bebert
sage
Reged: 07/21/08
Posts: 304
Loc: Louisiana
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Do any of you warm-up your camera prior to imaging? By warm-up I mean turn it on. I was thinking that doing so would yield a consistent noise profile across all subs. I've not seen this question before - apologies if it's already been addressed.
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Celestron C8
Orion 80 ED
Vixen 70s for guiding
CG5-ASGT
SSAG
PHD Guiding
Astronomik CLS EOS clip
Astronomik 12nm Ha EOS clip
Canon 300D(a)
Celestron 0.63 focal reducer
WO 0.8x FF/FR version II
My Astrophotography on Flickr
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Nils_Lars
Post Laureate
Reged: 01/04/08
Posts: 4254
Loc: Santa Cruz Mountains , CA
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Ya there was a thread on this a while back and people have different opinions but I like to shoot some warm up shots(30-40min worth) on the same time im going to shoot at to get the sensor close to temp.
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Erik
Orion Atlas Self Hypertuned (EQMOD)
Orion ED 80
Williams Optics VII reducer
Celestron 8" SCT
Orion Starshoot Autoguider
PHD guide
Canon 500D Gary Honis Mod w/Baader filter
Astronomik CLS , 12nm Ha , and OIII clip ins
Bahtinov mask
Canon EF 50mm f/1.8 II and Nikkor 180mm f/2.8 ED lenses
NexImage webcam
http://www.flickr.com/photos/31986095@N05/
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Jeff in Austin
scholastic sledgehammer
Reged: 02/26/07
Posts: 875
Loc: TEXAS
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I notice when I shoot darks for the library, the first 3-4 are not quite the same as the rest. I've just assumed the sensor and the surrounding area have to reach temp equilibrium. I first noticed this when shooting 85 deg F darks for summer imaging. YMMV if you're not in a hot climate, however.
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There's nothing like having a supportive family, including Second Grader w/ scope, curious toddler, and lovely wife.
Supporter of Austin Clear Sky Clock, Austin CalSky.
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hiro
professor emeritus
Reged: 07/17/07
Posts: 557
Loc: Tokyo
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I do not warm-up my equipment. I begin shooting short exposures first and long exposures afterwards in order not to waste even a bit of clear and dark hours. When the temperature is high, I usually shoot with pauses for about a half of exposure.
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hiro
Canon EOS 5Dmk2-sp2 by Seo san
Takahashi FSQ-106ED with reducer, extender, and "hiro design" off axis guider
Lenses by Nikon, Leica, and Zeiss
Takahashi EM-200 temma 2 jr / Kenko Skymemo-R
http://www.flickr.com/photos/hiroc/
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Hermit
super member
Reged: 10/26/08
Posts: 135
Loc: Northern California
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I installed a USB temperature probe in my Canon 450D/XSi. The temperature of the camera internally increases for at least 20 minutes after starting shooting or using live view if there is no break. The final temp ends up being about 12 to 15 degrees F above ambient, with a noticable increase in noise and hot pixels. So I would say it is best not to warm up the camera, in fact better to do whatever it takes to keep it from warming up in the interest of dramatically lowering noise.
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Meade LX90 LNT 8" Schmidt-Cassegrain
Standard Wedge, LX90 fork, LX200 tripod
Alan Gee II telecompressor f/5.6
Baader short 1.5cm T-adapter/T-ring
Astronomik CLS-CCD clip filter
Self modified Canon XSi with Baader UV/IR filter.
Meade Model 277 60mm refractor with Orion SSAG
Losmandy V-dovetails for balance and guide scope.
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Bert
sage
Reged: 02/17/06
Posts: 486
Loc: Australia
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This is from a thread I started some time ago. The camera is a Canon 5DH inside a custom Peltier fridge.
The graph below was generated by taking a ten second dark at 400 ISO straight after turning on the camera after the camera had equilibrated at a range of fridge temperatures. The raw frames were converted to linear tiffs and digitally developed with a break point of 1268 in Images Plus. IP was used to measure the value of the same hot pixel with the photometric function under point.
I fitted a third order polynomial to the data with the graphing software to get a best curve to fit the data.
We can now use this graph to measure sensor temperature directly. It is just a matter of taking a ten second dark at 400ISO and measuring the value of the same hot pixel.
With far more data I got quite reproducible results.
The sensors temperature is consistently 3.5C higher over the full range of fridge temperatures when the camera is on and at idle (not exposing) compared to camera off. This takes about twenty minutes to equilibrate from off.
If you set the camera taking exposures continuously the sensor temperature rises by 16.5 C from the off state. This of course is 13C above the idle state. It takes about forty minutes to reach equilibrium.
What all this means is that you should take at least 30 to 40 minutes of dummy exposures before taking any lights or darks. Then you have some sort of hope of them matching in temperature. This really depends how far your ambient temperature drops over the imaging run.
I now realise why my sensor does not get any condensation. Last night with the fridge Peltiers set to -15.0C the fridge temperature was at -10.5C and the sensor was at 6.5C. Ambient temperature got down to 5.0C!
