Re: bellows extension

From: Shannon Stoney ^lt;sstoney@pdq.net>
Date: 12/02/05-07:09:17 PM Z
Message-id: <a06230903bfb69ffc0846@[10.0.187.3]>

>Ohhhhh, Shannon, do I have the thing for YOU!
>I am finishing up teaching a large format class to 24 unsuspecting
>photo majors who probably would prefer that photography was 35mm and
>didn't include math nor a view camera. SO, to make their lives
>easier, I made a little chart of bellows factor.
>
>Bellows factor can be calculated very easily by the formula:
>
>bellows length squared
>divided by
>focal length squared
>
>which gives you a factor number that you multiply your shutter speed by.
>
>However, students who don't like math weren't thrilled with this
>formula, so I took every lens we had in checkout, figured out the
>inches of each lens, figured out infinity and then every factor for
>each inch of bellows. if you want me to I can send you the chart
>offlist.

OK, that will be great. I hope you won't give me a test on it
afterwards though.

I actually use the BTZS software on a palm. I figured out what I was
doing wrong, which may be interesting to everybody out there who used
ExpoDev. In the place where you enter the bellows extension, I was
entering the actual number of millimeters from the film plane to the
lens. WRONG. You are supposed to enter the amount of *extension*,
not the total focal distance. Ie, if your lens is 90 mm and it's
racked out to 120mm, you don't put 120mm; you put 30mm, or the
difference between the focal length of the lens and the focal
distance. It took me a while to figure this out. Now the exposures
are right.

--shannon
Received on Fri Dec 2 19:06:36 2005

This archive was generated by hypermail 2.1.8 : 01/05/06-01:45:09 PM Z CST