27. March 2008 by admin.

I was discussing this lens with another photographer who was interested in buying one, but hadn’t had much luck with Sigma in the past. He looked at some of the shots I took with it and liked them, but thought that the edges looked soft, which got me wondering… Looking at the areas he thought were soft I couldn’t tell if the effect was just a result of wide angle distortion, or if there really was a possible focal difference between the center and the edges indicating there was something wrong with the lens. To find out, I put together this test.

This is a shot taken on my 1Ds at 15mm, aperture was f11 or f16. The exposure is on the hot side because this was actually used as part of a blended composite I made. It does illustrate how this lens performs pretty well though. All shots have default Lightroom sharpening applied.
This shot can be used as the “key” for the other shots:

Here is crop number 1:

You can clearly see the ballesters on the bridge, and make out enough detail in the foliage.

Here’s crop number 2:

Again, the tree detail is pretty good. I’m actually pleasantly surprised at how well this lens resolves detail at the edges even at 15mm.

Here’s crop number 3:

This is taken right from the center of the lens, where you would expect it to be the sharpest. Not surprisingly it does seem to resolve slightly more detail than the edges. The difference is surprisingly small for a lens this wide (and in this price range) though.

Here is crop number 4:

Again, it shows that there really doesn’t seem to be any focal difference between the center and edges.

If nothing else, this test confirmed that this lens has surprising performance (particularly when stopped down). Even at 15mm on a full frame camera, I’m very impressed with it’s performance.

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26. February 2008 by admin.

 For years I never used a lens wider than 28mm.  This was the old standard “wide angle” lens for a 35mm camera.  For many years anything wider than that was kind of a “specialty” lens, and many of them weren’t even rectilinear lenses–they were fish eye lenses.  Times have changed…along with the digital revolution in cameras, a new crop of ultra wide angle lenses are now on the market at reasonable prices that put them in the reach of many consumers.  My personal favorite is the Sigma 15-30mm.   It’s big, but light weight, and at 15mm it’s got an enormous field of view on a full frame or 35mm camera.  It also performs well on 1.6 crop sensor cameras, but it really shines on a full frame sensor.  At first glance, most people tend to think of and ultra wide (wider than 24mm) lens as the tool of choice for getting those sweeping views when shooting landscapes.  But they’re really much more.  The distortion they create and their extreme close focusing ability make these lenses a very interesting creative tool.  As an example, see the photo below.  I shot this at 15mm on a full frame camera.  I was very close to the car, and the ultra wide angle really gives a unique stretched perspective you can’t get any other way.

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