Full Frame vs 1.6 crop
I've heard so many differing stories and opinions regarding the difference between a Full Frame sensor and a cropped sensor. In this example of debunkery, I'm going to refer to the Canon line and their 1.6 crop consumer sensors.
From the image above, we see that there is NO difference in physical zoom between the 2 rectangular sensor sizes. The 1.6 crop does NOT zoom in closer, effectively making say a 50mm lens on a full frame effectively 80mm on a 1.6 crop. Remember it is a crop of the image, hence 1.6 crop, not an increase in magnification which would translate to 1.6x multiplier. Understand the difference?
Also, the EF-S range of lenses from Canon are specifically designed to focus the image onto the smaller sensor size as can be seen from the size of the inner circle. This is one of the reasons why EF-S lens cannot be used on full frame bodies as the sensor would just have a severe black circular border where no light was capture. The other issue is the mirror flip up physically hitting the back of the EF-S lens.
In the end, with both sensors you are seeing the same image in terms of distance but the smaller consumer sensor is just cropped. This means that the Full Frame body is always going to provide you with more real estate to capture more of what an EF lens is seeing. It does not mean that the EF lens is performing differently on a smaller body.
Any questions class?