boviscopophobic
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Hello all, I'm currently evaluating two copies of a Tamron 15-30mm, one purchased and another rented for comparison. For my purposes (storm photography), I'm mostly interested in infinity performance at 15mm. Multiple online reviews stated that this lens has a fairly flat field and is sharp edge to edge, but this is not what I'm experiencing.
To test, I mounted the camera on a tripod, VC off, remote release, EFCS, etc. I used Live View autofocus to acquire focus on a distant white tower in the center of the image. Sorry about the haze, but that's what I had to work with. To mitigate any possible focus shifting, I refocused every time I changed aperture.
I ran through a series of apertures from f/2.8 through f/11. The results were consistent in all cases: good sharpness and a large depth of field in the center, but as you move left or right from the center you get a smeary mess, especially past the APS-C image circle. Stopping down improves the smeary edges somewhat, but never brings them into sharp focus. What does come into the DOF is the row of foreground trees along the bottom edge. It's as if there's a "runway" of sharp focus extending from the center bottom edge, up past the focus point and through to the mountains behind.
Given that both copies of the lens behave in the same way, I imagine this behavior is not a defect. How, then, are people getting images that are sharp edge to edge? Do you have to manual focus for the edges and then let the DOF handle the center? This is a rather more deliberate procedure than would be practical for my needs.
P.S. I have another aperture series (not included here) of a row of trees at about 50 yards distance, which is not affected by haze but shows similar field curvature. So the haze isn't the cause of the smeary edges here.
f/2.8
f/11
To test, I mounted the camera on a tripod, VC off, remote release, EFCS, etc. I used Live View autofocus to acquire focus on a distant white tower in the center of the image. Sorry about the haze, but that's what I had to work with. To mitigate any possible focus shifting, I refocused every time I changed aperture.
I ran through a series of apertures from f/2.8 through f/11. The results were consistent in all cases: good sharpness and a large depth of field in the center, but as you move left or right from the center you get a smeary mess, especially past the APS-C image circle. Stopping down improves the smeary edges somewhat, but never brings them into sharp focus. What does come into the DOF is the row of foreground trees along the bottom edge. It's as if there's a "runway" of sharp focus extending from the center bottom edge, up past the focus point and through to the mountains behind.
Given that both copies of the lens behave in the same way, I imagine this behavior is not a defect. How, then, are people getting images that are sharp edge to edge? Do you have to manual focus for the edges and then let the DOF handle the center? This is a rather more deliberate procedure than would be practical for my needs.
P.S. I have another aperture series (not included here) of a row of trees at about 50 yards distance, which is not affected by haze but shows similar field curvature. So the haze isn't the cause of the smeary edges here.
f/2.8
f/11
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