Padraic M

Not jealous at all because I have a new 'venerable' little ST80 that I'm enjoying very much! A bit nervous the neighbours will complain me to the police as I haven't had much opportunity to point it skywards just yet. Enjoy your APO!

Yes - longer subs increase the signal-to-noise ratio. As I understand it, longer total exposure time allows you to gather more of both signal and noise, but the signal increases at the square of the noise so your image improves overall. Except for read noise (RN), which is a constant value for each exposure. If you had a lots of really short exposures where the signal value was below the RN value, your image would be swamped by the RN. If you had a single really long exposure, the impact of RN would be negligible, but your image is likely to be ruined by satellite trails, cloud, or star trails (from poor tracking). The fine balance is to take multiple exposures that are long enough to gather signal with low RN impact, and short enough to reduce the waste of poor individual subs. Having said all of that, modern astro cameras provide very low RN values and this means that the advantage of using longer subs is decreasing as technology improves.

Hi @Scribblecrans, we all know that feeling but don't give up! It gets easier with experience. I agree that plate solving is the gold standard when it comes to accurately positioning your rig on-target for imaging, but I'm not sure if it will work particularly well with the Star Adventurer. It's a game changer for mounts with two axis motors as the PC can control the mount pointing position but I don't think the SA is like that? I've gone fully automated with my imaging equipment. This means that I never need to look up at the sky as the computer does its job - this has advantages of repeatability and accuracy, but it defeats the purpose of the hobby to a certain extent. So much so that I've just bought a cheap and good small scope for observation, while the imaging scope is doing its thing. So the last few nights I'm back to the task of manually finding faint targets in fairly bright skies, just like you. I think there are three key steps: - Be familiar with the sky in the region around your target. Understand what you're looking for, and plan out how you will get there. You will use the technique of Star Hopping to get from a known bright star/asterism to your target. As mentioned above, planetarium software, or books like Turn Right at Orion are almost essential; otherwise you are on a random walk (which can be enjoyable too for a while). - Get either a red dot finder (RDF) or a Telrad, to get you in the right general area (this is essential!!!). Your scope has a wide field of view, so once you have located the target in the RDF/Telrad, you can be confident that it is also in the camera fov. Personally I prefer the RDF. - Once you're in the right general area, bump up the ISO on your camera and take some test shots. You should be able to recognise star patterns as you're already close to target. This might be easier if you connect to a PC as the bigger screen might show more detail. Again, back to the first point above, if you're not familiar with the area, you won't recognise the patterns. Turn Right at Orion gives you a very good process to work one step at a time from a known point to a target point. Try to be systematic about how you move - if you think it's "5 Dec turns East" but you don't see what you're looking for, retrace your steps "5 Dec turns West" to the last known position and try again. If you go scrolling around looking for something, you'll get lost and have to start from the beginning again. If you go with a RDF or Telrad, you can align it with the main scope during the day, using a distant tree or chimney. Finally, here's an interesting post from DPReview that explains a very method that's similar to this. https://www.dpreview.com/forums/post/62267807

Cuiv is one of the developers of NINA. His videos are great.

Hi Stu, I'm not sure that you have a problem. I would imagine that any resistance you feel when turning the cogs by hand will come from the motor through the reduction gearing rather than from the worm. That step is to check if you have binding caused by tightening the worm too far. If the motor can rotate the axis through 360 degrees then you don't have binding - it will be pretty obvious if you've overtightened as the motor will be forced to a halt at some point in the rotation (or at least you will hear it struggling). The trick with backlash is to tighten just enough so that there is no binding. For my mount, there is still a small amount of backlash left in the worm but you do the best you can.

You'd better get used to it!!! 🙂

You're not doing anything wrong - NINA only includes DSOs. Google "NINA sky atlas stars" gives a reference from CN explaining why. Recommendation is to use planetarium software like Stellarium to find any target you want, then NINA framing wizard can import the coordinates into NINA and slew there.

Thanks to @Ags, I have now joined the ST80 owners' club! Also included some very creative packing!

