07-22-2012, 08:32 AM
[quote name='nandadevieast' timestamp='1342936764' post='19528']
If the exposure/histogram is similar, then does that mean the ISO 1600 is actually ISO 2400 (1/2 stop) on a SLT??
Also, less light hitting the sensor should have implications across the ISO range, why only high ISOs?
[/quote]
No, ISO 1600 is ISO 1600, no matter how much amplification is applied.
Like I said, ISO with digital is NOT about sensor sensitivity. With film it was, but with digital it is about exposure time.
ISO settings are about equalizing exposure times more or less. How long it will take to reach clipping. And that in SRGB space (so TIFF or JPEG depending on what method the manufacturer chooses to "determine" ISO settings), so the chosen tonal curve can make big differences too.
Just think of a 6mp and a 24mm APS-C sensor. The 24mp sensor has pixels that are 4 (!!!!) times as small pixels. So, per pixel, the sensor gets less light over the same period of time. Yet, both will take about the same time to make a photo at ISO 100 (or 1600).
Why? Because ISO is not about sensitivity, but about exposure time.
Same with different sized sensors. When you take a 12mp 2x crop camera, like an Olympus E-30, and a 12mp FF camera, like a Nikon D700, both have about the same amount of photo diodes. The FF camera has a sensor that is 4x the surface area of the 4/3rds one. It will collect 4x the light in the same exposure period. The pixels themselves are 4x bigger for the FF camera too. They too collect 4x the light during the same exposure time.
Yes, when you set both cameras to ISO 200, the exposure times are similar. Why? Because ISO is not about sensitivity like it was with film. The 4/3rds sensor signal gets more gain to reach ISO settings. Same with the SLT.
And it has "implications" across the entire ISO range, not only high ISO settings. Also at ISO 100 less light reaches the sensor in the same exposure time on an SLT.
If the exposure/histogram is similar, then does that mean the ISO 1600 is actually ISO 2400 (1/2 stop) on a SLT??
Also, less light hitting the sensor should have implications across the ISO range, why only high ISOs?
[/quote]
No, ISO 1600 is ISO 1600, no matter how much amplification is applied.
Like I said, ISO with digital is NOT about sensor sensitivity. With film it was, but with digital it is about exposure time.
ISO settings are about equalizing exposure times more or less. How long it will take to reach clipping. And that in SRGB space (so TIFF or JPEG depending on what method the manufacturer chooses to "determine" ISO settings), so the chosen tonal curve can make big differences too.
Just think of a 6mp and a 24mm APS-C sensor. The 24mp sensor has pixels that are 4 (!!!!) times as small pixels. So, per pixel, the sensor gets less light over the same period of time. Yet, both will take about the same time to make a photo at ISO 100 (or 1600).
Why? Because ISO is not about sensitivity, but about exposure time.
Same with different sized sensors. When you take a 12mp 2x crop camera, like an Olympus E-30, and a 12mp FF camera, like a Nikon D700, both have about the same amount of photo diodes. The FF camera has a sensor that is 4x the surface area of the 4/3rds one. It will collect 4x the light in the same exposure period. The pixels themselves are 4x bigger for the FF camera too. They too collect 4x the light during the same exposure time.
Yes, when you set both cameras to ISO 200, the exposure times are similar. Why? Because ISO is not about sensitivity like it was with film. The 4/3rds sensor signal gets more gain to reach ISO settings. Same with the SLT.
And it has "implications" across the entire ISO range, not only high ISO settings. Also at ISO 100 less light reaches the sensor in the same exposure time on an SLT.