Spongey

Thanks! Yes, drizzling the data helps with the blockyness of the stars, followed by star reduction and downsampling makes them almost fade into the background. I found some slight tilt in the image train but it's very minor and I don't think I'll be adjusting anything to try and get rid of it. If I focus on a star on the left third-line then the overall shape is quite good across the frame.

First light with the 268M and Samyang 135mm! Waiting for my scope to be manufactured so this lens will have to keep me going until then. My stars aren't perfect, but with 3nm filters they are hardly the star of the show (no pun intended). Part 1 of a 2 panel mosaic of the NGC7000 region This is only 2 hours of data shot at ~f/2.8, with the lens stopped down using step down rings to 49mm. Hoping to get some more Ha this week if the weather holds and then focus on Oiii and Sii when the moon has diminished! Cheers

It's also worth noting that this sensor has incredibly low dark current, even at higher temperatures. Shooting a 300s exposure at 0 degrees will only give you 1.1e- per pixel of dark current, which is still well below read noise.

My filter wheel is finally full! Replacement Antlia 3nm came in today, and Chroma LRGB and Oiii yesterday.

The specs quote a -30 degree delta for continuous operation, or -35 degrees for single frames. I can reliably cool mine to -10 degrees in a 21.5 degree room with the cooler at ~80% power.

Sure I find that two passes of DBE can be useful in heavily light polluted data like this, the first one with a higher tolerance, and a second with the default tolerance of 0.5. As the aim of DBE is to remove large scale gradients, I use 7 samples per row. More than this is generally unnecessary and can create some strange artificial gradient subtraction depending on the placement of your samples. Generally you want a sample size that is big enough to cover a decent amount of background (I wouldn't use below 10px samples), but you don't want to be struggling to find areas of background with no stars in. As the data is drizzled, and there aren't lots of stars in the frame, I used a sample size of 50px. I also reduce the minimum sample weight to allow the algorithm to pick and choose among the samples a little more than with the default settings. The first pass of DBE was run at a tolerance of 1.16 as shown below. This was the lowest I could get the tolerance while still accepting all of my samples. Finally, the correction mode was set to subtraction. For this image, the other default settings are appropriate and don't need changing. As seen in the background map produced, the process did a pretty good job of modelling the gradient in the image. This gives us a pretty good result, but there are still some traces of light pollution, particularly in the bottom right corner where it is strongest. For that reason, we run the same DBE process again on the new image. To ensure you have the same samples and settings as the first pass, you can drag the little triangle out from the DBE process window onto the workspace, close DBE, and then double click on the saved process icon with the new image open. HOWEVER, for the second pass, we change the tolerance value back down to the default of 0.5. This gives us better rejection between the samples and provides a better estimation of the background. If there are other gradients present in the image, then you can now move some samples to better model these regions specifically (note that if we are only dealing with light pollution, there shouldn't be any other major gradients). In this case I didn't move any, but you could add some more samples to the bottom right corner to help model the remaining gradient here if desired. Running this second pass only removes the trace of light pollution left in the bottom right corner, where it was worst in the original image, as shown by the background map here: The final image looks pretty flat, there is some large scale green/purple blotchyness that is common with OSC images, but that can be dealt with later in processing by darkening and desaturating the background. From here I would proceed with colour correction, noise reduction, stretching etc. Note that the image does not look very pretty here, but that is normal! STF is designed to show you everything the image has to offer by stretching the hell out of it. When you manually stretch, it will look much better. Hope this helps!

I'd pretty much agree with Dave's sentiment, you've got decent data here. However, it is worth bearing in mind that shooting broadband from Bortle 8 is never going to get you incredible results in a reasonable timescale (compared to a dark site). For reference, 20 hours in bortle 8 is approximately equivalent to only 1.25 hours in Bortle 1! This is typically why people tend to favour imaging in narrowband from light polluted areas; the gap between Bortle 8 and 1 is significantly closed when using narrow bandpass filters. It makes sense that after performing DBE you'll be able to see the noise profile of your image much clearer, as you've subtracted all that unwanted signal from the light pollution. On undersampled data such as this, DrizzleIntegration can help tease out fine details, especially if you have a large number of subs that are well dithered, but it will invariably add noise to the image. Whether or not you are willing to make this tradeoff is up to you and dependent on the image. All things considered you've got a good base to make a nice image from here, despite the challenging conditions! If you're interested in some further reading, this is a great article on SNR: https://jonrista.com/the-astrophotographers-guide/astrophotography-basics/snr/

I believe that most manufacturers use Aluminium as it's strong, cheap and light, but I know that LZOS uses a steel lens cell for maximum temperature compensation. Another user mentioned that TMB said that pinching should not be an issue with LZOS cells until around -30 degrees C (source). This had been called 'over-engineered' by some and aluminium tends to do the job just fine, except when it doesn't...

