Actually, ISO is not the same as ASA. Most people don't know the correct way of writing the ISO value. The correct way is ISO 100/21° , which is effectively the combination of ASA and DIN.
White Balance so easy, even our 5 year old can do it.- Melissa Strickland
[ QUOTE ]
I still call it ASA too - it's essentially the same thing and the numbers don't change so us oldies need our fond memories intact...(I'm 40 in a few months).
[/ QUOTE ]
I'm 45 and successfully made the switch - you can do it [img]/images/graemlins/wink.gif[/img]
White Balance so easy, even our 5 year old can do it.- Melissa Strickland
[ QUOTE ]
Actually, ISO is not the same as ASA. Most people don't know the correct way of writing the ISO value. The correct way is ISO 100/21° , which is effectively the combination of ASA and DIN.
[/ QUOTE ]
1. There is no ASA rating under current industry standards.
2. The notation "ISO 100/21°" is a creature of ISO 5800:1987, covering the determination of ISO speed ratings for colour negative phtographic film. It is a combination of the ISO linear and logarithmic scale notations. The letters "ASA" are not involved in the definition of the notation. The ISO linear scale notation essentially corresponds to the former ASA notation (now obsolete). The ISO logarithmic scale notation essentially corresponds to the former DIN notation (now essentially obsolete).
3. The notation "ISO 100/21°"is not provided for by the current ISO standard for determining the "speed" (I wish they had adopted the term "sensitivity") of digital cameras (ISO 12232:1998).
4. The correct way, for digital cameras, to write "ISO 100" is "ISO 100".
Best regards,
Doug
White Balance so easy, even our 5 year old can do it.- Melissa Strickland
Yes, I can well imagine that when we shoot at an exposure index of 50 (that is, expose for an ISO sensitity of 50) the highest-luminance portions of the scene may well result in the photodetector "wells" filling up (saturating), and of course a lower gain ahead of the ADC will not overcome that.
Still, that may be how the ISO 50 is implemented (rather than setting the gains for ISO 100 and then dividing the digitized outputs of the ADC by 2.
If the latter were done, then not only would we suffer the saturation I mentioned, but in the part of the tonal scale below saturation, we would have lower luminance resolution (the property we often describe as "bit depth"), leading to further degraded image performance. That would seem to be unnecessarily counterproductive.
So, my bet is on gain adjustment, not digital scaling.
Best regards,
Doug
White Balance so easy, even our 5 year old can do it.- Melissa Strickland
[ QUOTE ]
Yes, I can well imagine that when we shoot at an exposure index of 50 (that is, expose for an ISO sensitity of 50) the highest-luminance portions of the scene may well result in the photodetector "wells" filling up (saturating), and of course a lower gain ahead of the ADC will not overcome that.
Still, that may be how the ISO 50 is implemented (rather than setting the gains for ISO 100 and then dividing the digitized outputs of the ADC by 2.
If the latter were done, then not only would we suffer the saturation I mentioned, but in the part of the tonal scale below saturation, we would have lower luminance resolution (the property we often describe as "bit depth"), leading to further degraded image performance. That would seem to be unnecessarily counterproductive.
So, my bet is on gain adjustment, not digital scaling.
[/ QUOTE ]
In a perfect world, you should be right, but this is a corporation we're talking about, and they are most likely going to do what is simplest.
Of course, some RAW files would put this to rest, but I don't have any of the cameras that offer "ISO 50", and getting RAW samples is like getting blood from stones.
White Balance so easy, even our 5 year old can do it.- Melissa Strickland
Linear Mode
