 

Cheers,

Graeme

[brian_ellis16]

There is a rule of thumb to the effect that if the object on which you're focusing isn't closer than 8 times the focal length of the lens then you don't need to adjust for bellows extension (some people use 10 times to be a little more conservative or to make the math a little easier). I don't measure the distance with a ruler or anything, I just eyeball the object, estimate the distance in feet, and do some rough math in my head (e.g. 210mm lens, if object is not closer than 1680mm or about five and a half feet I don't need to adjust). This eliminates any adjustment at all for about 95% of my photographs. For the other 5% I add a half stop when I get closer than 8 times and a full stop when I approach 1:1 (i.e. when the bellows extension is approaching double the focal length of the lens). If I ever got all the way to 1:1 I might add a stop and a half.

 

There are formulas and gizmos that will have you adjusting in thirds of stops for every tiny increment of extension beyond infinity. That type of accuracy may be needed for slide film where thirds of stops can be critical but IMHO not for negative film. I think the 8 times or 10 times general rule and estimates of a half to a full stop after that works fine with negative film. Others of course may differ.

[jeff bishop]

Graeme and Brian, Thank you very much for the fast response!

[smieglitz]

At 1:1 magnification you have extended the lens twice its focal length and the

extension exposure factor is 4x or 2 stops. At an extension of 1.4 times the

focal length you have an exposure factor of 2x or 1 stop.

 

The extension relationship works like the f/stop sequence so that every time

you increase the extension by 1.4 times the focal length, the film will require

an additional stop of exposure compensation. (This works with any focal

length BTW.) At 2.8 times the focal length your extension factor will be 8x or 3

stops and so on.

 

The most frequent compensation adjustments typically will occur between

infinity and 1:1 magnification. Based on the above relationship and knowing

these two limits, it becomes easy to estimate an exposure compensation

factor by just eyeballing the extension of the lens.

 

For example, a 10" lens extended out 14" requires an additional stop. By 20"

it requires two stops, so at 16" I'd give it about +1 1/3 stops. At 12" I'd guess

about +1/2 stop would be appropriate. This matches pretty well with the

extension factor dial in the Kodak Pro Photoguide.

[jim_galvin]

At distances greater than about 10 times the focal length, exposure is the same as you have been doing: f/16 is f/16. For many LF tips, see

http://www.largeformatphotography.info/