wimvb

Excellent image. The "pincers" I have seen and imaged before, but that weak red glow to the right of M45 is new to me. Although, reexamining an image of M45 that I took 5 years ago, I can see a very faint hint of it. And I agree with @gorann, there are definitely repeating structures between M45 and the California nebula.

Be careful with this, it rarely is this simple. First you need to make sure that the Ha and Red background are similar. Next you need to have approximately the same noise level, or the max function will make the image noisier. If the Ha is noisier and generally weaker/darker than the red, the max function will only return the red plus the noise from Ha in the dark areas.

I used a variation of the following worflow with good results some time ago.

Before the days of Starlink, ccd imagers could get away with just capturing a handful of 30 minutes exposures, if the mount allowed it. But I think that is not practical anymore. Just make sure your exposures clear the read noise floor, and collect more and shorter ones. That way you can remove any that have too many satellite trails.

SNR in astro images is very tricky to define. As Vlaiv noted, using the highest pixel value for signal is meaningless, because this is probably from hot pixels. But metrics such as average or median pixel value for signal calculation are also just best guesses. The median value of a starfield with small galaxies should be a reasonable estimation for the background signal, and its variation a measure for noise. But in case of an extended nebula, the median value may represent the nebula rather than the background, and features in the nebula will affect the variation, ie "noise". Comparing SNR or using it for decision making during processing is not straightforward. For example, the old batch preprocessing script in PI would by default apply a weight based on the SNR (defined, I believe, as median (over image) / variation (MAD or AvgDev) ). But the result was that if you had high clouds during part of a session, those subs would get a higher median, a higher SNR, and therefore a higher weight in stacking. That goes against any common sense. In this respect, the weighting schemes of WBPP is much better, where more advanced metrics are used. The effect of increasing median value due to high clouds is easy to see in the PI Blink process. If you set a single STF for a blink sequence, you can see the subs getting brighter and the target getting "thinner" until it all but disappears in the background. If you apply individual STFs to the subs in the blink sequence, you see the images actually getting noisier and the main target starting to disappear. When using BPP (as opposed to WBPP) one should always use Blink first, to remove subs that would deteriorate the stack. So, as I wrote before, don't sweat the numbers, just enjoy the hobby.

I wouldn't trust the output of the SNR script on face value, as per this discussion on the PI forum. https://pixinsight.com/forum/index.php?threads/snr-estimation-stddev-vs-avgdev-in-statistics-process.18897/ In anyway, don't worry about the numbers, just enjoy the hobby.

That's a very nice set of images. Regarding LRGB imaging with a classic ccd camera, the general idea is to shoot RGB binned x2 to help get the noise and total integration time down. L at bin 1 with something like double the integration time of RGB to get the detail. This is different from LRGB CMOS imaging, where there isn't as much benefit from binning the RGB, and everything is captured at the same bin level. In your case, you captured 1 hour R, 1 hour G, 30 mins B, and 1 hour L. If you captured everythung at the same bin level, you could try combining the 4 masters into a composite synthetic L in order to get the noise down. Just use image integration with weight 1 and no pixel rejection. Then process the RGB master for maximized colour, and the L for maximized detail before LRGB combination.

Thank you, Lee. You're welcome re the directions. And IV is difficult to find. It is also not part of the Andromeda system, as it's about 10 times further away. So, although it occupies a place in the list of dwarf satellites of M31, it is in fact completely unrelated to it.

In M31. Super large Pleiades.

Where's the fun in that? Ok, spoiler alert

An unexpected clear(-ish) night gave me enough data to image M31 (the giant), M32 (a dwarf galaxy to M31), And IV (another dwarf galaxy) and star cluster ngc 206, all in one view. This is very little data and only very simple processing, just to check off two more dwarf galaxies in the Andromeda system. RGB: 12 + 6 +6 * 5 minutes (2 hours) L: 21 x 3 minutes (1 hour) Gear: 190MN with ASI294MM and Optolong LRGB filters. To find And IV: go down from M32 to just over 1/2 to the bottom edge. There are two brighter stars. The lower, blue one has And IV right next to it as a small fuzzy patch which is barely visible.

