To: dchaffee{at}mail.blitz-it.net,atm{at}shore.net
From: MLThiebaux 
Reply-To: MLThiebaux 


>>
>>I made a 1.6" minor axis diagonal that had smooth
>>.25 wave convexity and no TDE in 650nm and used it in a
9.6"f/7.4 newtonian.
>> With  this diagonal, the scope tested with obvious astigmatism in a star
>> test at 309x. I also performed a star test by fixing the diagonal at a 45
>> deg, angle in front of a stopped down 6" newtonian and saw
the same amount
>>of oval deformation at 360x.
>>
>...
>>Dan Chaffee
>>
...

What is the diagonal-to-image-plane distance in >the 9.6" newtonian?

>>Martial, I'm responding off list now due to difficulties. If you have a
response, by all means
>post my reply to the list along with it.
>
>>7.4 inches. I neglected to say that the curvature
>was relatively spherical and not cylindrical in
>its figure.
>
>DC
>
>
...


Dan,  I did the arithmetic on these numbers:

        focal ratio = 7.4
        diagonal-image distance = 7.4"
        diagonal minor diameter = 1.6"
        sagittal error across minor diameter = .25 lambda

==> Predicted wavefront error = .138 lambda, which doesn't suggest any image
deterioration.  Okay, something's wrong.  So play safe and stick to flat flats.

Martial Thiebaux
Rawdion Hills, Nova Scotia

--- BBBS/NT v4.00 MP