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SW 180mm Mak just ordered

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31 replies to this topic

#26 precaud

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Posted 22 December 2018 - 10:45 PM

I built a new DPAC test eyepiece today, so the DPAC rig is back in business. It works so well, it makes you want to measure everything in sight  smile.gif

 

And of course the first thing I wanted to look at is the SW180. Shown are outside and inside of focus with 133LPI Ronchi in double pass. (For those not used to looking at DPAC images, the errors shown are twice as bad as they really are.)

 

I've read several comments on the forum from folks saying they have never seen a "bad Mak". And here we can see why. These are pretty nice-looking lines. The camera didn't focus on the inside as well as it did the outside, dunno why. The setup was on a carpeted floor and camera was attached to the eyepiece holder, so getting lines to stand still was a challenge. Hard to say if there's a wee problem on the edge or if it is created by the reflections. Ideally, I would have preferred not to have all the lines symmetrical to the center obstruction, but that was hard to control.

 

Bottom line, this is another affirmation that this is a pretty nice scope.. Now if only the jet stream would get lost long enough to take it outside at night...

 

(BTW, I rotated the eyepiece between taking these two pics, trying to get the lines asymmetrical to the center. That's why they're at different angles. There's no astig...

Attached Thumbnails

  • dpacin.jpg
  • dpacout.jpg

Edited by precaud, 23 December 2018 - 09:40 AM.

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#27 Tyson M

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Posted 23 December 2018 - 03:11 AM

Awesome, I was wondering when someone was going to DPAC this scope.

#28 Peter Besenbruch

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Posted 25 December 2018 - 08:51 PM

Bottom line, this is another affirmation that this is a pretty nice scope.. Now if only the jet stream would get lost long enough to take it outside at night...

Very nice images.



#29 Ptkacik

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Posted 26 December 2018 - 11:16 AM

Regarding vignetting, my Orion Mak has a washer at the visual back with about a 25mm ID so there is only so much you can get out of it. A 45mm 100* eyepiece must vignette. I can't say what the limit is.

Regarding in and out of focus, Telescope-Optics (.com?) says that these Maks will not have the same views by design. I'm not sure how to Collimate except for centering the Airy disk.

Clear skies,
Peter

#30 Peter Besenbruch

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Posted 27 December 2018 - 09:28 PM

Regarding vignetting, my Orion Mak has a washer at the visual back with about a 25mm ID so there is only so much you can get out of it. A 45mm 100* eyepiece must vignette. I can't say what the limit is.

Regarding in and out of focus, Telescope-Optics (.com?) says that these Maks will not have the same views by design. I'm not sure how to Collimate except for centering the Airy disk.

It sounds like your Orion Mak came with a 1.25" visual back. Later Orions and Skywatchers come with a 2" visual back. Vignetting gets kicked further downstream to the primary baffle. While that opens things up a bit, the wider 2" eyepieces do exhibit noticeable vignetting.



#31 luxo II

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Posted 28 December 2018 - 10:36 PM

... the obstruction "hole" was dark on one side of focus but had rings on the other. 

Precaud, having had three, the SW 180mm maks do display slightly dissimilar rings inside/outside focus. There is absolutely nothing wrong with the SA correction at focus. Secondly that DPAC interferogram is quite nice, so enjoy your scope and don't fret about it. As Peter said, your scope can deliver usefully at 450X. A good friend of mine has an Intes M715D which he regularly uses above 400X for lunar sketching.

 

FWIW my Santel MK91 - which is an f/13 Rumak with separate secondary mirror - shows a star test which is absolutely identical out-of-focus and inside of focus, and not the slightest hint of colour. 


Edited by luxo II, 28 December 2018 - 10:37 PM.


#32 precaud

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Posted 29 December 2018 - 09:32 AM

Precaud, having had three, the SW 180mm maks do display slightly dissimilar rings inside/outside focus. There is absolutely nothing wrong with the SA correction at focus. Secondly that DPAC interferogram is quite nice, so enjoy your scope and don't fret about it. As Peter said, your scope can deliver usefully at 450X. A good friend of mine has an Intes M715D which he regularly uses above 400X for lunar sketching.

 

FWIW my Santel MK91 - which is an f/13 Rumak with separate secondary mirror - shows a star test which is absolutely identical out-of-focus and inside of focus, and not the slightest hint of colour. 

 

Thanks. but I'm not "fretting", just checking out a new scope. The DPAC result has given me good confidence. The dissimilar inside/outside focus rings were due to the scope not having stabilized while ambient temps were falling. I'm just about finished with an insulating setup that I'm hoping will help in this respect (the subject of a different thread). Tomorrow night looks like a candidate to test it, though temps will be brutally cold... our forecast high today is 24F. (Six years ago as an enthusiastic noob, I didn't let that stop me... today, it gives pause...)




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