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Old 12-03-2008, 05:33 AM
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skwinty (Steve)
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More noise from a blunt tool

Herewith another pdf as promised to Baz and Fred.
see deep space and Centaurus trifid thread.
Regards
Steve

Last edited by skwinty; 14-03-2008 at 05:11 PM.
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Old 13-03-2008, 09:11 AM
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Interesting document.

Thanks, I've printed it off.
Geoff
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Old 13-03-2008, 09:19 AM
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RB (Andrew)
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Some great info there.

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Old 13-03-2008, 04:08 PM
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Thanks Steve, very clear and easy to read.
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Old 13-03-2008, 04:13 PM
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Thanks all for the comments.
Will do more of these as I progress through the learning curve.
Regards
Steve
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Old 13-03-2008, 04:32 PM
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Steve, I might say though, the statement "Dark 5 times the total image integration time" just isnt viable these days, not even 2 times.

I sometimes and many imagers now image (especially NB) to a total of 5 or more hrs per filter. A 25 or even 10 hr dark is just rediculous. I have found 10 stacked dark subs at the same exposure as the image subs is about as far as you need to go (youd be hard pressed to see much difference in more than 3 dark subs), regardless of total image time. The noise reduction acheived in the dark past 10 subs fast becomes a case of diminishing returns, cant see the point in much more than about 10 subs.
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Old 13-03-2008, 05:24 PM
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Hi Fred
I agree. A 1 hour exposure and a 5 hour dark is excessive.
I suppose it depends on the amount of noise obsession you suffer from.
If you look at the icnr of the latest DSLR's then if you do a 30 min exposure the icnr will do a 30 min dark. I see that as a minimum.
I do also understand the point of dark frames exceeding the exposure time as the thermal electron generation varies from about .001 electrons/pixel/sec to about 30 electrons/pixel/sec depending on type of sensor and whether its cooled or not.
I think however that when you are shooting very faint DSO's where other noise dominates and buries the signal then you might be forced to go to these extremes.
My approach to this, as i use track and stack with short exposures is , if I shoot 60 second subs then I will do a few 120 to 300 sec darks, combine these darks into a master dark and use the master.
I will investigate this issue futher and post further comments as the rationale and math behind this approach is quite comprehensive.
Regards
Steve
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Old 13-03-2008, 05:40 PM
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Steve, I really am not sure why you would expose 120-300 sec darks (or do you mean 60 sec stacked subs) for a 60 sec image sub. Hot pixels in long exposure darks, if stacked sum for example, would not match hot pixels in the image subs. Stacking software will adapt to different exposure times, but I dont get the point, why not stack like for like exposure times, this would reduce noise and leave hot pixels at the correct level.
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Old 13-03-2008, 05:51 PM
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Thanks for the .pdf. ALthough i have to admit i shoot "ALL" my images in .jpg so sue me

Now go out there Steve and take some shots. will be good to see some unknown objects from your sky.
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Old 13-03-2008, 05:58 PM
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Holly cow Eric, you serious, Im stunned, amazing results with lowly JPEG then, cant believe it
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Old 13-03-2008, 06:07 PM
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Eric!? What!? jpeg? Shoot RAW you lazy so and so! Your images will improve even more!
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Old 13-03-2008, 06:11 PM
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LOL you guys have no idea how many times i get flamed for shooting my images in RAW. ... i guess laziness plays a huge part and how easy it is to play with .jpg files than RAW. yess im guilty now and will shoot in RAW when i get a new camera
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Old 13-03-2008, 08:19 PM
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Hi Fred
Sorry took so long to reply but had to rush off to the nuclear power station down the road.
I work for Nuclear Consultants International.
No major problem at the power station. I like to call myself an Unclear Engineer.
Will read some more tonight and post some tomorrow.
Regards
Steve
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Old 13-03-2008, 09:35 PM
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Hi,

I think when they say take 5 times as long darks as lights they dont mean take one dark 5 times as long they mean take 5 darks as long as the light.

If you go longer then you will get a different hot pixel response and would be removing good data because the dark would have many many more hot pixels.

You stack images to average noise and you should also stack darks to average noise as well.

If you go longer DSS for example will try and scale but this is not optimal.

Paul
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