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There aren't many images online of this small gem in Ursa Major, and even fewer show the extended disk of this spiral galaxy. What's more, the extended disk shows a claw like arm, so maybe this galaxy should be called the Crab galaxy. ngc 4041, the centrepiece of this image, is a spiral Seyffert type galaxy in the Great Dipper, about 70 Mly distant. It is a very active galaxy, with many HI regions where new star formation occurs. What is somewhat unusual is that these regions are scattered over the entire galaxy, including the nucleus. Hence the pink colour near the galactic centre. What is even more unusual is the very weak extended disk, which has an arm that appears to line up with one of the galaxy's arms. This faint structure is, as far as I could find, only described in one scientific article. In this article it is speculated that the "three pronged" extension could be due to a past interaction with another galaxy. Also in this image are several other galaxies, at approximately the same distance as ngc 4041. The larger of these, at the bottom of the image, is lenticular galaxy ngc 4036. This galaxy is in many ways the opposite of ngc 4041, in that it has no active star formation and is slowly losing its spiral structure. The remnants of a spiral are visible as weak disturbances in the disk. Here's a close up of ngc 4041 and ngc 4036 Technical details: Telescope/camera: SW MN190 and zWO ASI294MM 7 hrs RGB, 5.5 hrs L, and 2 hrs H-alpha Processed in PixInsight

Great work, Martin. Btw, you might want to replace your apod link with the permanent address https://apod.nasa.gov/apod/ap230317.html At the moment you link to the daily apod

Great image. Those are 10 hours well spent. If you compare to the APOD image, you should also consider this 19 hrs from Shropshire compared to "a range of telescopes in Central Thailand and at Observatorio El Sauce in Chile."

A MN190 delivers once again! Wonderful rendering of this nebula, Martin.

My thought exactly. It is definitely a SNR candidate.

The current version of astroberry is very stable and fast enough on a RPi4 with a 64 GB SDcard. You can connect to it from a web browser. For me, the set up time (from connecting to astroberry untill start of the first exposure) is about 8 minutes. This includes Unparking the scope Aligning using plate solving Focusing (with 4 s exposures per frame) Starting the guider Entering a sequence and cooling the camera to -10 C

Just make sure you (hand-)tighten the thumbscrew of the built in extension tube as firmly as you can,mor it may cause a wobble.

Lynd's Dark Nebulae are listed in Kstars, but as yet I have not found the LBN catalogue. I also have no idea how complete the list is. It should also be possible to import a catalog from eg the Vizier database, although I have never tried this. Unfortunately Aladin doesn't list labels by default, and is not intuitive to use. https://aladin.cds.unistra.fr/AladinLite/?target=20 40 32.000%2B67 20 42.00&fov=5.55&survey=CDS%2FP%2FDSS2%2Fcolor Great image, Olly and Paul.

I have a filterwheel to achieve focus at about 15 mm or so for the focus tube to extend out of the focuser. In stead of using the wobbly extension tube, it's better to leave the spacers in place. Just do a rough manual focus first to get into the ball park, as they say. Then use just enough spacers to get to focus. Normally, it would. But as I wrote, the focuser is a low profile type, and the focus tube won't extend past the internal baffles. This is by design, so you will get APO-like stars.

The 190MN has no diffraction spikes and the focuser is low profile.

Correct. The 55 mm rule is from the old dslr days. Most dslrs have their sensor 45 mm behind the front of the camera body (the lens flange). Add to that 10 mm for a camera adapter, and you have 55 mm. This made connecting a camera to optics easy, you screw the adapter onto the corrector or flattener, and then to the camera. You then slide the assembly into the focuser tube. The 190MN doesn't need a coma corrector, because the front meniscus corrects any coma. So there are no critical distances on the focuser side. You can dispens with the rings and just use one to attach the camera to the focuser. Easy enough. Btw, if you have the stock focuser, don't try to use the built in extension tube to fix the focus position; it is wobbly when extended. Push that tube all the way in and secure it in place so that it absolutely cannot move.

The OS may be 64 bit, but the app not necessarily so. It may be either completely 32 bit, or a mixture.

Not much activity here, it seems. Have you tried the indilib forum?

Definitely not (a myth, that is).

80 hrs @ f/8 vs 5 hrs at f/2. "F-myth"? 😉 Joking aside, this is an excellent image. Well done, Göran.

Blink to sort out bad frames Sub Frame Selector to measure frames, and to decide which to remove. WBPP will weigh the good frames during stacking. Can you elaborate on "horrible". Many times images may look poor after DBE, but they can still be processed into good quality ones. I'm certain we can offer advice with specific problems. Just post the stretched image as jpeg and, if you like, provide the unprocessed master for others to evaluate.

That’s my experience as well. But a few hours of Ha changes that. When I get these "blue knots” I do a few test exposures with the Ha filter to check

The MN190 is trickier to collimate because of the corrector plate which puts extra constraints on distances and coinciding rays and axes.

The reason I didn’t recommend it is that it isn’t a beginner’s scope. Imo, it’s better to have some experience with a standard Newtonian before tackling the MN190. It’s also heavy, compared to a standard Newtonian (not necessarily if compared to a large apo), and better suited for a permanent setup. It’s wobbly until you manage to fix the extension tube. Shimming it solves the issue. But yes, this shouldn’t be necessary to begin with. I have a Feathertouch on order to replace the stock focuser. Ordered it last August and so far hasn’t materialised.

Excellent image. The galaxy's structure, as well as the strong blue colour of the ring suggest recent star formation. In fact, there are many smaller Ha regions along the outer ring, like a ruby necklace. I would definitely add some hours of Ha data to bring those out, if I were you.

A simple newtonian of about 8 - 10", if you don't mind the star spikes and the occasional collimation. If you want stars to look good over the entire field, as well as somewhat easier handling, a slower model seems a safer bet. So, 8" @f/5 rather than 10" @ f/4. Opt for a good quality focuser, and a Losmandy plate to replace the more common Vixen dovetail.

Yes. And signal strength depends on exposure time, gain settings, bandwidth of the filters, etc. That's why even Vicent Peris won't attempt a more rigorous solution .

Your .05 is my c. I tweak this value, but most of the time it's between 0.3 and 0.5. That is with a 7 nm Ha filter and different gain/offset values for the red filter and Ha filter.

Thanks, @Rodd. The "no blue is necessary" theory is just that, a theory. If you have L, red, and green, you can theoretically re-create blue by subtraction. But that only works if the red that you collected is just as strong as the red component in L. Same goes for green. If for whatever reason the red component in L doesn't match the red collected signal, you either subtract too much or too little. Either way, you are not left with a clean blue signal after L - R - G. Also, any camera induced signal (noise, dark current, amp glow, pedestal) will have to be accounted for. That's why this only works in theory, but rarely in practice. Mind you, the same is essentially true when we do red-continuum subtraction, where we subtract red from H-alpha. That's why in the Pixinsight documentation/processing example a correction factor is used, and the median red signal is not subtracted: Ha - c*(R - med(R)) Anyway, in the image I posted here, I combined the data I had, all in good fun, with no aspiration for being "correct" in any way.

One more variation. This is also a HaRG map. The difference is mainly that I used linear fit before combining the data and no colour calibration afterwards.