wimvb

Normally, I would agree. But in this case the OP needs to diagnose possible problems with dithering. Following hot pixels across the image is a way to do that. For that, he needs to stack without rejection.

When you open the image integration process, under "Pixel Rejection 1", "no pixel rejection" should be the default setting. If not, just select it

I did a test exposure yesterday. unfortunately it's too late in the season to start a project on this target, as it needs a fair amount of data and dark nights. Next year ...

Watch it, Olly. The camera may be in a concrete slab rather than the original packaging: I agree that this is about amp glow. The newer ZWO cameras (including the ASI2600?) are supposed to be "amp-glow free".

Very nice. I imaged this cluster yesterday, but lack of proper darkness and poor guiding made me abort my attempt.

That's what I meant. I guess I was just not clear about it.

That depends. If you have dec backlash, then there may not be enough random movement to eliminate the drift pattern. If you stack the subs without pixel rejection, you will see hot pixels following the dither pattern. In pixinsight you can blink the unaligned images to see the amount of dithering and drift.

They are aware of this. There is an image processing competition with data from FLO’s/IKI’s own rig. https://stargazerslounge.com/forum/294-iki-observatory/

What software do you use? In pixinsight you can simply apply a star mask and desaturate the stars. Also, have a look at how large the rgb stars are compared to the L stars.

I downloaded the original TIFF (in your first post) and had a go at it in PI I used Photometric Colour Calibration with an Sb galaxy as white reference. Then Arcsinh stretch to get some colour. MMT noise reduction on chrominance to reduce the colour noise. Cleaned up the atmospheric/abberation effects in the stars with MMT (removed layers 1 - 4 in chrominance). Extracted luminance from the linear image, and sharpened detail with Deconvolution. I found that the stars PSF was a bit "fat", either poor seeing or oversampling. Repeated histogram stretch followed by HDR Multiscale Transformation to restore detail in the cores of M81 and M82. I used different settings for M81 and M82 with HDRMT (creative masking). LRGB combination Replaced LRGB stars with RGB stars. 90 degrees rotation.

Have either of you posted this problem on the indilib forum? One of the developers might be able to help.

Version 1 for me. The outer ring is very weak, and 9 hours isn't that much. I spent 15 hours on this target under Bortle 5 skies, and barely managed to isolate the ring from the background https://www.astrobin.com/hqagp6/E/

In essence you create two new images, Ha-R which is the original Ha image with all the background red subtracted, and a new combined red image, where the true Ha signal is added to red. Ha-R = Ha - x*(R - median(R)) where x<1 HaR = R + y*(Ha-R - median(Ha-R)) where y>1 https://pixinsight.com/examples/M31-Ha/index.html

That should help, but not for galaxies of course. When choosing nb filters it’s important to consider quality. Especially Oiii filters can show reflection halos.

Very nice. Bortle 7/8 is a bit brighter than what I have (Boryle 5).

Thanks, Olly. I agree. It's a great scope, especially when kept on a pier

Thank you, Gordon

The opacity functions as a weight which is applied. Stack1 × Opacity + Stack2 × (1 - Opacity) In case of a mostly uniform level of light pollution across the sky, the opacity should end up about midway. With the moon about or high clouds in one part of the sky, I imagine it could deviate. But if the opacity always ends up close to 0 or 1, the question arises if it wouldn't be better to avoid imaging in that part of the sky with lowest opacity entirely.

If you use shorter subs on one side of the pier because of light pollution, you should ask yourself if these subs really add to the image. Light pollution itself just raises the background level. But if you use a shorter exposure because of it, you record fewer photons from the main target. And because of the light pollution, those subs will also have more noise. The increased background is removed in processing, but the noise level is not, and neither are photons added to increase the main target. What I would do is to stack the short subs and long subs seperately, as Olly suggested. Then I would compare the long subs master image to the combined image. If there is no real improvement, I would probably not bother imaging on one side of the pier. To get the most out of a night, you can always have two targets on the same side of the meridian. Start with the target which passes the meridian first. Collect data on that target untill target nr 2 comes into view. Do this multiple nights until you have enough data per target.

Why would she need to? Clearly, it is the oarsmen who are topless. Or should that be "bare chested"? I have working knowledge of a few languages, and find the english language most suited for word play. (According to a former colleague, French is better for swearing.) A bit of plural trivia: as was already noted in this thread, the plural of 'datum' is 'data'. This is also so in Swedish. But, in Swedish, the plural of a noun ending in -a, is formed by replacing the '-a' with '-or'. So the plural of 'data' would be 'dator'. Which is the singular form of the Swedish word for 'computer'. The plural of which is 'datorer'. "Savvy?"

Thank you, Jeremy.

An updated version with more Ha: a total of 117 4 minutes subs of Ha Total integrationtime is now 14 hours and 52 minutes, most of this shot after astro darkness ended up here. (also posted in the competition section)

The dust and Hydrogen clouds of M51

My guess is that your subs are underexposed. What you see here is mainly the read pattern of the camera. Your scope is probably f/6 - f/7.5, depending on using a reducer or not. The filter reduces the light that enters the camer even more and the result is underexposure. You need an exposure time of a few minutes at ISO 800. Try to collect more data (2 hrs isn't much on this galaxy). The more light pollution you have, the more data you need to reduce the LP noise.

The Elephant trunk; Hydrogen-alpha and dust. SkyWatcher 190MN, ZWO ASI294MM with Baader H-a filter