Doug Kerr
Well-known member
For two years, we have done 90% of our dSLR work (on a Canon EOS 20D and then an EOS 40D) with a Sigma 18-200mm f/3.5-6.3 DC OS zoom lens. Often reviled as a "vacation lens" (works for me, as I am permanently on vacation), these large zoom ratio lenses can be vary convenient. Of course, there are inevitable performance penalties associated with such large zoom ratios, perhaps especially for lenses in this price range (roughly USD500).
For Christmas this year, Carla got me the successor to this lens, the Sigma 18-250mm f/3.5-6.3 DC OS HSM. Our quest was for:
• Perhaps a "better" focus mechanism (this lens uses the Sigma "HSM" system, somewhat comparable in concept to the Canon "USM" system - more about this later).
• Perhaps a "better" optical image stabilization system (although there had been no real reports of an "improved" design being used in this lens).
• Perhaps improved "reach" as a result of the greater maximum focal length. (More about "reach" in part 2 of this report.)
A secondary hope was that the lens was not any longer physically (from the flange out) when collapsed than the 18-200, so that we could still put our EOS 40D with the lens in place in its compartment in our favorite camera bag.
The lens is now in hand (we are not big on delayed gratification). I thought I would give a brief report on my observations to date.
Collapsed length
This lens is essentially the same length, collapsed, as the 18-200 (the specs show an increase of 1 mm).
Focusing system
The focusing system in the 18-200 uses a geared DC motor. The motor is fairly noisy. Often, focusing takes place in two steps: a period of the motor running, a brief stop, and then a short period of final motion - just a "hiccup". It is hard for me to relate this to what I think I know about the Canon EOS AF scheme. I will probably discuss this further in a separate thread.
I don't think the HSM AF drive in the 18-250 is any faster. I will be able to make some crude measurements of this later, and I'll report on that. But it gives no impression of being noticeably faster.
It does seem more "decisive" (in that I don't perceive the "two-step" mentioned above). And it is almost completely quiet.
As with the Canon USM focus drive system, there are two sub-species of the Sigma HSM (hypersonic motor) system:
• The ring form, which ordinary brings with it full-time manual focus capability (one can manually change the focus after an automatic focus operation without shifting the mechanism to "MF").
• The micro-motor form (which does not ordinarily bring with it full-time manual focus capability).
The system used on the Sigma 18-250 is the "micro-motor" HSM, and there is in fact no full-time manual focus. There is evidently a slip clutch so that an earnest effort to move the focus ring with the lens in the AF state allows the ring to turn (presumably before any violence is done to the gear train).
I have not yet made actual measurements of the AF accuracy of the body-lens combination.
My favorite quick check of lens behavior as a component of the overall process (widely reviled by nay-sayers as "ill founded") is to aim the camera at a focus target, half press to do AF, then release the shutter button and half press again. My belief is that if the focus mechanism does not move on then second half press, then:
• the lens has done its part of the job accurately.
• the camera is consistent in its focus error reporting.
The camera of course may have an inaccurate opinion of where correct focus is, a matter which is not revealed by that check.
Based on this, the Sigma 18-250 behaves very well.
Image Stabilization
The image stabilization system on my Sigma 18-200 was worrisome in its behavior. When it was first engaged (by half press after a period of inactivity), the image in the finder would jump, and when moving the camera slowly (finalizing aim, for example) often the image in the finder would "jump". This of course might be the result of a defect in my copy - I had never sent it back to Sigma for investigation.
Although not really problematical, in the 18-200, when the stabilization system was running, there was a fairly perceptible sound from the lens, like a small motor running at high speed in the distance. And when half-press was released for 3 seconds, there was a noticeable "clunk" as the system as "caged".
With the 18-250 there is none of that. The operation is silent, and 2 seconds of release of half-press (which I assume is when the system "parks"), there is a click so tiny I had to go into our anechoic chamber (/walk-in closet/tornado shelter) to hear it .
Thus this is clearly a wholly different system. But nobody seems to know anything about it. I sense it that it is "ready to go" almost instantly after half-press (with the older system, there was a period of perhaps a second before it "settled in", and firing before that can cause noticeable blurring.)
I'm in no position to judge the degree of stabilization performance. However, during some very quick tests, I found that I could consistently get really nice shots of Carla at an indicated focal length of 250mm (230 mm actual) at 1/30 sec.
Construction and fitting
The construction and finish of the lens is quite nice. The full range of the manual focus ring is only about 45°, not really conducive to "delicate" manual focus work. With the slide in the MF position, the focus ring is very smooth and almost supernaturally easy to turn.
There is a "zoom lock" slide, but as customary for Sigma lenses, this is really a "transport lock" - it can only be engaged with the lens at minimum focal length.
A nice surprise is that the lens came with the new-style Sigma front cap, whose release tabs are near the center such that one can easily remove the cap when the hood is in working position.
The lens comes with a nice bayonet-attachment petal style hood, although of course a single hood can hardly be optimum for such a wide range of focal lengths. The hood can be stored, reversed, and the lens operated that way (MF would be a little dicey - but doable). The lens takes 72-mm thread filters.
The image circle of the lens will not support any EOS format sizes larger than "1.6x".
At a distance of 500', the actual focal length at the maximum setting ("250 mm") is about 238 mm.
