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Old 04-05-2008, 07:23 PM
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[1ponders] (Paul)
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Interesting comparison. 20D (M) ICNR & none

I thought I'd have a bit of a look at the difference between images taken on successive nights at the same ISO (800), exposure (5 min) and very similar temperature (12-13deg) and compare In Camera Noise Reduction and using no darks at all. The results are impressive. These are zoomed in screen captures of the final processed tiffs, number 1 - no darks, number 2 - ICNR. (and yes I know the stars look different. ) Neither has had any sort of after camera noise reduction applied.
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Old 04-05-2008, 07:37 PM
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EzyStyles (Eric)
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excellent comparison Paul. ICNR definitely a winner here. With me, i guess im just too lazy to do twice the length of exposures as I always want to capture as many images in 1 night as possible thus i use master darks instead. LOL
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Old 04-05-2008, 07:55 PM
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[1ponders] (Paul)
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I can totally agree with you there Eric. I don't think I'll continue with the ICNR for much longer for that reason. What I need is a second camera so that I can image with one, take flats, remove it and set it to take darks at a comparable temperature to the lights. In the mean time put the second camera on the scope and start it taking lights and keep rotating them during the night.
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Old 04-05-2008, 07:56 PM
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[1ponders] (Paul)
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Hey I do have a second camera! Time to get the 300D modded
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Old 04-05-2008, 10:21 PM
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Good idea Paul that way, you certainly won't miss the time while taking darks on one camera, use the other to capture more photons. I think having a twin setup of 2 x 20D's modified will be ideal
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Old 05-05-2008, 03:48 AM
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Quote:
Originally Posted by [1ponders] View Post
I can totally agree with you there Eric. I don't think I'll continue with the ICNR for much longer for that reason. What I need is a second camera so that I can image with one, take flats, remove it and set it to take darks at a comparable temperature to the lights. In the mean time put the second camera on the scope and start it taking lights and keep rotating them during the night.
What a good idea. It's sort of expensive but takes all the pain of waiting around for ICNR to complete.

Paul
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Old 05-05-2008, 07:27 AM
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I always use ICNR for one simple reason. The night temperature in Melbourne can vary by as much as 15C over a night. This can also occur over just a few hours! It is impossible to get any sensible result with a library of darks.

ICNR beats the use of darks even if the temperature stays relatively constant.

To show how critical temperature is take a set of exposures with ICNR on after the camera has been on but idle for at least 10 min. Then look at the exposures just the jpgs will do. You will see your first exposure has dark holes that are deeper than the subsequent exposures. What has happened is the sensor had heated up by 2C as the first exposure was being taken due to the sensor and associated electronics consuming more power. So the ICNR 'dark' was actually taken 2C above the first light and the subtraction then caused darker holes due to the small difference in temperature.
If you do this from cold the sensor heats up by 4C! That is 2C rise from off to on and another 2C while taking long exposures.

I have now got my fridge working quite well and the next step is to control the temperature electronically. This is not easy with Peltiers but it can be done. Until this happens I will stick with ICNR.

Bert
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Old 05-05-2008, 07:37 AM
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I know what you mean about temp drops Bert. Where I lived before the temperature was fairly stable and only dropped slowly during the night (a couple of deg every few hours). Where I am now the temp can drop pretty quickly, but once it gets down it stays down so it does make a big difference during that critical drop period.
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