How long should I let my Canon 1000d chip coolbetween subs?

[Johnboy2011]

Can some one give me a pointer, should I let it cool for the same length of time as the exposure length or can I get away with shorter?

Thanks,

John

[MartinB]

Doesn't need to be the same time as exposure lengths. 20 seconds should do the trick

[Bizibilder]

When the outside temp is below 10-12 deg I just leave 5 secs between up to 5 min subs - I've yet to see any "glows". I have just taken a set of "darks" at 10mins and 12° C - These had quite a bit of redness showing when reviewing the subs as JPEG's.

[Sparrow]

I always used to just give mine 5 seconds but I have recently changed it to 20 seconds - I can't notice any great difference but to be quite honest - with the current temperatures, the subs are noisy anyway so well matched darks are an absolute essential.

The biggest improvement I noticed was when I started remembering to shut off the display on the rear of the camera - that has cut the noise down.

[swag72]

I leave mine for 1 minute between subs. Not long really when my last lot of subs have been between 15 and 25 minutes each!

[AndyUK]

After a little experimentation and review of EXIF data files, I've now settled on 30s. I used to think that leaving increasingly longer time would allow the chip to settle right back to the original starting point, but it would seem that whilst that may be the case, it would take a comparatively long time to get there... And especially at this time of the year, I'd rather be taking subs than waiting for the chip to cool right back down to ambient again.

I initially used 60s gaps with 600s subs, but found that even though the first one was at ambient temp, by the end of the 3rd ish frame, the temp had levelled out at ambient +10/12C, and even reducing the gap to 30s made no difference to the "end" temperature... and this was the same for any exposure (although with the lower exposures it took more frames to achieve the max chip temp).

So I now use 30s (but could probably come down to 20s...)

Although you're going to get more noise the warmer the chip temperature, of course the important thing is to ensure that the darks are taken at the same temp as the subs. Having discovered that the max chip temp levels out, I'm now trying to put together a library of 20 matched chip temperature darks for my standard exposures so that after completing an imaging run I can review the EXIF temps and select the correct exposure with the correct temp.

Another option (which Olly put me on to) to reduce noise in DSLR's is to get 2 or 3 of those flexible sports gelpacks and put them all in the freezer. You can then strap one of these around the camera (changing as necessary), but of course you'll still need the matched darks to go with it...