I was serious when I posted I can only print at night, so I can't make any more tests right now, and there is no place I can drive today to get a contact frame (thought I may be able to cobble one together today when I get done wasting my time on the computer )
Anyway I did want to digress, and discuss the results obtained WITHOUT the glass. **CAUTION** this post may involve mathematics so pleas skip to the next post if not interested.
In the initial post I disregarded any effects of diffraction. I am not sure, but this may be an error. DIffraction is a sometimes mysterious process (one of my favorite real life examples I witnessed was being in a jet plane and seeing its 'shadow' cast as a 'bright spot' when we were at just the right distance for the diffraction pattern to show the center of the bulls-eye as light vs dark.)
Anyway, the test picture that was obtained WITHOUT the glass was not outside the bounds of the test equation. That is, the negative was NOT displaced more than 0.5 mm above the paper. Yet , this image is 'blurrier' than expected from the equation.
One possible explanation is diffraction. The pictures posted show a magnified area of the center of the image which is an image of BLADES OF GRASS that are on the other side of a small river, about 50 METERS FROM THE CAMERA.
Using the 'thin lens' formula with these numbers I can find the width of these blades of grass as they appear in the negative. Distance to grass = 50000mm, Distance to negative = 210mm, size of grass blade = 1mm, calculated size of grass blade image = 0.0042mm.
To refresh my memory, here is a simple quote from a basic web site on physics:
"The amount of bending depends on the relative size of the wavelength of light to the size of the opening. If the opening is much larger than the light's wavelength, the bending will be almost unnoticeable. However, if the two are closer in size or equal, the amount of bending is considerable..."
What I was underestimating is that light diffracts more when forced to go BETWEEN two objects rather than around one large object.
I had estimated that the light just has to go AROUND big opaque areas of silver, but, in-fact, the light is being forced to go BETWEEN the little images of the blades of grass. This is causing more diffraction than I had realized. Not sure but just a thought.
OK if you don't like math and optics you can start reading again at this point....