Re: Bias value of Canon DSLRs?!

In article <g2j8sn$dud$1@xxxxxxxxxxxxxxxxx>, user@xxxxxxxxxxxxxx writes
Kennedy McEwen wrote:

Remember this is an ANALOGUE offset. For example, if the "target" offset is 128 on a 12 bit ADC then the total offset is only 3% of the entire analogue range and needs adjustment with a precision of only 0.25%. Analogue signals are simply not that precise or consistent and will vary by far more than this with age and over the operating temperature range of the unit.


Uh ... a good ADC should be accurate and stable to 11 or 12 bits with no problem,
even with age or temperature. 16 bits is a different matter, at that
precision only the best will be that accurate or stable over long times.

The ADC itself may be exceedingly accurate in the levels that its zero and full scale are set, but that isn't the problem - it is offsetting the analogue input by a fixed and consistent amount, not only over temperature but over millions of different circuits for their entire life.

OF course, the sensor pixels themselves will have a zero offset that varies with temperature
simply due to the properties of silicon, unless they have installed some
sort of temperature compensation. Most cameras as far as I know get that
compensation with a dark frame, if desired.

The only time a "dark frame" is used with the Canon cameras is when long exposure noise reduction is enabled in CF-02.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
.

Relevant Pages

  • Re: Bias value of Canon DSLRs?!
    ... offset is 128 on a 12 bit ADC then the total offset is only 3% of the entire analogue range and needs adjustment with a precision of only 0.25%. ... Analogue signals are simply not that precise or consistent and will vary by far more than this with age and over the operating temperature range of the unit. ...
    (rec.photo.digital)
  • Re: Bias value of Canon DSLRs?!
    ... offset is 128 on a 12 bit ADC then the total offset is only 3% of the ... entire analogue range and needs adjustment with a precision of only ... What is being offset is the analogue voltage input to the ADC, the digital output is only the consequence of that offset. ...
    (rec.photo.digital)
  • Re: Translating an embedded C algorithm
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    (comp.lang.ada)
  • Re: Translating an embedded C algorithm
    ... I'm using a small C function that does temperature ... measurement by linear interpolation of a lookup table as an example. ... -- AdcCount Raw ADC count. ... function MeasureTemperature(AdcCount: Adc_Reading) return ...
    (comp.lang.ada)
  • Re: anti-aliasing
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    (sci.electronics.design)