Re: bellows extension

What school is this?

S. Shapiro
----- Original Message -----
From: "Christina Z. Anderson" <zphoto@montana.net>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Friday, December 02, 2005 11:19 AM
Subject: Re: bellows extension

> 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.
>
> What was so fun is I figured out a down n' dirty method that when the
> bellows is extended 1.4x the focal length, you open up 1 stop; 2x is 2
> stops, 2.8x is 3 stops, 4x is 4 stops etc. etc! I thought I was soooooo
> cool (because it corresponded to fstops), but then when they had their
> midterm, NO ONE got those answers right on the test, even though I have
> this written in bold at the top of the chart. So even though I I felt the
> chart was so useful, I didn't write on it that they needed to read it.
>
> My consolation is that their work, despite the math, is realllly getting
> good.
>
> btw you usually measure from film plane to lensboard...
> chris
>
>
> ----- Original Message -----
> From: "Shannon Stoney" <sstoney@pdq.net>
> To: <alt-photo-process-l@usask.ca>
> Sent: Friday, December 02, 2005 6:59 AM
> Subject: bellows extension
>
>
>> Hi, I am using a new camera that I borrowed, a Canham. One thing I like
>> about this camera is the little marks on the side that show the extension
>> of the bellows, in millimeters. (My tachihara has this too, but for some
>> reason they are numbered in the wrong direction!) I am confused though
>> about two things: how to measure bellows extension, and when to adjust
>> exposure for it.
>>
>> 1) I assume that you start measuring at the film plane, but then where do
>> you stop? One book said at the center of the lens, where its narrow part
>> is, I guess approximately at the front standard.
>>
>> 2) The same book said that you use bellows extension when you are
>> focusing on something that is away from the lens by a distance of less
>> than eight times the focal length of the lens. So, for a 90mm lens, that
>> would be 72 cm. With anything closer than that, you need bellows
>> extension factor, and anything further away than that, you don't. Is
>> that correct?
>>
>> --shannon
>>
>
>
>
>
Received on Fri Dec 2 14:34:25 2005