11-29-2011, 10:59 AM
[quote name='Brightcolours' timestamp='1322557109' post='13327']
No, it doesn't. Indeed, the lens still lets the same amount of light pass through.
However, the SENSOR loses light gathering ability. Firstly, the smaller sensor "crops off" a lot of light that the bigger sensor did gather. Seen that way, the image is captured with a lot less light, with the smaller sensor.
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True but the per square centimeter amount of light is still the same... or am I wrong?
Doesn't add up completely. A 6MP Minolta 7D would have had better performance than 21 MP Canon 5D Mark II; 12 MP Canon 5D would have been similarly better than the 5D Mark II. Newer cameras have (or at least should have) more efficiency.
No, it doesn't. Indeed, the lens still lets the same amount of light pass through.
However, the SENSOR loses light gathering ability. Firstly, the smaller sensor "crops off" a lot of light that the bigger sensor did gather. Seen that way, the image is captured with a lot less light, with the smaller sensor.
[/quote]
True but the per square centimeter amount of light is still the same... or am I wrong?
Quote:Secondly, imagine the sensors having a similar amount of light gathering photo diodes. Which would then result in similar resolution images. The smaller sensor will have a lot smaller photo diodes. The smaller diodes gather a lot less light. Resulting in a weaker signal per pixel. The smaller sensor will need a lot more amplification to reach the same ISO setting. And ISO settings are signal amplification in themselves...
Simply put: ISO is not ISO. One ISO setting form one sensor is NOT the same as one ISO setting from another sensor. The amplification applied can be very different.
So, with the same lens and the same aperture diameter, and two totally different sensor sizes, what is NOT the same:
- the field of view
- the field of view/aperture diameter ratio (f-value)
- the light gathered per image
- the light gathered per pixel
- the amplification needed to reach a certain ISO setting.
With equivalent lenses (use the crop factor to find equivalent lenses) what is similar:
- field of view
- aperture (diameter). f-value won't be the same.
- DOF
If you use equivalent ISO settings (meaning: different ISO settings for each sensor format, which apply the same total signal amplification if the sensors have a similar amount of pixels), what then also is the same:
- exposure time
- noise profile (assuming the sensor technology is similar)
Doesn't add up completely. A 6MP Minolta 7D would have had better performance than 21 MP Canon 5D Mark II; 12 MP Canon 5D would have been similarly better than the 5D Mark II. Newer cameras have (or at least should have) more efficiency.