Hi Andrew,
It was my pleasure! I've got some more to try when I can find the time.
If I remember correctly, the process went something like this:
Set up a Cooke triplet with the appropriate image plane size and focal length. Set the positive glass types to N-BK7 ( what most catalog positive lenses are made of). At this point you'll have a really nice Cooke with RMS spot diameter ~20um for 4x5 image plane.
Constrain the outer lenses to plano-convex. This is a better approximation to the lens shapes of an ideal Cooke than an equi-convex. Also set the outer glass types to N-BK7. Reoptimize at this point. I optimized for P-V Wavefront (this is my preference), but I track spot size. I also set the stop either before or after the middle lens, depending on what gives better merit function value.
Set the element focal lengths to be equivalent to common values in the catalog. It's fairly straightforward to find a suitable combination.
Now I've basically reduced the variables to the center negative flint lens. In a Cooke, the choice of glass types corrects color. So I have to do this now. The outer glass is set to N-BK7. The most common flint for catalog negative lenses is SF-11, which doesn't work well with N-BK7 to correct color. If you were to optimize for a flint to pair with BK7 youd find the design settles on N-F2, but that isn't an option for catalog optics.
There's no catalog flints really available to pair with catalog crowns to correct color, which never made sense to me (except maybe catalog lenses are for tinkerers, professors, or people who just don't know any better).
So the real sneaky part that makes this work is that Fused Silica is another choice for "flint" that has low and similar dispersion like BK-7 (Abbé of both are in the 60s), but index is different enough that it's not the same glass. If you use a fused silica lens for the flint, then at least color is reduced enough for acceptable spot sizes. Set it up as an equi-concave lens for design symmetry.
Now it's just a matter of finding catalog lenses that are close to what you have. Zemax has a tool which allows me to rapidly filter through stock lenses from all the vendors for focal length and diameter, element type. I don't think Oslo has that unless they've incorporated it recently. If not, then just flip through the Edmund and Thorlabs catalogs. Once selected, optimize lens spacings to give you the proper focal length and final aberration correction. Don't constrain focal length too tightly, just keep it roughly normal or it'll go short (smaller focal lengths make smaller spot sizes).
The diameter of the fused silica lens constrains the f/#. If that weren't the case, then I would instead stop the design down until the RMS spot diameter is about 100um across the field. This allows you really nice contract prints and maybe enlarge 2x or so from a wide open photo. As it is, this design is about there anyways and provides good performance. Not as good as a true Cooke of course, but surprisingly good enough with maybe some pleasing softness.
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