Re: Micro or macro photo with pinhole photo

Guillermo, thanks! I've never been satisfied with a photo taken with the
subject less than distance of the focal length. I had just assumed it
couldn't be done. I'll have to revisit this some time.

Gregg

At 10:35 AM 10/28/01 -0500, you 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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Received on Sun Oct 28 18:02:05 2001