07-22-2012, 01:07 PM
[quote name='nandadevieast' timestamp='1342958614' post='19531']
Hi,
Little confused here...
If you're saying ISO's are about managing exposure time...in that case the ISOs from different cameras should not be equal and same. For example, ISO 1600 from A57 is not the same as ISO 1600 from LX5, right?
I always thought that ISO 1600 is 4 stops from ISO 100, which should be true for all the cameras. Then if it is a fixed value, how can it be about exposure time??
Maybe i am unable to understand this <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='
' />
[/quote]
Lets introduce an imaginary sensitivity rating called Meh.
Suppose the LX5 with its really small photo sensitive diodes has a sensitivity of 50 Meh.
And lets suppose the A57 with is quite a lot bigger photo sensitive elements has a sensitivity of 250 Meh.
The difference is made by the much bigger surface of the "pixels" from the A57,which simply can "catch" more photons during the same exposure time.
Now we want photographers to make photos with each camera. Suppose they have "comparable" lensing, with a similar field of view, and the same f-value (f4 for instance). With the A57 with a sensor of 250 Meh sensitivity, a "correct" exposure would for instance last 1/250th of a second.
When we make the same photo with the LX5, it would then take 1/50th of a second, just because the sensor is so much less sensitive due to its smaller photo sensitive elements.
As you can imagine, this would be a bit troublesome for photographers. With every camera, with the vast variety of sensors available, exposure times would be very hard to get a grasp on... All would need different exposure times with the same familiar lens settings (field of view, f-stop).
That is where "ISO" comes in. It is a standard to equalize all different sensitivities, and make exposure times predictable, over all the different cameras and sensors. Camera makers are free to amplify the signal to whatever factor they need, to reach a certain ISO setting.
For ISO 100, for instance A57 would need a 1.5x amplification factor (just a made up number) to get its 250 Meh sensor to reach ISO 100. The LX5 would then need a 7.5x amplification to reach ISO 100.
We as camera users do not see how much the signal is amplified, we just get easily handled ISO "standard" settings, a nice abstraction layer to keep things simple and usable.
Stop thinking of "ISO" as a sensitivity rating, it is not (with DIGITAL). It is an exposure index rating.
Hi,
Little confused here...
If you're saying ISO's are about managing exposure time...in that case the ISOs from different cameras should not be equal and same. For example, ISO 1600 from A57 is not the same as ISO 1600 from LX5, right?
I always thought that ISO 1600 is 4 stops from ISO 100, which should be true for all the cameras. Then if it is a fixed value, how can it be about exposure time??
Maybe i am unable to understand this <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='
' />[/quote]
Lets introduce an imaginary sensitivity rating called Meh.
Suppose the LX5 with its really small photo sensitive diodes has a sensitivity of 50 Meh.
And lets suppose the A57 with is quite a lot bigger photo sensitive elements has a sensitivity of 250 Meh.
The difference is made by the much bigger surface of the "pixels" from the A57,which simply can "catch" more photons during the same exposure time.
Now we want photographers to make photos with each camera. Suppose they have "comparable" lensing, with a similar field of view, and the same f-value (f4 for instance). With the A57 with a sensor of 250 Meh sensitivity, a "correct" exposure would for instance last 1/250th of a second.
When we make the same photo with the LX5, it would then take 1/50th of a second, just because the sensor is so much less sensitive due to its smaller photo sensitive elements.
As you can imagine, this would be a bit troublesome for photographers. With every camera, with the vast variety of sensors available, exposure times would be very hard to get a grasp on... All would need different exposure times with the same familiar lens settings (field of view, f-stop).
That is where "ISO" comes in. It is a standard to equalize all different sensitivities, and make exposure times predictable, over all the different cameras and sensors. Camera makers are free to amplify the signal to whatever factor they need, to reach a certain ISO setting.
For ISO 100, for instance A57 would need a 1.5x amplification factor (just a made up number) to get its 250 Meh sensor to reach ISO 100. The LX5 would then need a 7.5x amplification to reach ISO 100.
We as camera users do not see how much the signal is amplified, we just get easily handled ISO "standard" settings, a nice abstraction layer to keep things simple and usable.
Stop thinking of "ISO" as a sensitivity rating, it is not (with DIGITAL). It is an exposure index rating.