I have a heating strap around the lens just outside the fridge which keeps the lens at 24C. This is where the drop in filter is. This keeps the air around the filter above the dew point (I hope).
Now we all also know why nothing beats ICNR apart from a constant temperature fridge!
Any questions, and I will attempt to answer.
Bert
Edited by Bert (11/11/09 01:51 AM)
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Jerry Lodriguss
Vendor
Reged: 07/19/08
Posts: 887
Loc: Voorhees, NJ
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Hi Bert,
Interesting data.
But there really is no reason to worry about either warming up the camera, nor letting it cool off or pausing between exposures.
With Images Plus automatic dark frame matching, none of this is necessary. The program automatically compensates for the difference in temperatures between the darks and the lights.
I have been using a dark frame library with a master dark every 10 degrees F. I created these master darks a couple of years ago, and they still work fine. I just pick the closest temp to the lights.
Clear dark sky time should be spent gathering photons, since this improves the signal in the signal-to-noise ratio, and there is no other way to do this except by gathering photons.
Shooting under cooler conditions is always desirable with a DSLR to reduce thermal signal and its associated thermal noise, but with a normal DSLR, we can't control the ambient atmospheric temperature, so that is pretty much of a moot point also. :-)
Jerry
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A Beginner's Guide to DSLR Astrophotography
http://www.astropix.com
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Bert
sage
Reged: 02/17/06
Posts: 486
Loc: Australia
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Hi Jerry below is a picture if my 300mm F2.8L setup. The Canon 5DH is cooled by a Peltier fridge. I can set the temperature with the PID controller and the environment the camera is in is held at constant temperature (+0.1 or -0.1 C). With the proper sensor warm up procedure darks match lights exactly. I also have the luxury of having a sensor 25C cooler than ambient. Futher the lens is thermostatically heated to a constant 20C so focus does not change with ambient temperature.
The major problem with Melbourne weather is that ambient temperature can drop by as much as 25C or more over a night.
This happens on clear nights for obvious reasons.
So trying to guess what temperature darks to use was a nightmare.
Chasing focus all night wasted time as well.
As an example it is 34C outside at the moment by early tomorrow morning it will be about 12C.
The fridge allows me to collect at 1600 ISO with almost no thermal noise after subtraction.
Bert
Edited by Bert (11/11/09 02:37 AM)
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Jerry Lodriguss
Vendor
Reged: 07/19/08
Posts: 887
Loc: Voorhees, NJ
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Hi Bert,
That is quite a setup!
It just seems to me that if you want to go to that much trouble, you could just use a temperature-regulated CCD camera.
Please don't get me wrong, I'm not criticizing your methods at all, I'm sure you get great data with that setup and methodology.
It's just that the overwhelming majority of people who shoot with DSLRs do it for the convenience, and this kind of setup kind of defeats that purpose. Not to mention trying to set something up like that at a remote location, running off of 12 volt deep-cycle batteries!
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A Beginner's Guide to DSLR Astrophotography
http://www.astropix.com
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Bert
sage
Reged: 02/17/06
Posts: 486
Loc: Australia
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You are correct Jerry but I do all my data collecting from my ROR obs in my backyard. I use a Canon 5DH as I consider that the sensor leaves any CCD for dead at the same temperature. Also it is not trivial to to get an all electronic Canon 300mm F2.8L working on an astro CCD.
Bert
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HHastro
sage
Reged: 05/22/07
Posts: 289
Loc: Germany, City of Hamburg
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Hi:
To make it simple:
I start imaging with the 20 Da (autodark) 1 1/2 hour after sunset to have a look at the sky bg. Time enough to refocus the ACF when temperature cools down. 2 1/2 hrs. after sunset (at 53°N) subs could use for stacking. Locations more south have different and much shorter times.
Bruno
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Meade 12" ACF with GEG f-6.5, 2000mm,
TAK e200 f-4, 800mm, 4" Genesis f-5,
Canon EOS 20 Da, EOS 350 D (both modded)
ST10XM w/CFW8, guidecam at GEG: ST2000XM
Mount: Mauz Mam 100.
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hiro
professor emeritus
Reged: 07/17/07
Posts: 557
Loc: Tokyo
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Nice measurement and result Bert,
Sensor of EOS 5D is warmer than air around the DSLR by about 16C, and it gets stable in 30-40 minutes. Thanks.
Bruno, the procedure is same as mine. I must wait for about 2 hours till tube and lens get cool and stable.
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hiro
Canon EOS 5Dmk2-sp2 by Seo san
Takahashi FSQ-106ED with reducer, extender, and "hiro design" off axis guider
Lenses by Nikon, Leica, and Zeiss
Takahashi EM-200 temma 2 jr / Kenko Skymemo-R
http://www.flickr.com/photos/hiroc/
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bebert
sage
Reged: 07/21/08
Posts: 304
Loc: Louisiana
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Thanks for the info guys - and for the detailed work Bert.
