ONIKKINEN

You can do this measurement at any time, you just get a different result. If you want to know what is the darkest possible sky for your location then obviously choose a night without the Moon and a target towards the zenith. Do note that you get different readings from different parts of the sky, but this is normal. Its also why its kind of pointless to declare a site "bortle 6" if one part of the sky is 7 and another is 5. Exposure time is not so important, just a single subexposure that shows a good amount of stars (a minute or two).

I have found this to be somewhat accurate: https://www.lightpollutionmap.info But for the actual measurement i use ASTAP and its SQM measurement tool. You only have to take a single subexposure, calibrate it, and then run the tool on it. Astap will then make an objective measurement on your sky quality and spit out a number in magnitudes per arc second squared (SQM). I would encourage you to do this actual measurement instead of trusting what some site says, because there can be quite a bit of local variation in conditions depending on how close the nearest light source to you is. Sure is, broadband will take a while but nothing you can do about that. Narrowband with a duoband filter of some kind is also possible and not at all ruined by the light pollution.

Hubble optics also makes fairly light mirrors, on their site some 12" primary mirrors are quoted at 4kg.

What level of light pollution do you have to deal with, and what sort of targets are you most interested in? With your lenses i am assuming you are mostly doing milky way/very wide field imaging, which is mostly broadband and no filter will really help with light pollution. If you wanted to improve emission nebulae within the milky way then you could slot in a narrowband filter of some kind, but not sure that's what you're after.

Funny, reminds me of one of the first times i used Astap, when i forgot to remove my bahtinov mask but it still actually was still able to platesolve the image somehow. I only realized as i saw the first sub come in through NINA and wondered where those horrible spikes came from. Astap+NINA is actually quite trouble free to use once you get the ball rolling. Also regarding flats, you should consider taking them as a part of your standard workflow as soon as possible, they are extremely important for allowing you to fully stretch the image before it breaks down and dust spots come visible. If you used NINA you would have access to the flat wizard, which will just auto expose for an optimal length and take the flats for you. You only need to place a flat panel on the scope for that to work (cheap LED tracing panel for example, or a tablet showing a white screen). But then with flats you also need to take bias/darkflat and dark frames. Keep them in mind for when you get the urge to try something new. Going from a DSLR to a dedicated computer controlled camera is a bit of a leap in terms of complexity, so probably best to focus on a couple of things at a time.

Astap will plateolve an image within a second or two at this field of view, as long as you are within a few degrees of mount to sky error =always, unless you bump the mount or something.

The 585 is a very capable deep sky camera, its just sold under the "planetary camera" flag (in most places) because it is uncooled and the sensor is not as big as some other models. I'd say dont get hung up on that at all, within this kind of budget it is easily the best camera you could buy. You still have hundreds of potential targets that fit on the chip with your 72ED, so its not really limiting your imaging much.

OSC dedicated astronomy cameras will still be significantly better in every aspect, so definitely worth it. For example Canon DSLRs have a red light blocking filter that passes only around 1/4th of Ha compared to dedicated astronomy cameras (or modded DSLRs). So you would be getting Ha at 4x speed compared to DSLRs. Mono with an Ha filter will be around 4 times faster than OSC, because every pixel will be capturing Ha as opposed to every 4th pixel of an OSC camera. So mono + Ha filter will be around 16x the speed of a DSLR and OSC will be around 4x the speed of a DSLR (ignoring other camera specs, in reality the difference is actually a bit larger because DSLRs are more noisy). UV/IR cut filters for astronomy purposes fully pass Ha so you lose none of it when using one, so its not the same kind of filter found on DSLRs. In short: definitely worth it to upgrade from a DSLR.

Passing IR makes proper colour calibration impossible, because more than the visible spectrum was passed. It will also dilute colours in general, because at around 800nm wavelength and above the bayer matrix of most cameras turns fully transparent, meaning the data is monochromatic and all colour information at this wavelength and beyond is lost. There is also the issue of optics. If using a refracting telescope, then passing IR will make stars enormous blobs due to chromatic aberration, because the lenses are not designed to operate on infrared wavelengths. Even with a reflecting telescope there can be issues, such as internal reflections within a coma corrector that cause stars to balloon in size, especially redder stars that are brighter in IR. I have experimented with imaging sans UV/IR cut filter with my newtonian but there were other issues too, such as the flocking of my tube being insufficient at reducing infrared reflections, and the mirror coatings being slightly transparent which caused stray light to pass through the back of the mirror (flats were impossible - complete waste of time). So i think to be safe you really should use the UV/IR cut filter.

Nice one, rich background and all the detail both faint and bright easily seen. Try the Generalized Extreme Studentized Deviate (ESD) rejection algorithm for satellite trails. It works extremely well with stacks that have many images such as this one. The default ESD significance setting of 0.05 could be a bit low, you could try 0.1 if they dont go away but i guarantee they will completely disappear with this rejection algorithm with the right settings.

My strategy for dealing with Windows quirks is to just never connect my mini-pc to the internet - and i never have since i bought it in 2021. No auto updates, no cloud anything, no issues. The only 2 crash/other issues i have had happened when my PC got rained on, but that's understandable.

I would bump up that offset a little bit, with random noise you would almost certainly get 0 value pixels occasionally.

