Main/PF 28mm 50mm Edge Softness Field Test Update (1/2/3)

Sigma 18-50mm f/2.8 DC Lens Review
Nicholas Johnson, 08/04/2005

I received my Sigma 18-50 2.8 today from Broadway photo for an astoundingly cheap $380 with a modest ground shipping charge. Honestly I was amazed that they sent it at all for that price since B&H sells it for $499 last I checked. I thought it would be a welcome addition to my bag on my Canon 10D.  Before this I didn't have any one lens that went from kinda-wide-to-kinda-long.  The Canon 17-85 IS won't fit on my body since its EF-S and I prefer f/2.8 lenses in the first place.  Anyway, on with the lens.

As you may have heard the build is quite good on the lens. It feels as sturdy as my old 24-70/2.8L but thankfully so much lighter. In common use it is a joy, though I expect I might miss the full time manual focus of Canon's USM focus. Strange that Sigma did not include a HSM motor on this lens considering its pro features and sharpness... I'm getting ahead of myself. In the auto focus department it seems a little iffy on the wide end, though DOF is heavy there anyway. The jumping focus, as in I auto focus many times on the same subject and the focus continues to change, reminds me a lot of the Sigma 12-24.  I've never trusted the focus on my 10D so I cannot blame the lens for anything in that department. his lens has the zoom ring turn in the correct direction however, unlike the 12-24 which turns in the Nikon direction.  I'm not sure if the Nikon mount 18-50s turn in the Nikon direction... hmmm.  Without HSM the lens is louder than all my other lenses, except the terribly loud Canon 28/2.8. Now for the sharpness test.

My first round of tests proved very flawed in testing sharpness but did show the amount of purple fringing / chromatic aberration you can get on an overcast day with this lens.  I also noticed that my Sigma 12-24 sorta sucks if it isn't stopped way down.  I already knew this but looking at the 100% crops compared to the other options the 12-24 really stands out.  However, neither the 12-24 nor the 24-70L showed ANY PF/CA even wide open.  Okay, the 24-70 had a little but this was major on the 18-50 both at 18mm and 24mm.  Here are the 18mm crops:

Full View:


f/2.8
 

f/4.0
 

f/5.6

f/8.0

Understand that the tree is not the point of focus in this image.  It should be well out of the depth of field for the f/2.8 image.  Still, this might be a problem for some photographers.

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