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Celestron C8
Orion 80 ED
Vixen 70s for guiding
CG5-ASGT
SSAG
PHD Guiding
Astronomik CLS EOS clip
Astronomik 12nm Ha EOS clip
Canon 300D(a)
Celestron 0.63 focal reducer
WO 0.8x FF/FR version II
My Astrophotography on Flickr
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waassaabee
Post Laureate
Reged: 11/26/07
Posts: 3028
Loc: Central California Coast
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Bert, That setup is incredible! My wife would have me locked up if she ever saw me with a setup like that. She thought I was nuts for adding a guidescope and laptop...
But I think I'm in the same school as Jerry and hiro. I do late twilite alignments and start shooting focus and framing shots as darkness sets in. By the time I have the guidescope calibrated and target framed, I'm shooting subs! I keep a dark libray like Jerry and if temps swing enough I can cover it. There have been nights where I check my weather station and see enough swing to break a series and build two images of one target, then combine them. But that's not the norm thank goodness.
A bit hat tip to you for all of your efforts and research though!
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Gary
34N 120W
-My kingdom for blue squares!-
WO Megrez 90FD/TV 0.8x FR/FF
AT8RC
mini Borg 50/Q-Guide/PHD
CGEM & CG5ASGT
Canon 350D Hap Griffin Baader mod
My Friend Flickr
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Bert
sage
Reged: 02/17/06
Posts: 486
Loc: Australia
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Thats ok. I thought that real measurements are the only thing that can give us any idea of what is going on. Guessing is not good enough.
I was in the situation that I knew every temperature ie ambient fridge and camera but NOT the sensor temperature.
Hope this bit of knowledge helps.
Bert
Edited by Bert (11/11/09 10:48 PM)
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waassaabee
Post Laureate
Reged: 11/26/07
Posts: 3028
Loc: Central California Coast
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I think it certainly reinforces the importance of matching temps for subs/darks!!
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Gary
34N 120W
-My kingdom for blue squares!-
WO Megrez 90FD/TV 0.8x FR/FF
AT8RC
mini Borg 50/Q-Guide/PHD
CGEM & CG5ASGT
Canon 350D Hap Griffin Baader mod
My Friend Flickr
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Hermit
super member
Reged: 10/26/08
Posts: 135
Loc: Northern California
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If you pick up a infrared thermometer, you can measure the sensor temperature directly without modifying your camera at all. With the camera lens off, put the camera in bulb mode, start an exposure so that the mirror flips up, then point the temperature probe at the sensor. These things cost around $25, and are used by radio control guys to measure batteries, engines, and the like without having to touch the object.
Here's the model I have:
Best,
Rob Crockett
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Meade LX90 LNT 8" Schmidt-Cassegrain
Standard Wedge, LX90 fork, LX200 tripod
Alan Gee II telecompressor f/5.6
Baader short 1.5cm T-adapter/T-ring
Astronomik CLS-CCD clip filter
Self modified Canon XSi with Baader UV/IR filter.
Meade Model 277 60mm refractor with Orion SSAG
Losmandy V-dovetails for balance and guide scope.
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Doubleglaze
sage
Reged: 11/01/07
Posts: 232
Loc: Pacific NW
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Hi Bert -
Awesome setup - gotta love wires and blinkin' lights!
I'm in the process of designing a peltier chamber similar to what you have made (mock up image below). I was thinking of making the chamber so I could take darks at any temperature setpoint then realized if I sized it right it could work on the scope as well - even better!
Just a couple of design questions for you if I could cause the thread to slip sideways a bit 
Those are some monstrous cooling fins on the outside - do you need all that cooling for the hot side of the TEC? What size TECs did you use? How much heat load do you need to remove from the chamber? What TEC V&I to achieve the cooling you're after? Did you think about a water loop on the outside? It would cut the size and weight of the cooling fins down substantially.
I'm not going to seal the chamber so I'd need to stay over the dew point at the sensor. I hadn't though about the effect of sensor heat up and also using a strip heater for the nose piece and optics side - your data helps with the design choices and sizing the TECs. If I could get the sensor to 5C after warm up (during image capture) from a 30C ambient I'd be pretty happy.
Total WAG, but I estimated the heat load at under 10W for a small plastic and Styrofoam insulated chamber. A set of pretty small TECs should be able to cool the relatively small volume without too much input power. I'm still working out the details but I have the concept laid out now. Now its a matter of finding time and space to make the prototype and then tweaking for performance.
EDIT: I found the old threads on this subject and got some of the info I was looking for. I'm not going to use a beverage TEC but pick one from the various vendors, so I can size it to minimize voltage and current draw. TE Tech is a good company for PID controllers but I'll either make my own PWM circuit or just use proportional control by dialing the power supply up and down manually.
Cheers
Mark
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Vixen VMC260L / Sphinx SXD
Pentax 75 SDHF
Canon 40D / 50mm f1.4 / 100mm f2.8 macro / 28-135 f/3.5-5.6 / 200mm f2.8L
http://www.astrophotogallery.org/u166-doubleglaze.html
Edited by Doubleglaze (11/14/09 06:58 PM)
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