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7Hrs 35nm Ha BCF modified 1000D

Psychobilly

By Psychobilly
in Imaging - Deep Sky

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Psychobilly

Psychobilly

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Megrez 72 with FF III 35nm Ha + IDAS P2 Filters on CPC 800 XLT Guided 500mm f8 PHD Guide 1.10.10a (Beta)

28x900s @ ISO 800 Lights (Kappa Sigma Stacked)

63 Skyflats (Kappa Sigma Stacked)

63 Bias Frames (Kappas Sigma Stacked)

0 Darks - I find they make matters worse with the 1000D

Stacked in DSS , Post processed CS3 with Noel Carbonis Astro Actions (False Ha) and Peter Shahs Star reduction (1 pass)

NGC7000-IC5070_28x900s_FalseHa_PSSR_QS.jpg

Fullsize Jpeg (7.1MB) Here..

Half Size Jpeg (2.2MB) Here...

Now I'm going to get some sleeeeeeeeeeeeepppppppppppp....

Peter...

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Psychobilly

Psychobilly

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Probably another 7 hours or so tempted to drop the ISO and go for longer subs for richer colour as well...

None of my existing dta nad I have a lot of it is up to beign added to this... the best data is very poorly framed witht he pelican onthe right edge... the data with similar framing is way to "shallow" and needs to be stretched too much... so thats not really worth adding either ... and its all post mount rebuild so the tracking andf guiding isnt as tight...

I may add some Monday or Tuesday night as I have a few other HA targets to image this weekend...

I also have every stack of this data set so may produce a composite crop showing the same region with 1,2,4,8,16, and 26 subs...

Peter...

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Aza

Aza

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I think its worth doing the new data then. With 7 hours RGB you will end up with a stunning image. I know what you mean though, too many targets and not enough time :)

I also have every stack of this data set so may produce a composite crop showing the same region with 1,2,4,8,16, and 26 subs...

This would be interesting. Do you mean to show the difference in image quality between the amount of subs? All processed the same or something?

I did something similar the other day:

Comparison Tests - Astro Photography by Arran Hill- powered by SmugMug

(of course it needs to be viewed in the original full size though to see the differences)

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Psychobilly

Psychobilly

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Thanks for the comments...

I have been looking at the weather forecast so I have decided to start on the colour for this one tonight... At least it an easy target as far as dome slews are concerned so I will get some sleep...

I am hoping 14 hours will be deep enough for me to leave this target alone until next year...as I am obsessed by it....

Peter...

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richardc

richardc

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that is looking sweet!

Comment on subtracting darks;

when we subtract darks what we are doing is removing dark fixed pattern noise. Some call it "despiking" the image (janesick: "Scientific Charge Coupled Devices" SPIE Press)

there's a spec for the sensor called Dark Signal Non-Uniformity (DSNU) that is a constant that quantifies the difference in dark signal from pixel to pixel. When we dark subtract we remove those "spikes".

but we also introduce additional dark shot noise because the darks have a shot noise in them and that is subtracted from the light frame and increases this random noise.

So the fix for that is to reduce the random noise in the darks and we do that by averaging a large number of them noting that the random (not fixed pattern!) noise decreases by the square root of the number of exposured so averaged. So for a 2x reduction of random noise it take 4x the exposure count.

So the main knobs we have to do this are cooling and the number of darks used.

when you said that subtracting darks makes matters worse, how many darks were combined for the master dark before subtracting out of curiousity?

if the sensor has very low DSNU (Kodak spec is 100% so they need dark subtraction) then there's no good reason to subtract the dark spikes. The Sony interline sensors are good in that measure: far better than Kodak in that one spec but sort of fall apart in other ways (resolution, QE for example).

I just thought it was worth mentioning this so that those who are curious about such matters will be properly informed as to the mechanisms at play.

rdc

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Psychobilly

Psychobilly

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Thanks for the science Richard...

I just go with what works for me and my setup with the minimum of effort... if the result looks fine to me i dont bother spending ages grabbing dark frames rather use the time grabbing lights... especially when the end result is going to be a 800x563 8 bit jpeg image... posted on a website...

Paul used to give us an insight into the wonders of the various CCD noise sources in the past... Now we are getiing it straight from the Master :)

Typically my master flats will be made from up to 100 frames as will my master bias...

Peter...

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richardc

richardc

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100 frames sounds more than sufficient. I assume there's no thermal regulation in the camera. is that correct?

if so that's probably why the darks make matters worse; no guarantee they were shot at the same temperature as the lights and no guarantee the lights were each shot at the same temperature

one thing about the DSLRs versus astrocams: they have to be capable of giving good results with a single exposure, although perhaps at a high average signal level. That means that the photoresponse non uniformity and the dark signal non uniformity both need to be controlled reasonably well in the wafer fab (processing issues).

That means you may find those sensors do better than the traditional scientific sensors in those spec areas. there's enough collective volume on them since so many consumer cameras are sold, so they can justify the fab and processing tweaks needed to do that.

Key to minimizing the dark spikes is very clean wafer processing that particularly getters out the metallic ion contamination that contributes to dark spikes.

DRAMs are also very sensitive to the same sort of contamination and for the same reason

Anway some may be interested in this stuff so that's why I post it.

rdc

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Psychobilly

Psychobilly

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I didnt say I want interested far from it as I come from an Electronics Backround and have spent a lot of time working on SS and flashlamp pumped laser design (Dye, ruby and Nd:YAg) ... and the like of CVI Tech Optics on custom optical interference filter design...

It just that my practical excperience with my camera they way thay I use it I get the results i want without darks... noe if it was the 350D then its a whole different ball game... and they are essential and need to be very carefully matched ... which is why i have stopped using it...

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