« on: August 28, 2014, 05:17:33 PM »
Sorry for another thread on this, but it seems to me that there are different definitions of what "extra reach" means as it relates to cropped sensors. For my own education/clarification, this is what I think, but I would welcome any corrections. These are imaginary scenarios to help define the parameters.
1) Extra reach = "I take two pictures of a bird from the same spot on my porch, one with a 7D, one with a 5DIII, both of them with the same lens. When I pixel peep on my computer at 100% resolution, my 7D "zooms in" further, i.e. the bird appears larger. (I'm ignoring how "good" the bird looks in either shot.) In this case, the larger image of the bird on my computer monitor has nothing to do with the 1.6 crop factor; rather, it has everything to do with the increased pixel density of the 7D as compared to the 5D3.
2) Extra reach = "I'm going to frame a picture of some non-moving subject in my viewfinder exactly as I want to print it off (using the Quick Print button, of course). So, I take the photo from X feet away from the subject using the 7D, and I take a picture of the same subject with the 5D3 from X/1.6 feet away i.e. move in closer. In this case, the "extra reach" of the 7D in terms of where I need to stand to properly frame the photo has everything to do with the 1.6x crop factor of the sensor. Also in this case, I believe that the background will be more blurred with the 5D3, but I don't know if that has anything to do with sensor size or if it's just because I'm 1.6x closer to the subject with the 5D3.
3) Extra reach = "I'm going to take a picture of a shy bird, so I'll stay 40 feet away when taking the photos. I want to print an 8x10 photo with the bird being the same size in the framed picture on both photos. If the bird happens to be the right size in my frame using the 7D, I'll need to crop the photo that I take with the 5D3. The amount that I need to crop out (as a percentage) is based on the 1.6 crop factor of the sensor.
One other point for scenario 3 - if I was hoping for the same resolution in both photos, then the FF sensor would need to have 1.6 * 1.6 (i.e. 2.56x) more pixels. I don't know the numbers offhand, but if the 7D happend to have a 20 MP sensor, then a FF sensor would need to have a 51.2 MP sensor for me to crop it down to the APS-C size image and still offer the same resolution (pixel density) as the 20 MP cropped sensor.
I know that I've ignored important variables like how well I can hand-hold the camera (shaky hands will be amplified in the 7D), AF accuracy, keeper rate, lens resolving power, etc. I'm just trying to clarify how "extra reach" comes into play with APS-C cameras.
Again, corrections to my assertions are welcome, as are use cases that I missed.