Sigma 18-125 expectations (and properties)

Started Aug 4, 2004 | Discussions thread
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Paul De Bra
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Sigma 18-125 expectations (and properties)
Aug 4, 2004

After over 500 shots with my DR and Sigma 18-125 (first 4000 shots were with kit lens) I feel I can safely summarize its properties, and also shed some light on why people may not be satisfied or think they have a bad copy (which I believe not to be true).

First thing to keep in mind is that this is a DC lens. It is designed for camera's with a 1.5 (or higher) crop factor. This means that the corners you see in the images are close to the edge of what the lens lets through. Corner softness or vignetting should always be completely absent in any lens that is made for 35mm cameras. Even the cheapest lens should not show any such artifact. However, with DC lenses and with the DR kit lens the edge of our photos is really the edge of what the lens supports.
Now for the properties of the 18-125:

Sharpness: generally good but at 18mm and f3.5 the corners are soft. (See Image064 in http://wwwis.win.tue.nl/~debra/photos/diamantroute/ ) Don't think you have a bad copy because the corners are soft.

Contrast: certainly better than the DR kit lens. Don't have any expensive lenses to compare with.

Blooming and purple fringing: very low. Much much better than the DR kit lens. Blown highlights do not have purple edges and do not eat into the rest of the picture.
Flare: also low. Have not yet seen it. Certainly better than the DR kit lens.

Vignetting: clearly visible near 18mm and near 125mm, even when stopped down to f8. Correctable in software. Don't think that you have a bad copy because you see vignetting at 125mm.

Chromatic aberration: mild CA mostly red/green. Changes with focal length. Less CA than the DR kit lens, but it is still worth correcting it in software.

Color reproduction: hard to tell. White balance has so much influence on color that I find it hard to judge the influence of the lens. Sorry folks I'm just not good at this.

Focusing: more difficult than with the DR kit lens. The lens is sharper which makes it difficult for the camera to decide where in the whole distance region that appears sharp the tru distance is. Mostly an issue at wide angle as the DOF is always large. This is not a lens-specific problem, but I mention it because I can tell it exists by looking at the distance scale. Having the distance scale is very helpful.

Weight and size: light and small. This is only possible with a DC lens. The whole optical channel can be smaller than for full-frame sensors or 35mm film.

Price: cannot be beaten. For around $300 or 300 euro (including taxes) you get an incredible package. It really makes it possible to turn a DR into an affordable near-P&S camera with nice zoom range and lower noise and better picture quality than any P&S camera on the market.

Hint for people who have a lot of L glass: don't even touch this lens. You are used to using the best part (the center) of the best lenses. You will find nothing but disappointment when trying all (not just the center) of this much cheaper lens. You get what you pay for. Nothing at $300 beats this lens. And if you think this lens is better than say a 17-40L or any other really expensive lens you know you have a bad copy of the expensive lens.

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former Agfa 1680 owner (was stolen by burglar)
Nikon Coolpix 950 owner (over 10.000 shots)
New Drebel owner (still only around 4.500 shots)
Public pictures at http://wwwis.win.tue.nl/~debra/photos/

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