Bellows compensation for 14" lens on 8x10

[Mark Sawyer]

Maybe it's just the crusty old curmudgeon in me, but I still like the basic method of what an f/stop really is...

f/stop = focal length / aperture

[aduncanson]

There is nothing wrong with your formula Mark except that:

1) You mean "image distance" not "focal length",
2) You cannot usually measure image distance directly,
3) You mean "entrance pupil" not "aperture",
4) It is not really possible to precisely measure the entrance pupil either, and
5) It requires doing division.

But none of that is to say that your process does not work, but...

It is simple enough to create a scale for a single lens that reads the correction directly in stops.

[Mark Sawyer]

There is nothing wrong with your formula Mark except that:

1) You mean "image distance" not "focal length",
2) You cannot usually measure image distance directly,
3) You mean "entrance pupil" not "aperture",
4) It is not really possible to precisely measure the entrance pupil either, and
5) It requires doing division.

But none of that is to say that your process does not work, but...

It is simple enough to create a scale for a single lens that reads the correction directly in stops.

Picky, picky, picky...

[Turner Reich]

This is not the easiest way, and for the life of me, I can't figure out why all the text books, manuals, etc. keep pushing that method.

I fully agree with Mark, I'd rather guess and bracket than to stand there with a calculator while the sun goes down.

[cjbroadbent]

.... It is simple enough to create a scale for a single lens that reads the correction directly in stops.

The Kodak Bellows Factor Scale (shown above), works for any lens and is a no-brainer.

[aduncanson]

The Kodak Bellows Factor Scale (shown above), works for any lens and is a no-brainer.

I agree, that is an excellent solution, particularly for the studio. Because it measures image size directly rather than bellows extension, It works without adjustment for lenses with especially long or short back focus (and I have both.)

As a practical question, do you think that it would work well if it were scaled down for use with a common 35mm film canister rather than your piece of 2" iron pipe? Or would the reduced scale make accurate reading difficult? (That answer might depend on whether one is shooting B&W negatives or color transparencies.)

[Greg Blank]

From what I have read related to the posted responses, it would seem that not one person has posted the Ansel Adams formula, which by all my experiences is the simplest and quickest way to calculate using a ruler and a calculator. I would add the following thoughts: Lenses up to and including 150mm lenses don't usually have bellows factor becuase you seldom extend the bellows beyond the lens focal length.
150mm sometimes


Indicated (Metered) f stop x Bellows extension / (divided by) Focal Length = Effective Fstop.

So: F 11 (Metered) x 300mm extension / 240mm (Lens focal length) = 13.75

Meaning you should open up 3/4 of a stop or close down slightly and add a full stop to time if possible.

The next stop up from 11 being 16, look at the relationship of 11 and 16 or whatever your Metered and or desired F stop is and go from there.

Hello!

I would like to know how to calculate, or if someone have already done this, a bellows compensation "ruler" for my 14" commersial ektar on 8x10 camera. Half stop intervals would be enough for me. For long now i have just added a stop or two for close ups, but would really like to be more accurate on my exposures from now on. So, help would be appreciated, since i got a bit confused while googling for an answer.

[wfwhitaker]

...Lenses up to and including 150mm lenses don't usually have bellows factor becuase you seldom extend the bellows beyond the lens focal length.
150mm sometimes...

How do you figure that? I suppose you never focus closer than infinity?

[Merg Ross]

How do you figure that? I suppose you never focus closer than infinity?

When I use a 150mm it is usually at double or triple extension; I do a lot of close-ups.

Will, I use your method, I prefer hands-free photography!

[cjbroadbent]

... do you think that it would work well if it were scaled down for use with a common 35mm film canister rather than your piece of 2" iron pipe? ...

Aluminium tube, not iron pipe! I would guess the 35mm canister is about the same size. and more practical (if you posess one). But paint it orange so as not to forget it in the set.