Have you changed your guide camera exposure time? Alternatively your guide camera / mount connection could be dodgy

It is worth noting that I used a dew heater on 100% for every single example I posted above, and it's hard to know for sure how much it really helped. I definitely think that my sample was an outlier in this regard as I've seen hundreds of images made with the esprit 100 that didn't suffer from this issue in the slightest.

Glad to hear it! Do let us know if the new scope performs any better

The FWHM is quite consistent over the frame, deteriorating by 0.5-1px in the corners, but this looks concentric around the optical axis so doesn't imply tilt to me. Eccentricity, however, drops significantly as you get out towards the corners though, and by looking at the offending stars it seems like a little more space is needed. Interesting that you're beyond the recommended distance already, what corrector is this? Also I assume you've accounted for filter thickness in your backfocus calculations?

Fantastic image! Based on this diagram it looks like you could do with adding a tiny amount. Your eccentricity looks pretty good across the frame, and only drops off in the extreme corners. What coma corrector are you using?

It's worth noting that this effect is very different to what we are discussing here and is caused by aperture masking. This has been modelled and explained by Mark Shelly in the following thread.

I agree that it is a terrible shame. The optics on my Esprit 100 were fantastic if it weren't for the pinching issue; I measured the Strehl ratio as 0.976. Interestingly enough the effects of minor pinching can be seen in the intra and extra focal images here. I don't recall the ambient temperature but it was not very cold, I'd guess ~10 degrees.

My Esprit 100 suffered terribly from this issue, and was even serviced by Es Reid to try and reduce the problem. However, even after having the lens retaining screws loosened, the pinching was still bad. The scope also developed a focuser fault, so I ended up returning it. The pinching was visible from temperatures as high as 15 degrees C (I never imaged warmer than this), but got much worse in the cold. The lowest temperature I ever used the scope in was -4.5 degrees C and almost every single star was hexagonal. The issue was also exasperated by me switching to a camera with smaller pixels early this year, and thus having a better sampling rate. Some examples (all at 1:1 except the first which is at 2:1): 15 degrees C ambient (Canon 6D): 8 degrees C ambient (Canon 6D): 7 degrees C ambient (Canon 6D): 5 degrees C ambient (Canon 6D): 5 degrees C ambient (QHY268M and 3nm Ha filter): -2 degrees C ambient (QHY268M and 3nm Ha filter): -4.5 degrees ambient (QHY268M and 3nm Sii filter): After this the scope was adjusted by Es Reid. The focuser subsequently packed up and I only got one night of imaging out of it, but here is an example of post adjustment pinching at 5 degrees C ambient (QHY268M and 3nm Ha filter): I feel like I certainly got a bad sample of the Esprit 100, as almost everyone else I've seen using it has excellent round stars. Rather than take the risk with a new copy though, I decided to go for another scope and see if that is any better (Askar FRA600). Sorry for the long post but I hope this helps Cheers

Thanks for the updated Ha stack @Grant, it is much cleaner and easier to process. Attempt number 2 with the new Ha stack follows. I tried to bring out a bit more of the Ha regions in this process, both in luminance and colour. Cheers

First attempt with this incredible data... It's great having some quality broadband stuff to work with Processed in PixInsight and Lightroom. Just a smidge of Ha was added using this method; the LRGB data alone looked great in the Ha regions so I didn't want to push it.

Congrats Ciarán for winning, well deserved if you ask me! Some great entries as usual. Looking forward to the next one already

My images in bin 1x1 are 51000kb. I am yet to use bin 2x2 and don't ever see myself using it to be honest

Nina Discord is the best place to go I'd say; it's quite possibly a bug somewhere that is a quick fix. I think you can turn off the automatic debayer in Nina to avid the error, but the FITS header will still say its RGGB or whatever it thinks it is.

You should also try updating the USB driver here. This should be incorporated into the AIO pack but some capture software has it's own SDK. Are you installing the latest driver into Maxim through the wizard?

This sounds like a lovely problem to have

Ah of course, my apologies I forgot you are using Linux. I'm sure the issues will be sorted out in time, but it might be worth pursuing the problem on the EKOS forum, I'm sure the devs there will be willing to help.

Hi Steve, I'd also recommend updating the QHY drivers to the ones I have linked above as it may be cause of your issues. Cheers