Bellows compensation

[ruslan safin]

Dear friends, I intend to photograph macro. This means I will stretch

bellows to the tilt and I will need compensation. I only remember

that if bellows extension exceeds the focal length of the lens 50%

than I need compensation about 1 step. Is that right?

Thank you!

[tim_atherton9]

Generally I find this to be the simplest practical option - all 100% free

 

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

 

or check out the Large Format site info at:

 

http://www.largeformatphotography.info/bellows-factor.html

[joseph_dickerson]

Rusla,

 

Bellows extension (squared) divided by focal length (squared) equals bellows extension factor.

 

It's as easy as that.

 

Good shooting.

[ken_burns1]

If the bellows is extended one focal length, the lens is focussed at infinity and there is no exposure factor. If the bellows is extended 1.4 focal lengths, the image is half life size and the exposure must be increased one stop. If the bellows is extended 2 focal lengths, the image is full life size and the exposure must be increased 2 stops. Everything in between can be interpolated easily. This does not apply to telephoto lenses.

[peter_witkop]

The way I figure bellows, which is simple enough to do in my head is this; take the lens focal length in inches (it would work in metric, but it's easier with inches), so my 210 is about 8 inches (close enough for this purpose anyway), then when focused measure the bellows draw. The differance between the two numbers if they were f-stops is the exposure compensation. So for example with my 8" lens, if I had a bellows draw of 10", that would be 2/3'rd of a stop compensation, since f/8 to f/10 is 2/3'rds of a stop. That's how I do it anyway, I have used the quick disk method, which does work very well, but this is simpler to me. Hope that helps :o)

 

Peter

[george_collier]

I remember Joseph's formula from the US Army photography

school, and it works (besides, we know they wouldn't be wrong).

Just remember, though that the resulting factor is just that. The

factor is the number of times you need to increase the light. In

other words, a factor of 4 (resulting from an extension twice the

focal length - and resulting in a 1 to 1 reproduction size, as

someone else pointed out) means add 4 times the light, or 2

stops. Or, if your head hurts from this (like mine sometimes),

just add some exposure - more than you think, but less than you

guess.

[oskar_ojala]

As others have pointed out, the formula is exposure factor = (extension)^2/(focal length)^2, which gives you 1 stop compensation (exp. factor 2) when the lens is extended to ~1.4x the focal length, giving a 1:2 reproduction ratio. A reproduction ratio of 1:1 then needs a compensation of 1 stop (note that this is easy with symmetrical lenses; non-symmetrical lenses make the measurement non-trivial.) In the field, it's most practical to have a rough estimate, eg. an extension of 1.1x focal length needs a 1/3 stop compensation. (and don't forget to calculate reciprocity too...)

[forrest_hartman1]

There's a quick calculation about whether or not you need exposure compensation due to your bellows draw.

 

In his book "Using the View Camera," author Steve Simmons says:

 

"The increased bellows extension only becomes a problem when working with a camera-to-subject distance that is less than ten times the focal length of your camera." (See pages 69-70 in the revised edition, a brief discussion about bellows and factors.)

 

Yesterday, I used my fuji 240mm to photograph a camel -- well, a stone sculpture of one, anyway. Recalling Simmons, I calculated that if my subject was closer than 2400 mm (i.e., 240mm x 10 = 2400mm, or 2.4 meters), I needed the compensation. In this case, my subject was about 4 meters away, so no bellows extension...And no extra math!