T3D ocular specs

[bercov@xxxxxxxxxxx (John Bercovitz)]

Since you've all had a chance to think about it, I'll throw out 
some specs off the top of my head because I can't find where I put 
the specs I worked out earlier and because they're very much 
subject to change anyway.  Think of these specs as something for 
you to shoot at or shoot down or support depending on your specs.  
These specs would also be what an off-the-shelf loupe would have to 
be able to do for the same price to be competitive.

Focal length 36 mm.

Field of 40 mm diagonal (across the diameter of the field).  You 
might think it should be 31 mm for 5P and 36 mm for 7P but these 
are only the diagonals of the apertures in the masks.  The 
apertures are offset from the lenses because the apertures set the 
window and the window is closer than infinity. The difference on 
the mask is an offset of (65-62)/2 = 1.5 mm  This ups the 7P 
diagonal to 39 mm and the 5P to 34 mm.

Eyepoint at 20+ mm (the spectacle point is at 16 mm and we need 
some clearance for a bumper on the lens holder to protect the 
glass).

Distortion < 2% (one would suppose this would be at the edge of the 
field since the distortion should be a cubic).

Resolution 2 moa (the resolution on the film is maybe 40 lpmm 
including many factors such as DOF and it is located at a distance, 
optically speaking, of 36 mm.  Arctan (1/40*36) = 2 moa).  Let's 
say a sine wave MTF of 50% constitutes resolution.  Wavelength of 
555 nm.

Allowable offset of eye from lens axis while retaining full specs: 
5 mm

Field flatness equivalent to a range not to exceed 0.5 diopters to 
allow for the elderly and enfeebled among us (that's me).  That's 
+/- 0.25 diopters

Color weighting to allow resolution resolution which is half as 
good at 700 and 400 nm as it is at 555 nm.  What should the shape 
of this weighting curve be?  Should it be mapped to the relative 
visibility (y bar) of the colors in some way?

How much error in magnification should we allow between the various 
colors?  I'd say what ever works out to 2 moa.  There are contrasty 
situations where this could become important.

Multicoat AR coating.

Let the cost of the finished product and environmental resistance 
drive the glass choices.  (In other words, expensive glass is OK if 
it solves the problem more cheaply than many extra elements of 
cheap glass as long as the expensive glass isn't weak in its 
resistance to the environement.)

OK, whud I leave out?

John B


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