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Old January 20th, 2005, 08:11 PM   #1
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How good is the XL2 autofocus?

As my eyes grow less precise, I find myself needing autofocus more than I used to. My Sony DSR250 has lightning fast, very solid autofocus. How is the XL2's autofocus compared to the DSR250/PD170, et al? And, yes, I am fully aware that manual focus is always preferable.
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Old January 21st, 2005, 12:06 AM   #2
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I think the auto-focus on the XL2 is one of the things that has taken a backwards step from previous models. Even my old GL1 performed better. The focus tends to shift back and forth between foreground and background, and zooming any faster than at a snails pace will make the focus go wild. I find myself having to use the focus ring VERY often to correct auto-focus problems. I love my XL2 in every other aspect, but I think Canon has done much better in the past with this feature. Hope this helps.
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Old January 21st, 2005, 12:18 AM   #3
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i dunno how the xl2 matches up with the dsr-250 in auto focus speed, but i do know that the xl2 has 3 different auto focus speeds, low, medium, high.

which is pretty handy because sometimes the focus is too fast and leaves the main subject, in this case you would swith to medium or low.


jason
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Old January 21st, 2005, 09:04 AM   #4
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<<<-- Originally posted by Jason Hakala : i dunno how the xl2 matches up with the dsr-250 in auto focus speed, but i do know that the xl2 has 3 different auto focus speeds, low, medium, high.

-->>>

Jason, are you sure about this? I don't see any difference in focus speed when I change this setting, and the way I interpret the manual, the setting only refers to the speed when changing to the preset focus, not to normal autofocus speed.

Richard
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Old January 21st, 2005, 09:31 AM   #5
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I'll disagree with brent on this one. The xl2 focus has been tuned to a slower (so it won't match the lightning fast dsr 250), but more steady parameter as compared to the xl1s. It rarely hunts in comparable situations, and is on par with the GL2 in terms of speed and steadiness. I've found its focusing ability in low light to be markedly improved over the xl1s (although that is essentially starting from zero). And in answer to bill's question, it has been improved also by the inclusion of the focus presets.

Barry
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Old January 21st, 2005, 11:20 AM   #6
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I'd say, this autofocus rocks!

I shoot a lot of fashion shows, now with the XL2. Always with autofocus. Honesty forces me to say that most of the times, these shows are lit properly, so you can shoot at 0 dB gain, at 5.6. I rarely see the focus hunt or loose it.
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Old January 21st, 2005, 01:09 PM   #7
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richard im pretty sure thats what it does. it controls the hunt speed of the focus, i know this because of one of the reviews on the xl2 in videomaker was talking about it, and they got the info from a canon rep. ive only had my xl2 for about a week and haven't really tested it out to much but from what ive tried it worked.

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Old January 21st, 2005, 01:15 PM   #8
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Also be advised that autofocus is going to react slower in 30p and even slower still in 24p. The slower the frame rate, the slower the autofocus can update itself.
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Old January 21st, 2005, 07:39 PM   #9
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<<<-- Originally posted by Jason Hakala : richard im pretty sure thats what it does. it controls the hunt speed of the focus, i know this because of one of the reviews on the xl2 in videomaker was talking about it, and they got the info from a canon rep. ive only had my xl2 for about a week and haven't really tested it out to much but from what ive tried it worked.

jason -->>>

Hi Jason. I think I saw that review too, but I don't see that setting make any difference at all to the autofocus speed on my camera. It does work fine on the return-to-preset focus speed however, so it's not just that a switch is broken on my cam. How much difference are you seeing between the slowest and faster settings?

Regarding the autofocus generally, I would agree with Jan that if you have a reasonable depth of field the autofocus is pretty good. I think it is hunting most of the time, but you only really notice it when you have the iris open wide and the depth of field correspondingly tight. Of course we should use manual when we can, but sometimes you just have to get the shot and when it's a moving target, autofocus is very useful.

Richard
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Old February 20th, 2005, 02:40 AM   #10
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Autofocus problems

I've noticed with my new XL2 that autofocus has issues. I got this camera to use for shooting in dynamic settings, lots of moving targets -- sporting events and whatnot. So this is a make or break problem for me, not just an annoyance I can work around. I've noticed that zooming in tight on somone's face often results in a blurry image. Sometimes it corrects itself quickly, sometimes not. If I zoom in on two people talking (and I mean upper torsos nearly filling the frame with a small gap in between), this camera will often try to focus on the background behind the two subjects! This is at an indoor ice rink, where I would expect the lighting to be adequate for good AF function. I'm shooting plain vanilla, 60i, 4:3.

In the interest of full disclosure, I'm new to this level of video camera. I never had this kind of problem with my trusty old Sony TRV-30. Its AF always "just worked" except in low light. It was a rude shock to suddenly start having AF problems with an "overengineered" camera costing three times as much.

So, is there likely a problem with my specific XL2, a general shortcoming for this model, or am I just doing something wrong?

Any clues greatly appreciated...

-cw-
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Old February 20th, 2005, 12:38 PM   #11
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Charlie,

I think there are a couple of issues leading to your problems that are design related, and not necessarily "flaws" in the xl2.

The first, and most important as it relates also to the second is that the Xl2 (and gl2) are the only cameras on the market with a true 20x optical zoom, as compared to the trv-30's 10x zoom. This extra length of zoom requires a much greater focus shift from foreground to background (One one of the differences you've probably noticed is that when you are zoomed all the way in with the xl2, that there is actually a noticeable blurring of the background--or foreground in your case!--, where as the trv-30 almost everything is sharp all the time under good lighting). A good way to test this is to limit the xl2 to half of its zoom range (slider bar at top of viewfinder). You'll find that at this zoom level most of the problems disappear (as does the depth of field). As you approach 20x zoom, the focus "travel" or adjustment increases exponentially, even between objects that are only feet or inches apart.

