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I have struck apon a conundrum that affects us in the UK more than most, due to the shortness of our weather windows when doing DSLR AP.

I just had my camera in the fridge overnight to create a set of BIAS and DARK frames at 15C sensor temperature.

When I am taking 180 sec exposures over say 3hrs, to keep the sensor stable at  any given temperature I need to insert delays. 

I have roughly calculated the deltas based on some timings, I still need to do further testing to refine these.

- 30 Sec gives me a delta of + 12C

- 45 Sec gives me a delta of + 10C

- 60 Sec gives me a delta of + 07C

So this beg the question, with our weather limiting the time for exposure, is it better to get a set of images say 60, at a range of temperature (12C - 20C) or less lights say 45 at a stable temperature 12C?

I am sure there is some SNR that can help to determine when it is better to just capture lights say 20, whereas if you have the above scenario, it is better to sacrifice some lights for stable temperature and less noise.

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With my Nikon D200 I used to have to leave half the light exposure time or 30s  (whichever was the longer) between frames to get stable ampglow and even then it would take around 6 exposurees before it would stablise... 

My Canon 350D would need around 30s  and for  the 1000D and later Canons  I just used to leave about 5s  between exposures...

Peter...

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With my Nikon D200 I used to have to leave half the light exposure time or 30s  (whichever was the longer) between frames to get stable ampglow and even then it would take around 6 exposurees before it would stablise... 

My Canon 350D would need around 30s  and for  the 1000D and later Canons  I just used to leave about 5s  between exposures...

Peter...

Thanks, I will play with the timing and see what happens with 5s.

I get a stable temp on my 3rd exposure, first is very close to ambient second is about half way, then 3rd, 4th 5th will all be stable.

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When I started to use the Canon battery pack that attaches to the underside of camera I get almost no amp glow from the right hand side where the battery normally goes.

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My exif temps look pretty stable running my 1100D through APT, with only a small mirror lock pause - though perhaps this is lying to me.    I did see a post recently about internal battery discharge raising the temps on longer exposures, so have just sourced an external PSU.

Edit - sorry the deltas are usually around +10C above ambient, but usually achieves this in a few subs - I note ambient temps for darks and lights, rather than EXIFs and try to match these within 5C.

Edited by SnakeyJ

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When I started to use the Canon battery pack that attaches to the underside of camera I get almost no amp glow from the right hand side where the battery normally goes.

Agreed, i use a battery grip and it does seem to keep some of the heat away from the camera body it also makes any external psu mods easier (ext psu socket etc) because they can be done to the grip itself.

Alan

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Good point on the battery guys, I already use a power source adapter and have virtually eliminated battery glow.

To SnakeJ's point on continuous long exposures the sensor will run at +-10C above ambient, depending on the exposure length.

(I think the longer you expose the hotter it gets, but still need to get to grips with this.)

According to further calculation that I have done based on research from here (http://www.christoph-kreher.de/Astro/DC.pdf)

I have deduced the following table for the 600D sensor on when to use darks based on temperature.

Analysis on Temp, ISO and Exp seconds before dark noise appears. (excludes read noise which is always present.)
SN°C  I400,  I800,  I1600    I3200   I6400
0°       3494   1747   873.5    436     218
5°       1558   779     389.5    194     97
10°      714    357     178.5    89       45
15°      338    169     84.5      42       21
20°      164     82      41         20       10

The idea is to expose for as long as possible without introducing dark noise, so no need for darks as dark noise not present.

Based on this analysis if I could keep the sensor (SN) temp at 10°C, I could do a 357Sec exposure @ ISO800 with no need for darks.

Due to lack of Peltier cooling, the only logical way to control sensor temperature above ambient is to insert the delays.

i.e if ambient is Zero, then short delays needed as the sensor will run at 10°C above ambient.

But if ambient is 5C, then a 60 sec delay should do the trick.

Hope this all makes sense and I am not fooling myself into wasting exposure time, trying to control temperature, to avoid using darks.

(Will use bias instead as will still need to take out read noise.)

Dithering also introduces a delay that allows for cooling in between and allows for Cappa Sigma, so avoid darks.

Edited by Christopher Davenport
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I had a session of taking darks last night, just to see what happens with my 60Da.

I started around 1730pm and went through the night with various sub lengths.

Camera was connected to it's external power supply and was sitting on a small table

in the obsy, flip screen angled out, internal temp approx 7°C, outside it stayed around 5°C for the whole test..

I did a batch of 3min subs followed by 5min subs and then finally 10min subs.

The external timer was set with a 10sec delay, just enough time to download each sub to card.

So approx just the 10sec delay between each sub.

