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DPAC image of my 12 inch orion intelliscope mirror

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#26 dave brock

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Posted 06 September 2019 - 02:41 PM

Up edge or down edge doesn't matter they will both detract the image quality the same amount.

Except that under typical viewing conditions where the temperature drops over the course of the night, a turned up edge is better than a turned down edge. TUE will tend to reduce and a TDE will tend to increase.

Edited by dave brock, 06 September 2019 - 02:43 PM.


#27 SandyHouTex

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Posted 07 September 2019 - 11:38 AM

It’s also important to note that in a double pass test the errors are doubled.  This looks to be a fine mirror.  I wouldn’t mess with it.


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#28 Steve Dodds

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Posted 07 September 2019 - 12:27 PM

After I gave him the results Itz send me the diagonal.  Half of it is 1/4 wave and half of it is 1 wave.  Pretty sure that was his problem.



#29 MKV

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Posted 07 September 2019 - 09:10 PM

After I gave him the results Itz send me the diagonal.  Half of it is 1/4 wave and half of it is 1 wave.  Pretty sure that was his problem.

Why do these significant-sounding details emerge late into the thread? Why not at the start? I notice that a lot.



#30 Itz marcus

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Posted 07 September 2019 - 09:44 PM

Why do these significant-sounding details emerge late into the thread? Why not at the start? I notice that a lot.

Hi,

I had not sent the diagonal at the same time as the mirror. Mr. Dodd first received the secondary this past Friday (sept 6)

Clear skies

Itz


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#31 MKV

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Posted 07 September 2019 - 10:29 PM

That's why it makes sense to wait until everything is tested to start a thread.



#32 Itz marcus

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Posted 07 September 2019 - 10:57 PM

Well, I wasn't originally going to have the secondary tested it was only after the primary was tested that I decided to see if the secondary was the cause. Nothing was done to provide half the info only I changed my mind re: the secondary. 



#33 MKV

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Posted 08 September 2019 - 08:15 AM

Well, I wasn't originally going to have the secondary tested it was only after the primary was tested that I decided to see if the secondary was the cause. Nothing was done to provide half the info only I changed my mind re: the secondary. 

Oh I understand that there was no ill intention. I never meant to imply that. But it's obvious that we never just use a mirror alone and that every piece of optic, obstruction, etc. contributes something to the exit wavefront. That fact is often overlooked for some reason. :o)



#34 Steve Dodds

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Posted 08 September 2019 - 08:41 AM

Most people never think about the diagonal, mostly because the diagonal folks are claiming 1/20 to 1/30 wave, they aren't..  Most of the diagonals I have tested are around 1/4 wave.


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#35 precaud

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Posted 08 September 2019 - 09:36 AM

Most people never think about the diagonal, mostly because the diagonal folks are claiming 1/20 to 1/30 wave, they aren't..  Most of the diagonals I have tested are around 1/4 wave.

 

Tested how?



#36 MKV

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Posted 08 September 2019 - 10:11 AM

Most people never think about the diagonal, mostly because the diagonal folks are claiming 1/20 to 1/30 wave, they aren't..  Most of the diagonals I have tested are around 1/4 wave.

That's true, and one more reason why folks who know better need to educate the public why it doesn't make sense to only test the primary mirror, or why a computer-designed configurations are meaningless without tolerances, etc. All this is pretty munch common sense. 



#37 MKV

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Posted 08 September 2019 - 10:16 AM

Tested how?

There are many ways to test flats. One is a water test described by Ed Jones in his videos on Youtube. ATMs should be familiar with these techniques. One can also buy relatively cheap optical flats 2-3 inches in diameter on eBay,  Amazon, etc. and test diagonals by contact interference ("Newton's rings"), etc. 


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#38 precaud

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Posted 08 September 2019 - 10:25 AM

There are many ways to test flats. One is a water test described by Ed Jones in his videos on Youtube. ATMs should be familiar with these techniques. One can also buy relatively cheap optical flats 2-3 inches in diameter on eBay,  Amazon, etc. and test diagonals by contact interference ("Newton's rings"), etc. 

 

Sure, but I didn't ask, what are the various ways flats can be tested; I asked the poster how they tested, which forms the basis for their statements.


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#39 Steve Dodds

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Posted 08 September 2019 - 11:25 AM

Tested with a 1/20 wave test plate with a partial coating (50%)  Visual only and I can't tell anything better than 1/10 wave.


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#40 precaud

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Posted 08 September 2019 - 06:59 PM

Tested with a 1/20 wave test plate with a partial coating (50%)  Visual only and I can't tell anything better than 1/10 wave.

OK, thanks Steve. So to what do you atrribute the difference?

 

Is it possible to set up a Zygo (I assume that's what they're using) such that everything measures better than it is?



#41 Steve Dodds

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Posted 08 September 2019 - 07:07 PM

All the tests should agree, although most of the tests suggested here won't work well with a coated diagonal.



#42 MKV

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Posted 08 September 2019 - 07:37 PM

In the water test you can add food coloring, even cerium oxide to cut down the intensity.



#43 precaud

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Posted 08 September 2019 - 07:38 PM

All the tests should agree, although most of the tests suggested here won't work well with a coated diagonal.

Yes of course, but that doesn't even touch my question...



#44 stargeeser

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Posted 17 October 2019 - 08:32 AM

After all is said and done what is the consensus of the quality of this mirror? Mr. Dodd estimated it at 1/6 wave with a strehl of .91 which seems to be pretty good. Others seemed to argue but not sure if they were taking into account that the errors are doubled in a dpac test.

Also, if one were to have a similar mirror would it make sense to refigure it or will there be no real gain at the ep?



#45 Itz marcus

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Posted 17 October 2019 - 12:01 PM

Hi,

Well I can't give my opinion as I had the scope tested because I can't do it on my own but that being said, I did follow Mr. Dodds advice and bought an Antares secondary (1/20 wave) and, although I couldn't test extensively yet, I did use it to look at Saturn twice. Both times Saturn was right over my house or my neighbor's house and both times were low in the sky (Saturn doesn't get high in my area this year or the next few years but it was low even for Saturn) and whereas before the new secondary I was lucky to get 180x I got 250x and it was sharp sharp. Cassini was sharp and to me, at least, visible as a space or a thicker line than I was ever used to with all my other scopes. Banding and shadows were really clear. I was just pleasant to look at. I would've have gone higher as I felt that 300x-350x was possible but I didn't have the ep to do it with (after 250x my next was with a barlow which would be 500x. I did it anyway and although just about everything I saw in 250x was there it just wasn't pleasant to look at- quite grainy/blurry). When trained on the double double (of course VERY high in the sky) I got a clean split at 125x and an unclean split at 100x. With the Trapezium I got "e" immediately every time I tried but only possible glimpses of "f" at 100x. Seeing at that time may not have been as good as when observing Saturn and the double double. Anyway, where I live that's about all I can observe (not literally but LP is pretty stinky). I do hope I made the right decision to not refigure the mirror which was made on the basis of being told that the refigure would be hardly noticeable if at all, but thus far I'm happy but waiting for the obsessing to begingrin.gif frown.gif !

Clear skies

Itz


Edited by Itz marcus, 17 October 2019 - 12:05 PM.

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