• What is the „best“ ISO?
• ISO Amplification?
• How can mathematics help?
• Example Images
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• Where does Noise and Amplification happen?
• The key point is, that most noise origins
BEFORE A/D or ISO-Amplifier
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• “Does this theoretical negotiation
correspond to the reality?”
– Methods of verification
• Driving tests on deep sky objects
• Driving tests on synthetic objects
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16 x 2 min @ ISO 1600
4 x 8 min @ ISO 400
1 x 32 min @ ISO 100
Nozzle feature
Stack of 16 x 10s @ ISO 1600
Stack of 8 x 20s @ ISO 800
Stack of 4 x 40s @ ISO 400
Stack of 2 x 80s @ ISO 200
3/24/2011 Reducing noise at physical layer – CEDIC 2011 8Single 160s shot @ ISO 100
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16 x 2 min @ISO1600
8 x 4 min @ISO800
4 x 8 min @ISO400
2 x 16 min @ISO200
1 x 32 min @ISO100
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0°C Single Shot
0°C Stacked
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• Low ISO is a great alternative
• But: You have to test your own camera to
find the best ISO settings
– Measure noise at different ISO-Settings and
different exposure times
– Find the best combination for YOUR model
– Testing will need only little time
– Testing will save a lot of observing time
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• If histogram is “low”, stacking will not increase dynamic
• If histogram is “high”, separation of A – B is possible
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• Long time exposures are very useful
• The higher the histogram, the better can the
image be processed by Photoshop
• You may need to do HDR
– Take short pictures to avoid saturation.
– Take long pictures to go deep.
– Combine them with software. (Photoshop, etc.)
• Question: What kind of noise will become
more and more important with long exposure
times?
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• Each 6° drop - the thermal noise is divided by 2
– Surface of the Sensor heats up: 42°C – 50°C during
long time exposures. (EOS 450D, 15min - 30min)
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16 x 2 min @ISO16004 x 8 min @ISO4001 x 32 min @ISO100
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0°C Single Shot0°C Stacked24°C Single Shot24°C Stacked
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Low
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• EOS 450D
– Single HQ Peltier
• Power: 40W
– HQ - CPU-Cooler
– Temperature drop at
sensor: >60°
– Min. sensor temperature:
-24°C after 5 min.
– “heavy overdosed”
– The PWM reduces cooling
power to 20% in order to
avoid ice on the sensor
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• EOS 1000D
– Single cheap Peltier
– Power 17W
– Cheap Chipset-Cooler
– Temperature drop at
sensor: <40°
– Min. sensor temperature:
0°C after 10 min
– “good enough”
– PWM at 80%
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• There is plenty of noise that is not affected
by temperature
– Read out, random noise, fixed pattern, etc…
• If you go lower than 0°C sensor surface…
– …you may see wonderful ice flowers
– …the thermal noise is far below read out noise
• No further optimization is possible
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• Abell 66, very weak PN
– 25,9 mag/sec²
– With cooling:
• More stars than in DSS
• more than 23mag of DSS
• Astroart says: 27-29vmag
• Observation
– 4 x 32min @ ISO 100
– EOS 450D @ 2°C
– Hakos, Namibia, IAS
– 50cm Newton 1500mm
focal length
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• Because the sensor will heat up:
– Cooling is very effective
– It is worth to spend time on cooling projects
• On my homepage you find detailed information
about
– Used material
– Dimensions of the copper finger
– Video tutorial
• With this information, project will consume less
than 40h time.
• Visit: www.sternschnuppen.de
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• Keep the well known stacking.
– Darkframes, Flats, Dithering, etc…
• Use low ISO
– Increase exposure time
– Optimize your histogram
• Cooling down the camera
– Even small effects will help
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Low
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