Upgrade from 17-85 to 15-85 worth it?

Started Jan 2, 2013 | Questions thread
OP Ryan Ly Contributing Member • Posts: 597
A simple test...

So I finally got some time to take some test shots with the 15-85 and I must say that the results are a bit mixed when compared to my Tamron 17-50 non-VC and 17-85.

Firstly, center sharpness is excellent. But this was never going to be the area of concern... corner sharpness is what I'm looking at. I'm not really comparing apples to apples since I'm looking at 15mm on one lens and 17mm on the other two but for all intents an purposes, it's still corner sharpness at f/8 and ISO100 on my 600D.

Corner testing is somewhat a mixed result and I'm hoping it's just me. My test is how sharp a particular palm tree in the corner of my shots is displayed. The Tamron 17-50 is tack sharp. The 17-85 is clearly soft.

With the 15-85, the first shot I compared looked soft at the corners. Then I checked another shot where the palm tree is soft but the trees in the foreground to the palm tree is soft. This is not the case with the Tamron. I have uploaded samples below:

15-85 IS - 100% top-right corner sample

Notice the palm tree in the top-right is blurry...

17-50 non-VC - 100% top-right corner sample

... and it's sharp on the Tamron. Note that the Tamron does have a yellowish tint - there's no UV filter on the Tamron though.

Anyone have any explanation for this?

Here's a more prominent sample of the 15-85 with the left side of this crop being the centre of the shot and the right side getting close to the right corners. In this one, the trees in the foreground are also getting soft.

Right corner softness more distinct in this one.

Is the lens a dud?

 Ryan Ly's gear list:Ryan Ly's gear list
Canon EOS 600D Nikon 1 V1 Canon EF-S 15-85mm f/3.5-5.6 IS USM Nikon 1 Nikkor VR 10-100mm f/4.5-5.6 Canon EOS 350D +7 more
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