Quote:
Originally Posted by bratislav
Peter,
...............
the "NASA glass" (KzFS-1) is actually inferior to both Fluorite and FPL53 as far as "abnormality" of dispersion. I'd be surprised if a modern EDT (with two best matching Crowns) couldn't surpass what the old 155 could do............
Bratislav
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The dispersion was not what made that glass special.
Foundries like Schott have a homogeniety index, which gives a lamba error for a given thickness of glass. Typically from H1 to H3. H3 is often unavailable. (higher = less distortion)
I understand the glass Roland used in the 155's was H4.
While I don't have the test data on my 155, I was lucky enough to get it for my AP 130mm. It has a strehl of 0.99.
The star-testing both scopes, they are very hard to split, hence I can only assume the 155 is a similar spec.