03-13-2012, 08:24 AM
(This post was last modified: 03-13-2012, 10:25 AM by Brightcolours.)
[quote name='Yakim' timestamp='1331626363' post='16638']
Someone please correct Klaus as well as he consistently makes claims like: [url="http://www.opticallimits.com/nikon--nikkor-aps-c-lens-tests/705-sigma1770284os"]f/4.0-5.6 (full format equivalent, in terms of depth-of-field - not speed)[/url]. Or is speed different than light gathering?
[/quote]
Feel free to correct Klaus if you feel like it.
Fact remains, that if you crop 3/4th of the projected image away, you are only left with 1/4th the light to form the captured image in the same period of time. This can not be a hard concept to grasp.
The only thing that remains the same, cropped or uncropped, is the amount of light which falls on a square [fill in your favorite size measurement]. With for any focal length / aperture ratio, instance f2, the same light per for instance square mm will fall no matter how big the sensor is that you put under it. But, that is really rather meaningless for photography, where one captures images, not square mm's.
A bigger sensor has MUCH more square mm's, and therefore will collect a lot more light to form the image.
Only if you concentrate on ISO 100 = ISO 100 = ISO 100, then the "speed" is the same. However, ISO 100 is NOT the same from sensor to sensor. It says nothing about how sensitive any sensor is, nor does it say what is the total amplification of the signal per sensor. ISO 100 is just the big equalizer, obscuring what is actually going on.
Take an easy understandable example, a 12mp 4/3rds sensor like for an Olympus E30, and a 12mp FF sensor like from a Nikon D700. Same amount of pixels more or less. But the pixels from the D700 have a much larger surface area, about 4 times the size of those from the E30.
So, in the same duration of exposure, the D700 pixels will have collected 4 times the amount of energy of the light. The E30 will then have to apply more amplification to reach the same ISO value. Or, you just set the D700 to ISO 400, and they will collect the same amount of light per pixel, will need the same amount of signal amplification.
So my understanding is that when Klaus types what you quoted, he means that with the same ISO setting, they have the same speed. And that indeed is not the same as the same light gathering ability.
Someone please correct Klaus as well as he consistently makes claims like: [url="http://www.opticallimits.com/nikon--nikkor-aps-c-lens-tests/705-sigma1770284os"]f/4.0-5.6 (full format equivalent, in terms of depth-of-field - not speed)[/url]. Or is speed different than light gathering?
[/quote]
Feel free to correct Klaus if you feel like it.
Fact remains, that if you crop 3/4th of the projected image away, you are only left with 1/4th the light to form the captured image in the same period of time. This can not be a hard concept to grasp.
The only thing that remains the same, cropped or uncropped, is the amount of light which falls on a square [fill in your favorite size measurement]. With for any focal length / aperture ratio, instance f2, the same light per for instance square mm will fall no matter how big the sensor is that you put under it. But, that is really rather meaningless for photography, where one captures images, not square mm's.
A bigger sensor has MUCH more square mm's, and therefore will collect a lot more light to form the image.
Only if you concentrate on ISO 100 = ISO 100 = ISO 100, then the "speed" is the same. However, ISO 100 is NOT the same from sensor to sensor. It says nothing about how sensitive any sensor is, nor does it say what is the total amplification of the signal per sensor. ISO 100 is just the big equalizer, obscuring what is actually going on.
Take an easy understandable example, a 12mp 4/3rds sensor like for an Olympus E30, and a 12mp FF sensor like from a Nikon D700. Same amount of pixels more or less. But the pixels from the D700 have a much larger surface area, about 4 times the size of those from the E30.
So, in the same duration of exposure, the D700 pixels will have collected 4 times the amount of energy of the light. The E30 will then have to apply more amplification to reach the same ISO value. Or, you just set the D700 to ISO 400, and they will collect the same amount of light per pixel, will need the same amount of signal amplification.
So my understanding is that when Klaus types what you quoted, he means that with the same ISO setting, they have the same speed. And that indeed is not the same as the same light gathering ability.