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Equipment Discussions >> Cats & Casses

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KDizzle
scholastic sledgehammer


Reged: 09/12/08

Loc: Woodinville, WA
Re: Planewave CDK 12.5" First Light new [Re: Jared]
      #5424131 - 09/16/12 05:38 PM

Jared,

Your ccdinspector screens inspired me to check my own equipment, especially since we both have similar stuff (great minds think alike, right ? ). I'm not really sure I understand the screens though or what they are telling me that I should be doing something about. Is the idea to get curvature/tilt/collimation as close to 0 as possible? Could you explain what the different values mean to you and what you do about them?


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EricCCD
Carpal Tunnel
*****

Reged: 04/14/04

Re: Planewave CDK 12.5" First Light new [Re: Jared]
      #5424383 - 09/16/12 08:56 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


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Jared
Postmaster
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Reged: 10/11/05

Loc: Piedmont, California, U.S.
Re: Planewave CDK 12.5" First Light new [Re: pop]
      #5424507 - 09/16/12 10:15 PM

Quote:

Very nice picture.

Why you change AT10RC to this CDK 12.5? It is a lot more expensive scope but less spot size and have dedicated flattener?

Thank you very much for your nice and useful post.

POP




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.


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Jared
Postmaster
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Reged: 10/11/05

Loc: Piedmont, California, U.S.
Re: Planewave CDK 12.5" First Light new [Re: KDizzle]
      #5424525 - 09/16/12 10:27 PM

Quote:

Jared,

Your ccdinspector screens inspired me to check my own equipment, especially since we both have similar stuff (great minds think alike, right ? ). I'm not really sure I understand the screens though or what they are telling me that I should be doing something about. Is the idea to get curvature/tilt/collimation as close to 0 as possible? Could you explain what the different values mean to you and what you do about them?




The FWHM values tell you how small your stars are--both the best values and the worst across the frame. Lots of things can affect these values including collimation, seeing, focus, tilt (affects the range of values), and curvature.

The curvature value is usually not something you can adjust except, perhaps, by changing the spacing between your field flattener and your imaging chip. It's basically a measure of how much bigger the stars in the corners are, so the size of the chip affects the value.

The tilt value lets you know whether your camera is square to the optical axis. It measures differences in star sizes in the different corners.

The collimation values measure how far out of round the stars are at the center of the field.

I think I've got that all correct. I'm responding from memory, so anyone feel free to correct me if I've got any of that wrong.


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Jared
Postmaster
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Reged: 10/11/05

Loc: Piedmont, California, U.S.
Re: Planewave CDK 12.5" First Light new [Re: EricCCD]
      #5424533 - 09/16/12 10:30 PM

Quote:

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.


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pop
sage


Reged: 02/11/05

Re: Planewave CDK 12.5" First Light new [Re: Jared]
      #5425084 - 09/17/12 09:43 AM

Quote:



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


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Jared
Postmaster
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Reged: 10/11/05

Loc: Piedmont, California, U.S.
Re: Planewave CDK 12.5" First Light new [Re: Jared]
      #5425577 - 09/17/12 02:35 PM Attachment (68 downloads)

Quote:

Quote:

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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Jared
Postmaster
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Reged: 10/11/05

Loc: Piedmont, California, U.S.
Re: Planewave CDK 12.5" First Light new [Re: Jared]
      #5425579 - 09/17/12 02:36 PM Attachment (53 downloads)

Top right...

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Jared
Postmaster
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Reged: 10/11/05

Loc: Piedmont, California, U.S.
Re: Planewave CDK 12.5" First Light new [Re: Jared]
      #5425581 - 09/17/12 02:36 PM Attachment (36 downloads)

Bottom left...

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Jared
Postmaster
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Reged: 10/11/05

Loc: Piedmont, California, U.S.
Re: Planewave CDK 12.5" First Light new [Re: Jared]
      #5425582 - 09/17/12 02:37 PM Attachment (37 downloads)

Bottom right...

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Jared
Postmaster
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Reged: 10/11/05

Loc: Piedmont, California, U.S.
Re: Planewave CDK 12.5" First Light new [Re: Jared]
      #5425583 - 09/17/12 02:38 PM Attachment (51 downloads)

And the center of the frame...

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jmiele
Patron Saint?
*****

Reged: 12/04/10

Re: Planewave CDK 12.5" First Light new [Re: Jared]
      #5426427 - 09/17/12 10:46 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


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wiruna
member


Reged: 08/11/06

Loc: Sydney, Australia
Re: Planewave CDK 12.5" First Light new [Re: jmiele]
      #5517226 - 11/13/12 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


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Jared
Postmaster
*****

Reged: 10/11/05

Loc: Piedmont, California, U.S.
Re: Planewave CDK 12.5" First Light new [Re: wiruna]
      #5520414 - 11/15/12 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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