Quote:
Originally Posted by glend
But is that Strehl noticeable in the use you want the scope for? Even visually, it just becomes a bragging number because neither the average eye nor sky conditions are going to be able to exploit that.
The colour correction (don't forget most Strehl is measured in green from the centre), and collimation are two big factors that can support or degrade actual field Strehl. Anything less than perfect collimation, thanks for the bump UPS, can negate the difference between 0.93 and 0.98. And then you have focus precision, etc etc.
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I am not an expert on the intracies of Strehls but it is a normally quoted measure for the sharpness of optics. I presume it also takes into account other aberrations.
For imaging >.95 strehl seems to be a common standard for todays APOs and >.97 only by the very best. >.90 was considered good about 10years ago.
So Strehl number for me rightly or wrongly would be very important as an objective measure of the perfection of the lenses. But yes TEC for example tune their lenses for the best result in green (more green in the eye than other colours and the Bayer matrix has 2 green filters for every 1 of red and blue). But red correction can be weak.
Astrophysics scopes often are optimised for imaging and it shows in their slightly better performance than TEC which are very good but not top of the class.
I have had some very high end refractors and yes you definitely notice it.
An Orion ED80 is a great little entry scope. Put it up against a TEC110 and the differences stand out.
Where the better scopes seem to rise above is in size of the corrected field (some are just too small limiting what camera you can use). The lack of false colour - a big one. I had a Tak FS152 which was the best visual scope I have had but for imaging it tended to give blue rings around bright stars.
Look through an AP140 and the stars suddenly are super tiny pinpoints. Never seen anything like that with any other scope.
Greg.
