Re: End of an era?


Roland Christen
 

Hi Jay,
BTW, are there any decent all-spherical Maksutov solutions in which the secondary is a separate piece of glass from the corrector? 
For any given aperture, the amount of 5th order spherical aberration is dependent on the size of the secondary obstruction and the F-ratio of the primary mirror. If you allow a long focal ratio primary and a largish secondary obstruction, then the amount of spherical 5th order is quite low and you can leave it all-spherical. So basically you are trading 5th order defect for central obstruction defect. Yes, you can use a separate secondary, but for any given focal ratio, a separate secondary will always result in a larger obstruction.

See below what happens if you do not figure the optic by hand to remove the 5th order. In the first picture it shows the performance of the 10" Mak with 23% obstruction and the optic figured to completely remove the 5th order defect.
In the second picture you can see the performance with all-spherical surfaces and no figuring. The performance of the all-spherical is not bad, the Strehl ratio is 95% and the P-V is approximately 1/6 wave, so it is diffraction limited. Some people consider that good, but it is not superb and i would not pass such a thing. In fact, there is a fattening of the spot diameter and a fairly large amount of unfocused light coming out of the outer diameter of the optic that inevitably surrounds the image in a hazy veil. The outer diameter is the trickiest part because that's where the most light is gathered, and you want to be sure that this part of the optical system focuses the light into the Airy disc, not into the surrounding diffraction pattern.

Rolando

Hand figured Spherical Mak:





All-Spherical Mak:


-----Original Message-----
From: Jay Freeman via groups.io <Jay_Reynolds_Freeman@...>
To: main@ap-ug.groups.io
Sent: Tue, Aug 4, 2020 5:31 pm
Subject: Re: [ap-ug] End of an era?

Intes and Intes Micro appeared to be different companies, but related somehow. Both made very nice optics.

BTW, are there any decent all-spherical Maksutov solutions in which the secondary is a separate piece of glass from the corrector? 

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