Resale of used Sigma lenses - Easy?

[mark u]

To return to Pierre's original dilemma:

 

I think you need to consider whether a 12-24 (even from Canon in due course) will best meet your needs for wide angle while you plan to use it on a 10D. If you re-read the Chasseur d'Images articles, you will see that Canon's 16-35 f/2.8 L only rated 3 stars when used on a 1Ds. Reason? Vignetting and CA at the image edges. Now this has much more to do with the sensor than the lens. The oblique angles at which the rays at the edge of the image hit the microlens layer above the sensor means that much of the light isn't actually focussed onto the pixels - result vignetting by the sensor. Worse still, again because of the angle, light that passes through say a green colour filter is quite likely to end up being converted to electrons in an adjoining pixel that's supposed to be red or blue - result CA. The key message of the C d'I methodology is that unlike with film, you cannot assess lens performance in isolation from the sensor/body. I think the problems with the 10D/Sigma combination are likely to be similar in principle. As further confirmation of these ideas, I looked at a couple of images taken on an SD10 with the Sigma 12-24 at 12mm. Of course, the SD10 has no colour filter array, and bigger pixels. The result was little vignetting or edge CA (though the images were affected by camera shake, being taken hand held at 1/13th and 1/6th, so they were not useful for assessing sharpness). Given this, I doubt whether you will see any significantly better performance on your 10D from any 12-24 than that available from the Sigma, so you have to decide whether this is acceptable to you. If it isn't, then your best option may be to pick up a small Rebel film body instead of a 12-24 lens and use it with your 17-40 f/4L which also will give you a slightly wider angle of view coverage (17 vs 19.2mm) with a good lens (even if it is more prone to barrel distortion that the Sigma 12-24/10D would be). The $400 you save should cover D&P for a while for your wide angle shots (even longer if you later don't buy an expensive Canon 12-24).

 

If you would still prefer to use the 10D for your wide angle shooting, then you can either buy the Sigma now, or wait until the Tokina appears (now seems to be August at the earliest) and see if that performs any better, or wait still longer for a possible Canon version.

 

With regards to Tokina, they have a reputation for extremely robust construction, reminiscent of a good lens of the manual focus era. The only guide to their skill in making wideangles is their 17mm prime. Probably their best regarded lenses are the 28-70/80 fast zooms, now it seems eclipsed by Tamron's 28-75; and their 100-300 f/4 (optically superior to any Canon x-300 released so far, including the f/5.6L).

 

So far as Canon are concerned, a 12-24 would actually be a good candidate for the EF-S mount, since the shorter rear element to sensor distance is an advantage in designing wideangles. However, ultra wides haven't been Canon's strongest suit historically, and it may be some time before they come out with an offering in this range. If it is an L when it comes, it will likely cost well over $1,000.