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.

BellowsExtension.pdf

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.

BellowsExtension.pdf

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