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Thank you, both. I’ve tried printing my astro images before, but I was never happy with colour balance and crispnessbof the prints. Mind you, that was on my own printer.

This is a 2 pane mosaic of this popular galaxy pair The lower half (M81) was captured during april, and the upper half (M82) dec 2021 (Ha) and march this year Since I have the habit of aligning the long sensor side with RA, framing this duo was easy, even with the old Ha data. I have published the two panes as individual images previously

This reminds me of a story that is told about a swedish cook who lived a few centuries ago, and is supposed to have started her recipes with "you take whatever you have" (man tager hvad man haver). In the op's case that is probable the Edge 8" and an osc camera based on the Sony 533 sensor. Binning 2x2 is easiest done by deBayering in super pixel mode. Ie, 2×2 RGGB colour pixels are combined into one RGB pixel. The 3.76 um pixels would give a pixel scale equivalent to a 7.5 um pixel sensor.

Keep life simple and don't worry about the moon. As long as it's not near full or doesn't show (as now), it won't have any effect. When the moon is more prominent, it will increase the overall brightness, but not deteriorate much untill it's almost full and near your target. With cmos, you want to keep the exposures as short as possible, in order not to overexpose the stars. Just make sure that you can't see banding in your images, because that means that you are exposing near the read noise floor. The old rule of thumb for DSLRs that you should have the histogram at about 1/4 or 1/3 from the left edge, doesn't apply to cmos. I have my exposure times set such that I only can see the very bright stars in the linear image. The target is never visible (unless it's a star cluster) in the non-stretched sub frames.

if you have the cooled version, you can reuse darks at the temperature which you use for lights. If the temperature is stable between nights, you can also reuse darks. But if you shoot without cooling, and the temperature differs more than a few degrees, darks may not work. Otoh, it never hurts to try. Also if your camera doesn't have amp glow, you may do without darks. Bias frames are never used with cmos. And darks can't be scaled to be used at different exposure times. What stacking software do you use? DSS and PixInsight both have what is called "cosmetic correction", which is a way to get rid of hot pixels, without having to use darks. So if your camera doesn't have amp glow, you can use that in stead of darks.

Very nice. One question: why do you use bias frames for calibration? With cmos cameras, bias frames can differ from the bias signal contained in darks and lights. The general rule is to shoot darks and flats at the same settings as lights (temperature, gain/offset, and for darks: exposure time), in order to get consistent calibration masters.

They also mention that the new ASIAIR has eMMC storage. Does anyone know if the latest ASIAIR is still based on Raspberry Pi? The Pi does not have native eMMC support. Also Pi's have been hard to get, with world wide shortage, which is only now starting to get better. According to the specs, the ASIAIR is based on the same processor as the RPi 4B, but it seems to have a different form factor

Or fast RASA systems, where focus is critical. It may be cheaper to have a focus knob and relaxed production tolerances, than no focus knob but strict tolerances. As the lady sang: "it's all about the money..."

It is probably the built in extension tube that shows play. You can fix this by tightening the thumb screw as much as possible, without resorting to tools. You can replace the stock focuser with either a MoonLite or a FeatherTouch. Both have adapters that fit. If you decide for a FeatherTouch, I hope you have a lot of patience. I ordered one last august, and so far it hasn't materialised.

Probably the last target for this season, M81 in HaRGB Telescope: SkyWatcher 190MN Camera: ZWO ASI294MM-Pro with Optolong RGB filters and Baader 7nm Ha filter Integration: 3 x 2 hrs for RGB and 10 hrs for Ha, captured between april 4 and april 11

I thought that chip manufacturers used a few pixel lines on the main sensor for that.

Any partial or clip in filters have edges that will create havoc in one way or other. In the end, OAG may just be simpler. Btw, from their FaceBook page it looks like ZWO will also release a new line of APO telescopes and a smaller (?) version of their mount

Cone error causes field rotation, noticeable after a flip. Cone error should be corrected by an X/Y-movement after an ideal flip. Instead, you move the mount in RA and DEC to recentre the target. It's a nuisance when imaging near the celestial pole, but the further away from it you get, the smaller the problem is.

