wimvb

I don’t use refractors, but know at least that the distance between flattener and sensor is critical, and needs to be 55mm, unless otherwise stated in the specifications. The wrong distance will give you elongated stars in the corners. The flange to sensor distance of most dslrs is approximatively 45 mm, and the camera adapter usually 10mm. Total 55mm. Others should be able to tell you how critical that distance is for your scope. The diffraction shadows around bright stars are a bit odd. If you look into the telescope, front to camera, and you see any tiny obstructions, you have found the probable cause. At 10 F, the lens cell may also start to contract, causing so called pinched optics, which will deform star shapes. No one ever said this hobby was easy. 😀

There's a reason why the heq5 has a higher payload; it's sturdier and a better build. But get the one with belt drive, it runs smoother.

And the mount used for this stunning image was ... (drum roll) ... A star adventurer. I agree that a short fl lens ("short" in AP is imo, anything up to about 400 mm fl) with a dslr can give spectacular results. But if you mount that camera on a SW EQ6-R, and have to haul that out every time there is a gap in the clouds, you'll probably lose interest in this hobby very soon. The EQ6-R with tripod weighs 25 kg, without counter weights (you probably don't need those with a 400 mm lens and dslr). A HEQ5 weighs 15.6 kg, and a CEM40 about the same. For a £ 1500 budget, I would get an HEQ5 with Rowan belt mod (£ 980), a guide kit (£ 220 - 250, total £ 1200) and either a 72ED Evostar (£ 270, wo flattener), or save another £ 300 to get that 300 or 400 mm lens. Just my €0.02

I guess you found out that there's no such thing as point & shoot in astrophotography. A few hints to improve your results, apart from having the correct gear with you (😉 ) Get to know the constellations and the main stars in them. This will speed up alignment. Decide for only one exposure time, regardless of target (except the Orion neb), also keep iso constant. Only plan ( = keyword) for at most two targets per night, one for earlier, the other for later. Forget about astro-tourism where you want to shoot all the landmarks in one night. Collect at least two hours of data per target, more if you have light pollution, regardless of your single sub exposure time. Better data will make processing easier. And finally, have fun. Despite all the misshaps and cold.

I agree with @tooth_dr on this one; start small. While the eq6-r is a great mount, I fear it won't see much use if you can't install it permanently, and can only use it with a camera and lenses. A friend of mine got great results with an 80ed on a heq5 and a used Moravian G2 with lrgb filters, from a balcony in a major city. If you have to set up every time, the heq5 will be much easier.

Could also be edge reflections then. I have possible edge reflections in my rgb blue filter (31 mm optolong), and plan to make rings to cover the very edges of the filters.

Ok, something needs fixing. What size filters do you have? If 31 mm unmounted, you may have reflections from the filters edge.

Before you do anything else, calibrate your lights with darks and flats. I've read posts on CN, where this kind of flats worked perfectly fine. Make sure it's broke, before you try to fix it.

Very nice image anyway

As I wrote before, check out Stan Moore's chapter in "Lessons from the Masters"

I think that Stan Moore in Robert Gendler’s book ”Lessons from the Masters” comes closest. There are also some interesting articles on Craig Stark’s website http://www.stark-labs.com

Have a little faith, Göran. Have a little faith.

this is what Juan Conejero wrote in 2011 about PixInsight: "Internally, most processes work with real or complex-valued pixels in either 32-bit or 64-bit floating point format, irrespective of the target image's data format. For 32-bit integer images, all internal calculations are always carried out in 64-bit floating point. The goal is to minimize roundoff and truncation errors, even at the cost of degrading performance. There are exceptions such as LUT-based transformations (histogram and curves for example) working on 8-bit and 16-bit integer images, and temporary working images used for structure or edge detection." https://pixinsight.com/forum/index.php?threads/inernal-processing-bit-depth.2776/post-20274

That's easy to fix: Morphological Transformation in PI to the rescue. Without putting too much effort into it.

Btw, that rig with six RASAs reminds me of the ED-209 unit in the 1987 movie Robocop.

Never mind the cables, as long as they go parallell to the sides of the cameras. The cameras edges will produce star spikes in this configuration.

This can be pixel rejection in stacking. Have you looked at a single sub, fresh from the camera?

At each side of the triangles, there is a shadow which reminds me of mirror clips. If you look into the telescope from the front glass, can you see lens clips? I agree with Adam, this is definitely not as it should be.

That does look like pinched optics. Image a slightly defocused star, to see what the profile looks like. if you google ”Suiter star test”, you will find more information on what diffraction patterns of pinched optics look like.

A bit late, but since you haven't got an answer on this question, here goes. Your best, and cheapest investment in this hobby is a bahtinov mask. You put it in front of the telescope when focusing. The mask will produce diffraction spikes in an X pattern with an overlappin I. When the pattern is symmetrical (the I on top of the X), you have best focus. You can buy a mask from almost any astronomi retailer, or make your own. https://www.firstlightoptics.com/offers/offer_starsharp-bahtinov-focus-masks_72309.html

I think this should be of interest as well. According to the formula used, and some quick measurements of the bunnies on your flats, the dust should be only 2.5 - 3 mm from the sensor, ie on the window where you found it.

I think that the vignetting is a bit excessive. But it's hard to assess this from the stretched image. How good is your collimation, especially the secondary?

I don't think there is a way. Some people have replaced the stock focuser on the MN190, but collimation afterwards is tricky, since you're not supposed to move the secondary up or down . In stead you have to move the focuser in order to centre it over the secondary.

There's a simple way to improve the focuser. You just need to put a narrow strip of tape (I used aluminium tape) between the extension tube and the focuser tube, since it is the estension tube that can wobble. This wedges the extension firmly in place.

Very nice result for such short exposure times. I think that in order for you to get more out of this, you will have to increase the exposure time per sub a lot. With 30 seconds, you're probably not clearing the read noise floor enough.