Imaging on the shortest night

Blog the previous nights viewing. Link to images on the gallery or simply describe what you observed the night before. Leave the technical and howto in another forum.
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rwilkinson
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Imaging on the shortest night

Post by rwilkinson » Sun Jun 22, 2014 9:40 am

Last night it was clear, and pleasantly cool outside compared with the sultry heat indoors, so I set up to try to catch a last glimpse of Comet PanSTARRS (now it's getting low in the sky).
I'd tried to find a good vantage-point to set up my tripod, but by the time I got the comet into my CCD's field of view there was a dark shadow moving across the image - and when I sighted down the 'scope tube it was the roof of next door's shed which was responsible for the "eclipse"!
The comet had disappeared from view a couple of minutes later, so I did an imaging run on M81 instead:
m81_mx516.jpg
M81 on 21-Jun (in twilight). 30x 1-min (unguided) with MX516 on StarWave 80ED at f/4.6.
m81_mx516.jpg (117.66 KiB) Viewed 6751 times
If M. Messier had seen it like this, he'd never have worried about mistaking it for a comet!

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Re: Imaging on the shortest night

Post by rwilkinson » Mon Jun 23, 2014 7:38 am

I had another go at catching the comet above the roof-line last night, setting up my tripod on a different part of the lawn - a position I'd never used before, as it's flood-lit by a street-light across the road!. But I did manage to catch the object for about 20 mins just before midnight:
2012k1_22jun.jpg
Comet PanSTARRS on 22-Jun-2014 (in twilight). 11x 1-min using MX516 on StarWave 80ED at f/4.6,
The gap in the star-trails is due to an "occultation" by a neighbour's TV aerial!
2012k1_22jun.jpg (121.76 KiB) Viewed 6731 times
And this is my set-up - see that like Keith, I use an old card-table and garden-stool!:
gardenimaging2014.jpg
Imaging set-up on the lawn in June 2014.
The old laptop controls my CG5-AGT mount via COM1 and the MX516 CCD via LPT1.
gardenimaging2014.jpg (334.04 KiB) Viewed 6731 times
I started setting-up just after 11pm (once I could see Polaris to do my polar-alignment), was imaging from 11:25 until 11:50 (when my target slipped below the roof-line), and then was all packed away by midnight.

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Re: Imaging on the shortest night

Post by bchamberlain » Wed Jun 25, 2014 11:34 am

M57-6min_800iso_+21c_00544stdev_20140624-00h56m37s543ms.jpg
M57-6min_800iso_+21c_00544stdev_20140624-00h56m37s543ms.jpg (28.92 KiB) Viewed 6712 times
This is one of 16 of M57 unprocessed. One unsuccessful attempt at processing with Iris up to now. I'm not getting your crisp round stars Ross. Probably it's the attachment of the guide scope to the rear of the 8" reflector. Not a good combination I'm told.

On another point. Can the red dot in my finder be focussed? It's taken on the shape of a cumberland sausage. Bill

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Re: Imaging on the shortest night

Post by rwilkinson » Wed Jun 25, 2014 2:52 pm

I don't think that you got the focus quite right Bill - do you use a Bahtinov mask?
And the aberrations seem to be more marked further from the centre of the image - maybe a field-flattener or coma-corrector would help (I don't need one for the tiny sensors in my cameras)?

But if you do get those 16 images stacked, then try some deconvolution in IRIS (using the RL2 command) - this is what it managed with just your single JPEG image:
m57_billc.jpg
I took the central portion of Bill's image and ran it through RL2 deconvolution in IRIS.
m57_billc.jpg (102.43 KiB) Viewed 6709 times

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Re: Imaging on the shortest night

Post by bchamberlain » Wed Jun 25, 2014 6:59 pm

Much improved with the deconvolution Ross. I'll try that though I'm not yet successful going through the whole Iris program.
I was puzzled myself with the stars near the edge of the field as I'm using a coma corrector and don't notice any distortion through an eyepiece. I used a bahtinov mask viewed on the laptop with BackyardEOS but can't guarantee being spot on as the UHC filter breaks the image up a bit and remote focusing would help.
I've enjoyed the few clear nights we've had though it clouded up around 1 a.m. Tuesday morning. Otherwise I was out till the sky started to lighten around 2 a.m. I'm looking forward to seeing the results from a new modded EOS 1100D. Thanks again for the advice. Bill

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Re: Imaging on the shortest night

Post by DRatledge » Wed Jun 25, 2014 8:00 pm

Bill,
Deconvolution is for making sharp images better. It shouldn't be regarded as a solution.
As Ross says you were possibly not at perfect focus (keep the bhatinov mask image for reference) but it looks more likely to be collimation or tilt of the coma corrector. All the stars are brighter on the left side. That points to mis-alignment somewhere. If it was just focus they would be symmetrical blobs - well symmetrical around dead centre. If you are sure collimation was spot on then try with and without the coma corrector. It's a question of gathering enough clues so as to work out where the problem lies. There isn't a lot to go wrong with a Newtonian so it should be simple to solve.

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Re: Imaging on the shortest night

Post by DRatledge » Thu Jun 26, 2014 11:02 am

Bill,
Looking at your image again after a night's sleep - is this just the right hand half of the full frame? Have you cropped it? That would make more sense for the left edge of each star being brightest.

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Re: Imaging on the shortest night

Post by bchamberlain » Thu Jun 26, 2014 2:42 pm

It's full frame David and by the way, it's a 1100D modded as you advised. I think collimation is the first thing I need to kook at. The focuser angle is adjustable the way it's mounted on the tube so if that's not correctly set, the coma corrector would also be out of alignment. Bill

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Re: Imaging on the shortest night

Post by DRatledge » Thu Jun 26, 2014 6:33 pm

Bill,
Start with collimation. You can tell if the focuser is not square if collimation changes from racked it to racked out. If your collimation is way off that solves everything.

You seemed to imply the UHC filter made focusing difficult. That points to something glass out of alignment. It could be from either the coma corrector or it could be the clip filter if you have not seated it properly. They have to be sat down flat. Next time save your bahtinov mask focus image. With a UHC filter they tell you a lot.

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Re: Imaging on the shortest night

Post by bchamberlain » Thu Jun 26, 2014 10:18 pm

Ross's visit this evening highlighted a string of errors on my part. More on that tomorrow.
Yes, collimation is out and the focuser alignment is the first thing to sort out. I didn't think to take exposures of the focus with the bahtinov mask on so no proof. Error no. umpteen. A lot learned tonight thanks to Ross.

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