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

[Wista45SP]

First post!

So I just bought my first 4x5 camera, a Wista 45SP w/ Schneider APO-Symmar 135mm f/5.6 lens. I decided that I will use a technique to calculate bellows factor for exposure compensation that requires knowing the length the bellows have extended in MM. I will be taking the lens focal length of 135mm and calling it "f/13.5" and taking the bellows extension measurement in MM, say for example 220mm and calling it "f/22" and counting the number of stops between f/13.5 and f/22 to calculate exposure factor. In this example it would come out to be 1.5 stops.

However, I need to be able to quickly measure the bellows extension length in MM to do this. I see little measurement tic marks on the side of the Wista 45SP tray. Are these markings in MM? Do I measure the extension of the bellows from the point where it's folded up? Please help me figure this out so I can start shooting. Any advice here would be greatly appreciated!

[Doremus Scudder]

I printed out a mm scales onto label stock and cut and pasted them on the rails of my cameras. That said, I don't use them for measuring bellows extension. I've got a lightweight tape measure in my kit for that. Adjusting for bellows extension is only necessary for close-up work.

I use a table of extension factors that I made years ago. It has factors for most of the lenses I use regularly and lives in my exposure record notebook. Here it is in case it may be of use to you. I measure the bellows draw in either inches or mm (there are two tables on the page, one in inches, one in mm) and simply look up the exposure adjustment. No figuring anything.

195878

Hope this helps,

Doremus

P.S: Welcome to the world of Large Format! You'll find a wealth of knowledge and information here. Check out photrio.com/forum as well for even more.

[Bob Salomon]

It’s a lot faster and easier to just know the magnification ratio you are shooting at.
¼ lifesize open ½ stop. ½ lifesize 1 stop. Lifesize 2 stops, twice lifesize 4 stops, etc.

If necessary, place a ruler in the scene and measure some increment that you chose against its size on the gg.

[Jimi]

I've been using this one for years - works well in my opinion: http://www.salzgeber.at/disc/

[Wista45SP]

I printed out a mm scales onto label stock and cut and pasted them on the rails of my cameras. That said, I don't use them for measuring bellows extension. I've got a lightweight tape measure in my kit for that. Adjusting for bellows extension is only necessary for close-up work.

I use a table of extension factors that I made years ago. It has factors for most of the lenses I use regularly and lives in my exposure record notebook. Here it is in case it may be of use to you. I measure the bellows draw in either inches or mm (there are two tables on the page, one in inches, one in mm) and simply look up the exposure adjustment. No figuring anything.

195878

Hope this helps,

Doremus

P.S: Welcome to the world of Large Format! You'll find a wealth of knowledge and information here. Check out photrio.com/forum as well for even more.

Thanks! So where exactly do I measure from in circumstances where I find myself using bellows? Do I measure from the bellows' closed position? From the ground glass? From the film plane?

[Pere Casals]

Do I measure from the bellows' closed position? From the ground glass? From the film plane?

Adding to what Doremus pointed...

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.


The true focal length can be a bit different from the commercially stated focal length, perhaps a few mm, this is irrelevant for the calculations.


It is important to proceed in this way for tele lenses (focusing infinite ), for example with a Tele Xenar 500mm you focus infinite with only 312mm of bellows, if using 312mm it would deliver an inaccurate correction becuase your effective extension is 500mm, as the rear nodal point is 200mm in front of the lens board in the outside of the camera.

Some short focals are "Angénieux retrofocus", inverted telephoto, it is the counter than a telephoto, of course not the case of your 135, just mentioning that the rear nodal point can also be well in the rear of the lensboard.

[Doremus Scudder]

Thanks! So where exactly do I measure from in circumstances where I find myself using bellows? Do I measure from the bellows' closed position? From the ground glass? From the film plane?

Pere has your answer, but allow me to simplify a bit.

To get total bellows extension for standard lenses, just measure from the film position (ground glass) to the center of the lens (the front of the lensboard is fine in most cases), i.e., film-to-lensboard. This will get you way close enough for even the most exacting work.

The exception to this is if you have a telephoto lens (which you don't). With tele lenses, the nodal point is somewhere in front of the lens. Tele lenses are rarely used for close-up work, so figuring bellows extension for them is less of an issue. If you do have to figure extension factors for a tele lens, then you need to use Pere's method above. It works for regular lenses too, but I find it easier just to measure film-to-lensboard distance.

You see that there are a number of ways to figure bellows extension. Take your pick of methods. I like mine, because I don't have to put rulers or discs in my scenes, which are usually outdoor subjects and delicate (try balancing a ruler on a flower...). Plus figuring magnification ratio is just one more thing I don't have to do when measuring and consulting a table.

