MartinB

This isn't something one reads very often on SGL!

Could you explain why? I've had my 2.7m pulsar for about 9 years now without a problem.

Ha ha! Imaging with a 200mm lens and the ASI 1600 feels like an all you can eat buffet! Attempt at imaging tonight being thwarted by cloud. Looked on Sat24 and, as usual, it looks crystal clear your way.

Thanks Rodd. I have a 50mm shot of Auriga and I might try to combine them sometime.

Thanks Vlav, agree with all that and you have shown nicely that read noise is doubled not quadrupled as I had suggested. The absolute value for read noise is related to gain of course. I also agree that binning doesn't increase the signal to shot noise ratio. Binning a CCD chip will deliver a larger benefit in improved SNR, because of reduction in read noise, than will binning a CMOS chip. This doesn't mean it's not worth binning with CMOS, in fact you are probably better off binning earlier than you would with CCD because of the pixel size. The low read noise and dark current advantages of CMOS aren't entirely lost when binned but when comparing CCD and CMOS there is obviously more to consider than read noise and dark current. I have a venerable QSI with a KAF 3200 chip. It has 6.8 micron pixels, a max QE of 87%, A full well depth > 60K, 7e dark current, just 3.2 megapixels, crude microlensing and a chip just a little smaller than my ASI 1600. I t couldn't be a more different chip to the ASI with very different characteristics but if I'm running my 10"LX200 it will still be my goto camera. In fact right now it is a clear night, my ASI is attached to a 200mm lens and my QSI is running on an FSQ106 reduced to F3.7. Despite the low count of bulky pixels I still think that old chip will do a decent job but I'd better go an check it!

The point about binning with CCD is that the read noise stays the same with binning but with 2x2 binning you are gaining four times the signal which is a major benefit especially when trying to capture very faint signal. When you bin a cmos sensor each pixel is read so the read noise is quadrupled, the final read noise will obviously depend on the gain applied. You could achieve a binned read noise of 3.4e but at the expense of dynamic range. An Atik one would have a binned read noise of 5e and a pixel size of 7.4, pretty handy for imaging at 1200mm. I am the proud owner of an ASI1600 and think it is a wonderful camera. I would happily use it at 1200mm but I don't think it fully matchs CCD at this focal length. However, a big apology...Peter wasn't asking for an opinion on CCD vs CMOS ! So Peter, please ignore all my CCD related comments!

The problem with small pixels at longer focal lengths is that atmospheric turbulence smears the signal across the pixels. The only problem with this is that you you don't benefit from the small pixel size and are better off binning your pixels. Unfortunately binning doesn't work as well with cmos as it does with ccd (the 4 binned pixels are still read individually so there is no reduction in read noise - low read noise enables shorter exposure times and gives increased dynamic range). For deep sky a ccd is probably still a better option for long focal lengths, but, as you have seen, results in practice often defy the theory!

This is true, which is why the op finds the choice perplexing! Other than very long focal lengths and assuming an adequate budget I am happy to recommend an asi 1600 pro or similar. Too many of these threads end up generating a lot of heat and little light. What are the principle issues that have been perplexing you Peter?

I have been deep sky imaging for 13 years and over this time have used a variety of cameras - DSLR, ccd, mono, osc. Recently I have been using an asi 1600 pro and wouldn't hesitate to recommend it to anyone. It's a contentious issue but I much prefer mono to osc. Why also make a very nice camera using the same chip.

Looks a very smart and well thought out piece of kit. I think it will be going head to head with something like the Canon 200mm F2.8 (which retails at around £700) which I am currently using with an ASI 1600 pro and EFW for wide field astroimaging. With the small small pixel size of modern cameras be they DSLR or astro cameras this focal length is extremely useful and permits lovely wide field views without sacrificing too much resolution, certainly a good alternative to mosaics. If I didn't have the 200mm lens (along with a x1.4 extender offering 280mm) I would definitely be interested. The Canon is an awesome performer though, even at F2.8, focusing needs some care and a steady hand but isn't too difficult. It isn't as sexy as that Red Cat though!

Thanks x6gas

The usual reason for not being able to merge the 3 channels to make an rgb is that one of the images is a different size or isn't greyscale.

Thanks Simmo and Thommy. I think the area you are looking at is probably being affected by the blue reflection nebulosity of the flame. Unfortunately I messed up the camera settings for the blue channel and the flame has come out very poorly. I suppose I should have done a separate blue channel process specifically to pull out the flame but it is so tiny with this FOV

With the cone as an example you can blend in blue using lighten to create a blended luminance. Blended luminance layers are particularly useful for narrowband targets with a lot of OIII such as planetary nebulae. I agree 50% will usually be a bit too much. My recently posted auriga Dso image used 45%, the Flame turned out duff but that is another story!

Thanks Des