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Improvement Advice - M81 M82 with small refractor


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Hi All. Attached is my latest attempt (M81 and M82). I'm just looking for advice on how to improve this image. I'm struggling to get any colour from it at all, it's as though it's a mono image.

Skywatcher 72ED, ASI533MC Pro, No filters, Bortle 5, Star adventurer (Guided with ASIAir Plus) - 300 sec exposures, darks, flats and dark flats - 3 hours 45 mins.

Stacked in DSS, Colour calibrated is Siril and then stretched in Photoshop using levels and Arcsinh curves. Then a couple of adjustments using the astronomy tools actions.

There is a heavy gradient and Gradient Exterminator has been recommended a few times but I haven't purchased this yet. Any more processing just introduces a lot more noise.

Stacked TIFF file also attached for reference.

 

Thanks in advance!

M81 M82.jpg

M81 M82 2 Nights.tif

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There seems to be something wrong with your scope. Either that or there is large difference in the quality of stacked subs.

image.png.b3a67e2470b548aa6aec124d72a9913f.png

look at these stars - they seem to have core to one side and coma like halo on the other.

If all subs are like that - it is a sign that optics of the telescope is misaligned or something. Stars should be point like.

Now it can happen that some of the subs used to stack the image have nice tight stars and others are simply out of focus and then stacking made combination of the two - but I doubt it by the looks of the stars in the image.

If you post single sub - we can see which one is it.

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Thanks for your help.

I imaged this over 2 nights so have included one light frame from each session.

It's been suggested that I invest in an IR/UV cut filter to reduce halos but I haven't as of yet.

Maybe I need to learn more about how to analyse the FITS files before stacking. Now I just open in the ASI FitsView application and delete any that have satellite trails or star trails and then stack the rest. I usually tell DSS to use 100% of the frames too.

Light_M81-M82_300.0s_Bin1_0006.fit Light_M81-M82_300.0s_Bin1_0011.fit

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I put your stacked image through my normal workflow in PixInsight and there is colour in there, but it needed dragging out.

As Vlaiv has already said, there is something not right with the stars. I my processing they have a blue halo on the right of the nucleus and the focus seems to be a bit out.

A UV/IR cut filter will help with the halos and I would advise going for a mid-range one. The cheaper ones don't always do what you expect them too. ;) 

With DSS stacking, you don't need to ditch the subs with satellite trails (star trails yes). In the Settings > Stacking Settings > Lights > Set the Stacking Mode to Kappa-Sigma Clipping and leave the other settings at default. This will remove the satellite trails for you.

If you want to remove the green cast, which is normal on OSC camera because the bayer pattern has 2x green to 1x red & 1x blue, then on the same setting page as above, look towards the bottom of the page and click on "RGB Channels Background Calibration" > make sure "RGB Channels Background Calibration" is ticked > click "Options" > on the new tab "Calibration Method" should be set to "Rational" and set "RGB Background Calibration Method" to Minimum.

Here's what I managed to get using a quick process of your stack:

643303368_M81M822Nights.thumb.png.a9fce6b86f2eb87bae1e5450be9fb170.png

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1 hour ago, CraigD1986 said:

It's been suggested that I invest in an IR/UV cut filter to reduce halos but I haven't as of yet.

That explains it.

IR/UV filter is a must. With fast ED doublet - it is forth looking into Astronomik L3 filter to restrict spectrum even further.

1 hour ago, CraigD1986 said:

Also, when I previewed using autostretch in Siri, the green Chanel has extremely green, which was odd. More so that usual.

That is normal for raw data as sensitivity in the green part of the spectrum is strongest.

You need to do color calibration to get proper colors.

I'll post my attempt of processing a bit later when I get the time to do it.

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Thanks for the advice. I’ll get a UV/IR filter ordered this week. Looking at the Astronomik L3 at the moment. Is there any reason I shouldn’t just get a light pollution filter instead like the Optolong L-pro though? Does this not do the job on an IR/UV Cut as well as remove light pollution?

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13 minutes ago, CraigD1986 said:

Thanks for the advice. I’ll get a UV/IR filter ordered this week. Looking at the Astronomik L3 at the moment. Is there any reason I shouldn’t just get a light pollution filter instead like the Optolong L-pro though? Does this not do the job on an IR/UV Cut as well as remove light pollution?

Whether LP suppression filter is beneficial - depends on how much light pollution have and what type.

It reduces both target signal and LP signal. It helps only if it reduces LP signal more than target signal - and that happens only if LP signal is strong and if it is of a certain type - that is best blocked by LP filter.

Since you are at Bortle 5 - I don't think you really need LP filter unless you are certain that most of your LP is from sodium lamps (high and low pressure sodium - yellow type street lighting).

Astronomik L3 will also be better at reducing star bloat as it cuts off offending far ends of spectrum (as a contrast - L-Pro lets light up to and past 700nm).

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