You have two concepts to consider with your 8" SCT. Firstly, even though it's got more aperture than your 4" refractor, it's got an f10 focal ratio. Your 4" may well have been an f5, which has twice the light-gathering power. Objects will appear half as bright in your SCT. This means that your skies had better be dark, and your eyes had better be dark-adjusted, especially for any faint deep-sky objects. SCTs really are better for planets than for nebulae or galaxies. The second concept is field of view. With such a long focal length, you will need to use a wide eyepiece on a small target to fit everything. Andromeda won't fit, nor will Orion. Both of these will be better in your 4" frac. At this time of year, you could try M13 the Great Globular Cluster in Hercules. It's a small, compact and very bright object that is high in the skies at this time of year. There are other clusters in the same area too. Also get some planetarium software for your PC and use it to check what field of view you will get with your scope and your eyepiece. Stellarium is excellent and free. You can enter in your scope details and your eyepiece details and the software will show you what you will see. Here's an example of M31 in a C8 SCT with a 26mm eyepiece - it will be nowhere nearly as bright as this but you can see that all you'll fit is the core as a fuzzy white patch. You won't see any detail. On the other hand, here's what M13 will look like:

Lovely detail there, and great composition with the baby pinwheel. Unusual presentation.

fwiw, I put my dew strap behind the plastic rim, and under the vixen plate; and the shield over the plastic rim. It may also go over the dew shield depending on how you make it. Hopefully this makes sense with the picture below - strap in blue position, shield in red. Doesn't seem to make sense to have the strap outside the shield. You're right in that the shield can be a bit shakey; it will stay in position as long as you don't use it as a handle. I haven't resorted to sticking velcro to the scope itself.

Treat yourself to a dew heater and shield for the C8 🙂 . On my first night with my C8, I was completely dewed up after about 20m minutes. Bought a heater strap and shield and haven't had an issue since. Enjoy all your new kit!

That looks identical to the Celestron one, so should be fine. The APS-C sensor at 22.5x15mm has a diagonal of 27mm, so an open aperture of 42mm won't cause any vignetting. For a full-frame EOS sensor, at 36x24mm has a diagonal of 43mm so M42 would cause some problems. I measured the distances with my own old 400D: ~45mm from sensor plane to camera lens mounting plate; 10mm for T-ring; 50mm for the SCT T-adapter gives 105mm overall.

I'd go the M42 route with a APS-C camera (OP has 750D).

Yes SCTs tend to use a 'SCT thread' back interface. https://agenaastro.com/articles/guides/miscellaneous/astronomy-threads-explained.html#small Don't forget that you will need the correct back focus between the end of the focal reducer and your SLR sensor. According to this article, that distance is 105mm: https://www.cloudynights.com/topic/756752-help-a-brother-out-what-is-the-real-backfocus-spec-of-the-antares-f63-sct-reducer/ so if you're ordering a thread adapter, you may also need to order an extender. That Celestron SCT T-adapter could be interesting as it seems to be very close to exactly the correct length, and it has the correct thread on both ends. The sensor plane is marked on a DSLR like this: https://www.photokonnexion.com/definition-focal-plane-mark/

@Knighty2112 An essential purchase in my view. Much more solid than the stock clamp, and it won't chew your dovetails either.

So have you decided what you're going to buy with the 500 quid you saved?

Amazing! Any idea what the total field of view is? Edit: Got it on AB: 6.364 degrees!

Not an expert on this, but I would imagine that you will use both. Starting with the best data (using the filter to remove as much of the LP as possible) means less work to do in APP. It is likely that there will still be some gradients or vignettes left in the image, even if you use a good LP filter and good flat frames.

The APP learning curve isn't that steep - when you've had a chance to experiment with a few more images you will get a better idea of what it can do. The tools on tab 9 are very interesting to play with. Yes it is - and that's what we mean by the data - but there are images and there are images! Dealing with sensor noise, bad vignetting, light pollution, thin cloud, poor focus, etc. etc. makes an image so much harder to work with. I notice that images captured in the city (Bortle 8 bright skies) take a lot of processing work, whereas images taken at a dark sky location (Bortle 2) just seem to 'pop out' on their own. The image format doesn't matter; fits and tiff are very similar in that they're both high quality loss-less image formats, but fits is an astrophotography-specific image format with lots of useful information stored in the image headers. You can see all of this in APP when you open a fits file. Just to add a little to the last post - on the Calibrate tab you can split a colour image into three separate images, one for each channel. Here are the blue, green and red channels; you can see in the blue channel that the top left corner is dark, and the image gets brighter as you travel to bottom right. Similar with green, but with a slightly different distribution. The red channel is actually very even from side to side (and it has more detail in the nebula). This gradient from side to side or corner to corner is very standard with light pollution, as the sky is brighter towards the horizon, or close to a light source. It's also very standard that the different colour channels will pick up the light pollution to different amounts, which means that the combined RGB will have an uneven colour balance across the frame. The Remove Light Pollution tool in APP is excellent at evening out this type of gradient, and really easy to use. There may be a better way to do this with a OSC/DSLR image, but as I said, I just do mono so I do it at the channel level and then combine to RGB. Blue: Green: Red:

