wimvb

Much has been written about the sometimes odd behaviour of the sensor inside the ASI294MM, the IMX492. To get the best dynamic range (highest full well depth), I have so far only used it at its lowest gain. On the other hand, I've always wanted to take advantage of the lower read noise at high conversion gain. Before just adopting a new setting, I've done some homework and read up on this as well as doing my own very unscientific testing. Robin Glover (SharpCap) has commented on this sensor on various occasions, for example here: https://forums.sharpcap.co.uk/viewtopic.php?t=5561&sid=0bc6040e8c7a98eb6cba4f0ae1215f51 I decided to test the behaviour of the sensor regarding saturation and found disturbing results. I set the temperature to 2 degrees C, offset to 5, bin 2, and used 5 and 20 seconds exposures with my flat panel at its lowest setting. At both exposure times, the sensor was saturated (20 s made sure of that) First a few images, one with low conversion gain (119) and one with high conversion gain (121) The same stretch was applied to both images The hcg image shows noise and some banding (maybe difficult to see in the jpeg). Next I measured the minimum pixel value of overexposed frames versus gain. Here's what I found The graph shows the lowest pixel value in a frame for 5 and 20 seconds exposures, vs camera gain setting. Gain 120 is where the high conversion gain kicks in. This is a disturbing behaviour because it means that not all pixels are saturated at gain just above the high conversion gain threshold. At gain 139 and above, the sensor behaves as it should, but between the switch to hcg (120) and 138, the sensor is not well behaved. This behaviour is documented in the IMX492 spec sheet. Tonight will be a clear night, although wiindy, and I'll try to do some test exposures at 0 gain and 139 gain, just to compare lcg mode with hgc mode.

Yes, but still very faint. Flat fielding needs to be perfect to show it (which it wasn't).

This is a not so often imaged area of the autumn sky. The constellation Pegasus contains a large amount of small galaxies, which by themselves aren't much to look at. But in a widefield image (if an image at 1,000 mm focal lengthcan be called that) the wide variety in galaxy shapes, sizes and distances becomes quite impressive. Annotated version: Image details: 7.5 hours of RGB data (no luminance), captured with the SkyWatcher MN190 and ASI294MM camera during two nights in early October. Relative humidity during both nights was 93% or higher, and the moon was more than 50%, so not the best of conditions.

That was my main requirement. Thanks. Do you need aps-c? I used the ASI174MM-Cool for a few years. Great little camera for dso, apart from the horrible amp glow. But if zwo ever release a cooled version of the ASI482 with 5.8 um pixels, I will be seriously tempted to get one. I think that asian focusers have improved so much over the last few years that Starlight Instruments and the likes must be hard pressed to keep up. And with so much going on at that company, I wouldn't be surprised if they go out of business.

Thanks, Colm. I originally planned to treat myself to a FeatherTouch focuser, but Astroshop kept pushing the delivery date forward. After one year, several mails, and reading about all the troubles Starlight Instruments was (still is?) going through, I did a bit more homework, and found that the Omegon Steeltrail Crayford focuser should match the MN190 base plate. I ordered that model and had money left to add a Pegasus AstromFocuscube, plus a Pegasus Astro powerbox advance. I'm happy with the replacement. It has much better stability than the original SkyWatcher low profile focuser with its wobbly built in extension tube.

Very nice. I agree with @tooth_dr regarding the green. Try scnr with its default settings. Once you've subdued the green, the other colours will come through much better. In histogram or curves, you can also target just the blue colour. Subtle adjustments can shift the colour balance.

Thanks, Chris. Yes there are quite a few fuzzies in the background. For some reason, no more than a handful are mentioned in Simbad/Vizier. This is uncharted territory in a way. Thanks. Detail on the galaxies could have been better in my opinioin. Warm autumn nights aren't the best for shooting galaxies. I agree with you aobut the ifn; it should be a whisper, not a shout. Thank you, Rodd. After replacing the stock focuser and re-collimation, the scope is ready for another season.

No longer a work in progress. https://stargazerslounge.com/topic/414033-ngc-7640-and-ugc-12588-in-hargb-wip/ It turned out that shooting flats with the camera at -10 degrees and 96 % humidity isn't much of a hit. I had ice forming on the sensor which ruined the calibration. I shot new flats, now at +2 C to avoid freezing, and reprocessed the data from scratch. The light frames weren't affected by the ice, either because I collected the data under better conditions, or simply because of the dithering and registration which reduced the effect. This is what I got from the data. I think reprocessing the original data payed off. Ngc 7640 is a barred spiral galaxy in the constellation of Andromeda. It is at a distance of 25 - 30 Mly and has a size of about 90,000 light years. Ugc 12588 is a spiral galaxy at about the same distance. Its size is only about 18,000 light years Both galaxies show signs of star formation, which is why I collected H-alpha data. 3 x 2 hours RGB 5 hours L 5 hours Ha As always, I used my trusted MN190 and ZWO ASI294MM camera Processed in PixInsight

A manager at a research facility where I worked ages ago had a variation of this message on his door: a clean desk is a sure sign of a sick mind. If I recall correctly, his boss had a much cleaner desk. Probably because that person received more high profile visitors.

