dark frame library ?

[Jockinireland]

I am thinking of setting up a dark frame library for each of my 2 Canon EOS 1100d cameras.

I do understand what dark frames are and how to take them. Its just that my time with a clear sky is so limited I hate having to put so much of it into taking darks. I cant always wait till moroning and anyway, temperature can be a problem doing that.

I'd therefore be interested to hear your experience or thoughts on the limitations of doing this. Particularly;

• I know the sensors will change over time and darks from today will eventually become obsolete - but over what time period would you think that would be?
  I know darks must be the same time, ISO and temperature as the lights but how accurate must this be for temperature - can I group sets of +/- 1 degree, 2 degrees or????, and what range is acceptable to applying those to lights +/- 1 degeree, 2 degrees or????

Thanks

David

[KathyNS]

The darks for my DSLR are classified according to the nearest 5 degrees Celsius. They are also very out of date, since I retired that camera several years ago! Darks are usually good for six to twelve months. You don't want to go longer than that in case you have new hot pixels developing as the sensor ages.

It is a bit easier archiving darks for a cooled camera, since I can preset the desired temperature.

[UlteriorModem]

Why waste good clean nights taking darks? In fact bad nights are the perfect time to collect calibration darks and bias!

Just put the camera in a cool dark place with the dust cover on it and do it indoors at your leisure, day, night, rain or shine

I used to put my cam in an ice chest with a grill to hold it up off the bottom. Sometimes would put a cold pack in there to try to get close to temps required.

[JayTee]

I do all my darks indoors, as you said, dark sky time is so precious. For the warmer temperatures I put my camera with the body covered in a dark closet and shoot my darks there. For colder temperatures,I use a Ziploc bag, the refrigerator, and an intervalometer to get the correct temperature range and exposure duration, etc.

It's all very logical to me, but my wife thinks I'm a bit odd.

Cheers,
JT

[Juno16]

Anyone have a similar process for Nikon (D5300) that does not divulge the sensor temperature?

I have read online lots of imagers using the D5300 that don’t shoot darks at all. I haven’t been that brave yet, but I guess that I could reprocess some data without darks.

Anyone here with any experience?

Thanks,
Jim

[goldstar]

Yes my wife thinks I'm a bit odd too. I often put my Canon in the fridge, freezer compartment or outside or in a cool box and snap away.
There is no way to regulate the temperature but as the camera warms and cools there is a large range of temperatures that can be selected into a dark library of ranges and as Kathy suggests a band of 5 deg C seems good enough.
If the camera is able to record and display the internal temp (mine can't except when I use IRfan prog to see it. Why doesn't Canon make this available in it's own SW?) then just set it up on the intervalometer and fire away for hours on end in a variety of cool environments.
A satisfying use of non-sky time. No frame is wasted. You will always find a dark temp to match your lights.
Unless, occasionally, like me the outside ambient temperature falls to below the temp of my freezer compartment!
Then I am happy because it's like having a cooled mono camera.....
Less noise than my wife makes on discovering a camera taking photos in her fridge!

[Stuart]

Just to throw a wrench into this, the issue with darks on DSLR is that the temperature will vary for the DSLR CMOS sensor during the evening. As you image, even though your ambient temperature may be one thing, your CMOS temperature will be another, and will change. So I have seen it argued that it's not useful to get darks for DSLR as you will be subtracting an incorrect dark signal (because of temperature variations) and you will be adding noise.

[JayTee]

My Canon DSLR (T3i) final images show less noise when I use darks during the processing. These DSLR sensors are relatively "thermally" noisy so darks, in my book, are a necessity. Even though you have to go into the EXIF data to find the "circuitry" temp, it is then just a matter of getting organized and putting those darks into their correct bin for later use.

Cheers,
JT

[STEVE333]

Hi David - I have been using a Canon EOS 1100D for about 5 years now. I had it modified about three years ago.

I use BackyardEOS (BYEOS) to control the camera, and, it allows you to customize the filename associated with each image. I make sure that the camera temperature is part of the filename. In that way I know what the camera temperature was for each image I take (Dark or Light).

To take darks for my Darks Library, I put my Canon (with the lens cap on and the viewfinder "cap" on) into a plastic ziplock bag which I then put into an insulated lunch bag along with artificial ice. I then use BYEOS to take pictures at the desired ISO and exposure time. By taking pictures as the camera slowly cools down and then slowly warms back up I get many Dark frames at all of the available temperatures. In order to have enough Dark frames at each temperature I usually end up doing two or three cool-down/warm-up runs. All of these runs are made during a day or night when I had available time. They never interfere with nights when real imaging can be done.

Once all of the Dark frames are collected I sort them into folders as shown in the top half of the picture below where temperatures ranged from 46F to 73F.



I have chosen to group my Dark frames to the nearest 5F when making the Master Dark Frames. The 11 Master Dark Frames I created are shown in the lower half of the Picture above. These are almost a year old, but, seem to still be working well. However, I may start working on a new set of Dark frames soon.

It was mentioned that the changing temperature of the DSLR during a nights imaging can be a problem. I've never found that to be true in my case. I just gather together all the Light frames that correspond to one of the MasterDarkFrames and perform Calibration on them. Then, from the Light frames remaining, I Gather together all of the frames corresponding to another one of the MasterDarkFrames and perform Calibration on them. I continue in this way until all of the Light frames have been Calibrated. This has always worked well for me.

Hope this helps.

Steve

[Graeme1858]

................. time with a clear sky is so limited I hate having to put so much of it into taking darks.

Excellent question and very helpful answers.

Thanks everybody

Regards

Graeme

[Jockinireland]

Thanks everyone for such helpful replies. I really don't know why I'd not thought of doing them in the fridge or cool bag.

Hi David - I have been using a Canon EOS 1100D for about 5 years now. I had it modified about three years ago.

I use BackyardEOS (BYEOS) to control the camera, and, it allows you to customize the filename associated with each image. I make sure that the camera temperature is part of the filename. In that way I know what the camera temperature was for each image I take (Dark or Light).


Hope this helps.

Steve

Thanks Steve, I use BYEOS too so your system will work perfectly for me. Except the degrees F. I'm a purely metric man and degrees F just confuse me till I can no longer think straight.

Great help everyone. Wife will, I'm sure, be unimpressed at wires coming out of the fridge for the next few days. But hey ho! Needs must and all that.

David

[Jockinireland]

I have chosen to group my Dark frames to the nearest 5F when making the Master Dark Frames. The 11 Master Dark Frames I created are shown in the lower half of the Picture above. These are almost a year old, but, seem to still be working well. However, I may start working on a new set of Dark frames soon.


Hope this helps.

Steve

Hi Steve,

So the camera is out in a coolbag churning through a Dark frame capture plan. But I have a couple of follow-ons related to master darks (sorry - really new at this)

How many darks would you put together in a master dark - as many as you have or just up to a given number?

I am guessing I could build the master darks in DSS (not sure how though) - or is it just stack in photoshop with a median average
Then ho to go about getting the master dark applied in DSS? Just put it in as the only dark frame? Or is there a proper way to do it?

Cant thank you enough Steve.

Rgds

David.

[Juno16]

Just to throw a wrench into this, the issue with darks on DSLR is that the temperature will vary for the DSLR CMOS sensor during the evening. As you image, even though your ambient temperature may be one thing, your CMOS temperature will be another, and will change. So I have seen it argued that it's not useful to get darks for DSLR as you will be subtracting an incorrect dark signal (because of temperature variations) and you will be adding noise.

My case exactly Stuart.
Since Nikon does not reveal its sensor temperature, or I haven’t found a way to locate it.

I really need to test stacked processes with and without darks.

I know that lots of folks image with the D5300 Nikon. Im curious what they do?

Thanks,
Jim

[UlteriorModem]

Hi Steve,

So the camera is out in a coolbag churning through a Dark frame capture plan. But I have a couple of follow-ons related to master darks (sorry - really new at this)

How many darks would you put together in a master dark - as many as you have or just up to a given number?

I am guessing I could build the master darks in DSS (not sure how though) - or is it just stack in photoshop with a median average
Then ho to go about getting the master dark applied in DSS? Just put it in as the only dark frame? Or is there a proper way to do it?

Cant thank you enough Steve.

Rgds

David.

A rough rule of thumb is about 10 or more frames of each duration. There is a point of diminishing returns I forget the number but I believe it is around 20.

I would stack them in DSS as well, actually I would use pixinsight but that's another story.

[bobharmony]

Great discussion on a wonderful question. I collect my darks on an unheated three season porch a couple of times a year. I really like Steve333's method of filing. Up to now I had just set up folders for ISO, and under that folders for each time length. Having the darks further broken down by temperature will be helpful. I also like his method of collection the darks, and may follow that route. My wife wouldn't think it strange to have wires running out of the fridge, she just wouldn't allow it .

I use BYEOS to define and run a plan, which I save so it is repeatable.

I have heard the issue that Stuart raised about the reported temperature not matching the sensor temperature on a DLSR exactly, but it is the best data point that is available to me, so I use it. Results indicate I am better off with darks that without them.

As far as the number of darks to use, I say use as many as you've got. The more you use, the less random noise the darks will add into the stacked image. There is diminishing returns from using more (I believe it's one of those inverse square root things). For example, using 4 darks will reduce the amount of noise in them by 2X, 9 darks get a 3X reduction. I like 49 as a number (7X) although I rarely have that many available at a particular temperature point.

Bob

[Jockinireland]

Thanks a million folks.

I've spend most of today collecting a ton of dark frames from a cooler bag with ice packs and now need to just index and store.

I didn't get a huge range of temperatures during the period but that's ok. Another couple of ice packs and a colder day will do that. I got a range of durations and ISO's and it was pretty much the same temperature as my last night out so I'm all set.

Thanks again

David

[Star Dad]

I usually end up taking darks AFTER I pre-process images - if there is a problem. I am finding that with my Canon 70D that I get surprised every once in a while when red,green,blue pixels suddenly pop into my images. I find that to be about every three months or so I have to update my darks. I do not take but one set of 20 - 1 minutes exposures - and those are usually indoors. I see a lot of folks worry about temps, but I have found that to be irrelevant (well at least for the Canon - my new ASI294MC may behave differently). One set of darks which I update whenever I see ANY aberrations, usually every three months or so. And that's it. 99% of my images are 1 minute exposures. I do take 30 second and 2 minute exposures on rare occasions and then I take 20 darks for each time.
Note that this may all change based on my recent acquisitions - but that will have to wait - I have angered the weather gods by getting a cooled camera and a Polemaster and so clouds have set in for at least the next week. I'd sacrifice a child, but she's an adult now (and just married this weekend). Her husband would probably object to the loss of his bride - and he knows where I live.