Technikardan - tips for measuring bellows ext.?

[tadler]

hi TK users. just wanted to know if you have a preferred way of measuring bellows extension on the TK?
do you use measure-tape or somehow the measures on the rail (it doesn't really work when the rail is collapsed)?
where exactly do you place the tape?
do you have tables for different focal lengths?
etc, etc... feel free to elaborate, anything will be useful to know. i'm using 6 diffeent focal lengths from 75 to 240mm.
thanks!

[vinny]

you only need to measure bellows extension when doing close up work. using one lens for that work will simplify things. Bellows extension is the same on all cameras so just measure from the lens board to the film plane, it's not super critical. Once you know the correction needed for a certain lens at a given distance, you won't need to measure that often.

[jeroldharter]

I try to stick with one lens also, but sometimes I end up focusing a bit close and need to give some additional exposure.

I use a table that includes the focal length of my lens, the bellows extension, and the exposure compensation in 1/3 stops.

The arithmetic is:

Exposure compensation = Focal length squared/bellows extension squared

So 1/3 stop is an exposure factor of 1.3, 2/3 stop is 1.6, 1 stop is 2.

Therefore, using a 300 mm lens:

Extension 340 mm = 1/3 stop additional exposure
Extension 380 mm = 2/3 stop additional exposure
Extension 425 mm = 1 stop additional exposure
...

You can make a small table up to the maximum of your bellows extension for each of your lenses so you are always ready.

[cjbroadbent]

Old tip from the 1970s Kodak spiral handbook:
Keep a bright 2inch object to put in the scene (I usee a 2" piece of alu tube covered in dayglow). Use a tape graduated in 1/3 f-stop corrections to measure the object on the ground-glass. if you don't find the scale on the web, I'll post it as a jpeg. (I roll up the scale and keep it in the tube). Works with any lens, of course.

[jeroldharter]

Old tip from the 1970s Kodak spiral handbook:
Keep a bright 2inch object to put in the scene (I usee a 2" piece of alu tube covered in dayglow). Use a tape graduated in 1/3 f-stop corrections to measure the object on the ground-glass. if you don't find the scale on the web, I'll post it as a jpeg. (I roll up the scale and keep it in the tube). Works with any lens, of course.

Calumet makes a tool like that:

http://www.calumetphoto.com/eng/prod...culator/cc9201

[tadler]

thanks.
yes, i know the tool by calumet and the other, circular one. what i was especially looking for is specific TK experience, because the double tapered bellows makes it hard to measure from film to lens board, so i have to place the tape lower, closer to the rails, on the L shaped arms which are quite thick. was wondering whther TK owners have a system, where exactly on the L arms they place the tape, in front and in the back, etc.
thanks.

[Leigh]

If you're trying to set the lensboard at a specific distance from the film, just remove the lens and measure through the hole with a ruler.
That path is unobstructed by definition.

I'm not sure why you want to do that since you must focus and compose for a given shot anyway.

- Leigh