180sec subs

2014/02/09 17:32:42 10022014 006.CR2 B    180s ISO:800                Canon 60D Temp:10C
2014/02/09 17:35:52 10022014 007.CR2 B    180s ISO:800                Canon 60D Temp:13C
2014/02/09 17:39:02 10022014 008.CR2 B    180s ISO:800                Canon 60D Temp:14C
2014/02/09 17:42:12 10022014 009.CR2 B    180s ISO:800                Canon 60D Temp:14C
2014/02/09 17:45:22 10022014 010.CR2 B    180s ISO:800                Canon 60D Temp:15C
2014/02/09 17:48:32 10022014 011.CR2 B    180s ISO:800                Canon 60D Temp:15C
2014/02/09 17:51:42 10022014 012.CR2 B    180s ISO:800                Canon 60D Temp:15C
2014/02/09 17:54:52 10022014 013.CR2 B    180s ISO:800                Canon 60D Temp:15C
2014/02/09 17:58:02 10022014 014.CR2 B    180s ISO:800                Canon 60D Temp:15C
2014/02/09 18:01:12 10022014 015.CR2 B    180s ISO:800                Canon 60D Temp:15C
2014/02/09 18:04:22 10022014 016.CR2 B    180s ISO:800                Canon 60D Temp:16C
2014/02/09 18:07:32 10022014 017.CR2 B    180s ISO:800                Canon 60D Temp:16C
2014/02/09 18:10:42 10022014 018.CR2 B    180s ISO:800                Canon 60D Temp:16C
2014/02/09 18:13:52 10022014 019.CR2 B    180s ISO:800                Canon 60D Temp:16C
2014/02/09 18:17:02 10022014 020.CR2 B    180s ISO:800                Canon 60D Temp:16C
2014/02/09 18:20:12 10022014 021.CR2 B    180s ISO:800                Canon 60D Temp:15C
2014/02/09 18:23:22 10022014 022.CR2 B    180s ISO:800                Canon 60D Temp:15C
2014/02/09 18:26:32 10022014 023.CR2 B    180s ISO:800                Canon 60D Temp:16C
2014/02/09 18:29:42 10022014 024.CR2 B    180s ISO:800                Canon 60D Temp:16C
2014/02/09 18:32:52 10022014 025.CR2 B    180s ISO:800                Canon 60D Temp:15C
2014/02/09 18:36:02 10022014 026.CR2 B    180s ISO:800                Canon 60D Temp:16C
2014/02/09 18:39:12 10022014 027.CR2 B    180s ISO:800                Canon 60D Temp:16C
2014/02/09 18:42:22 10022014 028.CR2 B    180s ISO:800                Canon 60D Temp:16C
2014/02/09 18:45:32 10022014 029.CR2 B    180s ISO:800                Canon 60D Temp:16C
2014/02/09 18:48:42 10022014 030.CR2 B    180s ISO:800                Canon 60D Temp:16C
2014/02/09 18:51:52 10022014 031.CR2 B    180s ISO:800                Canon 60D Temp:16C
2014/02/09 18:55:02 10022014 032.CR2 B    180s ISO:800                Canon 60D Temp:16C
2014/02/09 18:58:12 10022014 033.CR2 B    180s ISO:800                Canon 60D Temp:16C
2014/02/09 19:01:22 10022014 034.CR2 B    180s ISO:800                Canon 60D Temp:16C

300sec subs

2014/02/09 19:04:53 10022014 035.CR2 B    300s ISO:800                Canon 60D Temp:15C
2014/02/09 19:10:03 10022014 036.CR2 B    300s ISO:800                Canon 60D Temp:16C
2014/02/09 19:15:13 10022014 037.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 19:20:23 10022014 038.CR2 B    300s ISO:800                Canon 60D Temp:16C
2014/02/09 19:25:33 10022014 039.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 19:30:43 10022014 040.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 19:35:53 10022014 041.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 19:41:03 10022014 042.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 19:46:13 10022014 043.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 19:51:23 10022014 044.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 19:56:33 10022014 045.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 20:01:43 10022014 046.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 20:06:53 10022014 047.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 20:12:03 10022014 048.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 20:17:13 10022014 049.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 20:22:23 10022014 050.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 20:27:33 10022014 051.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 20:32:43 10022014 052.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 20:37:53 10022014 053.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 20:43:03 10022014 054.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 20:48:13 10022014 055.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 20:53:23 10022014 056.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 20:58:33 10022014 057.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 21:03:43 10022014 058.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 21:08:53 10022014 059.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 21:14:03 10022014 060.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 21:19:13 10022014 061.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 21:24:23 10022014 062.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 21:29:33 10022014 063.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 21:34:43 10022014 064.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 21:39:53 10022014 065.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 21:45:03 10022014 066.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 21:50:13 10022014 067.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 21:55:23 10022014 068.CR2 B    300s ISO:800                Canon 60D Temp:17C
2014/02/09 22:00:33 10022014 069.CR2 B    300s ISO:800                Canon 60D Temp:16C
2014/02/09 22:05:43 10022014 070.CR2 B    300s ISO:800                Canon 60D Temp:17C
 

