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Yet another Deneb-region image


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Last night was my first time out with the new-to-me 50mm lens on the canon. The camera was mounted on the NEQ6, which was aligned using Polemaster. I spent a lot of time playing around, seeing what it would do, going up to a try at a 300s sub, but I was not really happy with the result of that, but when I get the guiding sorted out, that should improve dramatically. At least I got to see what a 300s sub under my streetlights could look like. I suppose inevitably, I found myself imaging the area around Deneb.

I am new to imaging on the NEQ6, and was a little disconcerted at first by how similar the subs were. That may sound a little strange, but I am used to imaging on an AZ mount, with less-than-perfect tracking, so every time a sub would download, the image would noticeably change. These didn't. I kept having to check the number on the preview dispaly to make sure that it was actually downloading the latest sub. I should make it clear that I am not complaining about this - it is clearly a very good thing, but will require a little bit of mental-adjustment on my part.

This is a stack of 16/20 120s lights (ISO 800, f/4) with a 15s gap between them, together with 10 darks and 50 bias, taken using EOS utils (I could not get ATP to play ball at all, although it worked well with the CCD a few nights back). The SQM reading next to the camera lens was 17.90 and the temperature was 26ºC.

The resultant image was processed in PS7.0, following the procedure as detailed in MEPC pp 116-124. I tried having a go at the 'second histogram stretch', but all my efforts made the image worse (IMO). If anyone wants to have a go, you are most welcome to try. This is 30% size of the original. I have also included corner sections at full resolution because, rather to my surprise after what I had read about this lens, it appears to have significant coma, particularly in the top two corners.

That said, I am reasonably happy with this as a 'first go' with the gear - these were also my first 120s subs - but, as always, I will welcome any constructive criticism of my efforts.

Thanks.

deneb 16 upload 30.jpg

lower left.jpg

lower right.jpg

top left.jpg

top right.jpg

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Thanks, Pete.

I didn't try any at f/1.8 - what I had read suggested that that would be bad, f/2.8 would be somewhat better, but that f/4 would be "excellent". Mmm.

The 300s sub was not so much orange, but just very "bright". No doubt a consequence of the streetlights now being white instead of orange. I have attached a jpg 30% version for you to see for yourself. I guess given enough of them they could be made into something, but I am of the opinion (atm) that if I am going to have to take the same number of 5-minute subs to get a similar result as I get from 2-minute subs, that could be rather time-inefficient. Maybe more experienced imagers can see more potential in this sub than I can at present.

Thanks.

IMG_0009.jpg

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Here's your single sub with just DBE and dark point adjusted, but no other process applied. Processed in PixInsight.

denebdemonperformer_DBE.png

One image says more than a thousand words: Great*1000

Longer subs DO make a difference.

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Wow. Even allowing for my inexperience at processing my original batch, that certainly gives me reason to consider a batch of 300s subs when I get a chance.

In addition, I can now have a go at the 300s sub myself and see if I can get anything like the result you have. Knowing, and being able to compare with, what you have achieved, I can use this as a learning exercise, with your result being 'the answer at the back of the book'.

Pardon my ignorance, but what exactly is 'DBE'?

Thanks.

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DBE = dynamic background extraction, is a process in PixInsight for removal of gradients, vignetting, etc. It works so well that some astrophotographers buy PixInsight solely for this tool.

There's also another tool in PixInsight, called ABE = automatic background extraction, similar but less user interference required.

 

If you can get some 30 - 40 subs like these (300 s), you'll have the data to create a winner.

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On 27/08/2016 at 16:33, Demonperformer said:

Thanks, Pete.

I didn't try any at f/1.8 - what I had read suggested that that would be bad, f/2.8 would be somewhat better, but that f/4 would be "excellent". Mmm.

The 300s sub was not so much orange, but just very "bright". No doubt a consequence of the streetlights now being white instead of orange. I have attached a jpg 30% version for you to see for yourself. I guess given enough of them they could be made into something, but I am of the opinion (atm) that if I am going to have to take the same number of 5-minute subs to get a similar result as I get from 2-minute subs, that could be rather time-inefficient. Maybe more experienced imagers can see more potential in this sub than I can at present.

Thanks.

 

Quote

 

Unfortunately all lenses are not the same, even expensive ones vary.

Generally f/4 is the sweet spot with minimum abberations, some really good ones just about cut it at f/2.8.

The general rule for exposure, for your sky conditions and camera settings, is to expose so the in camera histogram peak reachs
at least 20%. A range between 20 and 40% is normally ok.

What camera lens are you using?

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