I use my AZ-EQ6 at -20 C with no problems to speak of. A friend has his EQ6-R 2 meters from mine, also running smooth.

If the temperature drops suddenly, there may very well be some moisture in the air that is condensating, ie clouds, dew or frost, which can affect guiding. Have a look at changes in DEC vs changes in RA. With good balance and decent polar alignment, DEC rms can be used as an indicator for seeing. If all corrections are one sided, PA or imbalance cause a high RMS. Stiction is most often clearly visible in the guide graph. Random moves in DEC are often caused by atmospheric effects. Those you can do very little about, other than to increase MinMo and/ or decrease guide rate/aggressiveness.

Statistical methods are generally used to decrypt cyphers. A good read on the use of statistics through the history of code breaking is "Code Breakers" by David Kahn. What you are describing, I believe, is a brute force attack. This is very time consuming for longer messages. With todays computers it is starting to become doable, but that's also why new methods and longer keys are constantly being developed.

Thank you, Olly. Not having a long fl, I try to frame the main object such that there is something interesting in the background. In this case faraway galaxy clusters.

No you're not. It isn't sub zero, just gray and rainy. Thank you.

Too dark (up here)

You better hold on to that scope. The small secondary should give you better contrast than the large mirror of the 190MN, but at the cost of sensor illumination. Teleskop Service in Germany apparently (still) have a few in stock. Thank you. I'm playing with the idea to capture all of the MW and Andromeda dwarfs that are visible from my location. It should keep me occupied for a few years. 😉 We'll see how that goes ...

Yes. The Comet hunter from Explore Scientific is no longer produced, even though it may still be in stock with some dealers. Neither is the Intes Micro. But Sky Watcher’s is still in production. The coma is greatly reduced to an equivalent of f/9 for a standard Newtonian, but as you write, no diffraction spikes to deal with.

The extension tube is retractable, a not-so-fixed part of the focuser draw tube. It's held by only one screw pressing against a compression ring, and can introduce wobble or tilt. The 190MN is a lot bulkier than a comparable refractor, and doesn't have a handle to carry it. I find it a bit tricky to put on a mount and it's more susceptible to wind than a refractor, out in the field. In all fairness, the swedish astrophotographer who tried it in the filed, did so at temperatures down to -25C. But its optics are fine, and it gives great images.

Thanks, Rodd. The 190MN is a great scope. I love mine, even though it took a while to get to know it. And it's certainly not an install-and-forget instrument. It's tricky to collimate compared to a Newtonian (but holds collimation very well, once dialled in), and the focuser with its built in extension tube is a weak point in the design. (Why one would have an eyepiece extension tube in an imaging scope is beyond me. I've ordered a FeatherTouch to replace the stock focuser.) It definitely needs to be part of a permanent setup. A Swedish astrophotographer used it for one season in a "portable" setup. He has since sold it and replaced it with a smaller refractor. Many people complain about its weight, which is probably double that of a comparable Newtonian, but less than a comparable refractor. This is the 190MN next to a SW 150PDS (6"Newtonian).

In my observatory, I have an AZ-EQ6 (my own) next to an EQ6-R (my friend’s). Both perform about the same. The EQ6 is two years younger and guides perhaps ~0.1” better. In my opinion, the EQ-6 has altitude adjustment bolts that are clumsier, while the alt adjustment on the AZ-EQ6 can almost get blocked by the telescope (newtonian), ie the lever can be difficult to pull out and push back in. I bought the mount because at the time it was one of few affordable mounts that could be adjusted to >60 degrees north without bending the alt bolts, and it was ”future proof”.

Thanks, Alan. The galaxy has no well defined edge, but even in sdss images it is not much larger than this. Since it will be visible from my location for another few months, I plan to collect more data. There may very well also be ifn near the noise floor.

Leo A is in the lower left corner. Dwarf galaxies tend not to be bright and big. This one may get more tlc if it ever clears up and I can collect more data.

Very nice image, with beautiful colour. Just a bit of trivia, that small galaxy is at least 800 Mly distant. If you click on the NED database link in the reference you provided, you reach the NASA Extragalactic Database (NED), which shows a distance of 250 Mpc (mega parsec). Multiply by 3.25 to get 800 Mly.