Why you should not judge image quality from web-sized photos

Many times I've read comments as "wow, what a sharp photo! The lens xyz is really sharp" or "I think that xyz is a sharp lens, I've seen very sharp photos on Pbase/photo.net/your website/etc." 

This is a wrong assumption: it is impossible to judge the sharpness of a lens from web-sized (700-800px) photos. If you want to see the real sharpness of a lens, you have to look at full resolution image samples, or 100% crop. 

Here is a demonstration. Both these two photos looks sharp at web size:

Photo 1

Photo 2

From these images, I think that everyone would think that they are both very sharp, and that both photos had been taken with high quality, professional lenses.

But actually, one is extremly soft, while the other one is razor sharp, as you can see from these 100% crops:

and this is a 100% crop from the second photo:

There is an huge difference, even though at web size both looks sharp! 

When you resize a photo for web, you get a low-resolution image, that does not show the actual detail of the photo, so it is not possibile to see the difference between a razor sharp lens and a very poor lens. When you are evaluating a lens, never thrust web-sized images! 

Do you have comments or questions?

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