Darks and Exif readings

[Carole]

I have got myself an EXIF reading bit of software, plus starting to use APT and that gives Exif readings provided you keep an eye on the screen (it doesn't seem to save them).  However I have noticed great variations in temperatures and I just wondered how reliable these readings are.

Am planning to start measuring my darks and light temperatures, but what do you do if the temperature varies throughout the session:

Just average them out?
Or do different stacks to match the lights and darks and then stack the stacks.  
If the latter it seems a bit laborious.

Having had a few problems with poorly matching darks in the past, am trying to improve things.

Carole

[The Thing]

What do you mean - "EXIF readings"? APT reads what is stored in the EXIF header in the file saved from the camera. It can read the EXIF temperature if the camera stores it in the image (350D doesn't, I think 450D and up do). This is the temperature of the CCD. N.B. EXIF data is stored in the image so APT doesn't need to store it again. Most image software e.g Photoshop, Windows, can read and display EXIF data and some will let you edit it as well.

APT can be set to add the temperature to the file name so if you do lights and darks you can match the temperatures easily.  If you have a 350D like me you need a TemperHum USB gadget to sense the temperature so APT can ad it to the filename.

BTW In Deep Sky Stacker I have found I need to go into the processing settings (bottom left) and set the Dark Multiplication Factor to around 3.0000 to get the software to subtract the darks correctly.

[MarkS]

BTW In Deep Sky Stacker I have found I need to go into the processing settings (bottom left) and set the Dark Multiplication Factor to around 3.0000 to get the software to subtract the darks correctly.

Sounds a bit odd?
But then again I've never really got on with DSS.

[Carole]

Some useful info there Duncan, but until I got this Kuso EXIF viewer, or used APT I have no way of tellings what the sensor temperature is, it doesn't show that info in Canon Utility or Photoshop as far as I am aware, or if it does I don't know where to look for it.

APT can be set to add the temperature to the file name so if you do lights and darks you can match the temperatures easily. 

That would be really useful, must find out how to do it.

However, this still doesn't explain why images done consecutively can vary so much in temperature.  A little while ago I did some experiments with my DSLR Coolbox (which I have not got around to using on an image yet) and did some darks in APT and then immediately afterwards did the same length and ISO subs in Canon and then read the Canon results in KUSO EXIF reader and there was a sudden change in termperature of several degrees.  Plus erratic changes in runs of subs.

Carole

[MarkS]

A little while ago I did some experiments with my DSLR Coolbox (which I have not got around to using on an image yet) and did some darks in APT and then immediately afterwards did the same length and ISO subs in Canon and then read the Canon results in KUSO EXIF reader and there was a sudden change in termperature of several degrees. 

Remember it is quite normal for the DSLR CCD to heat up during a run of long subs.  They can easily warm up by 15C or so during the first hour of an imaging session.

Mark

[Carole]

Remember it is quite normal for the DSLR CCD to heat up during a run of long subs.  They can easily warm up by 15C or so during the first hour of an imaging session.

Yes but they were going up and down, and varied when I changed the software.

I'll see if I can dig out my chart which I think it on my laptop.

Carole

[mickw]

I'm sure if you have Canon Camera Raw installed you can see all the exif data if you just move the mouse over the file.

APT reads the temperature from a remote sensor (TemperHum) so will read ambient temperature not sensor temperature - always locating the sensor in the same place helps.
I assume that there is a corelation between ambient and sensor temperatures when taking exposures of the same length with the same pause between them which should give an indication of "subs at the same temperature"

What software are you changing ?  If you are changing the capture software, are the capture/pause settings identical

[Carole]

The two capture software were Canon Utility and APT.
I had to read the Canon temperature via Kuso Exif and APT by it's own EXOF readings.

APT reads the temperature from a remote sensor (TemperHum) so will read ambient temperature not sensor temperature

Hmmm, so that's not a true reading then.

So looks like the Kuso EXIF readings will be the most accurate as they are taken from the file info, so glad I asked this question.

Thanks Mick

[mickw]

Just been through a whole bunch of images from me, Carole, Robert (to cover assorted Digic) and can't find any reference to sensor temperature in the Exif

Where is it hidden ?

I have got "view full info" ticked

[Carole]

Sorry, where are you looking Mick?

Carole

[mickw]

Load file into Kuso and read the info

[Carole]

If you're looking at stacked images, surely that wouldn't work as it's lots of images possibly at different temperatures.

Anyhow, individual subs in Kuso Exif it is in the second batch of data under Camera temperature.

Carole 

[mickw]

Doh

OK, I looked at MY images again
No reference to Camera temperature - must be a Digic 3 thing 

Been thinking though, if you are trying to get darks at the same temperature as the lights you're not going to know until you've taken them, plus you should really ditch the first couple of darks so the camera can get up to speed.  Unless you intend to check the temperature of every dark and light then batch them accordingly.

I'm beginning to think "ambient" is good enough for me, either that or a cooled camera

[Carole]

Been thinking though, if you are trying to get darks at the same temperature as the lights you're not going to know until you've taken them, plus you should really ditch the first couple of darks so the camera can get up to speed.  Unless you intend to check the temperature of every dark and light then batch them accordingly.

Yes I did go through every darks and lights on this occasion and read the temperature, but ended up with hardly any of the darks actually matching the lights, so had to go for average anyway.  I guess I wa really doing a bit of experimenting.  But at least I can now create a darks library with the correct temperatures.

I am starting to think the only way to get it spot on is by doing autodarks.  Will see how things pan out. 

Carole