We've discussed this at length at the Chabot Workshop. One way to
manufacture this type of mirror is to make a full paraboloid and then cut
out an off axis piece. The glass would have to be high quality and
stress-free for this to work. High quality, well annealed pyrex fits the
bill for this.
The alternative is to polish an off axis figure into the glass. That's
possible, but hard to do. I know of machines that have been built to do
this type of work for large telescopes, whose primaries are in segments. I
have not heard of an off axis polisher for three inch mirrors...
RO
----- Original Message -----
From: "Scott Baker" <astrosquig@No-Spam>
To: "The Astronomy Connection" <sf-bay-tac@No-Spam>
Sent: Monday, March 07, 2005 3:37 PM
Subject: RE: [TAC] Scope of confusion
>
> This is what I was wondering.
>
>
>
> If this was a 6 to 8 inch at f6 or f8, I'd be thinking," Ooooooooo, I may
> have to get one of those."
>
>
>
> At 3.6 f/13.6 I'm wondering ,"huh? what?"
>
>
>
> The other thing I'm wondering is that if an offcenter paraboloid works
> well optically, why aren't there more people making them? Is it the
> difficulty in making the mirror?
>
>
>
> It's such a simple idea, would it really be that hard to find an easy way
> to make that kind of mirror? Most commercial telescopes are made by
> machine anyway. is there a way to configure a machine to make an
> offcenter paraboliod?
>
> Michelle Stone <tac4mstone@No-Spam> wrote:
> I dunno.... compare the price to an Orion 80mm ED. Not much difference.
>
> Given the choice, I'd go with the refractor.
>
> Now once you get beyond 5 or 6 inches in aperture, the difference might be
> considerable... but they don't offer them in this size.
>
> Michelle
>
>> -----Original Message-----
>> From: sf-bay-tac-bounces@No-Spam
>> [mailto:sf-bay-tac-bounces@No-Spam] On Behalf Of Leonard Tramiel
>> Sent: Monday, March 07, 2005 12:55 PM
>> To: The Astronomy Connection
>> Subject: Re: [TAC] Scope of confusion
>>
>> Right,
>>
>> It will give better performance than a normal newt at much
>> less cost then the CORRESPONDING apo. (my emphasis)
>>
>> So you get a 3" scope that performs better than a 3" newt and
>> costs less than a 3" apo. But it cost more than a 6" newt, is
>> no more portable and performs worse.
>>
>> -Leonard
>>
>> ----- Original Message -----
>> From: "Jeff Crilly"
>> To: "The Astronomy Connection"
>> Sent: Monday, March 07, 2005 12:16 PM
>> Subject: Re: [TAC] Scope of confusion
>>
>>
>> >
>> > Without the diffraction spikes (and less bluriness) then possibly
>> > performance on the moon/planets is better than the normal newt,
>> > at substantially less cost than the corresponding apo?
>> >
>> >
>> > --- Peter Santangeli
> wrote:
>> >
>> >>
>> >> I'm confused. I just read the S&T article on Orion's 3" off axis
>> >> reflector.
>> >> I was actually interested in this, because it is clearly
>> so unusual. From
>> >> the article though, when compared to Orion's *cheaper* 6"
>> newtonian, it
>> >> has:
>> >>
>> >> - less light grasp (obviously)
>> >> - the same size tube
>> >> - (surprisingly!) less contrast
>> >>
>> >> What am I missing here? Apart from it being gimicky, what
>> advantages does
>> >> it
>> >> offer the observer?
>> >>
>> >> Pete
>> >>
>> >>
>> >
>>
>
>
Received on Mon Mar 7 18:34:27 2005