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Old 30-01-2014, 04:59 PM
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gregbradley
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Join Date: Feb 2006
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How do you measure bias drift? Do you check background ADU of a series of bias images taken at the same time and same temp?

I get the idea from Richard that it may also tend to shift when ambient temps change.

Here is a copy of a post by Richard today where he measured his Microline. Bias seems extremely stable.
So this overscan callibration may only be of benefit if your camera has bias drift.



Richard Crisp
Today at 3:14 AM
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I did a little bit of temperature testing in an older ML4022 to measure the bias value under different ambient temperature conditions and different sensor temperatures


I operated the ML4022 in three different ambient temperature conditions: Room, Refrigerator, Freezer


I didn't have a quality thermometer handy but would estimate the ambient temperature was about 70F in the room. I guess the Refrigerator temp was around 38F and the Freezer was probably below 20F maybe as cold as zero F.


here are the results for -20, -25, -30 and -35C sensor operating temperatures


Bias Values (ADU)
op temp-20-25-30-35freezer977977977979refrigerator987988989991room991991992993

Since my night temps usually fall within the range of 70-40F the room temp and refrigerator temps cover my normal range. It is rare for me to encounter really cold freezing temperatures.


looks like the spread for my expected conditions is in the range of 2-4 ADU.

Richard Crisp




Greg.

Last edited by gregbradley; 30-01-2014 at 06:12 PM.
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