Doug Kerr
Well-known member
For several years, we have used as the "walkaround lens" on our EOS 40D a Sigma 18-200 mm f/3.5-6.3 DC OS. As you may recall, a while ago, we looked into improving our situation in this regard, the major motivation being to get an increase in the maximum focal length (we were of course actually seeking improvement in "reach", a parameter that considers resolution as well as focal length).
We purchased, tested, and returned two candidates: the Sigma 18-250 mm f/3.5-6.3 DC OS HSM and a Tamron AF 18-270 mm F/3.5-6.3 XI Di II VC LD.
Briefly, we found that in each case, the increased maximum focal length was accompanied by a more than corresponding decline in resolution such that no greater "reach" was actually attained. There were also some other anomalies that, although not major, helped solidify our decision not to adopt either of those lenses.
Recent work done here on AF system behavior helped illuminate some of the shortcomings of the current Sigma lens in the area of autofocus, and there are some irregularities in its optical stabilization behavior as well.
As a result, we again opened the issue of "upgrade" and decided to try out the only remaining contender, the Canon EF-S 18-200 mm f/3.5-5.6 IS USM.
Canon EF-S 18-200 mm f/3.5-5.6 IS USM (B&H photo)
First indications are quite encouraging. Whether its improvement over the Sigma would actually warrant the cost ($595.00 + $31.95 for the hood, B&H) is another matter altogether.
On the image quality front, I find that hand-held at 200 mm, f/8 (shutter speed about 1/1600), with AF, there is a perceptible (but not substantial) general improvement in image sharpness. I have the feeling that contrast is also improved over the Sigma.
Lateral CA is better in some places and worse in others. I have not looked into the geometric distortion story.
The maximum focal length for focus at a distance of 500 feet is about 6% greater than the Sigma (I don't have the actual number yet).
In any case, I haven't done much actual image work with the lens yet. The rest of this initial report will be only on "engineering observations".
The construction of the Canon lens is quite nice. Among other things, even when fully extended (for the top range of focal lengths), there is negligible play between the three telescoping sections.
The zoom ring works smoothly through its range, and has a fairly long throw. The lens will shift in focal length when pointed downward or upward at a substantial angle. There is a zoom lock, but it can only be engaged at minimum focal length.
The autofocus operation seems faster than on the Sigma lens (at least in situations where focus search is not required); this is, however, a difficult property to quantify. In any case, it seems that the focus normally "settles" after only two "rounds" (typical for my other Canon lenses), whereas the Sigma generally took five "rounds" to settle.
Focus search speed is graded with focal length setting, and seems fairly conservative.
The lens uses a DC micro motor, and does not have bona-fide full-time manual focusing. The manual emphasizes that we should not touch the ring when it is turning under motor power nor attempt to turn it by hand with the AF/MF switch in AF (in which case the motor drive is engaged).
Nevertheless, except when the motor is actually moving, it seems quite easy to turn the focusing ring, obviously taking the motor along for the ride. There is clearly no type of braking in effect after the completion of focusing movement (there may well be dynamic braking just at the end of the movement). But I find it hard to believe that turning the ring in this situation, with the switch in AF, actually puts any untoward strain on the gear train. So I am not at all reticent about "tweaking" the focus with the ring with the mode switch still in AF (of course being sure that the motor has stopped being driven).
By the way, the focusing ring is fairly narrow and is well-separated from the zoom ring (which minimizes the likelihood of contact with it when it is moving under motor power. But it is not difficult to grasp and operate when needed (even with the hood in place). There are no distance markings on it. It has a modest throw (I think about 80°) and works well for manual focus (either legitimate or otherwise).
The image stabilization (IS) is well behaved and seems effective. I have no way to quantify the degree of its effect.
The IS seems to "come up" very quickly. It seems as if the IS is shut down very quickly after the shutter release button is fully released. This is probably beneficial with regard to battery consumption.
The lens is 1 mm longer than the Sigma (when collapsed), about 1 mm greater in diameter, and the same weight (21 oz, not including the hood).
