Hi Greg,
From the 'net I found fresh speculum had a 66% reflectivity, and IIRC he did not use a secondary due to the large light loss. So on a good day he was at 66% of a 72" mirror, which would give ~ 58" equivalent light transmission aperture, which I am pretty sure bested any achromat of the time.
I think one of his biggest problems was it was frequently cloudy
>
:S
From the 'net I found fresh speculum had a 66% reflectivity, and IIRC he did not use a secondary due to the large light loss. So on a good day he was at 66% of a 72" mirror, which would give ~ 58" equivalent light transmission aperture, which I am pretty sure bested any achromat of the time.
I think one of his biggest problems was it was frequently cloudy
> :S 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?
thanks
Greg N
David Simons