The second issue is related to you description of two people talking with a gap in between them. (remember anything related to this issue is made more of a problem by the 20x zoom). The camera is doing exactly as its told if you place that gap in the center of the frame. The camera doesn't know what you want to focus on, so it designates an area at the center of the frame as its focus area. This is a classic situation where almost all autofocus systems fail. (Canon does produce a nice indexed focus system on its still cameras, and I do wonder why it isn't incorporated in the video cameras).

Regarding the zooming in to a face, with the camera taking a second to correct the focus. This is also by design, although the xl2 may do it slower than the smaller lens of the trv-30 (remember the 20x)...the xl2 is not capable of zooming and focusing at the same time (I'm not sure if any camera is) so once you finish your zoom, the autofocus takes over to correct any mis-focus from when the camera was at its wider zoom. A typical way of handling this issue is to prefocus on the face (manual zoom) and then pull wide and rezoom to a perfect shot.

All autofocus systems will show the problems you've listed, given the right circumstances. The trv-30 will show it less than the xl2 due to it's shorter lens. Additionally the xl2's autofocus is tuned a little slower than other systems to eliminate the hunting that can happen (again mostly at longer zoom ratios) especially in low light.

Hope this helps.

Barry
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Old February 20th, 2005, 03:33 PM   #12
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Barry,
Thanks very much for your thoughtful response. What you're saying about the 20x zoom makes sense, but I don't think it completely applies. Even taking all that into account, I'd still have to characterize this XL2's AF performance as "weak, a little slow and too small of a spot." I understand it's center weighted, but this is nuts. (And I agree wholeheartedly about the indexed focus.)

I think part of the problem is that we're in the realm of subjective judgements. And I've been spoiled by the apparently very good AF on the TRV-30. Also, you have a better understanding of the optical miracle that Canon has wrought here and will be perhaps a little more forgiving of quirks, while I (being a stubborn, demanding SOB new to high-end cameras), expect my design miracles without shortcomings. i.e., "They should have designed an AF that can handle a 20x lens, period."

Regardless, your suggestion of limiting my zooming to 10x and observing the results is a good one and I'm going to give it a try. This also makes me wonder if a related contributor to my problem is "zoom fever" as a result of having a new toy with this capability. In other words, the problem may subside somewhat as I get more seasoned and learn to use zoom more sparingly? Right now I feel compelled to fill the frame with my subjects, near or far.

There are a lot of things I really like about this camera and would rather not have to go through the hassle and disruption of hunting down something else.

Just curious... If someone came to you and said "What's the best sub-$5000 camera for shooting live sporting events?", what would you answer? Anyone else care to take a shot at that one?

Thanks again,
Charlie
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Old February 20th, 2005, 08:20 PM   #13
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"They should have designed an AF that can handle a 20x lens, period."

I think they have... it's just that "instantaneous, perfect focus" is not really a reality with long lenses. I've used 600mm still camera lenses, and they can often be fooled by foreground - background issues, and because the focus shifts can be several inches at the lens, these goofs stick out a lot more than a short lens that is moving 1/8" or less during a focus adjustment.

Yes the xl2 is a little slower than I'd like...although I'd agree also that I prefer this to the hunting that can happen with a faster focusing situation like the xl1s with the 16x isII.

Anyway, good luck with it. Hopefully it will start to feel normal to you in short order.

Barry
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Old February 21st, 2005, 12:49 AM   #14
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I have to admit that I was less than enthusiastic about the auto focus performance on my XL-2 with stock 20x lense. But, I tend to run in manual so that I have the exposure meter to work with and I will say that most focus hunting I have seen is with less than optimal exposure. I would like to see Canon adopt a hybrid auto focus which has been done with some Kodak and Sony still cameras. Those things can focus in near total darkness.

Barry, the more expensive lenses can zoom and focus at the same time because they have separate servos for each. For cost reasons, Canon has elected to continue using a shared servo approach in the XL auto lense.

Another point about the Canon's auto focus is that it NEEDS to see good contrast in the scene and vertical lines if possible.

One reason that some of the smaller cameras may focus better is due to the fact that they shoot an infra-red beam and use it to focus with. IIRC, the Canon uses the image on the CCD's which is why it needs contrast and vertical lines to work with. Naturally, the IR approach is going to perform better in low light scenarios.

And finally, the three speeds on the Canon for focus are for the focus preset only. AF works at one speed forj 60i, slower at 30p and slower yet at 24p as Chris stated. I believe it is the Sony HDV that has the different speed settings for the AF which I think are labeled High, Medium, and Low.

regards,

-gb-
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Old February 21st, 2005, 02:29 PM   #15
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Thanks Barry and Greg. Shared servo... Ack!! Sounds like I need to save up my pennies for a *really* expensive camera. You think $50k oughta do it, or am I looking at more like $100k? ;-)

Seriously, I'm feeling rather humbled right now. I knew in advance that I'd probably be doing mostly live sports. I also suspected that would be a rather demanding task (though I figured more so on me than the camera). As far as selecting a camera went, I did my research and knew the XL2 gets good reviews and is regarded as top of the heap by many owners. I did not however go the extra step and research whether the XL2 was the best fit for the kind of work I'm doing. ...and perhaps it *is* the best fit for its price range and I really do need to save my pennies. And I've only done one event with this thing so far. Maybe I just need a little more time to get acquainted.
(Further reassurance welcomed!)

Curious, does anyone manually adjust both focus and zoom while panning/tilting for live events? That seems just a bit too demanding for me, but I'm just a beginner. Also, based on what Greg said about the single servo, sounds like I can't both focus and zoom at the same time anyhow, even manually.

-cw-
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