Reach of APS-C sensors

I keep reading about the better "reach" of the APC-C sensor over full frame. In

fact isn't the magnification the same assuming the same lens is used. The

smaller sensor mearly doesn't capture a portion of the picture. In fact you

could crop the full frame image to the crop sensor image. So where is this

mythical reach? Shouldn't we use different terminology than the word "reach"?

 

Am I missing something?

We do. We call it a crop factor. The APS-C has the same field of view (being that it's basically cropped) as the FF sensor with a lens that is 1.6 times longer. Example, a 50mm lens looks more like 80mm on the APS-C.

 

You could in fact just crop in on the FF sensor. However, the image quality is better on the APS-C over the FF cropped version. I believe the reason for this has to do with the pixel density. That part is too technical for me to explain. I'm sure Bob A can chime in with more details on that.

Higher pixel density is the term you are looking for. It's the equivalent to finer grain film, allowing finer detail to be recorded with a given lens at a given magnification.

Any time the sensor has more receptors per a given area, it has more "reach".

 

If you have 2 sensors with the *same* number of receptors per area, one is full frame 24x36mm and the other is some crop factor, then there is no advantage: cropping the full frame image will yield the same as the crop sensor.

 

But more typically, the crop factor sensor has signif. *more* sensors per area. For example, with the Canon 40D and 5D:

 

If you put the same telephoto prime lens on both bodies, take a shot center on a certain focal point (say a bird), from the same distance, and then crop the 5D image down by the 1.6 crop factor, the cropped image will have x and y pixels quite a bit lower than the 40D shot.