In Part 2, I will speak about "telephoto reach" and show some test images with the new lens (and the older one as well) mainly of interest in assessing that.
Best regards,
Doug
"So, what do the nay-sayers say?"
"Well, 'nay', I suppose."
For Christmas this year, Carla got me the successor to this lens, the Sigma 18-250mm f/3.5-6.3 DC OS HSM. Our quest was for:
• Perhaps a "better" focus mechanism (this lens uses the Sigma "HSM" system, somewhat comparable in concept to the Canon "USM" system - more about this later).
• Perhaps a "better" optical image stabilization system (although there had been no real reports of an "improved" design being used in this lens).
• Perhaps improved "reach" as a result of the greater maximum focal length. (More about "reach" in part 2 of this report.)
A secondary hope was that the lens was not any longer physically (from the flange out) when collapsed than the 18-200, so that we could still put our EOS 40D with the lens in place in its compartment in our favorite camera bag.
The lens is now in hand (we are not big on delayed gratification). I thought I would give a brief report on my observations to date.
Collapsed length
This lens is essentially the same length, collapsed, as the 18-200 (the specs show an increase of 1 mm).
Focusing system
The focusing system in the 18-200 uses a geared DC motor. The motor is fairly noisy. Often, focusing takes place in two steps: a period of the motor running, a brief stop, and then a short period of final motion - just a "hiccup". It is hard for me to relate this to what I think I know about the Canon EOS AF scheme. I will probably discuss this further in a separate thread.
I don't think the HSM AF drive in the 18-250 is any faster. I will be able to make some crude measurements of this later, and I'll report on that. But it gives no impression of being noticeably faster.
It does seem more "decisive" (in that I don't perceive the "two-step" mentioned above). And it is almost completely quiet.
As with the Canon USM focus drive system, there are two sub-species of the Sigma HSM (hypersonic motor) system:
• The ring form, which ordinary brings with it full-time manual focus capability (one can manually change the focus after an automatic focus operation without shifting the mechanism to "MF").
• The micro-motor form (which does not ordinarily bring with it full-time manual focus capability).
The system used on the Sigma 18-250 is the "micro-motor" HSM, and there is in fact no full-time manual focus. There is evidently a slip clutch so that an earnest effort to move the focus ring with the lens in the AF state allows the ring to turn (presumably before any violence is done to the gear train).
I have not yet made actual measurements of the AF accuracy of the body-lens combination.
My favorite quick check of lens behavior as a component of the overall process (widely reviled by nay-sayers as "ill founded") is to aim the camera at a focus target, half press to do AF, then release the shutter button and half press again. My belief is that if the focus mechanism does not move on then second half press, then:
• the lens has done its part of the job accurately.
• the camera is consistent in its focus error reporting.
The camera of course may have an inaccurate opinion of where correct focus is, a matter which is not revealed by that check.
Based on this, the Sigma 18-250 behaves very well.
Image Stabilization
The image stabilization system on my Sigma 18-200 was worrisome in its behavior. When it was first engaged (by half press after a period of inactivity), the image in the finder would jump, and when moving the camera slowly (finalizing aim, for example) often the image in the finder would "jump". This of course might be the result of a defect in my copy - I had never sent it back to Sigma for investigation.
Although not really problematical, in the 18-200, when the stabilization system was running, there was a fairly perceptible sound from the lens, like a small motor running at high speed in the distance. And when half-press was released for 3 seconds, there was a noticeable "clunk" as the system as "caged".
With the 18-250 there is none of that. The operation is silent, and 2 seconds of release of half-press (which I assume is when the system "parks"), there is a click so tiny I had to go into our anechoic chamber (/walk-in closet/tornado shelter) to hear it .
Thus this is clearly a wholly different system. But nobody seems to know anything about it. I sense it that it is "ready to go" almost instantly after half-press (with the older system, there was a period of perhaps a second before it "settled in", and firing before that can cause noticeable blurring.)
I'm in no position to judge the degree of stabilization performance. However, during some very quick tests, I found that I could consistently get really nice shots of Carla at an indicated focal length of 250mm (230 mm actual) at 1/30 sec.
Construction and fitting
The construction and finish of the lens is quite nice. The full range of the manual focus ring is only about 45°, not really conducive to "delicate" manual focus work. With the slide in the MF position, the focus ring is very smooth and almost supernaturally easy to turn.
There is a "zoom lock" slide, but as customary for Sigma lenses, this is really a "transport lock" - it can only be engaged with the lens at minimum focal length.
A nice surprise is that the lens came with the new-style Sigma front cap, whose release tabs are near the center such that one can easily remove the cap when the hood is in working position.
The lens comes with a nice bayonet-attachment petal style hood, although of course a single hood can hardly be optimum for such a wide range of focal lengths. The hood can be stored, reversed, and the lens operated that way (MF would be a little dicey - but doable). The lens takes 72-mm thread filters.
The image circle of the lens will not support any EOS format sizes larger than "1.6x".
At a distance of 500', the actual focal length at the maximum setting ("250 mm") is about 238 mm.
In Part 2, I will speak about "telephoto reach" and show some test images with the new lens (and the older one as well) mainly of interest in assessing that.
Best regards,
Doug
"So, what do the nay-sayers say?"
"Well, 'nay', I suppose."