The Reality of the "Crop Factor"

[Kayaker72]

So, in addition to enjoying photography, I also enjoy the science behind photography.

I didn't find what I considered to be a "smoking gun" reference for the ratio of "bucket edge"/photosite being one of the reasons smaller pixels are not observed to have the same efficiency as larger (or higher pixel density sensors vs lower pixel density sensors).

Most references regarding pixel density talked about what you would expect:

• Diffraction
• Noise or, signal to noise ratios
• Specifically, various noise due to the electronics tends to limit IQ from smaller pixels
• Inherent issues with dynamic range

Then, I found some talk about the "adsorption length" of the different wavelengths of light. The IQ with smaller pixels from red wavelengths may be limited before blue. Most of this is summarized in the "clarkvision" link below.

I did find a reference that the actual photosite is only about half of the sensor area with the other half being the structure and electronics. There is also a lot of talk about inefficiencies with the microlenses, especially as you move away from the center of the sensor. Basically light hitting the above pictures straight on would be focused straight below. But light hitting it at an angle would be less so. Sony, for the Ar7, was offsetting the location of the microlenses as they moved away from the center of the sensor to try to account for this effect. But efficiency with microlenses is an issue.

Two good references:

http://www.clarkvision.com/articles/...ter/index.html
http://www.cambridgeincolour.com/tut...ensor-size.htm


By the way, Roger Clark ran a model (first link) assuming a Quantum Efficiency of 45% and estimated that the optimum IQ on a FF sensor would be 33 MP. Interesting, as the 7DII's QE is rated at 59%, so perhaps the "optimum IQ" would now be obtained with more MPs.

BTW, if anyone knows of a good link on this topic, I'd be interested. Granted, I am still making my way through Roger Clark's work.