The overall conclusion on this lens is that it is a worthwhile upgrade.
I expect to have some actual photographs soon!
Best regards,
Doug
We purchased, tested, and returned two candidates: the Sigma 18-250 mm f/3.5-6.3 DC OS HSM and a Tamron AF 18-270 mm F/3.5-6.3 XI Di II VC LD.
Briefly, we found that in each case, the increased maximum focal length was accompanied by a more than corresponding decline in resolution such that no greater "reach" was actually attained. There were also some other anomalies that, although not major, helped solidify our decision not to adopt either of those lenses.
Recent work done here on AF system behavior helped illuminate some of the shortcomings of the current Sigma lens in the area of autofocus, and there are some irregularities in its optical stabilization behavior as well.
As a result, we again opened the issue of "upgrade" and decided to try out the only remaining contender, the Canon EF-S 18-200 mm f/3.5-5.6 IS USM.
Canon EF-S 18-200 mm f/3.5-5.6 IS USM (B&H photo)
First indications are quite encouraging. Whether its improvement over the Sigma would actually warrant the cost ($595.00 + $31.95 for the hood, B&H) is another matter altogether.
On the image quality front, I find that hand-held at 200 mm, f/8 (shutter speed about 1/1600), with AF, there is a perceptible (but not substantial) general improvement in image sharpness. I have the feeling that contrast is also improved over the Sigma.
Lateral CA is better in some places and worse in others. I have not looked into the geometric distortion story.
The maximum focal length for focus at a distance of 500 feet is about 6% greater than the Sigma (I don't have the actual number yet).
In any case, I haven't done much actual image work with the lens yet. The rest of this initial report will be only on "engineering observations".
The construction of the Canon lens is quite nice. Among other things, even when fully extended (for the top range of focal lengths), there is negligible play between the three telescoping sections.
The zoom ring works smoothly through its range, and has a fairly long throw. The lens will shift in focal length when pointed downward or upward at a substantial angle. There is a zoom lock, but it can only be engaged at minimum focal length.
The autofocus operation seems faster than on the Sigma lens (at least in situations where focus search is not required); this is, however, a difficult property to quantify. In any case, it seems that the focus normally "settles" after only two "rounds" (typical for my other Canon lenses), whereas the Sigma generally took five "rounds" to settle.
Focus search speed is graded with focal length setting, and seems fairly conservative.
The lens uses a DC micro motor, and does not have bona-fide full-time manual focusing. The manual emphasizes that we should not touch the ring when it is turning under motor power nor attempt to turn it by hand with the AF/MF switch in AF (in which case the motor drive is engaged).
Nevertheless, except when the motor is actually moving, it seems quite easy to turn the focusing ring, obviously taking the motor along for the ride. There is clearly no type of braking in effect after the completion of focusing movement (there may well be dynamic braking just at the end of the movement). But I find it hard to believe that turning the ring in this situation, with the switch in AF, actually puts any untoward strain on the gear train. So I am not at all reticent about "tweaking" the focus with the ring with the mode switch still in AF (of course being sure that the motor has stopped being driven).
By the way, the focusing ring is fairly narrow and is well-separated from the zoom ring (which minimizes the likelihood of contact with it when it is moving under motor power. But it is not difficult to grasp and operate when needed (even with the hood in place). There are no distance markings on it. It has a modest throw (I think about 80°) and works well for manual focus (either legitimate or otherwise).
The image stabilization (IS) is well behaved and seems effective. I have no way to quantify the degree of its effect.
The IS seems to "come up" very quickly. It seems as if the IS is shut down very quickly after the shutter release button is fully released. This is probably beneficial with regard to battery consumption.
The lens is 1 mm longer than the Sigma (when collapsed), about 1 mm greater in diameter, and the same weight (21 oz, not including the hood).
The overall conclusion on this lens is that it is a worthwhile upgrade.
I expect to have some actual photographs soon!
Best regards,
Doug
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