Bellow extension expsosure help!

[Scott --]

I just carry a tape measure and use John Cook's method.

[davidp]

i saw Geoff Bowker's bellows extension charting package on the LF page, but my computer wont open it? (im on a mac). Does anybody know somewhere where I can open or view it?

[erie patsellis]

Scott, I worked with John at one studio I worked at many years ago, Don't let his words fool you, he was about as much technique as you needed to get the job done, and he is still sorely missed. I learned more about C41 and (mostly E6) process control and tweaking from him in casual conversation around the studio than I have learned since.

[lenser]

David,

In case it helps, here are the Calumet system and one from EZ View that I picked up on eBay a while back. They work the same way as described earlier and the EZ View also has an angle finder as part of the kit. That's perfect for matching the front and back standards and for matching the angle of art on a wall with the angle of the film plane.

Both make my life a lot easier.

[CG]

John Cook's method is great - but it is even better than he wrote there since it doesn't matter what measuring system you use. Sometimes a lens more easily fits the series of F Stops when you use inches, sometimes metric. Since as others have noted, it's not the total extension, but the relationship of actual extension to the extension at "infinity" - that is the nominal focal length - that matters, whatever measure you find convenient works.

I keep a much longer list of f stops handy since long lenses in milimeters can generate big numbers. I run my list from f 0.5 way up to f 1440. Most are not numbers one would use for actual apertures, but handy for very quick BEF (Bellows Extension Factor factor determination. It just happens that the list of f stops is a log or power series and makes up what is the equivalent of a slide rule.

You can make it into a real slide rule by making a second scale slider that is marked 0,1, 2, 3, 4, etc...
fstop scale- movable slider scale
1 . . . . . . . 0 slide this next to the infinity focal length in whatever measure
1.4 . . . . . .1
2 . . . . . . . 2
2.8 . . . . . .3
4 . . . . . . . 4
5.6 . . . . . .5
8 . . . . . . . 6
11 . . . . . . 7
16 . . . . . . 8
and so on


example: 4 inch lens at 11 inches actual extension:
slide the 0 on the slider next to the 4 on the fstop scale like so
4 . . . 0
5.6 . . 1
8 . . . 2
11 . . 3
the 3 on the slider will then be next to the f 11 mark. That will tell you it's 3 stops Bellows Extension Factor to compensate.

read over to the slider scale for the Bellows Extension Factor.

Use inches, meters, decimeters, centimeters, millimeters, yards, or cubits even. They'll all work just as well.

It's much harder to put in print than to use. I hope I've made it comprehensible.

Best,

C

[Gary L. Quay]

Steve Simmons wrote a very simple formula that I use. Every one half of the focal lenght of the lens requires 1 extra stop of light. So, when my 12" lens is at 18", I increase exposure by 1 stop. I can do the math in my head. For fine tuned studio work I use the Quick Disc.

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

--Gary

[Drew Wiley]

I used to use a tape measure marked for each of my lenses (it's important to measure between the actual film plane and nodal point of the lens - easy to do on
a Sinar). But now it's so much easier just to use the Calumet calculator, plus it
doesn't weight anything or take up space in the kit.

[Jim Noel]

I have not read the entire thread but in ase your original question has not been answered. It doesn't really matter whether you have the extension on or not. If the distance from lens to object is less than about 8 times the focal length, you need to consider bellows extension factor calculating with any of the methods already offered.

[eddie]

Steve Simmons wrote a very simple formula that I use. Every one half of the focal lenght of the lens requires 1 extra stop of light. So, when my 12" lens is at 18", I increase exposure by 1 stop. I can do the math in my head. For fine tuned studio work I use the Quick Disc.

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

--Gary

what gary said!

[C. D. Keth]

Just figure out the bellows extension for each of your lenses beforehand and print it in small font on a piece of paper. Stick it to your lensboard. Combine that with the tape measure sewed into the edge of my darkcloth and I always have the right extension factor instantly.