[tibbitts]

I'm testing a 60-250, and it's almost as amazing as everyone says, except for this problem at short focal lengths and under about 8ft:

Example

That's just a quick screen capture from faststone, but this isn't some raw-processing artifact or other subtle problem. The problem is best illustraded by the edge between the white line and blue at the top of the images (and this crop is from the top of the overall image.)

One image is from the 60-250, and the other from the much-maligned Tamron 70-300 LD Di. Admittedly the Tamron photo was taken from slightly farther away (Pentax was at 60mm vs. 70mm for the Tamron), but they're both 100% crops. The Pentax is amazing past about 10ft. at all focal lengths, and is okay at longer focal lengths at closer focus distances.

What's got me a confused is that whenever I test lenses based on my limited experience, I've come to expect decentering, because it seems to be so common. Or at least not perfect centering. The Pentax is very equal on all sides/corners up to the ability I have to test (AA filter @ 16mp) except at this combination of short focal length and short distance. Here, the Pentax is closer to the Tamron in the center of the image, but has the same issues and very poor performance at both the top and bottom. So if this is decentering it's different than what I'm used to, where usually one edge or corner is soft.

Incidentally, both AF with no adjustments and live view MF produce identical results.

What would cause his problem?

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Last edited by tibbitts; 03-06-2016 at 07:56 AM.

[CarlJF]

Could be front/back focus and you need to apply AF micro adjustments. This problem most evident on close focus, long focal lenght shots, where you doesn't have much depth of field.

[tibbitts]

Could be front/back focus and you need to apply AF micro adjustments. This problem most evident on close focus, long focal lenght shots, where you doesn't have much depth of field.

I tried multiple test with live view and MF and got the same result. So while I've had to use the micro-adjustments (more like macro, probably needs slightly more than 10) on my Tamron 17-50, I can't get this lens any sharper when I focus manually with live view.

It doesn't show up on the screen capture very well, but besides the visible green "bleeding" under that top white line that you can see, there've very faint purple bleeding at the top of the white line (extending down into the white area from the blue paint.)

Also longer focal lengths from the same distance produce good results with either AF or live view MF.