Originally posted by jimH If you crop a photo you are taking a small portion of the image that has been registered on the sensor and you have stretched the image by cutting away many of the pixels that make up the image, thereby "stressing" the image . . .
The photo from the longer focal length lens should have more detail and should be clearer than an image of the same object taken with a shorter focal length lens and cropped to get the same overall coverage . . . If you compare a long focal length lens with a short focal length lens by cropping the image from the short focal length lens, you aren't comparing apples and apples, since one image will have a disadvantage because it was cropped while the other was not. (Clear as mud)?
Yes, it is clear, thank you the detailed answer. OTOH . . .
While it all makes perfect logical sense, what if after comparing a cropped picture to the longer FL, the cropped picture looks as good or better? Now an observer has their sensory input to deal with, but no explanation if what you say is always true. In other words, either I am not seeing well, or there is another way to account for the 180mm crop looking better than the 300mm non-crop.
For example, the DA 55-300 is known to lose substantial resolution at 300mm, but the VL 180mm is optimized for its single FL. So while there may be more pixels present in the 300mm shot, they might be rendered relatively soft (compared to, say, a prime 300mm); whereas the 180mm is exceptionally capable of resolution (as tests have proven). So when cropped, though containing less pixels, the 180mm started out so much sharper that it still outperforms the zoom at its least desirable FL (just offering a hypothesis to account for observations
).
And this was actually why I started this thread, to ask if just such a thing might be possible between a superb prime lens and a mediocre lens (at 300mm anyway).