[LargeFormat] Intro and BEllows extension chart

[Brock Nanson]

----- Original Message -----
From: "john frost" <johnfrost@sprintmail.com>
To: <largeformat@f32.net>
Sent: Sunday, January 19, 2003 10:42 AM
Subject: Re: [LargeFormat] Intro and BEllows extension chart


> Too bad you spent the time doing that task. I have done that myself,
> before someone told me how to do it with the camera lens.
>
> If you are using a 5.6 inch lens (measured from film plane to lensboard
> at infinity focus), and your are set up on a target that causes your
> film plane to lensboard measurement to be 8 inches, then you have a one
> stop extension. A measurement of 11 inches would be a 2 stop extension,
> yielding a 1:1 ratio, or life-size image.
>
> The thing to remember, is use the same units all the time.
>
> john (:>)) no more bellows charts for me....

I've always carried a chart around with me, but as I don't do much in the
way of close-up work, I've never needed to consult it.  From what I
interpret here, the factor used for a 'stop' aperature-wise (1.4) is
directly applicable to bellows extension.  And I suppose, when you think
about what an f-stop actually is, this makes perfect sense.  Your focal
length is effectively changing, while the aperature remains the same.  Thus
the ratio that is the 'f-stop' changes.

Do I have this right?  If so, I thank you for turning on the light!

Brock