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Bad Guiding or something else?

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9 replies to this topic

#1
E_ri_k

E_ri_k

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Hey guys, I have been having problems with my final images for a while now, with the stars not being round. A few people have commented on them saying that it might be a guiding problem. I have run a few tests over the past few nights, but with no real consistent results. Last night I took some images with various settings, PEC on/off and Guiding on/off to see what was going on. If someone could help me out it would be great, because I am at a loss as to what I might be doing wrong????;)

I am using a G-11 and gemini 2 and a 10" reflector.

I know I have PE. I used pempro, and I had consistent error over 8 worm cycles. I uploaded a new curve to the mount, and there was an improvment.

I took a few images of M41 las night, with Guiding on/off, PEC, and no guiding at all. To me it looks like the guider is over-corecting, however the drift direction does not correspond to the N-S E-W direction of my test image? This makes me think there may be some Coma involved also. I have a MPCC, which is spaced out roughly the correct 55mm from the sensor. The large stars appear round though?

The unguided image is the bet I think.

Should I maybe set the RA Agresivness down really low, or check the spacing of the coma corector?

Erik

Attached Thumbnails

  • 5min G RAG70 HY50 PEC.jpg
  • 5min G RAG70 HY50.jpg
  • 5min G RAG90 HY50.jpg
  • EW.jpg
  • m41 60.jpg
  • 2808.jpg

Edited by E_ri_k, 07 May 2012 - 01:00 AM.

GSO RC 10 CF, G11 Gemini 2, Lodestar Guider, ONAG, HEQ5 Pro, Vixen ED80, QHY 10

#2
Mr Q

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Erik, have you done a star test to see how good the colimation is? The link below will show you how to do a star test and what to look for. The test only takes a few seconds but perhaps if the colimation is off a little, this could be your problem?http://www.andysshot...ollimating.html
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#3
E_ri_k

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I always collimate with my laser, but I must admit I rarely do a star test. Can a very small error in collimation create trails lake that?
GSO RC 10 CF, G11 Gemini 2, Lodestar Guider, ONAG, HEQ5 Pro, Vixen ED80, QHY 10

#4
E_ri_k

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Been thinking it may be tube flexture as well? Going to investigate that first.
GSO RC 10 CF, G11 Gemini 2, Lodestar Guider, ONAG, HEQ5 Pro, Vixen ED80, QHY 10

#5
Starlight 1

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I do not do imaging ,but from post on here (RA Agresivness down really low around 20) But I am going with camera sensor is out of line.

#6
steppenwolf

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The coma corrector doesn't seem to be doing its job properly at the moment so I would certainly tackle that - I have found the MPCC excellent on a range of different instruments including two very different 10" reflectors.

It would be very useful to see a full frame image (doesn't have to be full size) so that we can see the stars in other areas of the frame.

Regards,

Steve
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#7
E_ri_k

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Maybe I'll drop the agresivness down quite a bit then. I never thought of going that low.

Here is a complete image. I think the stars on the edge are elongated, suggesting a bit of Coma, but the stars are not completely round in the centre of the frame either.

Thanks
Erik.

Attached Thumbnails

  • 5min G RAG70 HY50.jpg

GSO RC 10 CF, G11 Gemini 2, Lodestar Guider, ONAG, HEQ5 Pro, Vixen ED80, QHY 10

#8
swag72

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I use a totally different setup to you, so really can't comment on the coma side of things, but I have just sorted out my guiding issues that were giving me some nice elongated stars!!

I can't pinpoint exactly what the issue was, but it seemed to boil down to 2 things.
1) The guide star was miles out from the target, so I wedged and packed the guide scope bracket so that it was running more in line with the imaging scope.
2) There may have been a little movement in the guidescope within the bracket - Solved by the above packing.

Not sure which one of these was the culprit - But may just give you something to think about to look for with guiding issues.

Hope that helps.

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#9
ollypenrice

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To disentangle guiding from coma/spacing/anything optical is easy. Just take some very short subs, 2 seconds, on stars bright enough to be small but clear. Errors always show up most clearly on small stars. Big ones often look round even under poor guiding.

Are you guiding while running PEC? I never do that.

I know PHD works and I use it on one mount, the Mesu roller drive, but on my own mounts I use AstroArt 5. I find it has by far the best graphics for seeing what is going on. Maybe I say this simply because I'm familiar with it but offers you a bullseye target with every single guide hit's location recorded. Graphs eventually go off the page but this doesn't so if you have had a bad hit at any point in the run it is instantly visible. Other error patterns become visble as well. Backlash shows as two 'clumps' of guide hits either side of mesh, for example.

Olly

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#10
E_ri_k

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Thanks guys. I was going to put up a couple of photos from last night bit my computer crashed and my hard drive is stuffed....basically I can see a lot of coma im the image but it is not all pointing to the centre of the image. the top right points to the centre but the bottom left points across the image. when can i will put up a image. I have a baader mpcc spaced out 56mm from the mounting surface to the ccd surface.
GSO RC 10 CF, G11 Gemini 2, Lodestar Guider, ONAG, HEQ5 Pro, Vixen ED80, QHY 10




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