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Originally Posted by Starkler
I have read that some ED designs can produce weird star test results without there actually being anything wrong with the scope.
My ed80 has sharp rings inside of focus and mush on the outside. This I hear is due to the different colours refracting at slightly different points away from focus. In focus images are great and thats the important thing.
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What he has got is mush both sides of focus.
But outside is better than the in , but both have excessive flarring like heat abberation.
We allowed it to cool down inverted but even by the end of the night this flareing didn't change at all, not one bit.
The inside focus has a couple of out side rings that can be seen but the inner rings on the star are surrounded by large amounts of blue and flareing and are quite ill deformed.
Out side is some what better but not what you would expect.
Focused stars (sirius) were surrounded by a lot of blue.
Now this is as compared to my C80Ed and if you have a looky at the review I did a while back the star tests are there of it. Inside , out side and focused stars images are excellent for a ED doublet.
He also can't crank the mag up as much as mine with out it washing out.
One would expect to be able to do the 60x / inch on a good night .
The night was not perfect but was able to get this and more.
So it appears there has to be some thing major wrong.
I have an old chinese acromate that has a better star test with less blue.
I thought the idea of the Ed triplet and doublets is to reduce the distance all the colors come to focus especially in the blue green area and different designs and glass work at different wavelenths better , but there all trying to get all the spectrum focused at the same focal plane.
I am very interested in finding out what is wrong.
What i should have done but plane forgot to do is take a snap shot of the star tests done that night , but every one present observed the testing.
I was to busy fondling my new Nagler
P.S. we swapped diagonals and used various eyepieces as well.
Mark