Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Astrophotography and Sketching >> Beginning and Intermediate Imaging

Pages: 1 | 2 | (show all)
bouffetout
scholastic sledgehammer


Reged: 11/21/12

Loc: Canada
Dark frames temperature ?
      #5611489 - 01/08/13 08:22 AM

I would like to start a dark frame library but don't know few things ...
If I take darks at -10 Celcius ,How much degree higher and lower ,+/- ,can I use those ???
Is a master dark as good as putting all the darks in DSS ???
Can I make my darks during cloudy nights using only the camera and cap on ,or do I have to fit it to the scope ???
Thank you all for answering !
Maxx


Post Extras: Print Post   Remind Me!   Notify Moderator  
guyroch
Vendor (BackyardEOS)
*****

Reged: 01/22/08

Loc: Under the clouds!
Re: Dark frames temperature ? new [Re: bouffetout]
      #5611589 - 01/08/13 09:38 AM

You typically can match darks +/- 3c.

You can (and you should) take darks during cloudy nights. The camera cap is all you need.

You don't have to fit your camera back on the scope. A dark is just that, a picture with no light photons reaching the sensor so lens/scope does not matter. But duration and ISO do matter so make sure you match those to your light images.

Hope this helps,

Guylain


Post Extras: Print Post   Remind Me!   Notify Moderator  
bouffetout
scholastic sledgehammer


Reged: 11/21/12

Loc: Canada
Re: Dark frames temperature ? new [Re: guyroch]
      #5611601 - 01/08/13 09:46 AM

Merci Guilain !

Post Extras: Print Post   Remind Me!   Notify Moderator  
jgraham
Postmaster
*****

Reged: 12/02/04

Loc: Miami Valley Astronomical Soci...
Re: Dark frames temperature ? new [Re: bouffetout]
      #5611869 - 01/08/13 12:32 PM

I'd just be careful not to lay the camera on its back while taking darks. I have no data to prove this, but I'd be a little concerned that changing the heat losses through the back of the camera could have an effect on the sensor temperature. +/-3C is good up to about 25-30C (sensor temperature), between 30C and 40C +/-2C is better, and above 40C (yes I've imaged with a sensor temperature above 40C) the temperature needs to be pretty well matched.

Post Extras: Print Post   Remind Me!   Notify Moderator  
bouffetout
scholastic sledgehammer


Reged: 11/21/12

Loc: Canada
Re: Dark frames temperature ? new [Re: jgraham]
      #5611885 - 01/08/13 12:42 PM

Dude! imaging at 40 Celcius...40 C at night ? during the day it must have been terribly hot !
You have a good point there ,when I image ,my camera's back touches nothing and temperature exits differently depending the angle of the camera.
Thank you for helping me !
Maxx


Post Extras: Print Post   Remind Me!   Notify Moderator  
Magellan
Pooh-Bah


Reged: 01/26/06

Loc: Enfield, NS Canada
Re: Dark frames temperature ? new [Re: bouffetout]
      #5611975 - 01/08/13 01:41 PM

I have been using Darks taken in August for images shot in January. I take Dark Flats and Bias frames at light temps, seems to work for me. What does a more seasoned APer feel about this thought?

Post Extras: Print Post   Remind Me!   Notify Moderator  
jrcrillyAdministrator
Refractor wienie no more
*****

Reged: 04/30/03

Loc: NE Ohio
Re: Dark frames temperature ? new [Re: Magellan]
      #5611999 - 01/08/13 01:56 PM

Quote:

What does a more seasoned APer feel about this thought?




Looking at the noise v. temp charts for the chips, there's a difference at even 1 degree C. A degree or two probably isn't too bad, though - and I know that with an unregulated camera that much error is inevitable even within a given session. You can check - take two darks at different temperatures and subtract the cooler one from the other. What remains is the noise that the warmer dark won't correct at the lower temp because of that much temp error. Reliable darks is just one more reason for selecting a dedicated astro camera.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Magellan
Pooh-Bah


Reged: 01/26/06

Loc: Enfield, NS Canada
Re: Dark frames temperature ? new [Re: jrcrilly]
      #5612002 - 01/08/13 01:59 PM

Interesting thought. Maybe I should start taking darks after my lights, a bit of a pain but at least I am using a dedicated modified 450D.

Post Extras: Print Post   Remind Me!   Notify Moderator  
jrcrillyAdministrator
Refractor wienie no more
*****

Reged: 04/30/03

Loc: NE Ohio
Re: Dark frames temperature ? new [Re: Magellan]
      #5612035 - 01/08/13 02:16 PM

Quote:

Interesting thought. Maybe I should start taking darks after my lights,




When I used a DSLR I relied more on handling the noise during combination. If you dither the frames via the autoguider, the noise will move around relative to objects in the image and a median combine will deal with whatever the darks miss.


Post Extras: Print Post   Remind Me!   Notify Moderator  
guyroch
Vendor (BackyardEOS)
*****

Reged: 01/22/08

Loc: Under the clouds!
Re: Dark frames temperature ? new [Re: Magellan]
      #5612077 - 01/08/13 02:34 PM

Quote:

I have been using Darks taken in August for images shot in January. I take Dark Flats and Bias frames at light temps, seems to work for me. What does a more seasoned APer feel about this thought?




That is fine for most, but consider adding a few new darks and retiring a few older darks from your library every now and then. This will keep you library up to date with your camera sensor changing over time.

