gorann

No astrodrkness for me, so I apart from mixing concrete to add a new pier to one of my obsies I have reprocessed some images. This one is 5 hours with my Samyang 135 f/2 captured in May with an ASI 2600MC and IDAS NBZ filter. I now looked in vain for any comparative wide field images of it, but could not find any (but I am sure there are some). It strikes me how much nebuosity it is around the major targets in this area - and if you do like I done here and lift the background a bit more than ususal with a curve there is no dark sky to be found at f/2. Cheers, Göran

Impressive Steve! So I downloaded the Star Tool trial and tried to fix stars in a RASA8 image (ASI2600MC with IDAS NBZ). I have zero experience with this program so I immedeately got stuck when I tried to make a star mask. The image was either all green or I saw no green. So nothing looking like a star mask. Before I make a major effort of figuring out how it works, I wonder if I could ask you to try the Star repair on my image. It has quite eggy stars in the corners, and if they can be easily fixed with this method you would have convinced and motivated me of making an effort to understand how to do it myself. So far I have been fixing eggy stars in PS but that is quite a time consuming process. The image (Sh2-160) has been moderately stretched, so it is not in the linear stage. Cheers, Göran 20220423-24 Sh2-160 RASA1 PS1(curves+GXMM+flipped).tif

Great result indeed! My only issue is the slightly confusing orientation. North is now to the right rather than up so I would rotate it 90°.

Yes, that is indeed impressive given your circumstances. I can understand that processing was a challenge, but those IMX571 cameras allow for great deeds.

Amazing, and I can see your point Steve but Hubble is shortsighted (like me) and where we will beat it every time is in wide field, like with a RASA, and even if we go close up with a SCT or 6" refractor we can chose objects Hubble has not done, and there is no lack of them. So, just stay out of Hubble terriotry, it is in any case rather narrow.

Looks very promising Rodd but as you say better seeing makes quite a difference at that focal length. Nights with average seeing I only do short FL imaging, and save the long FL for those rare nights with great seeing. But then I have the luxury of having both systems permanently set up. I can see that you hesitate to change scopes from night to night.

That is a striking image! I think I prefer the darker one: more dramatic as Olly said.

Perfect Olly! Here you really utilized the magic ability of the RASA to get the dark dust shining. Star XTerminator and Noise XTerminator are great for this type of targets and now constantly in my tool box. I do exactly as you to get the stars back but use blend mode lighten. I may try blend mode color dodge next time to see what it does. Like you I usually also give the stars a bit of gaussian blur. One problem I often run into with this method is dark ringed stars. If that happens I select the stars (Select -> Color Range) and widen the selction a few pixels and then use a curve to brighten the area around the stars. However, I cannot see that you had this problem with this image - stars look great (apparently even impressed Vlaiv😄). I just wonder why you did a two-panel mosaic and then cropped it back to the FOV of one panel? You ended up with the same FOV as I got with one panel on my go at LDN1251 with the RASA. Was it nothing more worth seeing? Cheers, Göran

Hi Miguel! Are you still happy with the camera? I am quite tempted by the price and have three questions: Does it have a heated front window? Does it have the HCG function that drastically reduce read noise at a certain gain (like the ASI and QHY variants)? Have you tried the Omegon software (Omegon AstroPhotoCapture) to run the camera?

Nice, especially for this time of the year. From memory I get a feeling it is a mirror image that should be flipped.

It is something you get with the ZWO and QHY versions of the latest sensors (IMX 410, 455, 492, 533, 571) and seen as a sharp reduction in read noise when you move the gain over a certain threshold. Something kicks in in the amplifyer. Not sure if it is built into the Sony chip or in the amplifyer used by the camera manufacturer. I use that setting all the time with my ASI2600 and 6200 to be able to get more subs out of a give time period and assume it will significantly increase my S/N I get that night. Here is what it looks like for your sensor on the ASI6200, so everyone would use the gain 100 setting. ASI and QHY give these curves for all their cameras (e.g, https://astronomy-imaging-camera.com/product/asi6200mm-pro-mono). ZWO writes "When the gain value is set to 100, the HCG high gain mode is turned on. We’re not saying it’s magic…but we’d like to think it is pretty close. With the HCG-mode turned on, the readout noise is greatly reduced, and the dynamic range is basically unchanged."

I do the opposit approach - I down sample when I am done with the image to a scale that does not reduce resolution. I tried a few times working on downsampled raw images and was not convinced it helped in any way, but....

This thread is getting more an more interesting and I look forward to ATIKs explanation of how it all works. It would be very odd if they did not provide the HCG option.

I like your version a lot Valiv! Detailed, soft and spoky! Why did you downsample it before posting? I like to zoom in, especially here where we try to see what we can get out of the data and learn from that.