Well Stuart, that's a very fine image to start with, both as an 'early work' and for 45 minutes of exposure. I'm not an SLR expert but I had a go in APP and Gimp. My suggested version is below. My main problem was that there is a strong red cast in your version, and actually quite a bit of vignetting in red. I'm not sure if that's a feature of SLR or OSC cameras (I've only done mono) but I started by loading your FITS file into APP as a Light frame (it objected but did it anyway), and separated the channels into red, green and blue. As expected, there was quite a difference in light pollution response in green and blue, so in the combined rgb image the white balance changed across the image. I used the Remove Light Pollution tool on all three channels and then recombined them as RGB. That unified the background quite a bit. I cropped out quite a bit at the edges. There was very little other colour modification required, but in the Calibrate Star Colours tool I just tweaked the slopes and constants very slightly, and saved the stretched image to 32-bit TIFF. In Gimp, there was some Levels work to be done, and then I needed to desaturate the Red channel a little for the background (by masking out the nebula). I scaled the image down by 50% too (equivalent to binning 2x2 I think) because you didn't need the resolution, and there was some colour mottling in the background. Finally then just exported as JPEG and here it is below. I didn't do any noise reduction, and you might like to keep some more colour saturation in the stars but I quite like it. Btw the data was really nice to work with.

It's hard to disagree with what Geoff said earlier. I just wanted to reinforce the point that planetary and DSO imaging are poles apart, and really need completely different equipment, software and processing techniques. Best to pick one for now, and stick with that. Lunar kind of fits in the middle, so whichever way you go, you can do lunar. For planetary, you don't need to worry about guiding. If your mount tracks reasonably well you'll be ok; you'll shoot video sequences of the planet rather than long exposures. Likewise, the ASI uncooled cameras are designed for short exposure planetary, while the expensive cooled ones are for DSO long exposure. Software wise, SharpCap is a good candidate for capturing those planetary videos, as is FireCapture or even ZWO's own ASICAP. Registax or AutoStakkert will do your post-processing for you. For DSOs, you're more likely to use APT or NINA for capture, and AstroPixelProcessor, StarTools or PixInsight for processing. I have both a Celestron C8, which I hope to use as soon as I get to see a planet again (!), and an 80mm refractor. I set the C8 up for DSO for the first time recently with an off-axis guider, but I'm glad that I have the experience from the refractor behind me as using the SCT for DSOs is challenging. Many DSOs won't fit in the narrow field of view of the C8. Finally! I'd suggest not using an ASIAIR for now, just connect to your laptop and get to understand the capture and control techniques first hand. One simple step-up option could be to look at a C6 or 5" Mak with your current AZ-GTi mount - just keep it within the 5kg weight specification? Otherwise, you won't go wrong with either the 8" or 9.25 SCT on a hefty mount like the CGEM or a HEQ5/EQ6 class. Use Stellarium to preview what field of view any combination of scope and camera will give you before you decide what to buy.

That makes sense - the HEQ5 would be a BIG improvement! Definitely you will benefit from using flats and darks. You don't need bias subs for that sort of camera. SIRIL will stack them nicely for you. Next step might be to try guiding for longer subs? I attached a finder/guider shoe to my 130EQ by drilling a few holes. It's made of tough stuff! Of course you will need a guidescope - FLO has a nice cheap astro essentials 200mm one https://www.firstlightoptics.com/guide-scopes/astro-essentials-50mm-guidescope-finderscope.html and you'll need another camera too. I use an ASI290mm Mini which is ideal, or you could try the T7M from aliexpress which is cheaper.

Have you all forgotten the midges??? In Ireland (and I believe in Scotland) the saying is "the midges are eating me alive!".

You're doing remarkably well with the 130EQ. How did you manage to get focus with that camera - is there enough back-focus, or are you using a Barlow? I would have expected you to need one of the ZWO 'mini' cameras to get the sensor inside the focuser drawtube. The spherical mirror is only one of the issues. I found the focuser unusable for imaging, and there's no option to upgrade except with an angle grinder. The mount is so flimsy that even with 30s exposures you'll need a wind-less night. I like your dumbbell nebula pic though. Some people are getting really good DSO images with lucky imaging, which is normally used for planets. You will definitely get better results with more data, and with no option of guiding (or even proper tracking) on this scope, you could aim for 1,000's of very short images? Hope your PC is up to it!