Just my 2 cents.

Guylain


Post Extras: Print Post   Remind Me!   Notify Moderator  
bouffetout
scholastic sledgehammer


Reged: 11/21/12

Loc: Canada
Re: Dark frames temperature ? new [Re: Magellan]
      #5612120 - 01/08/13 02:59 PM

Because it was a cold August and a hot January ???
Beautiful pictures you have on Flickr.
Maxx

Edited by bouffetout (01/08/13 03:03 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
bouffetout
scholastic sledgehammer


Reged: 11/21/12

Loc: Canada
Re: Dark frames temperature ? new [Re: guyroch]
      #5612137 - 01/08/13 03:10 PM

I thought that dark frames lasted for the time I used the same camera...How long can I use a master dark then ?

Post Extras: Print Post   Remind Me!   Notify Moderator  
bouffetout
scholastic sledgehammer


Reged: 11/21/12

Loc: Canada
Re: Dark frames temperature ? new [Re: jrcrilly]
      #5612145 - 01/08/13 03:14 PM

Thank you for answering ,but you kind of lost me there !
Maxx


Post Extras: Print Post   Remind Me!   Notify Moderator  
guyroch
Vendor (BackyardEOS)
*****

Reged: 01/22/08

Loc: Under the clouds!
Re: Dark frames temperature ? new [Re: bouffetout]
      #5612152 - 01/08/13 03:19 PM

Quote:

I thought that dark frames lasted for the time I used the same camera...How long can I use a master dark then ?




A camera sensor will deteriorate over time, new dead pixels will show up, etc...

Adding new dark frames to your library and removing older ones will ensure your library is up to date with your sensor.

Guylain


Post Extras: Print Post   Remind Me!   Notify Moderator  
John Wunderlin
Vendor - Spike-a Focusing Mask
*****

Reged: 10/01/04

Loc: Mineral Point, Wi
Re: Dark frames temperature ? new [Re: bouffetout]
      #5612155 - 01/08/13 03:20 PM

Quote:

I thought that dark frames lasted for the time I used the same camera...How long can I use a master dark then ?




I've heard it suggested you replace them every 6 months, but I've never seen anyone back that up with an actual study. One thing I wanted to mention is that it's a good idea to use a pause between frames to let the DSLR's chip cool between shots. When I was using a DSLR I discovered that the chip heats up significantly if you take many exposures in a row which effectively changes the temperature you are targeting. I can't remember if this happened with my 350 or 450, but I'll bet a lot of cameras will have this issue.


Post Extras: Print Post   Remind Me!   Notify Moderator  
bouffetout
scholastic sledgehammer


Reged: 11/21/12

Loc: Canada
Re: Dark frames temperature ? new [Re: guyroch]
      #5612164 - 01/08/13 03:24 PM

Thanks again dude !

Post Extras: Print Post   Remind Me!   Notify Moderator  
Magellan
Pooh-Bah


Reged: 01/26/06

Loc: Enfield, NS Canada
Re: Dark frames temperature ? new [Re: guyroch]
      #5612173 - 01/08/13 03:30 PM

thank you for the Flickr comment I am thinking about doing a new set of darks anyway with dark cloudy skies coming, thats the best time me thinks. I can't dither with the Nextguide wish I could.

Post Extras: Print Post   Remind Me!   Notify Moderator  
bouffetout
scholastic sledgehammer


Reged: 11/21/12

Loc: Canada
Re: Dark frames temperature ? new [Re: John Wunderlin]
      #5612181 - 01/08/13 03:31 PM

Thank you John ! How long do you suggest the pause ? I do 5 seconds pause ,is it enough ?
Maxx
Beautiful astropics in your gallery...WOW !!!


Post Extras: Print Post   Remind Me!   Notify Moderator  
John Wunderlin
Vendor - Spike-a Focusing Mask
*****

Reged: 10/01/04

Loc: Mineral Point, Wi
Re: Dark frames temperature ? new [Re: bouffetout]
      #5612202 - 01/08/13 03:46 PM

My educated guess is that 5 seconds would be enough, but I'm afraid I didn't test- shortly after I discovered this issue, I bought my ST8300 and rarely do DSLR imaging any longer. I'm sure 5 seconds would be much better than none.

Post Extras: Print Post   Remind Me!   Notify Moderator  
jgraham
Postmaster
*****

Reged: 12/02/04

Loc: Miami Valley Astronomical Soci...
Re: Dark frames temperature ? new [Re: John Wunderlin]
      #5612326 - 01/08/13 05:06 PM

Heh, heh, that's 40C sensor temperature, not ambient air temperature.

I've been using uncooled cameras for the past 9 years and handling the darks is always a mixed bag. My CCD does automatic dark matching in real-time which is nice, but even there I update the libraries at least once a year. On the DLSR side I switched to using the internal dark subtraction. I used it last night with 600 second subs and my source images looked great! I haven't taken a stand alone dark frame with my DSLR in over a year. If you want to see something interesting look at the sensor temperature as a function of time as you take your darks. Also, look at each individual frame. As time goes on the sensor keeps getting warmer and the darks noisier.

Fun stuff.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | (show all)


Extra information
11 registered and 14 anonymous users are browsing this forum.

Moderator:  Knuklhdastrnmr, fishonkevin, WOBentley, rflinn68 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 579

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics