The Lazy Astronomer

Moon aside (although that'll be less of an issue by Tuesday/Wednesday anyway), if even half of this comes to fruition, I'll be a very happy bunny indeed!

Not sure if we're still suffering from the dust or not - didn't notice any orange skies yesterday, but it did appear to me that there was a sort of haziness in the glow of the moon - my glasses are always filthy though, so not ruling out some very localised dust!

Ha is 656(.something)nm, so you won't lose any Ha signal (well, a tiny bit because L3 has ~95% transmission at that wavelength, but it's inconsequential). It should be a good match for your scope; being a doublet, it won't be perfectly corrected at the extreme ends of the spectrum, so cutting them off should produce less bloated stars - I use the L3 with my triplet.

Stellarium allows you to filter out objects below a specified angular size - I've been using it whilst looking at what galaxies to image in the upcoming months and filtering out all the smaller ones that my 550mm focal length just can't do any justice 😔

Oh, I'd been lead to believe that for CMOS, the read noise was not just added together, but added and then divided by sqrt of the number of pixels binned, so read noise doubles for a 2x2 bin. Is this not right? Edit: I've just realised my mistake - I didn't use the increased read noise figure in the calculation 😬

I'd be interested to see a side by side comparison, with identical processing, if you have the time. The 10x1min stack would have had more doses of read noise, but I wouldn't have expected a noticeable difference just viewing the images, so this is most intriguing.

Nothing! You are applying the equation correctly to come to 1280s. The reason it's so high is due to your tiny pixels and relatively dark sky. There are a few things you can do to lower the time: 1. Accept a slightly increased level of noise and use a lower C factor. 2. [Removed as not correct] 3. Consider moving to London for higher light pollution levels 😁 If you can't (or don't want to) expose this long, then don't worry about it too much - experimentation is very much encouraged in this hobby, and you may find that you're happy with the images you produce using exposure times lower than what is suggested as your minimum. For L, select 'none' from the filter drop down list, and for RGB, select 'red/green/blue' (or divide the L electron rate by 3, whatever's easiest). And, on the bright side, the long exposures will mean less hard drive space used up 😁

Thanks - after doing this I then had to go back and add v2 in feature scripts as well, but all sorted now. Looking forward to taking it for a spin shortly 👍

@mike1485: is there another step I need to do to remove ghs v1? I followed the above, and got a message saying everything had successfully updated, however when I open it via utilities>scripts it opens v1

Yes! Real time preview was the only thing missing for me really (although it was only slightly inconvenient to click the preview stretch button). Will be downloading later - thanks for your continued efforts.

That seems to be a pretty good brightness level there. For further improvement, you possibly have some stacking artifacts as the top and left edges of the frame are noticeably brighter, so maybe consider cropping those. And then maybe there's a slight gradient, as bottom left corner looks darker than top right (excluding areas affected by stacking artifacts, of course).

I don't know what software you use, but rather than set the black point subjectively (by judging the brightness by eye), you could consider setting it more objectively, by moving the black points such that the pixel values of the background have equal intensity in RGB, and are around 5 - 10% of the maximum pixel value.

My opinion: attempting AP as an absolute beginner with the over 2000mm of focal length offered by the 8SE is a fools errand. In fact, the 8SE is not particularly well suited to DSO imaging altogether (great for planets and moon though), so stick to the lenses for now. The shorter the lens, the easier it should be in terms of tracking errors, so start short. An example target for a 50mm lens: everyone's favourite, Orion. - pretty much the whole constellation will fit in the frame, and there are a LOT of nebulous regions in here. Granted most will be faint, and may not show up well on your camera (unless it's astro modified??). Only real issue is it's getting a bit late in the season for Orion now. Piggybacking will probably be fine to start out with, but the alt az nature of the mount will limit you somewhat (not to say that great things can't be done with alt az - check out the no EQ DSO imaging thread), so maybe consider your next purchase to be a star tracker of some sorts (or maybe, dare l suggest it, an HEQ5 😁). A cursory look on Google tells me your camera has a pixel size of about 4.3um, read noise of about 3e- at ISO1600, and a QE of around 40% (important note: I did not read further to verify this), so subs of as short as ~5s would be adequately exposed with the 50mm lens for your skies.

To my (admittedly untrained) eye, there isn't any obvious tilt in the image. I'm not sure if my eyes are playing tricks on me, but I think I can see some remnants of the dust bunnies in the calibrated image, which would lead me to believe flat correction is the issue. If you absolutely nuke the stretch on the calibrated master, does anything more obvious come to the fore?

I get this if my target's gotten too close to the tree at the end of my garden - the shadows of the branches can be pretty much undetectable in the image until it gets properly into the tree. The only thing that gives it away is the diffraction spikes. However, when it happens to me, the spikes are the same or similar on all bright stars, but yours are in different orientation in different areas of the frame... 🤔

Good effort - as above, I'd say blend in some shorter exposures for the core. There may also be a tad too much noise brought forward - consider less aggressive stretching or some noise reduction. FYI - RGB imaging through a mono sensor is true colour (in terms of data capture anyway), not false colour.

Perhaps, but we'd probably have to wait a very looong time for the shell to expand to that sort of size (Wikipedia says the crab nebula is about 1000 years old).

Siril appears complicated at first, but it's actually quite simple and straightforward once you get used to it - check out the tutorials on their website.

When you say struggling, what do you mean? As above, you need software to control the camera, which one are you using?

Yes - total RMS is a good measure, but ideally the RA and DEC RMS should be the same as each other too. Your polar alignment is fine, phd2 can usually deal with anything under 5 arcminutes pretty well. Bad polar alignment will usually show up as lots of guide corrections in the DEC axis. What mount do you have? For the size of your scope, l would have thought you must have a fairly decent mount, so 1.75" RMS seems a little high.

Yes For simplicity, calculate your image scales to include any binning. I wouldn't worry too much about this, just aim to be achieving guiding performance (in arcseconds) of less than half your main camera imaging scale. If you're not able to achieve that, then consider changing binning or phd2 settings (use the guiding assistant too).

If I'm reading that right, then you're binning your guide cam x2 for an image scale of ~3.4"/px, and also binning x2 for your imaging cam for a scale of ~1.2"/px. A 0.45px movement in the guider = 1.53", which equates to a movement of ~1.3px in the imaging camera.

This is one of my main gripes with Startools. I'm someone who likes to fiddle around and tweak things (quite often detrimentally, to be honest 😅), so I can easily spend many hours over several days processing. Not being able to pick up from where l left off was irritating. That said, Startools does write a log file of every action you perform, so it is possible to retrace your steps, as it were, if you want to get back to a certain step and carry on processing from there.

You're likely to get many opinions on this as stacking and post processing software is plentiful. My opinion is Deep Sky Stacker is probably the easiest to use in the beginning as it's pretty automated, just don't even consider using it for post processing as it's really not suitable for that. Siril is another free option for a stacking program, which does have some decent post processing ability as well. Gimp is a good free alternative to photoshop if you resent the idea of a monthly subscription. At the 'paid for' end, most (all?) offer trial periods for you to evaluate them. I'd recommend trying them out and seeing which best suits you. Some examples of software to try include: APP, AstroArt, Startools and Pixinsight. You will often find people use a mixture of different software to do different things, depending on what they get on best with in the software they use.

Oh yeah, I didn't word it very well - I didn't mean an actual error in Stellarium, l was concurring that it must be something in the settings that's caused Stellarium to think the moon is somewhere where it isn't, and at the same time seeing if the OP could verify this by judging the moon's position relative to nearby stars in the program, and real life.