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NGC7000 , my first DSO attempt


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2 hours ago, Lee_P said:

My telescope is a "closed system" so to speak

Thanks again @Lee_P ! I suspect that my filterwheel might do some dust trick to my sensor when I turn it from 1 to 2 and 3.. I will try an over three days shot (after the rainy weeks) with none filters attached to see. 
 

37 minutes ago, bobro said:

To keep things simple I've settled on 2-3 min subs as appropriate for my setup

Do you differ alot of sub-exposure time when it comes to. Hanging filters, or do you try to keep it the same? 
 

@bobro and, thaks for the image adjustments.. You really nailed it! I understand now that image adjustment is another expertise that will take me years to learn… And, thanks for that, so I can improve over the next decade 😃

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1 hour ago, bobro said:

> Plane or satellite trails are readily eliminated with kappa-sigma stacking, allowing these subs to contribute to the image.

+1 for this. Was about to post when I saw bobro had beaten me to it. You don't need to discard your satellite subs unless they're really interfering with the final image. You MAY decide to discard cloudy subs as they are probably not contributing anything to the end image. But depending on your stacking settings, they may be automatically discarded anyway. I will generally use all or at least 95% of my subs unless something disastrous happened during the night like a cable snag or full cloud.

Re flats; if I'm imaging on multiple nights with the same rig, one set of flats will do. Dust generally won't redistribute to any great extent. Just make sure that you don't make any non-trivial changes to the imaging train; leave the camera, focuser, filter wheel etc. attached and in the same position. Don't rotate the camera wrt to any of the components. Don't make big changes to the focuser (e.g. racking completely inwards for storage). Refocusing for a different filter or a temperature change is fine as it's likely to be a tiny movement.

ideally you shouldn't move the scope before taking flats, but I regularly do that and it usually works fine (e.g. weather doesn't look good and I need to bring the scope inside in a hurry; or I have to go away and don't have time to do flats first; or I take the rig inside then realise the old flats aren't working.

I use Nina for capture control, so first thing in the morning after a night of imaging I use the Nina Flats Wizard and a cheap flat panel (an artist's LED tracing panel €10 from ebay wrapped in a t-shirt) to take flats for each filter. Usually done in 5-10 minutes. 30 flats and 30 dark flats for each filter. After the first stacking, you will have created a Masterflat and Masterdarkflat so you can delete or archive the source flats/darkflats.

You will be able to tell when you need new flats as you'll see the circles and vignettes appearing. I take it you didn't use flats for your M31 above? When you see those circles it tells you that either you need new flats, or if you have new flats, that your process for capturing flats isn't working. 

 

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On 26/09/2021 at 19:31, Lee_P said:

You can always add "just one more night" of data into the stack.

On this point:

I haven't used ASIStudio for stacking so can't say anything about its capabilities. I've used DSS a lot in the past, and currently use Astro Pixel Processor. You can stack multiple sessions with either of these packages, using different sets of calibration frames for each session. With APP, you can even stack different sessions taken with different scopes and cameras! 

A standard technique that imagers on this forum use, is to revisit a target, possibly even years later, and capture more data. If using the same camera, you can probably reuse your dark (or bias) frames, but you will almost certainly need new flats and dark flats. Each stacking session consists of a set of light frames with matching darks/bias and flats/darkflats. The stacking software will apply the correct calibration frames to the correct lights while stacking. If you are using the same calibration frames for everything, you can just add all of the lights to the same session.

As a crude example, take a look at this experiment below. I had a wide-field capture of the Bubble nebula region, taken with a 400mm refractor from last year.  This is a mono Hydrogen-alpha 1.5-hour integration. I then set up a Celestron C8 SCT at 2032mm with the same camera, and centred the Bubble nebula and captured an additional 5.5 hours.

APP registered and stacked the widefield lights and the long FL lights with no issue. You can see that I didn't apply flats as there is vignetting (and some light pollution) but what you can also see is a huge reduction in noise in the central area because of the extra total integration time.

image.thumb.png.fb2f35b6491d8b2e10567aae6ff6cfd2.png

Now with a little crop, rotation and simple curves adjustment in Gimp, I can get a passable Bubble close-up!

image.png.07188195e2db73d25a7cf3e96f2e8c3e.png

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17 hours ago, Padraic M said:

On this point:

I haven't used ASIStudio for stacking so can't say anything about its capabilities. I've used DSS a lot in the past, and currently use Astro Pixel Processor. You can stack multiple sessions with either of these packages, using different sets of calibration frames for each session. With APP, you can even stack different sessions taken with different scopes and cameras! 

A standard technique that imagers on this forum use, is to revisit a target, possibly even years later, and capture more data. If using the same camera, you can probably reuse your dark (or bias) frames, but you will almost certainly need new flats and dark flats. Each stacking session consists of a set of light frames with matching darks/bias and flats/darkflats. The stacking software will apply the correct calibration frames to the correct lights while stacking. If you are using the same calibration frames for everything, you can just add all of the lights to the same session.

As a crude example, take a look at this experiment below. I had a wide-field capture of the Bubble nebula region, taken with a 400mm refractor from last year.  This is a mono Hydrogen-alpha 1.5-hour integration. I then set up a Celestron C8 SCT at 2032mm with the same camera, and centred the Bubble nebula and captured an additional 5.5 hours.

APP registered and stacked the widefield lights and the long FL lights with no issue. You can see that I didn't apply flats as there is vignetting (and some light pollution) but what you can also see is a huge reduction in noise in the central area because of the extra total integration time.

image.thumb.png.fb2f35b6491d8b2e10567aae6ff6cfd2.png

Now with a little crop, rotation and simple curves adjustment in Gimp, I can get a passable Bubble close-up!

image.png.07188195e2db73d25a7cf3e96f2e8c3e.png

That's a great visualisation of the concept, makes it really clear :)

 

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