Yes, but in no way as good pixels as in the IMX571 of the ASI2600 (or other brands with that sensor). You can always bin but I never found a need to do that. It is just no way the 071 can compete in image quality. I think the hang up on pixel size is a left over from the CCD era where pixel size was almost directly correlated to sensitivity. That does not apply when comparing CMOS sensors of different generations.

With astrodarkness gone up here now I could of course not resist your data - I knew it would be good as many times before, so thanks for posting it Rodd!

Rodd, maybe this one is more to your liking regarding the colors (tweaked the channel curves a bit).

Hi Rodd, Adrian @Adreneline is right, putting the stars back is a bit tricky. They easily get dark ringed (panda eyes), which I think looks awful, but I found various ways to fix that. The easiest (in PS) is to select all the stars (using Select -> Color Range) and then expand the selection (usually about 3 pixels) and feather it (1 pixel). Then I use a curve on the selection to brightenn the area (ring) around the stars. It may be necessary to do it selectively on different parts of the image depending on the background (nebulosity of dark sky). There is probably a similar way to do it in PI. Yes, Rodd, I was unsure about the colors. I did bring down the blue in the dark sky after I added the stars, but it can be easily adjusted up again if someone likes that better. I always found it difficult not to end up with a pink/mageta color on this nebula because of the Oiii shell around it. If I move it towards deeper red then the shell becomes less obvious also on the main part of the nebula and is mainly seen around it. Assuming it is the Oiii on top that Ha that turns the red to pink, maybe that is how it should be. Here is a tif file (16 bit since it is done in PS) that you can play with. As you say the image would probably benifit from being tuned down a bit, making it less contrasty, I just wanted to see how far I could go. Rodd NGC6888 HOO Gorans version.tif

Rodd, I had a go at your data using the h90 and o65 and started off as HOO and then tweaked the green towards blue as I am no fan of green in AP. After a series of initial stretches I made a starless version (with Star XTerminator in PS). That one was treated with the new RC-astro Noise XTerminator and then stretched and HiPass filtered (all in PS). I also used a bit of Topaz Denoise to sharpen it a bit and reduce the noise further. Then I brought the stars back at a reduced level (as a layer adjusted with a curve in PS). I also tried to fix the oblong stars in the corners a bit. Here are the starless and starred versions. I also added a less pink vesion. Cheers, Göran

I did not know this. I have used Star XTerminator for PS for a while and where is the image with just the stars? I use the original image for bringing back the stars (blend mode Lighten in PS). I think it is a great image by the way Rodd! But have a go at trying starless processing. It really helps getting the weak signals out. I could not live without it now.

With a dual band filter and an OSC you can pick that Oiii up. This is what I got with an NBZ dual-band (Ha+Oiii) filter (RASA8 and ASI2600MC) even under a full moon which is generally not great for Oiii (but OK for Ha). Cheers, Göran

Reagarding 071 vs 2600, you should go for the 2600. I had an 071 (now sold) and in addition to amp glow, lower sensitivity and more noise, it was also often fogging up. So I regularly had to take it apart to dry the silika pills inside in a microwave, and opening it up leads to dust paticles on the sensor unless you have a cleanroom. Never have had to do that with the three 2600 I now have. I also thought the 071 was discontinued (or soon to be).

You can tell the sofware running the CMOS camera to bin (e.g.2x2) and it will save smaller files. I do not do that since hard drives are cheap (on average I image 50 - 100 nights a year with two or more scopes with APS-C cameras each night and it still takes me 2 years to fill a 5 Tb harddrive that costs about 200 GBP). I guess I do not like the feeling of loosing data, even if I do know that it may be empty data and I may as well save binned data. Binned data is also faster to stack and process. But if I save it all then I have different choices of how to bin it, some better that other (Vlaiv tried to explain it once). What I do is usually to downsample the final processed image to a degree where I see no loss of resolution. I guess that is also a form of binning.

6 x 8 is better than 6 x 6. You should really consider building it yourself. I came up with an alternative roof solution for my obsies, which makes the build a bit easier. And it was later copied by my friend @wimvb

I have built myself three obsies here (I live on the contryside so garden space is no issue). Two of them are 250 x 250 cm and very convinient. Then I for some reason tried a smaller design (180 x 180 cm) on the third one and I regret it. Very complicated to move around in there, and a higher risk of disaster. So if you can find something bigger than 180 x 180 cm (6 x 6 feet) I would highly recommend it. Also, you may soon realise that your equipment will keep in a much better condition if you insulate the obsy and use a small radiator to keep it a few degrees above ambient temperature. That means less humidity, so no mold on the lenses, no corrosion of the mekanics, and humidity is not good for the electronics. But with a small obsy, adding insulation would make it even smaller.