There's the catch. You would be guiding through any filter, which limits the number of usable stars, especially when imaging away from our own galaxy. Even with an osc, using lp filters or dual band filters can be a problem.

The data from that image was from the FLO contest. At the time, I thought that the arcs were part of the Ha data.

The data is from february 2020, but the processing is from just now. I used the XT toolset to completely reprocess 15 hours of LRGB data on this pair of galaxies. Gear used: SkyWatcher 190MN with ZWO ASI174MM-Cool camera. The camera was discontinued by ZWO a year or two ago. I still don't understand why, because it is a very nice deep sky camera. The sensor isn't large, but the pixels are, and the sensor had one of the highest Full Well numbers when it was introduced. The read noise is quite high, for today's standards, but if you use the camera in "CCD mode", ie with low gain, it performs very well.

some 500 actually, according to the PI annotation script. 😄 Very nice image, Göran

Wow!. I have never before noticed the blue arcs coming out of M82. Evidence of past mergers?

My thoughts too. Thanks.

Thanks, Adrian. I'm not sure about the exact cause. At first I suspected the focuser extension tube. But since I have more vignetting at the same side, I now suspect that it's caused by the edge of the secondary mirror. Light that hits that edge is diffracted, and that could cause such a flare. Collimation is otherwise very good, as slightly defocused stars show round, symmetrical doughnuts across most of the field. When astro season ends by the end of the month, I will try to get to the bottom of this, but for now, I live with it.

Thank you, Rodd. I don't know if it's devine, but I have a computer screen that is absolutely unforgiving; it shows every small blemish. Even images by a well known astrophotographer and YouTuber can show an unflattering background sometimes.

Thanks, Bryan. Star control in galaxy images is always a bit tricky. Star removal and then reinsertion destroys the very small, redshifted background galaxies, and usually isn't an option. Most of the time I just reduce only the largest stars with a star mask and careful erosion.

A lenticular galaxy (ngc 2768) and a spiral galaxy (ngc 2742, or ngc 2816). One which is all but dead (as far as star creation goes), and one which is very active. Both these galaxies are located in Ursa Major, at a distance of 65 - 70 million light years. Towards the left there are two colliding galaxies, pgc 25980 and pgc 25982. These are only small galaxies, they are closer to us than ngc 2768 / ngc 2742. Also in the field are numerous background galaxies. In fact, most of the reddish "gnats" are galaxies and not stars. There are so many, that I have only indicated the galaxy clusters to which they belong. These galaxies are between 2.5 and 5.5 billion light years away. What peaked my interest was a small blue dot at the top of the image. According to Simbad, this is a Seyfert 1 galaxy. It has a red shift of 0.763, which puts it at a (Hubble-) distance of 10 billion light years. Despite this large red shift, the light that we receive is still in the blue part of the optical spectrum. This means that the light that is transmitted lies well within the UV part of the spectrum. Technical details: 16 hours and 48 minutes exposures with Ha and RGB filters under a 67% moon (on average), using the SkyWatcher 190MN and ZWO ASI294MM

Nights are getting shorter and shorter up here. So while I was waiting for ngc 2768 to pass the meridian, I pointed my scope towards the whale and hockey stick galaxies in Canes Venatici This is only 1.5 hrs of RGB data (6 x 5 minutes exposures per filter). Not all satellite trails were caught by the rejection algorithm. I will revisit this pair once I'm finished with ngc 2768, and get more colour data as well as H-alpha. It would be nice to also catch the tidal streams coming from the whale galaxy. That is also the reason for the odd framing, one of the streams extends towards the lower left corner.

Thanks! M81 is just below the image edge. I would either have to rotate the camera or create a mosaic to get it in. Having a fixed camera orientation has certain disadvantages, but the benefits outweigh them, imo. It allowed me to use last year’s H-alpha subs with minimal loss near the edges.