maybe on topic

[Brian W]

Hi all, I have become interested in the history of visual observing. Lately I have been re-reading E. S. Holden's monologue on the central region of M-42.

I have 2 questions (1) from what I have read and the sketches I have studied our 8" LB gives comparable views to what they were seeing back then? (2) on Feb. 11, 1806 Sir W. Herschel talks of using a 'double eyepiece' in a 10 foot reflector. Any ideas on what a 'double eyepiece' might be?
Brian

[CarlJoseph]

A quick google didn't turn up anything terribly useful, except this entry in a Popular Science article (http://books.google.com.au/books?id=wCgDAAAAMBAJ&lpg=PA43&ots=nR_LcBB2ue&dq="double%20eyepiece"&pg=PA43#v=onepage&q=%22double%20eyepiece%22&f=false). :shrug:

[snas]

Brian,

Would that be a binocular eyepiece? I use a binocular microscope at work, far easier to resolve what you're seeing than with a monocular eyepiece. I'm surprised that this is not standard in astronomy. Is there a reason for this??

I seem to recall that William Herschell used a 4 foot long refractor but not sure what diameter it was. That must have been pretty awesome looking through your scope and knowing that almost everything you looked at was a new discovery.

Have a good one

Stuart

[snas]

Oh, look at that. I didn't read Carl's link to the Popular Science article. I guess that is more likely what they're referring to as a double eyepiece. But I still wonder why we don't use more binocular eyepieces in astronomy.

Regards

Stuart

[bojan]

Well, it's because it is expensive (two eyepieces instead of one), bulky, light path is significantly longer (creating focussing and vignetting issues) and it reduces the amount of light for each eye (by splitting available quantity of light in two), effectively making the objects to appear 50% dimmer.
And we are in constant struggle to collect as much light as possible...

[snas]

Thanks for that Bojan. That all makes perfect sense when someone explains it.

Stuart