# Thread: First Post! - How Do I Measure My Bellows Extension To Calculate Bellows Exposure?

1. ## Re: First Post! - How Do I Measure My Bellows Extension To Calculate Bellows Exposure

I do what Doremus does. I have tables for my most used lenses. Recently I found myself using a 125mm lens instead of the 135mm in my notebook, and just took an educated guess, and it worked out fine.

2. ## Re: First Post! - How Do I Measure My Bellows Extension To Calculate Bellows Exposure

Bellows factor is unlikely to be the most significant point-of-failure in technique. Get a ballpark figure and work backwards. Composition considering light, interpreting fundamental exposure, processing, printing will f*ck you up enough. We cannot just make a list of our worries at the keyboard and consider it a work flow. That ain't even a start.

The hardest start is starting. Keep it simple at first, recognize mistakes. There is no recipe.

3. ## Re: First Post! - How Do I Measure My Bellows Extension To Calculate Bellows Exposure

Originally Posted by Pere Casals

The extension has to be measured from film plane to the rear nodal point of the lens. Problem is that the nodal point can be in an arbitrary place inside the lens, or well in front of the lens in case of tele lenses. You may use the Flange Focal Distance that is in the specs of the lens for weird calculations...

But in practice what you do is focusing at infinite (wide open), in that position of the front standard you have the nominal 135mm effective bellows extension, this is your reference point. If you move the front standard forward (say) 20mm to focus a closer subject then your bellows extension will increase +20mm: You have 135+20 = 155mm extension.

So you focus infinite to have 135mm effective bellows extension, then add to 135mm what you move the lens forward to focus closer, so you have the effective extension of your shot.
Now THIS is what I am talking about!

Thanks a bunch to everyone else for chiming in as well. Learning a lot already...

4. ## Re: First Post! - How Do I Measure My Bellows Extension To Calculate Bellows Exposure

Unless you're using telephoto lenses, the rear nodal point is around the aperture's location. If you want to find your rear nodal point, focus your 135mm lens at infinity, and measure 135mm forward from the ground glass.

Personally, I think the best way to figure bellows extension is just to figure out your actual f/stop. It's just a ratio, a fraction, if you will. Measure your bellows extension; that your focal length. Measure your aperture opening diameter through the front cell, (it magnifies a little, and you have to let that figure in); that's your aperture. Divide focal length by aperture. That's your actual f/stop. That's all it is.

5. ## Re: First Post! - How Do I Measure My Bellows Extension To Calculate Bellows Exposure

What Jimi said. Works great for me.

6. ## Re: First Post! - How Do I Measure My Bellows Extension To Calculate Bellows Exposure

Originally Posted by Mark Sawyer
Unless you're using telephoto lenses, the rear nodal point is around the aperture's location.
Of course, teles are those that would induce noticeable errors if used with close subjects and not being aware about rear node location.

Convertible Symmar and Symmar-S (plasmats) have the node some 3-5mm in front of the lensboard. Super-angulons (biogons, IIRC) have the node 7 to 20mm in the rear.

This the data for SCH vintage compiled by MAubrey:

Comparing numbers of "Effective FL" with "Flange FL" we find were the rear nodal point is actually, measuring from lensboard's outer side.

https://www.largeformatphotography.i...s+-+Sheet1.pdf

7. ## Re: First Post! - How Do I Measure My Bellows Extension To Calculate Bellows Exposure

Originally Posted by Pere Casals
Super-angulons (biogons, IIRC) have the node 7 to 20mm in the rear.
Are Super-Angulons really Biogons under a different name?

8. ## Re: First Post! - How Do I Measure My Bellows Extension To Calculate Bellows Exposure

Originally Posted by Jac@stafford.net
Are Super-Angulons really Biogons under a different name?
No. Look at the cross-sections.

9. ## Re: First Post! - How Do I Measure My Bellows Extension To Calculate Bellows Exposure

Originally Posted by Dan Fromm
No. Look at the cross-sections.
Well, it's a biogon derivative...

At least here says "The lenses branded Super-Angulon (sold by Schneider Kreuznach and Leica Camera) are based on the construction of the Biogon."

https://en.wikipedia.org/wiki/Zeiss_Biogon

Here it explains how it is seen the tilting pupil effect, (of russian influence, after it was redesigned)

https://www.largeformatphotography.i...l=1#post817068

10. ## Re: First Post! - How Do I Measure My Bellows Extension To Calculate Bellows Exposure

Originally Posted by Dan Fromm
No. Look at the cross-sections.
I have, Dan, and indeed the cross sections are profoundly different. After reading just one more assertion that a SA is a Biogon I had to ask lest my head explode. Thanks for your help to the rest of us.

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