Antique Glass

My modest glass collection includes a pair of blanks for an achromat. They are both plano-plano, 1" thick, and 6.25" in diameter. One is marked "Crown 8959 BSC2" and the other "Flint 4258 DF2."

Can anyone tell me anything about these glasses? Are they worth the time and energy required to make an achromat from them, or would it be better to start afresh with modern blanks with known indices?

Somewhere I have indices someone gave me for BSC2 and DF2, so I suspect I could come up with a reasonable design. At worse, I might have to adjust one surface to bring the color in?

There are several projects - largely household stuff - ahead of anything like this, but I am trying to get rid of stuff with no future. I need some room in the workshop!

Clear skies, Alan

>>There are several projects - largely household stuff - ahead of anything like this, but I am trying to get rid of stuff with no future. I need some room in the workshop!

Clear skies, Alan
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Alan:

I can't provide you with the optical info you need but a friend of mine devised the "garage sale rule" for clearing out unwanted items... I probably needs some modification for use here but it goes like this:

"To determine if an item is worth keeping, just ask yourself this question:

If you were to see it in the free box at a garage sale (astromart) would you take it?"

I can testify that this criteria is powerful in clearing out "junk" and projects that will never happen. If it isn't going to happen with me, then I try to get it into the hands of someone who just might make it happen.

In the current case, I would PM Herbert, ask him his address and send him a box and then keep on riding my bicycle(s) and viewing the stars...

8)

Jon

Herbert,

Thanks! I have Baker's book, and this never caught my eye, or, if it did, it didn't take. I spent some time looking for my values for the indices for BSC2 and DF2 and had no luck. (I hope they were not tucked away in the copy of Taylor's book that went missing.) At least I have values for one wavelength now.

Clear skies, Alan

I found my crib sheet with the indices for BSC2 and DF2, so I'll try to sit down with ATMOS later this weekend.

BSC2 Crown
V = 64.55
n(d) = 1.51707
n(c) = 1.51461
n(f) = 1.52262

DF2 Flint
V = 36.60
n(d) = 1.61715
n(c) = 1.61218
n(f) = 1.62904

Clear skies, Alan

I played with this a little last night using BK7 and F4
which are very close to the glasses provided. It
was already pretty optimal. Turning on the automatic
solutions didn't do much. It did find a solution with
thick elements (I let it go to 1" thick) and microscopically
better color correction. But the initial design
was already quite good -- just a nice solid achromat
with usual color aberrations and some minor off-axis
coma+astigmatism.

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