Re: Help with elliptical secondary source?

From: Dan Chaffee (dchaffee_at_blitz-it.net)
Date: 11/24/04 

Date: Wed, 24 Nov 2004 08:14:50 GMT

On 23 Nov 2004 11:48:10 -0800, n_perkins2003@yahoo.com (Nate Perkins)
wrote:

>Tim Auton <tim.auton@uton.groupSexWithoutTheY> wrote in message news:<fuo4q05fvu2brlrq737jh3d95ccoeiv6r2@4ax.com>...

>>
>> What's your primary? If it's a 1/30th wave Zambuto then find something
>> as awesome as possible and pay the premium, if it's a home-made 1/4
>> wave then a top-grade secondary might not be the best use of your
>> cash.

>I'll take your advice and go with a lower cost secondary.

I do not necessarily agree with this. You do NOT want the diagonal to
be the weakest link in the chain. If your primary is smooth with say
.25 wavefront undercorrection, it's still a fairly good mirror. If you
buy a flat with too much curve too it, you will immediately notice
astigmatism in high power star images, reducing your .8 strehl
optic to well below that number.

A high quality diagonal in that size is not *that* expensive, and I
for one have never regretted the extra effort in making, or in your
case, buying a high quality optical component. What if you upgrade to
a better primary some day? You'll likely lament the taking the cheap
route back in the "good old days":-). Try Protostar; consistantly
recommended by critical observers and ATMs.

D Chaffee

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