Re: Kudos and a Query

I'd be quite sure that Pinhole resource would have the e-mail address. You
could inquire from them.
----- Original Message -----
From: "Howard Wells" <sandwell@earthlink.net>
To: <pinhole-discussion@pinhole.com>
Sent: Tuesday, October 30, 2001 12:11 PM
Subject: [pinhole-discussion] Kudos and a Query

> I know I am not alone in my appreciation of the tremendous resources
> available on this list, Guillermo being a prime example. I always learn
> something from his posts. Thank you Guillermo, thank you all for your
> intelligence, artistry and civility. It is always an inspiration.
>
> I've already altered an ancient Leonardo to be a close-up camera. I've
> also been using a PhotoTechnicalGroup (f512) camera with good effect.
> Well-built, easy to use, only lacks a graphloc back.
>
> Does anyone have an email address for Dominique Stroobant? I had
> communicated via his son Ishmael's hotmail account years ago but would
> like to get in touch with him again. His 17mm pinhole for Leica thread
> mount is still my most beloved pinhole, especially for hand-held work.
> Thanks,
>
> Howard Wells
> http://home.earthlink.net/~sandwell/
>
> Guillermo wrote:
> >
> > ----- Original Message -----
> > From: "Gregg Kemp" <gregg.kemp@pinholevisions.org>
> >
> > > Guillermo, I don't remember ever seeing your correction formula
before.
> > Is
> > > that theoretical, or have you tested it?
> >
> > Theoretical, Gregg, as I haven't done any close up work myself.
> >
> > For those (few) people interested in were that correction factor comes
from,
> > here it is:
> >
> > ******************
> > Pinhole is in most ways, not different than glass lens photography.
> >
> > The lens conjugate equation is:
> >
> > 1 / F = 1 / I + 1 / O
> >
> > where I = distance pinhole to Image plane; F = Focal length and O =
> > distance pinhole to Object being photographed.
> >
> > We can simplify that to: F = I x O / I + O
> >
> > When the Object being photographed is at infinity ( O = infinity ):
> >
> > I + O = O
> >
> > therefore the formula F = I x O / I + O becomes:
> >
> > F = I x O / O and that becomes
> >
> > F = I
> >
> > In other words, when the Object is far away (more than 10 times the
distance
> > pinhole to film, in practical terms), the Focal length of the camera is
> > equal to the distance pinhole to film plane.
> >
> > Now, when the Object being photographed is close to the pinhole lens
(less
> > than 10 times the distance pinhole to film, in practical terms), the
Focal
> > length of the camera is given by (as I stated above):
> >
> > F = I x O / I + O
> >
> > For close up work, then, "F" has to be substituted (in any of the
formulas
> > for optimum pinhole size) by:
> >
> > I x O / I + O
> >
> > For instance, the formula I use is:
> >
> > D = 0.0073 x SQRT( F )
> >
> > where D = pinhole diameter in inches; F=pinhole camera focal length and
SQRT
> > stands for square root of
> >
> > For close up work that formula becomes:
> >
> > D = 0.0073 x SQRT( I x O / I + O )
> >
> > As I said before, F = I for infinity, therefore I can write the
infinity
> > formula as
> >
> > D = 0.0073 x SQRT( I )
> >
> > Base on that, I can also rewrite the close-up formula as:
> >
> > D = 0.0073 x SQRT( I ) x SQRT ( O / I + O )
> >
> > There you have the correction factor:
> >
> > SQRT ( O / I + O )
> >
> > BTW, there are many formulas for optimum pinhole size but all have
within
> > them "SQRT(F)", therefore, the above correction factor should apply fine
to
> > all of them.
> >
> > Let's see an example:
> >
> > Our pinhole camera has a distance pinhole to film I = 8" and the
Object
> > being photographed is O = 12" away from the pinhole, what size of
pinhole
> > is the optimum to use:
> >
> > The optimum pinhole size for infinity is:
> >
> > D = 0.0073 x SQRT ( 8 )
> > D = 0.020" (aprox)
> >
> > Correction factor is: SQRT ( 12 / 8 + 12 )
> > Correction factor is: 0.774
> >
> > Pinhole size for close up work (object 12" from pinhole lens)
> >
> > D = 0.020" * 0.774
> > D = 0.0155"
> >
> > BTW, all the above is nothing but a sort of "bellows" correction.
> >
> > For people with mathfobia but that have read this msg up to this point,
here
> > are some corrections factor based on how many times the camera
> > "pinhole-film" distance the object is away from the pinhole lens:
> >
> > less than 10 times => correction factor = 0.95
> > less than 9 times => correction factor = 0.94
> > less than 8 times => correction factor = 0.94
> > less than 7 times => correction factor = 0.93
> > less than 6 times => correction factor = 0.92
> > less than 5 times => correction factor = 0.91
> > less than 4 times => correction factor = 0.89
> > less than 3 times => correction factor = 0.86
> > less than 2 times => correction factor = 0.81
> > less than 1 times => correction factor = 0.70
> > less than 0.5 times => correction factor = 0.57
> >
> > Another couple of formulas than may help the original's question poster
are:
> >
> > Magnification M = I / O
> >
> > Therefore the Correction factor can also be written as:
> >
> > Correction factor = SQRT [ 1 / (M+1) ]
> >
> > So for instance, if she wanted to photograph an object 2" tall with a
> > camera having 8" between pinhole and film and get a magnification of
2X,
> > she will need to position the object at a distance:
> >
> > O = I / M = 8 / 2 = 4"
> > O = 4 inches
> >
> > and the pinhole size (diameter) should be:
> >
> > D = 0.0073 SQRT(8) * SQRT[ 1 / (2+1)]
> > D = 0.012"
> >
> > The image size will be 4" and therefore the minimum format size needed
is
> > 4x5 (portrait) or perhaps -better- 5x7" to allow for some cropping.
> >
> > Guillermo
> >
> > _______________________________________________
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>
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Received on Tue Oct 30 14:42:39 2001