The following discussion is meant for the scientist. It makes
many assumptions and is not all inclusive. The problem lies in that
we have a hybrid design. Some of the equations do not factor in
optics/lenses. Most of the equations are for true lensless pinhole
cameras. The diameter of the aperture determines the resolution
and is limited by the laws of diffraction. If the hole is too small, an
Airy disk is formed or the farfield limit is reached. One must choose
a hole diameter between the farfield and the optical limit.
Resolution is distinguishing betweeen two lines or neighboring
points. In the case of geometric optics, resolution is 1.5 times the
pinhole size. Making many assumptions, the exact size of the hole is
irrelevant, any hole 1 mm or less will suffice here. For example, if
the hole is 20% larger than the mathematical optimum, light
gathering increases by 40% and R decreases only by a factor of 2.
 

Exposure Considerations
 

In general, film responds to light in a linear fashion. At long
exposure times reciprocity failure may have to be addressed. Also
the color dyes shift at really long exposures. Most of the exposures
outside are 5 secs, indoor times range about 30 sec to 2 minutes for
ASA 100. When using B/W film inside, a corrected time might be
needed. See table 1 below. Note: We did not use any compensation
for reciprocal failure for T-Max 400 B/W C-41 process Kodak film.

Depth of Field Theory
Table of symbols and definitions
D = diameter of aperture as seen from the front of lens
N = f stop D = f/N
Ne = effective f number, based on geometric factors not absorption.
M = magnification
F = focal length
p = pupil magnification

Light from an object spreads out in a cone whose base is
refered to as the entrance pupil. ( the lens element in front of the
aperture forms a virtual image of the physical aperture).
The exit pupil is the image of the aperture as seen through the rear
lens elements. We can express the depth of field equation as.

           Ne = (2sin(qx))-1

However for macro analysis this is not enough. It is possible to skip over the complex math and arrive with the working equation for the wide angle lens.

               Ne =N(1+M)/p)
 

p = exit pupil diameter/entrance pupil diameter.
P is greater than one for wide angle optics.
 

Circle of Confusion
 

    Light from a single object passing through the aperture is converged into a cone with its tip at the film plane (focus point). If the point is behind or infont of the film a circle or conical shape is projected. This is the circle of confusion. The farther away the tip is the larger the circle. If the circle is small the image appears to be sharp. 0.03 mm is the working limit for 35mm photography. One can see why f/22 is close to the aperture limit on most conventional optics. If the lens is at infinity, the distance to the rear principal point is called the hyperfocal distance. To futher confuse things, rear and front depth of field figure in. As distance increases, the rear depth of field is greater than the front depth of field. If we photograph an object at two different focal lengths, the shorter lens (ours is a 25 mm) has more rear depth of field at the same f stop.
 
 

Film types

       In our opinion, Kodak 100 Royal Gold has excellent latitiude with mini lab C-41 processing, therefore exposure mistakes are not readily seen unless they are gross errors. One needs to use slide film to see how C-41 process prints can shift colors. There is no benefit to using faster films, images come out equal.
 
 

Image Quality

      The camera lens is a two element design with a 25 mm focal length. The new aperture is 25mm/0.3mm or f/75. The plastic lens does remarkable well considering its low tech design. It is assumed that it is aspherically molded. Most CD players use similar designs. The focus is somewhat soft there appears to be zones where sharpness varies. We like it compared to contrasty modern optics. Note: a Leica and a Minolta manual focus SLR camera system was used on the modification photos and the law of diminishing returns is apparent here. The $1000 plus SLR system photos are not 100 times better than the recycled camera photos. We are not implying that we need to scrap the Leica but most people assume more is always better. We believe in the old school photography methods, modern bells and whistles do not guarantee good pictures, practice and a basic understanding of theory does. There is a distortion/reflection band on the perimeter of the negatives, it could be what is called "tunneling''. It vanishes if the panoramic insert is used. All scanner/photo manipulation software allow for cropping of undesirable regions. Also light falloff and vignetting is somewhat seen. Can refer to Fourth Cosine law for further details. All optics experience this light falloff. In conclusion, we elicit positive feedback and ongoing internet discussions on the http://www. rec. models. scale newsgroup. We also wish to acknowledge all of the various sources we used.

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