Can you help ID glass for an objective

Hello,

I am starting to put together a project to make an objective. I have a 5.5 inch pressed blank set that I would like to use. Unfortunately I am uncertain of the glass documentation.

The plano/concave blank has " F621" written on it.

The convex/convex blank has "BSC" " 1.517" " 64.5" written on it.

I found a reference table for glass types on the Newport Glass web site. In that list I find a reference from Hoya for BSC2 with optical data of 517645. Using the guide information for the table makes me think that this is the same material I have?

Also, I found a reference to a Hoya glass known as F6 with optical data of 636353 but nothing as F621. Could F6 and F621 be the same?

Does anyone know a site with a more extensive list of glass types?

Does anyone have this glass and associated optical data?

Any feedback on how to ID this glass would be very appreciated.

Thank you,

Anthony

Anthony,

This is only a suggestion.

You may be able to get some data on the flint blank by determining the glass density. The flint glasses have enough difference in the densities that it is sometimes possible to isolate the glass. This won't give exact indices or dispertion values but it will narrow down the choices. I would doubt the F621 refers to F6 from Hoya. (At one time I tried hunting down F628 and I came up empty. I would love to hear if anyone else has something to offer)

The crown glasses are often very close to each other in densitiy so this technique won't help much with your problem there. However, it may be reasonable to go with what you have and take the glass to be as labelled, BSC2.

I have an old B&L glass catalog that shows a Borosilicate Crown 1.517, 64.5 and a dense flint 1.621, 36.2. I can send you a copy if you PM to me.

Alternatively, grind and polish the glasses into lenses and measure everthing you need to know. Then regrind into the lens you want.

good luck with your project,
dan