Further on ISO invariance
Jun 3, 2016 20:59:32 #
Apaflo wrote:
... The fact is that DC is something that is very hard to find in the wild. ...
It's a lot more common "in the wild" than A/C. A/C is always man-made. D/C is present in lightning, static electricity and many other natural forms.
Give it up. You are in way over your head.
BebuLamar wrote:
AC has a frequency. What do you think this frequency may be?
You have been outed! You can't answer that one.
Cameras use D/C.
Jun 3, 2016 21:17:20 #
BebuLamar wrote:
AC has a frequency. What do you think this frequency may be?
I'm assuming you are asking about the frequency of the sensor output. It is 1/2 the clock rate for the sensor output. If the sensor locations are being read out at one 20,000 sensor per second, the highest frequency of the output signal will be 10 kHz. Keep in mind that the output is a modified square wave, hence there will be a significant level of odd harmonics too.
Jun 3, 2016 21:27:40 #
Apaflo wrote:
I'm assuming you are asking about the frequency of the sensor output. It is 1/2 the clock rate for the sensor output. ...
That has nothing to do with the voltage measured at the sensor It is still a D/C voltage.
You are totally clueless. Give it up.
Jun 4, 2016 02:12:43 #
Light is a wave this is true visible light ranges between 4 x 10 power 14 to 8 x 10 power 14. A red frequency light then has
400, 000, 000, 000, 000 cycles per second. our fastest shutter speed is 1/8000 of a second (0.000125 seconds) so that means a minimum of 50 000, 000, 000 complete cycles occur during a 1/8000 exposure.
If we look at audio signals about the highest frequency is about 20,000 hz and the best sampling rate is around 96,000 hz about 4 samples per second but the minimum sample frequency needs to be at least twice the highest frequency or 40,000 hz in order to describe the waveform coming in.
What we do with audio and light is very different. With audio we move a speaker coil with an electrical signal that mimics the sound wave that was captured, 1000's of samples a second. with light we capture a charge which is very much a single voltage proportional to the light recorded at a single photo site over a given capture time but repeated over millions of photo sites. The sample time is your shutter speed between 1/8000 of a second to 30 seconds usually. With a max sample rate of maybe 10 - 100 times a second.
Selmsie is mostly correct Direct Current is a current that flows with a constant voltage where in an AC current the voltage cycles.
The analog to digital converter is measuring a voltage at a particular instant in time. it really doesn't matter if the signal that created that voltage was ac or dc. There is no current it is a static charge! As the voltage is held constant for sampling then DC is closer :)
You cannot look at a single sample and determine if it was generated by an ac or dc source and light is of such high frequency it appears to be a DC source.
400, 000, 000, 000, 000 cycles per second. our fastest shutter speed is 1/8000 of a second (0.000125 seconds) so that means a minimum of 50 000, 000, 000 complete cycles occur during a 1/8000 exposure.
If we look at audio signals about the highest frequency is about 20,000 hz and the best sampling rate is around 96,000 hz about 4 samples per second but the minimum sample frequency needs to be at least twice the highest frequency or 40,000 hz in order to describe the waveform coming in.
What we do with audio and light is very different. With audio we move a speaker coil with an electrical signal that mimics the sound wave that was captured, 1000's of samples a second. with light we capture a charge which is very much a single voltage proportional to the light recorded at a single photo site over a given capture time but repeated over millions of photo sites. The sample time is your shutter speed between 1/8000 of a second to 30 seconds usually. With a max sample rate of maybe 10 - 100 times a second.
Selmsie is mostly correct Direct Current is a current that flows with a constant voltage where in an AC current the voltage cycles.
The analog to digital converter is measuring a voltage at a particular instant in time. it really doesn't matter if the signal that created that voltage was ac or dc. There is no current it is a static charge! As the voltage is held constant for sampling then DC is closer :)
You cannot look at a single sample and determine if it was generated by an ac or dc source and light is of such high frequency it appears to be a DC source.
Jun 4, 2016 11:21:34 #
Gentlemen, I thank you all for the information. I'm still not sure that "severe underexposing" at base ISO and correcting in post makes sense for my particular camera in terms of noise and dynamic range, but I guess some testing is in order. It seems like this thread has run its course...
Cheers,
Chris
Cheers,
Chris
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