Or more accurately the “post-shoot digital zooming thing”. Or the “making use of 24MP” thing.
The premise is that with a high resolution sensor you can crop quite a small portion out of the full frame and still have a reasonably sharp image to present. This is the opposite of demonstrating why high MP sensors aren’t any advantage once the picture is reduced to ‘normal’ size. Let’s see how it works.
The camera: Sony a6000 with 24 MP sensor. The lens: Pentax Super Takumar 50mm f1.4 (the sharpest lens I own). The subject: a dollar store decoration cardinal standing in for a real bird because it won’t fly away while I’m photographing it. The distance: approximately 50 feet.
This is one picture cropped four ways and ending up at 1500 x 1000 each time.
As you can see, 1/16 of the full frame is about the maximum limit. It is already “soft” and it still doesn’t reveal the bird very well. Of course 50mm isn’t much focal length (about 75mm equivalent) so for actual birding a longer lens would do better. What we’re studying here is the cropping effect on resolution. This size is slightly larger than my ‘normal’ image presentation, and it is noticeably soft even to my eyesight. Applying the “unsharp mask” doesn’t help.
So what do we learn? We learn there is no substitute for being close to the subject in the first place, whether in actual distance or by use of telephoto lens (which adds its own problems due to looking through increased atmosphere). You can make use of some digital zooming this way, but don’t expect it to be a substitute for multiples of focal length.
By the way, this is the third experiment I did like this. I’m using the examples from this one because they present the best demonstration with the best lens. I have also done it with the 135mm Vivitar, with similar results. If anything the longer focal length adds to the drop-off in sharpness because longer lenses tend not to be as sharp. In other words the digital cropping will not only magnify the image, but any flaws in it as well.
The third experiment utilized the Soligor 85-205mm zoom and a Pentax 2X extender as I was trying variations to see how having an actual long lens would affect the field of view. Or to put it simply, to see if buying the 50-210mm Sony zoom would give enough focal length to make birding pictures possible. The result was “no”. Disregarding the softness of the lens, the field of view was not magnified sufficiently to make for good identification of the bird.
As you can see, for birding a long focal length is desirable because you probably won’t be able to get close to them physically. In fact having the wide zoom range is valuable because you never know how far away you will be when you spot something. This is why I like the Nikon P610, although it needs a faster zoom control and better viewfinder. Hence my recent reference to the desirability of an actual DSLR with a tiny 1/2.3 sensor. But that’s not going to happen. Nor will any manufacturer come up with a digital “sport finder”: a wider frame of view with a centered square indicating the actual image area so small objects can be spotted more easily and brought in close. Perhaps some camera has this, but I haven’t seen it.
I’m still at sixes and sevens about the Sony a6000. It is a very good camera and does produce excellent results. For the most part it’s easy to use and has great lens adaptability. There are only a few flaws, and I can’t quite decide if they are too much to put up with. I think I need to use it more before determining whether it’s worth sinking additional money into or selling it off for whatever I can get.