Very nice. According to Simbad, the yellowish structure to the right is a "bubble", and the left one is a Hii region, an emission nebula, with several stars and young stellar objects.

Image quality-wise it can compete with telescopes that are in an entirely different price range. But I agree with you on the weight. I wouldn’t want to lift it every imaging night. If you can have it on a permanent site, I would absolutely recommend it. Otoh, the MN190 probably isn’t heavier than a 150mm APO. 😁

The luminance data had several issues in the background, but I figured out a way to apply it to the galaxies alone. I just uploaded the not-so-wip version in my original post LHaRGB, roughly 16 hours integration time

Thanks. It is, although I still have to do a tiny collimation tweak. The secondary wasn't properly centered under the focuser. Last spring I replaced the stock focuser with an Omegon low profile focuser and at the same time adjusted the secondary. On close inspection it looks like I should move the secondary a tiny bit more.

Thanks. The xT suite of course. BxT for deconvolution. In my opinion, it would be possible to get similar results with "conventional" deconvolution, but BxT is just easier and allows sharpening of details that have a lower snr. StarxT is tricky on galaxy images because it tends to remove galaxy details and background galaxies as well. Here I used it with a mask to protect the main galaxies. Together with BxT it does a better job of keeping foreground stars under control than Morphological Transformation.

Edit: scroll down for the LHaRGB version ************************************************************* Astro season started with a cloud cover, but recently we've enjoyed a few gaps. There's still a lot of moisture in the air, but thanks to the Pegasus Power Box Advance and a dew band, I haven't had any condensation on my telescope. Ngc 7640 is a barred spiral in the constellation Andromeda. The galaxy is slightly smaller than the Millky Way and about 24 Mly distant. As many other galaxies, the ones in this image are very seldom imaged with H-alpha filter. In my experience, if a galaxy shows blue "knots", that is an indication of star formation, and those young stars were at one time born from Hydrogen clouds. I decided therefore, to collect H-alpha and not just RGB. This image consists of 78 4 minute exposures (about 5 hours) with a H-alpha filter, and 3 x 24 5 minute exposures with RGB filters, for a total of more than 11 hours of data. As usual, imaged with my SW 190MN and ASI294MM camera. I've also collected luminance data, but I didn't like the quality and haven't used it. Maybe I will collect new L when the weather allows. Both galaxies have small H-alpha inclusions, and to my knowledge, this is the first amateur image to show these. close up ****** New version with L ****** and close up

The Coathanger is always upside down, so the image orientation is as it should, and Nessie won't get a headache. The image solver on Astrobin also shows that the image orientation is as it should. On AB, the dot on the red rectangle in the sky plot indicates the upper left corner of the image https://www.astrobin.com/lak9k2/#sky-plot

Diffraction spikes is one of the reasons I bought the MN190. I'm so relieved to no longer being bothered by them. Instead of flocking, you could try black matte paint.

My guess is that it's the low number of subs that prevented adequate pixel rejection. As the OP wrote, the purpose of the test was to evaluate settings, not to create a final image. The settings look ok to me.

I wonder if I got the same data as anyone else? i find that there are a lot of "hot pixels" in the masters that are difficult to remove with cosmetic correction in PI. This is probably due to there being only 6 or7 subs in each stack, too few for proper pixel rejection. The exposure time seems ok, as no stars are over exposed. Here's a crop of the Sii master, showing the bad pixels

How many subs in the stacks? Not 3, I assume? I may have a go this evening.

I bought it a month or so ago, directly from the publisher. Don't buy from the great river company, they charge 3× the price for some reason.

Either that, or move the observing chair. 😉

Double post

😁 It just happens that a year ago, I decided to upgrade the stock focuser with its wobbly extension tube and ordered a FeatherTouch, with adapter ring. This is supposed to be a drop in replacement. Unfortunately, the FeatherToch turned out to be vapourware. So this summer I've installed an Omegon focuser, which was a drop in replacement (except for a thin shim, because it was slightly too low). But I digress. Back to the original discussion...

Couldn't agree more.