FWIW, my most-used lens for close-up work is a 135mm lens, like the one you have.

Best,

Doremus

[Jac@stafford.net]

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

Edit: Jimi beat me to it.

[drew.saunders]

Welcome to the forum! Here's what has worked for me regarding bellows extension.

Looking here: http://camera-wiki.org/wiki/Wista_45

I see the photo is of your model, the SP. Rather than trying to find the rear nodal point of the lens and measuring 135mm from that to the film plane, I would suggest finding something quite far away that you can easily focus on. Tall buildings are good for this. Once you've done that, measure the distance between two easy to use landmarks on the front and rear standards. I'd suggest the front of the rear "box" and the rear of that arm in the front standard. That won't be anywhere near 135mm, but it will be an easier thing to measure. Looking at the camera, I'm going to take a wild guess that when using a 135mm lens focused at infinity, the front of the rear box to the rear of the front standard might be about 70-100mm. To make the math easy, I'll go with 100mm.

Exposure compensation based on bellows extension is: Infinity plus 1/6 will require 1/3 of a stop of compensation. For a 135mm lens, that means that if you rack the bellows out 1/6 of 135mm, or 22.5mm, you will need to adjust by 1/3 of a stop. So, if your two landmarks are 100mm apart, then if you focus and you're in the neighborhood of 122.5mm, then you know to adjust by +1/3 of a stop (f number of shutter speed).
+1/4 of infinity extension requires +1/2 stop compensation (33.75mm longer than your reference)
+1/3 requires 2/3 stop (45mm)
+1/2 requires 1 stop (67.5)
+2/3 requires 4/3 stop

etc.

I have Excel crank all those numbers out for me and make a nice little sheet that I can print out and tape to the front of each lensboard.

I hope this makes some sense. It's worked for me for years.

Drew

[Dave Dawson]

Unless your subject is closer than in your case 1.35 metres...Forget bellows extension factor...end of

Cheers Dave

[David Schaller]

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.

[Jac@stafford.net]

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.

[Wista45SP]

Adding to what Doremus pointed...

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...

[Mark Sawyer]

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.

[Kevin Crisp]

What Jimi said. Works great for me.

[Pere Casals]

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.info/forum/showthread.php?154149-Spreadsheet-of-Schneider-Vintage-Lens-Data&highlight=Schneider+Vintage+Lenses+-+Sheet1.pdf
https://docs.google.com/spreadsheets/d/1z8unfhH1qkNWmZHwIuRu1gjtlD49uncG6Pjfog8GAkY/edit?usp=sharing

[Jac@stafford.net]

Super-angulons (biogons, IIRC) have the node 7 to 20mm in the rear.

Are Super-Angulons really Biogons under a different name?

[Dan Fromm]

Are Super-Angulons really Biogons under a different name?

No. Look at the cross-sections.

[Pere Casals]

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.info/forum/showthread.php?84348-Schneider-Kreuznach-Angulon-and-Super-Angulon&p=817068&viewfull=1#post817068

[Jac@stafford.net]

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.

[Dan Fromm]

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

https://www.largeformatphotography.info/forum/showthread.php?84348-Schneider-Kreuznach-Angulon-and-Super-Angulon&p=817068&viewfull=1#post817068

You trust wikipedia? ¡Ay!

f/4.5 Biogons have 8 elements in 5 groups, aren't particularly symmetrical. f/8 SAs have 6 elements in 4 groups, are quite symmetrical. f/5.6 SAs have 8 elements in 4 groups, are also quite symmetrical.

[Pere Casals]

You trust wikipedia? ¡Ay!

f/4.5 Biogons have 8 elements in 5 groups, aren't particularly symmetrical. f/8 SAs have 6 elements in 4 groups, are quite symmetrical. f/5.6 SAs have 8 elements in 4 groups, are also quite symmetrical.

It would be interesting to know what makes a lens a biogon derivative, or even a biogon, because even the 1951 biogon is quite different from the 1934 original.

...but if the SAs and the Nikon SW 9 f/8 are not biogon derivatives then many people are wrong.

I guess... "The basic design principle is that you have a group with negative power at each end of the lens, surrounding one group with positive power on each side of the aperture. However you slice and dice or cement these groups is immaterial to the basic concept." (A.C.)

[Dan Fromm]

...but if the SAs and the Nikon SW 9 f/8 are not biogon derivatives then many people are wrong.

There's a lot of that going around, alas.

[Jac@stafford.net]

All I know is outcomes. Later Biogons in my typical applications work so very well in managing distortion and fall-off while SA lenses strive to be more and fail. I enjoy living within the later Biogon limits.