The Crescent Nebula and M33 images - taken using SGP

I’ve been using SGP for a few months, and have been lurking around the forum, but have only just joined the forum,so I wanted to say “Hi”. I live in Somerset in the UK and run a Tak FSQ106ED on a 10 Micron GM1000HPS mount with an Atik 460ex mono camera in a 7ft diameter observatory.

Here are my most recent images - all taken through gaps in the seemingly never ending cloud we get here in the UK:

Hope you like them.



Beautiful work! Hard to believe that you took those images with a 4 inch scope! The new sony CCDs are excellent tools!



Agreed, well done Steve.

Thank you Jose and Joel - I’m pleased you like them.


Nice pictures!

Beautiful images, especially the Crescent (with the Soap Bubble - fantastic!).

Can I ask a couple questions about your technique? First, you used darks. I use them with my SXVR-H694, but this is the first time I’ve heard of anyone else using them with an ICX694-chipped camera. The common wisdom says this chip needs no darks, though my 20-minute NB subs clearly benefit from them. What is your experience?

Second, 45 minute subs! How close is that to sky limited?

Again, really beautiful work.


Many thanks!

Hi Kevin. Thanks for your kind comments.

In answer to your questions - I always use darks, bias and flats. I did a comparison with some 45min HA subs last weekend of the difference between dark,bias and flat calibrated, dark, super bias and flat calibrated, bias and flat calibrated, super bias and flat calibrated and flat only calibrated…and the difference was very marginal indeed. It came down to a qualitative visual judgement and I went for dark, bias and flats as the “slightly smoothest”. Incidentally each of these combinations used identical dithered frames, the same preprocessing script and the same image registration and integration settings in Pixinsight.

The only reasons I’ve decided to use darks is that, when you get up to 20 odd 45 minute subs; anything you do is, in my opinion, going to offer marginal benefits …and so long it doesn’t make matters worse - why not use darks? The other thing that I found interesting was that the real difference was in the PI pixel rejection maps in Image Integration - the non dark version clearly showed the differed hot pixels and were more of a snow storm when stretched. To me, this shows that the Winsorised Sigma Clipping and darks both work well with 20 frames!

Sky limited - I don’t know is the honest answer - I just make a judgement of the risk of wasting a huge amount of time if a sub goes astray against the benefit of going deep. So long as only the centre of large stars saturate - I’m happy.

I’ll read up on what Sky Limited really means, but I think it relates to Camera Gain and A-D conversion stuff??

Hope this makes sense and thanks again for your nice comments.


Thanks for the details, Steve. I keep telling myself that I’m going to move to PI . . . any day now! I’m replacing my processing PC in the near future, so I think “any day” is rapidly approaching.

“Sky limited” here would mean that the shot noise component of an image is much higher than the read noise component. If it is, you don’t gain much from longer exposures, and since long exposures are more vulnerable to bad things like airplane trails you may as well stick to the shorter ones. Shot noise is closely related to light pollution, and I’m not sure how long my NB exposures would need to go to be sky limited. I’ve never really analyzed mine, just kind of settled on 20 minutes by default. OTOH, judging from your images, I’m probably telling you stuff you already know. :smile:


Cheers Kevin - thanks for the first explanation of sky limited that makes sense!:smiley:

I don’t know if it’s ok to discuss other software on here, but I guess that since SGP is capture and PI is processing it’ll be ok. If it isn’t - sorry!

Anyway - I think PI is superb - make sure you get a 64 bit machine - they don’t support 32 bit anymore, download the free trial and watch Harry Page’s videos.

It’s a real learning curve, but well worth it. I only use SGP, PI & PHD2 these days - there’s no need for anything else in my opinion.


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Welcome and Great Work!..