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Equipment Discussions >> Mounts

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Starhawk
Space Ranger
*****

Reged: 09/16/08

Loc: Tucson, Arizona
Re: ASA DDM60 Pro vs. GM1000HPS new [Re: EFT]
      #6146609 - 10/19/13 12:25 PM

Ed,

I was doing several experiments during that hour of tracking with the GM 1000HPS. Besides taking photos to get some idea of the mount's movement, I wanted to experiment with the effects from an aperture mask on a C11 (like what happens to coma?) In the one scene, I took images in these configurations:

(1) f/10 at prime focus.

(2) Unobstructed aperture mask series- it covered the entire front of the telescope with a single offset aperture:

(A) 76.2 mm aperture
(B) 50.8 mm aperture
(C) 31.75mm aperture

(3) return to unmasked f/10 prime focus.

So, there was a large increase in airy disk size inversely proportional to the reduction in the aperture, and so I wound up with coverage for the whole time, but with bigger stars in the middle and smaller stars at the beginning and end.

I also to a series afterwards on the Orion Nebula using the Starizona f/7.5 reducer/ flattener which is about ready to post. The amazing thing on that one is how out of 56 frames I took for it, I lost only one to mount movement, where I was touching the camera to start the interval series. I did that two more times and had usable frames. I lost three frames to neighbors' lights coming on.

-Rich

Edited by Starhawk (10/19/13 12:27 PM)


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Starhawk
Space Ranger
*****

Reged: 09/16/08

Loc: Tucson, Arizona
Re: ASA DDM60 Pro vs. GM1000HPS new [Re: EFT]
      #6146839 - 10/19/13 02:53 PM Attachment (20 downloads)

OK, So here we go- this is the set I did on Orion just as it cleared the local electrical lines. These were made using a stock C11 NexStar 11 GPS XLT OTA with the Starizona f/7.5 reducer/flattener at 2100mm focal length. The series is shot through the 2" Celestron UHC LPR filter. My Baader UHC filter is currently mounted in a Pentax K adapter for Hyperstar. The image is a set of 14X1 second frames, 11X10 second frames (three lost to neighbors' lights), and 27 x 30 second frames (1 lost to me touching the camera). First I have the whole frame reduced for CN (Parent is 4900 pixels wide, so that wasn't happening). The second is the upper left at native resolution, so you can see the stars are round, and satisfyingly coma-free.

The GM1000 HPS was very happily steady for this series- for each interval set, the first frame was made with my hand on the camera, and the mount was stable in 2/3 cases where this was done.

Now, the camera was set to high sensitivity (ISO 25100) for the brightest shot, which does result in background noise. Breaking out the interval timer remote would result in longer exposures. And since longer exposure is more effective than deeper stacking, that's a better answer.

-Rich


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Starhawk
Space Ranger
*****

Reged: 09/16/08

Loc: Tucson, Arizona
Re: ASA DDM60 Pro vs. GM1000HPS new [Re: Starhawk]
      #6146848 - 10/19/13 02:56 PM Attachment (12 downloads)

This is the upper left corner at native resolution. Note the atmospheric chromatic aberration thanks to shooting low to the horizon. I haven't corrected for it to allow an as-shot image to be available.

Also notice how the local sky glow still comes in on the blue channel- that I have reduced, but did so by scaling rather than clipping so the performance of the UHC filter in a broadband light pollution environment is visible.

-Rich

Edited by Starhawk (10/19/13 02:58 PM)


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Starhawk
Space Ranger
*****

Reged: 09/16/08

Loc: Tucson, Arizona
Re: ASA DDM60 Pro vs. GM1000HPS new [Re: Starhawk]
      #6146880 - 10/19/13 03:11 PM Attachment (11 downloads)

This is the center of the field taken just as it was produced by my HDR stacking- I used a Mac program called HDrtist for that step. I am pleased to have 5 trapezium stars come through this way. Kind of an odd thing about the C11 is how no matter what you do the stars are a little blobby with the central obstruction. Overall I would have to say I wholeheartedly recommend the Starizona f/7.5 reducer flattener if you have a plain SCT. What isn't so obvious to me is if the money is better spent on a standard SCT and planning on hyperstar and the reducer/flattener, or if the Edge HD with reducer is a better plan with hyperstar for the same role.

The reason I am putting such a high value on Hyperstar is it is the one configuration of a SCT which really gets to deep magnitudes without relying so much on the mount, and is also the only one which can produce really tight stars thanks to the reduction in focal length.

In any of these cases, the GM1000HPS is certainly proved to be capable to carry a long focal length and I'm not even sure how much weight it will really take since it wasn't vibrating while touching the focus knob of a C11. The obvious answer is more weight than that.

I'd like to hear back on where you all are after looking at my results, which were largely generated because of this thread. I have probably one new-moon night coming up where I can really use this, and for personal reasons, I'd really like to have some pretty pictures to show for it. So, on my own, I'd probably either use it for hyperstar, and go to somewhat longer exposures just to see how deep an image I could get, but that is probably going to be under 5 minutes in any case. Or I could try doing some DSOs with the AP 130 EDFGT, which produces really nice sharp images. I will likely do those with the Astro Tech flattener, which seemed to be effective in my short test earlier. Or, I may put in the AP reducer and see if I have image collapse in the corners or not. In any case, if left to my own devices, I'm probably not going to long focal lengths unless I do another engineering setup (maybe next weekend) and try out chasing satellites.

-Rich


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Hilmi
Post Laureate
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Reged: 03/07/10

Loc: Muscat, Sultanate of Oman
Re: ASA DDM60 Pro vs. GM1000HPS new [Re: Starhawk]
      #6146959 - 10/19/13 04:04 PM

Could you please try a single 5 minute or more exposure at long focal length at any random target? This will give an indication of tracking performance of the mount.

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Starhawk
Space Ranger
*****

Reged: 09/16/08

Loc: Tucson, Arizona
Re: ASA DDM60 Pro vs. GM1000HPS new [Re: Hilmi]
      #6147069 - 10/19/13 05:11 PM

Hilmi,

That shouldn't be a problem. I'll see about doing it on something straight overhead to get atmospherics out of the result. I'll do the full pointing model, so it should be as good as it gets.

What focal length would you like?

-Rich


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Hilmi
Post Laureate
*****

Reged: 03/07/10

Loc: Muscat, Sultanate of Oman
Re: ASA DDM60 Pro vs. GM1000HPS new [Re: Starhawk]
      #6147680 - 10/20/13 12:07 AM

I work at 1600mm so as close as you can get to thag.

Thanks


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