John Sheehy wrote in post #17466958
A larger sensor has the potential for a higher quality image, but that requires certain conditions, such as using a shallow DOF not possible on the smaller format, using the entire sensor or most of it (a larger area of it compared to the smaller sensor), or using a lens that is not optimized for the smaller format. However, that is not always the case. For example, I think I get a sharper image with about the same noise with my 7D2 and 17-55/2.8 IS at 17/2.8 as my 6D with the 24-105/4 at 24/4.
There we go; that is exactly what I was talking about. The 6D has no
greater usable ISO range than the 7D2 for shooting BIFs with the same lens, distance, and shutter speed
. ISO is not some blanket noise penalty on anything you do with a capture. The whole idea of the question "what is the highest usable ISO?" on a camera is absurd, IMO. ISO has no direct relationship to noise; what must also be factored in is how much the final display of the subject is going to be magnified, relative to the size captured on the sensor, in inches or millimeters. The larger sensors generally are only "usable" at higher ISOs because you can make the subject larger on the sensor, by using a longer focal length. You can not claim this benefit when you are already too far away from the subject and are focal length limited. An 8x10 inch sensor will not help you get better "IQ" of a subject at a certain distance, with a certain lens. You have to make your composition fill the frame to get the benefit.
IMO, if you really want to understand your choices, you have to think in terms of resolution and noise per unit of sensor area
, just like film has certain qualities based on emulsion, regardless of film size. Blanket statements about larger sensors having better high ISO performance do not mean that they have better "film"; they just have a bigger "sheet" of it, which is of zero value if you don't use a bigger piece of the "film". What you do get, however, is more jump or jitter room on the sensor, so you will have less birds without heads and without feet if you can't follow the bird well, at the cost of less pixels on the subject with the larger pxiels of current FF cameras.
Well, the 5D3 has compromises compared to both the 6D and 7D2. The 5D3 has more banding noise than either; this shows up in the shadows of very low ISOs, especially at ISO 250 with HTP (highlight tone priority) and an f-ratio of 2 or less. Neither shoot as fast as the 7D2, and the 7D2 has better noise character than the 5D3, and has less visible noise in FLL (focal-length-limited) situations. The 7D2 is superior to the 5D3 in practical DR at base ISO; the 5D3's banding ruins the DR. The 5D3, however is the fastest-focusing FF camera Canon makes short of the 1Dx, which costs more than 2x as much as the 5D3.
You see, Canon doesn't make things simple and just make one camera completely better than another, as if you just had to chose between budget and quality; you need all three cameras to get everything the three of them collectively offer!
I think you're right about that. It is way too easy to turn a (technical) turd of an image into a gem when images are displayed small. Small images can hide the noise, the noise created in sharpening and boosting contrast or levels, and make a soft image look sharp by pixelating it and substituting the gridded pixel boundaries for natural subject edges. I feel embarrassed for people who wet their pants over the "sharpness" of 1/2 MP or smaller web images. You can take a shot with a 75-300/5.6 USM and two 2x TCs stacked and make a sharp web image out of it! Same with ISOs; unless a camera has serious banding noise issues, you can make any ISO a camera officially sports look fairly noiseless by using NR and/or reducing its display size enough.