Re: bellows extension

>Hi Shannon,
>
>The focal length for lenses is measured with the lens focused to
>infinity. First, to find the place "where you stop" on the front
>standard (where the lens is), focus on something distant (mountain,
>moon, you get the picture, so to speak) and then measure from the film
>plane a distant equivalent to your focal length. If your lens is a 200mm
>for instance, you'd measure 200mm from the film plane to find the point
>on the front standard from which all your bellows compensation reading
>should be measured. You might want to mark this point with a Sharpie or
>pencil.
>
>Now about Bellow Compensaton (BC) in general. I always found it easier
>to use inches instead of mm when figuring BC. This way you can treat the
>measurements like f-stops and intuitively calculate your BC. First you
>convert your focal length into inches. In the case of the 200mm lens,
>that's 8 inches. Then, whenever you focus on something closer that makes
>you rack out your bellows, just measure the extension in inches. Say
>you're shooting a product shot of your computer mouse and you want it
>life-size on 4x5 film. You focus and find that you have 16 inches of
>bellows draw. The difference between 8 (your focal length) and 16 is TWO
>STOPS. That is, the difference between f8 and f16 is two stops. It's
>that simple.
>
>I'm sure others will have even simpler methods to calculate BC but this
>one always worked for me.
>
>On the same thread, another good reason to always carry a camera is
>because your aperture ring is also a pizza calculator. A pizza that's 16
>inches in diameter is four times as much pizza as an 8 inch pizza. Cool!

Thanks. I will try all this today.

  How interesting that aperture stops can measure pizza size! I
wonder if you could order an f/5.6 pizza, when you're not very
hungry. Is this all because of the magic of logs?

The 90mm lens I am using now (thanks, Clay!) is 3.5". So if it's
racked out to 7", that's two stops I guess. Somewhere in between
would be about 5 1/4", which would be one stop. I guess you could
mark all these places on your camera.

--shannon
Received on Fri Dec 2 10:05:15 2005