You can quite easily prove yourself wrong by trying to build a go-to platesolving astrophotography rig for under 500£. You will find this to be impossible, and the Seestar is the only viable option (maybe some of the other smart scopes too, not upto date on pricing of other models). This whole discussion is meaningless if we dont take the pricetag into account, and we should as it is one of the most important factors.

There are some pretty damn impressive images on Astrobin taken with a Seestar: https://www.astrobin.com/search/?q="ZWO+Seestar+S50"&d=i&subject=&telescope=&camera=&date_published_min=2011-11-09&date_published_max=2024-03-27&sort=-likes Of course its possible someone has not been honest and some other telescope was used, but i find it hard to believe that people would bother doing that.

Im thinking some of it may be high cloud and background extraction produced some blotches. If you look through your subs youll see if there was something extra. Could be wrong and its just dust. Plenty of dust at this declination.

There is a 254 hour image of M51 on Astrobin :https://www.astrobin.com/7hwtz0/?q=M51&camera= Doesnt quite look like the nebulosity matches, but some of it is definitely the extended halo around M51. Field of view is smaller in that one too, so hard to say for sure. Maybe a bit of high cloud and background noise coupled with actual dust?

You lose only the pixels that are rejected, not the whole image. Usually rejection rates are below 1% of all pixels so not an issue at all. The rejected pixels are replaced by the median value of that pixel from the stack so there will be no evidence left that there ever was a satellite trail in the first place.

Rejection when stacking will remove them easily. There could be a hundred trails in total and none will be visible in the stack at the end. DSS has kappa-sigma clipping which works well with a modest number of images (a few dozen at least to get the best result). Siril has winsorized sigma clipping that does the same thing. Siril also has the Generalized extreme studentized deviate test (awful name) method, which is very good with a large number of frames, think close to or more than a hundred. At the end of the day satellite trails are meaningless in subexposures and get rejected.

16k is more than enough for even the brightest targets (maybe M42, M31 and the like). This looks like the same gain as ZWOs gain 100 on the 2600MC, or gain 100 on my RisingCam IMX571, I'd say look no further, that's your go-to gain (300 that is). I struggle to think of a scenario where you would actually need the 50k full well enough to justify the much higher read noise. Actually i dont think there is one, since with 2.4x the read noise you would need to expose 2.4^2 = 5.76 times longer to swamp read noise by the same amount as you would be with gain 300, so the 3x full well capacity is kind of meaningless.

Yeah 300 seems like the optimal value. No real point in going with a higher gain as read noise really doesn't go down that much but you lose a lot of full well capacity.

Neither should i really "shout across the ravine" since i dont have a Seestar, nor am i planning on getting one. I get that, from a buy once philosophy standpoint the Seestar is not a good long term investment, if someone is planning on sticking with the hobby for lets say 5+ years and would like to re-use parts of the first purchase (like you could with a traditional setup). But if 500 bucks is all there is to spend and one wants to image deep sky objects, then there is no better option. Not sure even doubling the budget would get a reasonably better option (not to even mention the setup of all the automatic voodoo required for live stacking astrophotography). I dont think the "buy once, use for 10 years" thing is intended for the target audience for the Seestar. Its a gateway drug, a kick in the back down the hill of Astrophotography. Since it doesn't cost an arm and a leg you can grab a ledge before the freefall and claw yourself out of the hobby if it wasn't your thing after all.

I get the feeling that Ed had decided before the review that he will not like it because it seems he is a bit anti-technology for some reason, which is odd since his videos are usually pretty good and more on the objective side than subjective. I find it very odd that he decided to compare the Seestar to a Takahashi on an equatorial mount, you cant probably even get a flattener for the Tak for the price of a Seestar. Very tone deaf for sure. I also dont quite buy the idea that you shouldn't buy one now because there will be a better one in a few years. If we followed this logic then we would never buy anything, since technology is always on the move.

I would not bother with the bahtinov mask at all, really the HFR readings from NINA are all you need and the bahtinov mask is an extra step with no benefit. As long as you arent completely out of focus and stars are visible you get a reading and can take it from there. You can mark your focuser drawtube in rough focus, so you dont need to guess when setting up on subsequent nights and can jump straight to the actual focus part. I use 3s exposures looped in NINA and focus manually based on the HFR reading. After you have used your kit for a few nights you get an idea on what kind of HFR to expect, so it really doesnt take too long to find the smallest HFR. NINA will also plot your subs when you image through a sequence, so you can see if focus has gone out and when refocusing is necessary. As for offset, make sure you have enough. Too much is not an issue but too little is, my RisingCam IMX571 requires at least 600 offset, so i just left it at the default of 768 and never looked back. You can measure the required offset by taking a bias frame (same gain as intended imaging gain) and seeing if the min value is above 0. If it is 0, increase until it isnt.

Another trick is to install an aperture stop (less than 1mm) to the collimation laser, which will make the laser spot on the primary large enough to cover the entire center marker. Then you can collimate using the shadow of the center marker rather than just the reflected laser. Makes it easy to see how much adjustment is needed and to what direction, since the reflected shadow is now bigger than the central hole on the target plate the laser has. I have not had any luck with barlows on my laser, have tried 2 barlow elements and a few different methods of laser to barlow attachment and they all disagree with each other - so not accurate.

Great images once again! Always happy to see this thread updated, really a treasure trove of tack sharp extremely classy lunar RGB images.