DSLR cooldown period?

[AndyUK]

Hi there - I'm only just getting into imaging and have assumed that if taking, say, 30s subs with a DSLR, I need to leave another 30s interval before taking the next one... Is this right, or does the chip cooldown quicker than this?

Obviously dark subtraction will probably take care of much of the hot pixels, but I just wondered if there was any particular guideline...

[George]

Depends on the DSLR, the Canon 300d & 350D both suffered from amp glow when doing long exposures over 2 or 3 minutes and benefited from a cool down between exposures. There's no hard or fast rule as ambient tempreture plays a part in how long between exposures. I found 30 seconds ample between exposures.

If your only doing 30 second subs amp glow shouldent be a problem.

The newer 1000D, 550D etc dont suffer from amp glow.

[brantuk]

30 secs sounds about right according to my info - check the Astronomiser website - there's a lot of very good and specific advice on dslr's there

[AndyUK]

Cheers both - With my 300D I've noticed quite a few hot pixels even with 30s subs. I haven't tried anything larger yet as a) I haven't attempted drift aligning yet I haven't PEC trained the mount, so I'm starting off with faster exposures and then intend to slow down bit by bit until I'm comfortable (and of course get to grips with a and b, although a guide camera would be nice )

It'll be intriguing to see how much of a problem the amp glow is and when it really starts cutting in - Sods law predicts that with my camera it will cut in sooner rather than later... so something else for the shopping list.

[themos]

Isn't it the case that what you want is steady conditions (no matter what the sensor artefacts are) for your lights and darks so that calibration can remove the artefacts? I'd say keep the interval short but take lots of subs before the main imaging run so that the camera has reached equilibrium . The darks are best taken in between the lights but if the temperature can be controlled they can be taken later, provided the camera has reached equilibrium.

My experiments with my 450D suggest that more than half-an-hour of shooting is required before equilibirum is reached. I was shooting one-minute darks, one after the other, and the statistical properties of the images were still drifting 30 minutes later.

[AndyUK]

Hi Themos - It's very interesting that you should mention this...

Last I night I took 165x30s subs (using a remote to set exposure duration, interval and number). Once I'd started it off, I left it alone to get on with some other work, periodically going back to check every 20 mins or so. I did notice on the screen that there did seem to be more hot pixels after about an hour or so, but assumed that the darks I was going to take at the end would sort that out...

With darkness currently being pretty limited (c. 11pm - 3am), I didn't want to "waste" the darkness by taking darks.

However, I can now see that I need to change my opinion on darks as obviously they are as important as the subs, especially when the ambient temp is changing - Thinking back, it did appear warmer when I started, but looking at the earlier frames didn't show as many artifacts as appeared about an hour later (which confirms what you've noted), and certainly there are indeed some pixels that aren't as strong in the darks I took 3 hours later (when it felt somewhat cooler).

Again, being new to this, I'm on a steep learning curve here, but I can certainly see the wisdom of taking a dark immediately after a sub in order to get it as close as possible, although in practice (as I don't really want to touch the scope too much), I guess I need to change my process and take them perhaps after every 5 or 10 images or so (and then it should be reasonably easy to pick them out later), and, as you've suggested, expect to throw away the first 30 mins lapsed time of frames prior to stacking...

Thanks again for your advice - I'm trying to get myself into a "process" mindset so that everything can be replicated each time, and this certainly helps!

[Psychobilly]

My Nikon D200 used to take about an hour for the ampglow to stabilise and needed a gap of about 50% of the sub length between subs...

The Canon 350D was similar but the glow was much more localised than the Nikon D200.

The 1000D and 500D only show glow if you use liveview...

All the cameras have benefited from being run fro external power supplies where the voltage drop is done "externally"

Roll on winter...

Peter...

[AndyUK]

Cheers Peter - I did order a power cable to attach to my leisure battery yesterday, so this may help a bit, but I'm getting the feeling I might benefit from a new camera... If just wish I could afford it.

As you say, roll on Autumn / Winter...

[Psychobilly]

Which cable did you get Andy (Astronomiser) now does them with the voltage reg in an external box rather than inside the battery housing... this has always seemed to be the right way to do it as far as I was concerned as any heat source inside the camera just adds to the noise...

Once I had the external supplies and wasn't limited by the life of the internal batteries , I used to start my camera taking shots (to be dumped) about an hour before I wanted to use it in anger to try and let it stabilise...

Peter...

[AndyUK]

Hi Peter - I didn't see that one on the Astronomiser site... The only one's I saw were the battery attached to a cigar lighter. I don't supposed you have a link for it, do you? I've just searched the site and couldn't find it anywhere. (I guess I could always email...)

[Psychobilly]

Try this one Andy..

Astronomiser - Automated Astronomy and AstroImaging Solutions

Peter...

[AndyUK]

B*gger...! I'll see if I can upgrade the order... Thanks very much!

[Beyond_Vision]

I agree with Themos you would want the temperature to stabilise. There is no advantage in switching off for a short time in between subs as the camera would not cool down by any significant amount.

I have never bothered having no more than a 10s second gap between exposure when using a timer remote. The 10s was only to allow the camera to write to the memory card etc.

Regards

Kevin

[AndyUK]

Hi Kevin - Thanks very much for your comment - Could the "wasted" subs be taken by setting up c. 30 mins earlier to use the twilight period to get the camera to equilibrium, or would the additional light at that time make any difference...? (My apologies if that's a silly question...!)

(Themos - I followed your advice the other night and took 10 before, 10 mid session and 10 after... The results were indeed much better - Thanks again!)

[Jangri]

Hello,

I just registered on this forum, because I have a "problem" that has been bugging me for a while.

Earlier this summer I went out at night to take some long exposiure pictures with my Canon 450D with a Transcend 16GB memory card (class 6 it says). (to make a timelapse of the milkyway from southern Norway)

I' had read up on the techniques on the interweb, and decided to take 30 sec exposiures with a 30 sec cooldown.

I rigged up my cam on tripod, and had a remote. The camera was set to 30 sec. exposiure.

And here's the problem:

When the cam had taken the 30sec exposiure picture, it said "BUSY" for over 30 seconds. I don't remember the exact time the camera was in busy-mode, but I would guess up to 45-50 seconds.

The weather was about 12-15 degrees celcius (rough guess).

But I have recreated the same problem in my livingroom, with camera at room temperature.

I would believe that this is not normal, and hope anyone here can tell me what's wrong?

Should I upgrade to a more "high end" memory card, or is there anything wrong with the camera?

[omneferuss]

sounds like 'in camera noise reduction' is going on..... check settings to see, and turn it 'off' if not required ?

[themos]

It's in the Custom Function menu II #3, from memory.