[LargeFormat] Bellow extension and film refraction

[Robert Mayrand]

On 1/7/02 3:11 PM, "lnphoto" <lnphoto@twmi.rr.com> wrote:

> the easiest bellows formula I know of is to divide the distance between the
> lensboard and the ground glass by the focal lenght of the lens. This will be
> the number of stops you need to open up.  If you square this number you will
> get the exposure factor. Multiply this number by the time read by the meter
> to get your new effective exposure.

Does this mean that you even got to do some adjustment at infinity?
6 inch lens / 6 inch of bellows extension = 1 = I stop increase and time
exposure stay the same??? It seem there is something wrong here.

I also found the web site with the quickdisk (small disc you put in the
picture and measure on your groundglass) for calculation, but I would prefer
the measure between GG & lens board, maybe I'll do a ruler with the info for
each lens.......unless such a device is already available somewhere on the
the net?

Sorry about the refraction and reprocity mixed up, thanks for giving me a
cue about that, I'll go check on the film manufacturer web site to get the
data....i thought it was a bit more complicated then that! Thanks again!

Robert
Mtl, Quebec