Re: [ATM] Looking for information on a telescope design

["vladimir sacek" <vla@toast.net>]

Scott (Ewart),

> You and others keep mentioning doublets and even triplets, but
> that's not what Clyde uses.  A 4-element Petzval does make a difference.
> I'm talking about a refractor with an extremely well corrected 4-degree 
> true
> field (on its own).

I wasn't talking about any particular Mersenne, rather in general.
Significant differences in the field quality from one arrangement to another
are possible, and it needed to be better understood. Clyde said in the
very beginning that it boils down to the imaging instrument, and so did I 
and,
I think, Scott Milligan. But we were not able to say, more specifically, 
what
are the requirements and the consequences. It seems to be surfacing now.

As you can see in my previous post, I did (finally) check out the Petzval
refractor, and you are quite right: it can make all the difference. With it,
there is no need to go through the trouble of placing the objective as close
 to the secondary as possible.

>
> Why build Mersenne? Because it's different is as good a reason as any.
>
> Vlad

I can now add one more good reason: because it can have near-perfect field,
other than visually inconsequential field curvature. Better than comparable 
RC.
But central-obstruction-wise it is not significantly ahead from other 
two-mirror
systems. And any of them can be made
with conveniently low eyepiece location. There is a number of factors
other than optical quality involved, and they matter differently to 
different individuals.
Best you can do is to spread them all down in front of you and decide for 
yourself.

Vlad 

_______________________________________________
ATM mailing list http://www.atmlist.net/