Re: ATM 3" 75mm or 4" 100mm eyepieces

[spooner@page.az.net (Michael Spooner)]

K1JJ@aol.com wrote:
> 
> In a message dated 96-08-20 00:24:45 EDT, you write:
> 
> >
> >>  Say you had a 10" diameter 245mm eyepiece giving a mag of 18X and exit
> >pupil
> >>  of 30mm!  What would the view look like here with a Kelner?
> >
> >This one is fairly easy to check yoursef. Get a ~50mm f.l eyepiece and
> >put it behind an f/1.4-1.8 camera lens. The difference between what you
> >see in that arrangement and what you would (or wouldn't, to be more
> >precise) in your Newtonian with 250mm f.l. eyepiece is that central
> >obstruction will be big enough to COMPLETELY cover your eye's pupil,
> >i.e. you will see nothing.
> >
> 
> Bratislav:
> 
> Ahhh....Nows that's what I was looking for!  Ya know, I do remember that
> central obstruction effect when trying various "camera lens" as an
> experiment, and seeing the BIG secondary floating around in the field!
> 
> Also the analogy of only using 9 inches of the 22" mirror also hits home.
> 
> In fact, it seemed with a smaller 10" F5 Newtonian (55mm Plossel eyepiece)
> the view had almost a "television " look to it where the eye relief was about
> 1.5" and you could actually see like looking at a camcorder screen...I think
> you know what I mean. For a real trip, try this with  8"-10" Newtonian
> binoculars sometime.
> 
> Think I'll use some of the other ideas posted also concerning various
> sources, and limit it to a 75-80mm 3" eyepiece now.
> 
> Anyone know how to get ahold of Joe Sunseri or John Dietch?
> 
> Also ANYONE hearing of a CLEAR aperature  (3"-4" diameter)  75-100mm eyepiece
> please let me know! It will save the trouble of re-inventing the wheel here.
> 
> Thanks.
> 
> Tom Cathey

well, if you take two 80mm binoc. objectives and put'em face to face 
you'll have a poor man's 160mm f.l. symmetrical eyepiece. 
But geez, you'll be able to sit in the house to view and still have 
plenty of eye relief! A lot of these objectives have a f.l. of 325mm. 
Tough to get a shorter eyepiece f.l. without high cost if you want an 
image you can recognize. I made an eyepiece out of two 35mm objectives, 
but I don't use it much. I'm a high power freak anyhow. Not that it does 
me a lot of good with these STUPID clouds. 
There, I feel better.

Regards,
Mike 

'Optician- a pitcher with a nice curve.' 
(groan... sorry, guys)