Re: Re: Bellows factor

I've only lived at my new house here in Northern
California for a year--still no darkroom!--but so far
the laws of physics seem to apply. I've only made a
few shots with this new extension, so it's actually
hard to say whether the apparent lack of effect of the
bellows is real or not. I will report more in the
future if my location really does bend the laws of
physics. In the meantime let me say that if Zernike
could produce an extension frame for the 4X5 camera
with a lip and felt on BOTH sides he' d make it really
easy to do this kind of thing. The only troublesome
part was that I had to use the sides without felt back
to back on two frames, which required tweaking to
avoid light leaks.

By the way, the formula I eventually used simply says
divide the square of the new length by the square of
the old length to get the bellows factor, so in my
example that was 32.5 centimeters squared (1056)
divided by 5 centimeters squared (25) equals 42.25. So
42.25 times my original 2 second exposure at 5
centimeters is 84.5 seconds--more or less the same
answer others reported but by formulas that seemed
more complicated (to me anyway).

Colin

--- John Yeo <jonnieo@thegrid.net> wrote:
> I don't remember guillermo explaining it, so here's
> my shot at it.
>
> Every time the bellows extension is doubled, you
> have to increase exposure
> by 2 stops. If you extend the bellows by a factor
> of 1.414 (the square
> root of 2), you must double the exposure.
>
> so... sqr(2)^x = extension factor. x is the number
> of stops
>
> He is extending the bellows by a factor of 6.5.
>
> sqr(2)^x = 6.5
> x log sqr(2) = log 6.5 logrhythm
> properties
> x = (log 6.5) / (log (sqr(2)) simple algebra
> x = 5.4
>
> you must add 5.4 stops of exposure, so 2 * (2^5.4)
> is 84.44 sec. As for why
> colin's exposures weren't matching this, i am
> baffled. Maybe he lives in a
> part of the world where the laws of physics don't
> apply :P
>
> John
>
> So, you would have to multiply the exposure by
> 5.4----- Original
> Message -----
> From: "Guy Glorieux" <guy.glorieux@sympatico.ca>
> To: "Pinhole List" <pinhole-discussion@pinhole.com>
> Sent: Friday, November 30, 2001 3:14 AM
> Subject: [pinhole-discussion] Re: Bellows factor
>
>
> >
> >
> > "G.Penate" wrote:
> >
> > > just plain physics of light.
> > > This case is in no way different than if you
> were using a glass lens.
> > > <snip>
> > > 84.5 seconds (uncorrected for reciprocity, time)
> >
> > Guillermo,
> > Can you remind me how you worked this out.
> > Guy
> >
> >
> > _______________________________________________
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>
>
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Received on Tue Dec 4 00:00:10 2001