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Re: Refractory history question

Started by Lorne Johnson, 08/06/2007 12:02PM
Posted 08/06/2007 12:02PM Opening Post
There are plenty of uncoated refractors around today. My experience has been with an 1890 5 inch Alan Clarke, and a D & G 5 inch (both f 15). I don't believe that a visual observer will could see the difference in throughput between those and coated optics. Reflections, certainly but not throughput. (When comparing a a different coated D&G and my MN56 Maksutov Newtonian, we could tell a throughput difference on faint objects on those scopes.)

Greg Nowell said:

When Lord Rosse started his 72 inch Newt in 1840, I'd like to know what the competition was in the refractor domain. With speculum coatings he was going to get only .4 x .4 or 16% light throughput, and that was when the mirror was "fresh." So he was basically getting the equivalent of a modern 20 inch.

But refractors such as they were then didn't have modern coatings, so they probably lost a lot of light too. So here are my questions:

1. Light throughput of an 1840s era achromat doublet?
2. Maximum refractor aperture achieved in 1840?

Greg N