Taken with 300mm F2.8L lens. Seven exposure levels from 7sec at 200 ISO to 2 min at 800 ISO all at f/2.8. Converted from Raw to Tiff and corrected for flats with ImagesPlus.Stacked and aligned with Registar. Used EasyHDR to produce final image.
All exposures taken with camera in fridge at -8.0 C at an ambient of 17 C. Used the fridge mark III with two Peltiers and two heat sinks. It easily gets 25+C below ambient even with the heat load of the camera taking long exposures.
Those are some massive thermaltake blowers I bet they sound like you're in a hurricane when you're using the thing. Are the ends of those TECs and the thermaltake heatsink/fan takes the heat off the hot side sending the other side into massive amounts of cold? I've seen (and have 2) those babies freeze water in a few seconds and boil water in a few seconds.
Mike it does take some time stacking each exposure set and then getting each to match in size and area with Registar. If everything is done correctly in EasyHDR then it is simply amatter of adjusting levels of the final LDR in PS.
It is well worth it as I can get any amount of dynamic range in the final LDR image up to about 20+ bits or stops. This is more important with wide fields because of the variation in intensity of the objects. At 200 ISO and a seven second exposure the brighter stars are nearly saturated. As you can see all the stars have colour and the dim nebs come up noise free.
Ingo the fans can be speed controlled and once the fridge is down to 20+c below ambient I turn them down from flat out to a whisper. These fans are high quality ball bearing and well balanced so vibration is not a problem. Even the TAL200K with a focal length of 1800mm shows no image deterioration due to vibration.
The heat sinks are CPU heatpipe coolers and the hot side of the Peltier is less than 35C depending on ambient.
I replaced the original peltiers with these from Jaycar.
Temperature Differential (DT) (Th=27 degrees C) : >=68 degrees C
Optimum Input Voltage (Vmax) (Th=27 degrees C): 15V
Optimum Input Current (Imax) (Th=27 degrees C):8A
Maximum Cooling Power (Qmax): 68.09W
I run them at 13.8V and 6A as this seems to be optimum for their current physical installation. If the voltage is increased from 13.8V the fridge temperature goes up. Peltiers pump about half the heat of the energy used to drive them. So I estimate this fridge is pumping about 80+ watts.
With one Peltier running I get 15C drop from ambient and with two 25C drop from ambient with the camera exposing. With the camera at idle or off the fridge temp drops by 2 or 4 degrees respectively.
The real advantage of the fridge is I can get noise free data at 800 ISO and only a tiny amount at 1600 ISO at about -5C. In winter should be able to get -20C with ease. The longest exposure was 2min at 800ISO. Four minutes at 800 ISO was too saturated to use.
Below are images from just the 2min at 800ISO data. The nebs look fine but the stars are washed out. The background is also lighter due to skyglow.
Here you go Ingo. The fridge is held the same way on the other telescopes except the focuser holds the fridge support.
The only contact the fridge has with the camera is the polystyrene foam 'door'. There is some bubble wrap behind the foam around the lens to give a better seal. I am working on a better 'door'.
Here you go Ingo. The fridge is held the same way on the other telescopes except the focuser holds the fridge support.
The only contact the fridge has with the camera is the polystyrene foam 'door'. There is some bubble wrap behind the foam around the lens to give a better seal. I am working on a better 'door'.
Bert
Thanks for the images. Gives me an idea for my chat channel telescope project
edit: I just noticed the focus mechanism. It's awesome . What camera do you use? Did you say a 1D Mark III?
I bet they sound like you're in a hurricane when you're using the thing. Are the ends of those TECs and the thermaltake heatsink/fan takes the heat off the hot side sending the other side into massive amounts of cold? I've seen (and have 2) those babies freeze water in a few seconds and boil water in a few seconds.
