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Planewave CDK 12.5" First Light

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#26 pop

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Posted 17 September 2012 - 08:43 AM


I wanted the 12.5" for the extra light grasp and focal length. Plus, the AT10RC doesn't give round stars in the corners of a really large imaging chip, which the Planewave does. I suspect the AT Ritcheys could do better with bigger chips if they had dedicated flatteners. They aren't really in the same league in terms of optical quality or fit and finish--the Planewave is a significant step up. I haven't done a Rodier yet on the Planewave, but just based on quick star tests the spherical correction is better.

I think the AT Ritcheys are a wonderful value--I prefer them in general to the Celestron Edge scopes. The Planewave is better still.


Thank you very much for your nice answer. I will wait your nice photos in using this scope.

Best Regards,
POP

#27 Jared

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Posted 17 September 2012 - 01:35 PM

Jared,

Congrats! Looking very good and promising! Will you have full-res images of the stars at the corners of the M27 image available like you had your M15?

Eric


Happy to provide corner crops tonight when I get home.


O.K., here are the four corner. These are the absolute extreme corners--the full image had very slight cropping to remove some areas where the different frames didn't overlap--so it won't perfectly match the earlier view.

This is a stack of ten separate five minute calibrated luminance frames. I manually applied a single curves adjustment in Photoshop, but no other processing of any kind.

It appears I still have a small amount of focuser tilt--you can see more curvature and astigmatism in the bottom right corner than in the rest. Still, it's pretty good for a 42mm imaging circle viewed at 100%.

First, the top left...

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#28 Jared

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Posted 17 September 2012 - 01:36 PM

Top right...

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#29 Jared

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Posted 17 September 2012 - 01:36 PM

Bottom left...

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#30 Jared

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Posted 17 September 2012 - 01:37 PM

Bottom right...

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#31 Jared

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Posted 17 September 2012 - 01:38 PM

And the center of the frame...

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#32 jmiele

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Posted 17 September 2012 - 09:46 PM

Looks like a winner to me Jared. Well matched for you expertise. I expect we will be seeing some spectacular imaging from you this winter.

Also, Glad the visual seems to be usable as well. That's a bonus. I know you tossed that image together quickly to give us all a peek, but the processing really is quite good. Also seems the STL is a nice match for it. Thing I like about the SBIG ST(L) stuff is the ability to use the AO Devices. They are a big help at taking a shot back at seeing. :)

Anyway, as expected - excellent stuff sir.

Best,
Joe

#33 wiruna

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Posted 13 November 2012 - 03:00 AM

Hi Jared
I'll soon have a similar setup--same mount, same scope, different camera. I have a question about your use of the AO unit. Is it necessary with the AP900 and the 2500mm focal length or could you get good enough tracking without using it?
Geoff

#34 Jared

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Posted 15 November 2012 - 12:38 AM

I've been doing a fair amount of comparing my results using AO vs. ordinary auto guiding, and so far the AO system has shown a small but consistent improvement in FWHM values versus the guider. The differences seem to be around 0.2" FWHM improvement on nights of average or better seeing when I have a guide star bright enough to allow 2 Hz corrections, and more like 0.1" FWHM when guiding at 1 Hz or slower.

I don't have anything really conclusive yet. Traditional guiding on the AP-900 is certainly enough to achieve stars that appear round, so you don't need an AO unit to get good results, but I do believe that the AO system gives a small but measurable advantage in resolution.

Before I can post more than preliminary results, though, I've still got some optimization to do. I'm in the process now of adjusting mirror spacing to introduce a small amount of over correction into the system since my Planewave has a small amount of under correction in the optics when spaced according to the Ronchi grating. Also, I haven't done a drift alignment on the mount yet, so even my AO images include the occasional "bump" from the autoguider when the AO gets near the limit of its travel--I suspect this may be "robbing" me of a little bit of resolution that would be there if I had better alignment.

The goal I have set for myself is to consistently produce (on nights of reasonably good seeing) five to ten minute subexposures with less than 2" FWHM across the field of view. I'm pretty sure e equipment is up to the task once I get everything dialed in, but that's getting pretty close to my typical seeing limited conditions (based on short subexposures of a couple or three seconds), so everything has to be working juuusssstt riiiiiggghhtt.






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