CDS-5D 냉각온도 변화 변화에 따른 다크프레임 분석 by Brice Grassin,

This analysis report was based on the dark frame images of cooled 5D markIII and these were taken at the temperature range +20C ~ -30C .
Below linked images are the unscaled original dark images.

http://www.centralds.net/imsi/Dark_20C.CR2
http://www.centralds.net/imsi/Dark_20C.JPG
http://www.centralds.net/imsi/Dark_10C.CR2
http://www.centralds.net/imsi/Dark_10C.JPG
http://www.centralds.net/imsi/Dark_0C.CR2
http://www.centralds.net/imsi/Dark_0C.JPG
http://www.centralds.net/imsi/Dark_-10C.CR2
http://www.centralds.net/imsi/Dark_-10C.JPG
http://www.centralds.net/imsi/Dark_-20C.CR2
http://www.centralds.net/imsi/Dark_-20C.JPG
http://www.centralds.net/imsi/Dark_-30C.CR2
http://www.centralds.net/imsi/Dark_-30C.JPG

Below is the results of analysis by Brice Grassin,( contact@bgimage.fr )

First, let’s start to see histograms about pixel population around the default Canon 5D mkIII’s pedestal (sort 20°C -> -30°C):

 

-> Nothing unusual; the shape is pretty good at low temperature with a population quasi inside the offset +/-128 ADU.

High frequency waves in the population are typical of the FPN (fixed pattern noise), present at all temperatures on 5D cameras.

 

Let’s see now closer, with a deeper analyse and especially how main noises are affected by the low temperatures:

-> Standard deviation of the dark frames (in blue) are very well reduced, even when temperatures are not extremes. Between 0°C and -10°C it seems to have a pivot point.

Beside, RON’s sigma (in grey) is down too with low temperatures (unexpected!). This fact could be interesting in some configurations, when RON (read on noise) is a limiting factor.

 

After noises, let’s take a look on how the cooling device is efficient:

 

-> The cooling system working very well in fact! >90% of efficiency is reach before -10°C.

Noise reduction is well link with the cooling efficiency and the amount of reduction is very significant just from 0°C.

 

Beside, under -10°C the system looks to saturate; gain is <2% from -10°C to -30°C.

This fact tells us that the 5D MkIII CMOS can’t do very much in question of noise. Mostly when we know that the sensor can not go under -48°C because of micro-lens.

 

And for the end, let’s check how the cooling device helps in dynamic range:

-> Of course we are speaking about dynamic range in a single frame here, where the theoretical maximum is around 9.6 stops for the 5D MkIII @ISO 3200.

But this value is for a very short exposure time, far of the 120s here.

So this is very interesting _in absolute_ to see that the dynamic range reach 9.3 stops @ -30°C. And it represents a gain close to 24% from the same exposure time @ 20°C.

For sure, almost 2 stops of gain per frame can be significant after compositing 10 or 20 frames in deepsky imaging.

 

Well, I hope you find all of this interesting. I think you will take time to read all those graphics.

Of course there is a lot of things to say about all these datas if we take time to make links and afterthought. It is a work through the time and with experimentations to measure gains.

 

Brice Grassin,
BGImage • Imaging solutions & consulting (France)
contact@bgimage.fr