600sec subs

2014/02/09 22:11:37 10022014 071.CR2 B    601s ISO:800                Canon 60D Temp:15C
2014/02/09 22:21:47 10022014 072.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/09 22:31:57 10022014 073.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/09 22:42:07 10022014 074.CR2 B    601s ISO:800                Canon 60D Temp:16C
2014/02/09 22:52:17 10022014 075.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/09 23:02:27 10022014 076.CR2 B    601s ISO:800                Canon 60D Temp:16C
2014/02/09 23:12:37 10022014 077.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/09 23:22:47 10022014 078.CR2 B    601s ISO:800                Canon 60D Temp:16C
2014/02/09 23:32:57 10022014 079.CR2 B    601s ISO:800                Canon 60D Temp:16C
2014/02/09 23:43:07 10022014 080.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/09 23:53:17 10022014 081.CR2 B    601s ISO:800                Canon 60D Temp:16C
2014/02/10 00:03:27 10022014 082.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/10 00:13:37 10022014 083.CR2 B    601s ISO:800                Canon 60D Temp:16C
2014/02/10 00:23:47 10022014 084.CR2 B    601s ISO:800                Canon 60D Temp:16C
2014/02/10 00:33:57 10022014 085.CR2 B    601s ISO:800                Canon 60D Temp:16C
2014/02/10 00:44:07 10022014 086.CR2 B    601s ISO:800                Canon 60D Temp:16C
2014/02/10 00:54:17 10022014 087.CR2 B    601s ISO:800                Canon 60D Temp:16C
2014/02/10 01:04:27 10022014 088.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/10 01:14:37 10022014 089.CR2 B    601s ISO:800                Canon 60D Temp:16C
2014/02/10 01:24:47 10022014 090.CR2 B    601s ISO:800                Canon 60D Temp:16C
2014/02/10 01:34:57 10022014 091.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/10 01:45:07 10022014 092.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/10 01:55:17 10022014 093.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/10 02:05:27 10022014 094.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/10 02:15:37 10022014 095.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/10 02:25:47 10022014 096.CR2 B    601s ISO:800                Canon 60D Temp:16C
2014/02/10 02:35:57 10022014 097.CR2 B    601s ISO:800                Canon 60D Temp:16C
2014/02/10 02:46:07 10022014 098.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/10 02:56:17 10022014 099.CR2 B    601s ISO:800                Canon 60D Temp:16C
2014/02/10 03:06:27 10022014 100.CR2 B    601s ISO:800                Canon 60D Temp:16C
2014/02/10 03:16:37 10022014 101.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/10 03:26:47 10022014 102.CR2 B    601s ISO:800                Canon 60D Temp:16C
2014/02/10 03:36:57 10022014 103.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/10 03:47:07 10022014 104.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/10 03:57:17 10022014 105.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/10 04:07:27 10022014 106.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/10 04:17:37 10022014 107.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/10 04:27:47 10022014 108.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/10 04:37:57 10022014 109.CR2 B    601s ISO:800                Canon 60D Temp:16C
2014/02/10 04:48:07 10022014 110.CR2 B    601s ISO:800                Canon 60D Temp:17C
2014/02/10 04:58:17 10022014 111.CR2 B    601s ISO:800                Canon 60D Temp:16C
2014/02/10 05:08:27 10022014 112.CR2 B    601s ISO:800                Canon 60D Temp:16C
 

Edited by wxsatuser

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Nice Mike, Thanks for posting these.

Good stuff, it looks like the amount of time that the sensor is exposing does not affect the temperature for long exposure.

Although I did do 20 BIAS @1/4000 with 30sec delays and the sensor stayed at 6C through the run.

I had to fire up the live view for a couple of minutes to get the sensor to settle at 15C.
Then rerun my BIAS which then took at the correct temperature.

From memory on my dark run batch in the fridge set at 5C, ISO settings did not affect the temperature.

I ran my fridge 180 sec dark at ISO800, 1600, 3200 at 5C. Sensor temp stayed at 15C

So ISO and Exposure time does not affect temperature, once camera has settled at ambient + 10C

Now to fiq out how to reduce the +10C delta, I will continue to investigate.

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Holy smokes, guys!

This topic is not in my starter book however I am aware of sensor backglow or sth like that. Just throw me out already.

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