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Re: [ATM] Need Design Suggestions for a 16" f/1.1Spherical Mirror
Well, the thing is, as I’m just about to take delivery of a 5" F1
1/20wave spherical salad bowl (well it does have a 2" hole in the
middle, so the salad would have to be of the chunky kind).
So now I'm trying to work out a corrector lens combination that will
enable me to make a usable visual use scope out of it, at present I'm
exploring two to three element systems, but well we'll see, might have
to put a secondary mirror in there somewhere to get the image to a
useful location.
Clear Skies, Thomas.
www.tjanstrom.com
www.norsewines.com.au
-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf
Of Scott Milligan
Sent: Thursday, 29 September 2005 9:09 PM
To: 'Scott Ewart'; atm@atmlist.net
Subject: Re: [ATM] [SPAM]Re: Need Design Suggestions for a 16"
f/1.1Spherical Mirror
Veggies.
Scott Milligan
-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf
Of
Scott Ewart
Sent: Thursday, September 29, 2005 2:15 AM
To: atm@atmlist.net
Subject: [SPAM]Re: [ATM] Need Design Suggestions for a 16" f/1.1
Spherical
Mirror
A friend showed me an interesting mirror that had been given to him.
It's a 13.75" clear aperture spherical mirror with a focal length of
6.625".
That's right, f/.5 (not even). It's .75" thick with a 3" hole. I was
told
it came from some kind of projector, and it had a secondary (if only he
still had that).
It sounds like it's way too fast for a Schmidt camera. Can he make
some
kind of Cassegrain out of it for photography? If so, what type and what
figure on the secondary? Gregorian, maybe? Can we get the field flat?
Or should he just put the dip in the hole and arrange veggies around
it?
Scott
----- Original Message -----
From: "vladimir" <svla@isp.com>
To: <atm@atmlist.net>
Sent: Wednesday, September 28, 2005 5:34 PM
Subject: Re: [ATM] Need Design Suggestions for a 16" f/1.1 Spherical
Mirror
| Been playing with large, very fast spheres and what - if any -
| optical purpose they can serve. The best I came up with is
| a 2-mirror 3-reflection system that is stopped down to 37% linear
aperture
of such sphere (although third reflection does use nearly its entire
surface).
|
| The second mirror, placed after the prime focus, also spherical but
convex, directs diverging light back to the
| primary, which then focuses behind the secondary, which is
| contained within the converging cone at its location.
| The field can be made essentially flat, with some remaining
| coma/astigmatism, but with overall field quality still good for
| imaging purposes. An example with the above mirror is this effective
| 150mm f/2.5 system:
|
| R1: -900mm
| primary-to-secondary: -674mm
| R2: -1000mm
|
| Minimum obstruction (by the secondary in the converging
| cone after third reflection) is 60%. The spot size increases
| from bellow the Airy disc diameter at the field center to about
| 0.025mm nearly 1 degree (6mm) off-axis, due to combined
| coma and astigmatism. The blur size decreases
| with slower primaries.
|
| The parameters are fairly constant: 37% stopping down,
| ~2.2x increase in primary's F# and 60% minimum c.o. System
| scales fairly well with either primary's F# or aperture.
|
| Baffling the system seems like lots of fun, but doable.
| All in all, who have a large fast sphere at hand, and some
| spare time, can consider making a "partial" use of it.
|
| As for more conventional systems, they would likely have
| very tight misalignment tolerances with this fast primary.
| Enough to make them impractical for the amateur arena.
|
| Vlad
|
|
| _______________________________________________
| ATM mailing list http://www.atmlist.net/
|
|
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