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# Thread: LF: Applying Bellows Extention To Exposure

1. ## LF: Applying Bellows Extention To Exposure

I'm reading Stroebel's "View Camera Technique" and have come to understandings that I would like to confirm as valid.

When shooting a subject greater than 10X the lens focal length (4x5 135mm = 5.1") a bellows extension factor must be applied to the camera exposure.

EXAMPLE: With a 4x5 camera and a 135mm lens, a subject greater than 50 inches from the camera will need a factor applied to either/or combined shutter speed and apature to achieve expected negative exposure.

BELLOWS FACTOR: From Ole Tjugen (oftjugen@online.no) on June 1, 2002.
Bellows Extension Squared Divided by Lens Length Squared = Bellows factor.

In the above example, a focused image of a subject longer than 51 inches from the film plane with a bellows 6 inches extended would require a bellows factor of 1.44 or one and one-half stop increase [(6X6) 36 / (5X5) 25] = 1.44 or 1-1/2.

In your estimation are these understandings of mine correct?

2. Bruce,
That looks correct, apart from the 'greater than 50 inches' bit. Shouldn't that be less than 50 inches? The example you give is correct in terms of the exposure factor - but a 5" lens that is 6" from the film plane will be focussed on an object about 36" (or thereabouts) from the film plane, not 51". However, if a 5.3" (135 mm) lens was 6" from the film plane, then the object would be about 52" from the film plane, but the bellows factor would then be 1.28 - not significantly different from 1.44.

As you can see, the 10x rule roughly corresponds to a maximum error of 1/3 stop - a 'standard' limit on error - before applying the bellows factor.

I hope this makes sense.

Best,
Helen

3. Math isn't my forte, I use one of these http://www.bhphotovideo.com/bnh/cont...u=61584&is=REG

4. Brian, how does that thing work?

Bruce, how goes it with the Busch?

5. I use the \$10 Calumet Exposure Calculator, #CC9201 , which consists of a small square target that is placed in the scene, and a little ruler used to measure it on the GG. Quick, easy, compact, and works with any format and focal length.

6. It is basically a ruler that has the exposure compensation marked for various lenses. Sine I am now only going to use one lens, I will most likely just mark it on the bed of my camera.

7. I cheat. I have a meter (Minolta Flash III) that allows me to take readings directly off the ground glass.

8. I use this, http://www.salzgeber.at/disc/index.html . It's easy & free

9. Originally Posted by bmac
Math isn't my forte, I use one of these http://www.bhphotovideo.com/bnh/cont...u=61584&is=REG
I've been looking for something like this, since my math skills seem to deteriorate in the field. Does it only work with 4 X 5?

Cheers,

James

10. You can also use this:

http://www.salzgeber.at/disc/

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