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Is PAE tolerances achievable.

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#1 RedzoneMN

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Posted 13 November 2019 - 12:35 PM

Have viewed the sky with refractors and C14 sct and thoroughly enjoyed it for 10 years.

Currently looking at large reflectors aka 20-24 inch truss dobs from JP, starstructure, teeters.

Thinking of F3.3 but put off by the almost impossible PAET tolerance of 0.18 mm.

Is this even achievable? What tools will help me with this?

Any help appreciated.

#2 MitchAlsup

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Posted 13 November 2019 - 01:00 PM

Yes, the tolerances are tight, but not so tight as they become unachievable.

 

I just completed a 13" F/3 which has even tighter tolerances (than F/3.3).

What you need in order to achieve said tolerances::

a) a geometrically stiff mirror frame

b) a geometrically stiff truss

c) a geometrically stiff upper assembly

 

The word geometrically is used in that you want the structure itself to provide the stiffness, not just building it big and heavy to provide the stiffness.

 

This book will help:: "Portable Newtonian Telescopes" Albert Highe.


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#3 Vic Menard

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Posted 13 November 2019 - 01:07 PM

...Thinking of F3.3 but put off by the almost impossible PAET tolerance of 0.18 mm.
Is this even achievable? What tools will help me with this?

A 0.5mm read with a calibrated Cheshire is pretty easy, and that's a 0.25mm PAE. But there are other issues that may make you consider Mike Lockwood's star alignment procedure  http://www.loptics.c.../starshape.html

 

But remember, the PAE tolerance you're quoting is for high magnification (30X to 50X per inch of aperture). For moderate magnification (up to 20X to 25X per inch of aperture) the tolerance can be relaxed, a little. If you're using a Paracorr 2, a 2X increase on the tolerance may be visually noticeable. A lot depends on your visual acuity and your expectations.

 

FWIW, I find that my 22-inch f/4 StarStructure is easy to collimate with tools and it holds collimation well, but I usually max out around 450X.


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#4 RedzoneMN

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Posted 13 November 2019 - 01:36 PM

Thank you for the replies. Was not aware that the PAET numbers were for high power viewing.

Would the Catseye tools help me achieve the stated tolerances in Collimation?

#5 Vic Menard

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Posted 13 November 2019 - 03:51 PM

...Would the Catseye tools help me achieve the stated tolerances in Collimation?

Yes. waytogo.gif




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