Re: Refractory history question

I think an added factor that determines how well a telescope can "see" is resolution. If the 72" mirror was well corrected the image of a star would be much smaller and therefore more intense than a 20" modern telescope, so the limiting magnitude should be better in the larger lower % reflective instrument than converted aperture would indicate.

Dave

Hi Greg,

Sorry, I was getting Herschel and Ross criss-crossed.

Herschel only had a 48" scope !

Greg Nowell said:

Here's a picture of Lord Rosse's secondary mirrors. (I was at Birr Castle last week). So when his mirrors were fresh he was at roughly 50% light throughput, but apparently this would rapidly degrade to 16%. regards Greg N

Greg Nowell said:

Here's a picture of Lord Rosse's secondary mirrors. (I was at Birr Castle last week). So when his mirrors were fresh he was at roughly 50% light throughput, but apparently this would rapidly degrade to 16%. regards Greg N

Greg, the card in the photo clearly states that these were secondaries for other telescopes, not the 72" which didn't use a secondary.

Don Wyman