Explain Set Point Temperature Cooling of Astro Cameras

[jolasa1]

Maybe not the right Forum to ask about cooled astro cameras (since this is usually a cooled CCD question), but I not have one of the new Primaluce cooled/modified Canon 700 da cameras that I want to use with BYE.

 

 

Canon 700D, modified

Double Peltier cooler cools the camera sensor down to 30 degrees centigrade below ambient temperature  (86 degrees F below ambient).

So if ambient is 25 C, camera sensor can cool down to -5 C.

So if ambient is 20 C, camera sensor can cool down to -10 C.

 

Is the following logic correct?

 

if you set the Set Point temperature to 0 degrees centigrade, and the ambient temperature is 25 degrees centigrade, then the camera sensor will be cooled to 0 degrees centigrade, which is a sensor temperature drop of 25 degrees centigrade (ambient - drop of 25 = 25 - 25 = 0).

 

set Set Point to -5 degrees C, then sensor cooled to -5 (ambient - drop of 30 = 25 -30 = -5.  Which is the limit of cooling, 30 degrees below ambient.

 

 

Anybody know the best sensor temperature for the Canon 700D to eliminate as much dark noise (thermal noise) as possible?

 

I am guessing a bit below 0 degrees C, based on one of the SBIG camera manuals (but of course SBIG are CCD and DSLR's are CMOS sensors).

 

 

JonS

[astroman133]

First, a 30 degree C temperature difference is equivalent to 54 degrees F, since there are 1.8 degrees F per degree C.

 

Your logic for calculating the target (setpoint) temperature is correct. I would suggest that you give yourself some cushion so that the cooler does not have to run at 100% all the time.

 

I would suggest cooling to the lowest temperature that you can consistently reach, regardless of the ambient temperature.  That way you can take dark frames at that temperature and then use them for every session throughout both the winter and summer conditions.  For my CCD camera, with a -45 degC cooler, I cool it to -10 degC (18 degF) yearround.

 

If you follow this then you would consider the warmest temperature that you expect to image at and cool to 25 degC, not 30 degC, below that.

[s3igell]

Also, be realistic about the TEC Cooling: That "30*C below Ambient" is a maximum, and will be impacted by Humidity and Cleanliness of the Heatsink / Fan.

 

Speaking of Humidity:  

Does this Modified Camera have a Sealed Optical Window??  Without one, you'll need to be concerned about Condensation around the Sensor and also around the Metal of the Mirror-Box.

 

This is an area where the Dedicated Design of an AP CCD has innate advantages with Optical Windows and Desiccants, along with Integrated TEC Coolers.

Designers of DSLRs instead expect that the Camera Lens will be present to participate in the Weather-Sealing of the Camera Sensor area.

[admin]

Anything related to astronomy is fair game here so your post, although not related to BYE, is very mush welcome and in context.

 

Regards,

[jolasa1]

Galactic Halo

 

Yep, this accessory is available - a Canon t-ring with a built-in 2 inch filter that can be used to seal the camera insides from the outside

 

[jolasa1]

And this cooled camera has a built-in dew heater also

[jolasa1]

Anybody know where the temperature probe is inside the Canon 700D ( which reads the EXIF temperature that BYE displays?.

 

I think I read somewhere it is located on the DIGIC Processor, not the CMOS sensor itself.  Which means there will be a difference between Set Point temperature and EXIF temperature.

 

JonS

[astroman133]

Galactic Halo is the rank of frequent posters on this site, not a username. s3igell is his username.

 

BTW, when I cool and warm my CCD camera I do it in stages, like a diver coming up from a deep dive where they come partway up, linger there for several minutes, ascend further and repeat. 

 

I cool by no more than 10 degrees, and pause for 3 minutes before continuing.  The same for warming. During cooling this helps prevent frost on the sensor. It also helps to mitigate thermal shock to the sensor over repeated cooling and warming cycles.

[astroman133]

Your question about the location of the temperature sensor has been asked and answered in several threads. Here is one from just a couple of days ago:

 

https://www.otelescope.com/index.php?/topic/1672-sensor-temperature/#entry11073

[s3igell]

Anybody know where the temperature probe is inside the Canon 700D ( which reads the EXIF temperature that BYE displays?.

 

I think I read somewhere it is located on the DIGIC Processor, not the CMOS sensor itself.  Which means there will be a difference between Set Point temperature and EXIF temperature.

 

There will ALWAYS be a Difference between the Set Point Temp and the EXIF Temp - because the Thermometer utilized by the TEC's Controller will also NOT be on the Sensor.  Instead, it is likely attached to the TEC's Cold-Finger, or possibly Wedged between the Sensor and the Digic5 Chip.

 

The Important Thing is that the TEC be able to repeatedly Cool the Camera's Innards to a Repeatable Temperature (whether that is 2-3 Degrees off of the other Reported Temps or not...).

[astroman133]

s3igell is correct. There are likely 2 temperature sensors. One is built into the camera. Its value is included in the EXIF data. The other is part of the cooler and is used to control its functionality.  If you are not asking too much of the cooler, it should regulate the power to the cooler to maintain the cooler's temperature at the requested setpoint. The two readings may always be different, but what is most important is that the difference is repeatable.