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To compare the Minolta 50mm f1.7 lens with another lens, to judge its sharpness at the center and edges while focused at infinity. The challenge came from posts to two web boards stating that the 1.7 was soft on the edges, and did not do well when focused on infinity. A while ago, I read a comment where someone stated that the Minolta 35-70 f3.5-4.5 (RS) was about as sharp as the 1.7, when stopped-down. So, I arbitrarily compared the two lenses at f4.0 and f8.0. (Since then, I read someone else's comment that the ideal f-stop for the 1.7 was f6.3.)
I think the 50mm f1.7 is still the superior lens, but it's amazing how well the 35-70 does at f8. And even at f4 it's not too bad considering that the aperture is wide open at that point. Then again, it's not so good either.
Unfortunately, I had set the zoom lens to 45mm instead of 50mm, but I don't think that's a fatal flaw in this test. I don't feel like redoing it at the moment, so I'm going to let it ride.
Below are two 100% crops -- no additional sharpening and cropped without re-encoding JPEG, both recorded at f8. One curious thing is that with the Tamron fully zoomed to "50mm", it could not equal the field of view of the Minolta. So, there is slightly more "zoom" to the 50/1.7. (I don't think this is too much of a problem comparing photos focused at a distance, but up close, it could be.)
So, which is which? You can tell by examining the filenames.
The two crops below were taken from different photos that were focused on the fence and shrubs, and again taken at f8. While the focus wasn't deliberately set at this edge area, I felt that an edge comparison was needed. Since the two lenses have different focal planes out towards the edges, even when focused at the same point in the center, it probably is better to use a further subject, and this may not be the best comparison. I'll have to redo this test, but for now, it's what I have, so I'm going with it. With that disclaimer...
Which is which lens?
I think that the focus on the photo on the right is further back, so I think it ends up being a draw. The main point to this comparison is that neither lens is unusually soft at the edges at f8. (The Minolta 50/f1.7 is known to have softness issues at the edges at the wider apertures. See previous test.)
After running these tests, I no longer worry about which of these lenses are on my camera. Both are capable of extremely sharp images, particularly at an aperture of f8. Given the flexibility of a zoom, I can highly recommend the Tamron 17-50/2.8. But if you happen upon a budget Minolta 50/f1.7, you can see how useful it might be if on a budget.
Last updated: June 7, 2008.