Time between subs

[mynameiscd (Andy)]

Hi all,
Is there a golden rule to help how long the delay should be between subs to let the sensor cool.
At the moment i use 5 seconds between everything from lights, darks, flats, and bias.
I'm not guiding so im lucky to get about 2 minutes or less.
Im keeping it simple now so no laptop to see the temp on each frame.
What im trying to workout if i do longer subs then do i need longer cooldown time.
Im using a moded 450d

Cheers
Andy

[leon]

Andy,

It all depends on the ambient temp at the time, if it is very warm, less time for each image, if it is cold and frosty go as long a you want

5 seconds is fine but 3 is OK as well it all depends on how quick your camera can download the data.

I used to take a 300 second sub at 400ISO with a gap of 3 seconds for download than a 300second dark, and start the process over and over, using a Canon 5D.

That ended up being a 12 minute image

This can make it a long night, just to stand around in the frost , but the end result was worth it, I have some fantastic Deep Space Images.

I did over two night 37 images of Eta Carinea, and that is one of my best results but it was a total of 7.4 hours just standing around over that time frame.

At 5 seconds you will be fine.

Grab your self a nice bottle of red and enjoy the night unless you have to go to work early

Leon

[xelasnave]

How bad is your noise is the question?
Darks will help in any event.
I find a benefit of a less than perfect PA is that over many exposures you get an "automatic" dithering... and that helps with noise...but startools really helps with noise.
When I set up my widefield mount and camera I am going for a cool box for the camera and as I now have an intervalometer make the interval 30 seconds...because I can☺.

My suggestion is try a run with 5 second intervals, say 3 to check Leons advice☺ and maybe something longer and see if you can detect any difference....
Alex

[xelasnave]

And Leon I am not sure I approve of your suggestions to younger members to drink on the job...if one needs a way to "kill" time may I suggest doing something for ones partner to make their life more enjoyable or perhaps practice night gardening which would be good practice for later night gardening...not many folk do it these days but you can get so much done whilst the plants are sleeping.

Alex

[rcheshire (Rowland)]

Yes and no... longer subs will eventually warm the sensor as high as its going to get under the conditions. Which means the first few subs average temperature may be less than subsequent frames.

There are two ways of looking at the problem of getting reasonable average temperature consistency over subframes. The difference is that shorter cool down time increases the average temp over the subs compared with a longer cooling time - assuming that subs and delay are consistent and ambient air temp doesn't vary too much.

Some people advocate no delay whatsoever to keep the sensor at roughly the same temp throughout.

Take darks in the same way as the lights and if there are clouds, fit them in between holes to save time.

[mynameiscd (Andy)]

Thanks Leon, Alex, and Rowlad.
I use an intervalometer so a typical sequence is normally
5 sec delay start
60 sec shutter open
5 sec delay between
60 frames
I do this with lights only and with darks i cut to 20 frames.
These are done back to back
So with a sequence like this its only an extra 5mins for 60mins.
Im not really having a problem with noise but its just general question on how quick the rebound time is with older canon cameras is.
Alex its ok for Leons comment about having a red. I think there is nothing wrong to have a drop as long as it doesn't rule your life. Just checking and I've been sobber now for 1392 days now and there is one thing I still miss and thats being under the stars with a good drop of red.
I might try a demo night with shorter delays and longer ones to see if theres any difference.
Cheers all
Andy

[assbutt94]

I leave about 20-25 seconds between exposures, and always make sure the back screen is off (it will generate heat while on).

[Startrek (Martin)]

I’m using a Canon 600D with Stellarium, BYEOS for goto, acquisition, frame focus and capture
I find that the sensor temperature ( it’s actually the micro electronic chip board adjacent to the sensor ) increases dramatically when on live view for extended time during acquisition, frame and focus. When my capture plan is set with a 2 sec or 4 sec delay and pause taking say 40 x 2 minute subs, the temperature comes down slightly and stabilises through the early period / duration of the capture plan on a mild evening
I think the outside ambient air temperature is more of a governing factor when experiencing higher than expected camera sensor temperatures during your capture plan
I think if I set my delay and pause to 5 , 10 or 20 seconds during a hot summers night it’s not going to achieve much of a reduction ( ie: the use of extended live view initially heats up your camera very quickly and never quite recovers to an acceptable temperature )
My 2 cents .......

[mynameiscd (Andy)]

Thanks assbutt94 and Martin,
Im using my phone using DSLR controller so there shouldnt be a problem with live view creating heat.
Ill try 10 seconds tonight as its still about 22° and its going down to 13° minimum.
Im trying 90 second subs as soon as it drops to about 19° and see what happens
Thanks for the info about sensors.
Cheers
Andy

[Karlzburg (Karl)]

ISO choice will have an impact on sensor temp, I have run tests on my set up to see how much it can make a difference.
A 60 sec iso 1600 ran at 47 deg after I changed times and iso in APT I took a 180 sec iso 400 it came in at 33 deg. I found even between 400 and 800 there was sensor temp difference using the same times.
I use a 700D for imaging, it sucks a bit on high ambient temps but have worked out how to get around it without cooling and still have good sub times, depends on what I'm imaging on the night.
I use 4 sec delay between subs.

Karl

[rcheshire (Rowland)]

OK. More info. We are mostly thinking about the implications of the delay as astrophotographer's, rather than a technical requirement of the camera.

It takes several seconds to process a RAW file. Given the length of exposures it probably doesn't matter too much. A series of short exposures in quick succession would slow things down a little, though.