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New EXOS-2/PMC-8, need advice on tracking [1 Attachment]


David Pickett
 

Robert,

The progress shown by these photos is most encouraging, and I appreciate you keeping us informed.

Jerry is the expert, but FWIW, some comments:

At 06:20 13-12-17, r_hoskin@... [ESPMC-Eight] wrote:

Here's a selection from tonight's images. No seagulls, but still some problems. Thanks for any assistance!

Cold out: 13F/-10.5C
Camera focus not as good as the first time -> fuzzy stars. Live view, scope nearly vertical, cold...
General area is Cassiopeia. D5300/ISO200.
Focuser rotator ring tightened. Camera cables tethered to the scope and not weighing on camera.
Better PA than before, but not good. Tried alignmaster, and it did not go well. Gave up and eyeballed Polaris.
DSC_0193_017.jpg is a 5 minute star trail. The mount's off. Trails are fairly smooth this time, although some trails are individually perturbed briefly. Seeing, perhaps?
Much improved!

DSC_0177_018.jpg is a 10-second tracked shot. Round (fuzzy) stars.
Focus?

DSC_0214_019.jpg, DSC_0215_020, DSC_216_021.jpg are a series of 3 60-second images in a row. Notice that a) the stars change shape, and b) the image shifts slightly from shot to shot.
DSC_0224_022.jpg, DSC_0225_023.jpg, DSC_0226_024.jpg are a series of 120-second images in a row. As before, the stars change shape, and the images shift. Curiously, DSC_0224_022 shows elongated S's (Safeway logos :-) when enlarged, but these fade, with 0225 being a little hooked, and 0226 smoothing out to streaks.

What do you think about the overall image shift, and the trailing in the 120-sec images? Is that all polar alignment, or do I also have a tracking rate problem?
It seems to me that you should eliminate the polar alignment problem first and then see what is left.

The star shape variations from shot to shot are interesting. Opinions?
FWIW, Cleardarksky.com rated seeing 'bad', for a site a few miles away from me. But... if most of the stars are varying at the same time, I guess that means that there's still movement somewhere.
It looks to me that the fainter stars are showing consistent shapes, which is good.

How do you do your polar alignment? With ES only? If so, why not have several runs, using different stars? I have a Polemaster, which makes it easy. I read that Sharpcap http://www.sharpcap.co.uk/sharpcap/polar-alignment is quicker and it seems to be the method of choice at present; but I dont think it would work with your camera. One way or another, mastery of PA is essential for the photos you want ot take.

Keep at it in the bracing weather you have -- it is cold here, but the skies are totally overcast, day and night!

David