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Old Jul 12, 2006, 12:58 PM   #1
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I'm interested in a fast camera for sports photography. Unfortunately, no point-and-shoot is fast enough. So I began looking at DSLR's. Specifically the Canon 20D and 30D, as well as the Nikon D200. But, I noticed in the various review websites, the measured times vary for the exact same variable.

Like when measuring "Power On to First Shot", dpreview says the 20D takes 0.3 seconds. Yet imaging-resource says it takes 0.25 seconds. That I could chalk up to rounding up. But then stevesdigicams says it takes 0.6 seconds.

The same measurement on the 30D is also highly variable. Dpreview says its less than 0.2 seconds. Imaging-resource says its 0.1 seconds. Stevesdigicams says its 0.4 seconds.

Then when I try to compare "Full AF" timing, I get the same variability in measurements. Imaging-resource states the 20D takes 0.16 seconds whereas stevesdigicams states it takes 0.3 seconds.

The 30D measurements for "Full AF" timing is 0.245 seconds from imaging-resource and 0.3 seconds from stevesdigicams.

I realize that "Full AF" will depend on the lens being used as well as how far it is extended, but the numbers are probably the best times they measured. There is still tremendous variability.

Since the numbers seem to be all over the map, it makes it very difficult for me to make an educated decision as to which is fastest.

They all seem to perform admirably in continuous mode, so that isn't a problem. But when you need to get a single shot off fast, it really matters. A quarter second later is too late. There are point-and-shoots that fast.

So which is the fastest and why do the reviews have such variability?
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Old Jul 12, 2006, 1:37 PM   #2
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They're all right. ;-)

Light will impact Autofocus Speed. If you're in low light, trying to focus on a subject without much contrast, it may take longer. If you're in good light, focusing on a subject with lots of contrast, it will be faster.

If light gets very low, some models may continue to focus (although with slower times), and others may try for a couple of seconds and "give up", even if they're very fast in good light.

The brightness of the lens used impacts Autofocus Speed. For example, a lens with a largest available aperture of f/1.4 is exactly 16 times as bright as a lens with a largest available aperture of f/5.6 (and a camera always focuses with the aperture wide open) So, the AF sensors can "see" to focus better with a brighter lens. Although a lens that's not as sharp at wide open apertures can give slower focus times (and how sharp a lens is wide open will vary considerably by lens). You have to take each lens on a case by case basis.

The way a lens is geared will also impact Autofocus Speed. Some lenses (for example, macro lenses) are geared for finer focus adjustments (and have a wider range of focus distances available). A lens like a 70-200mm f/2.8 is usually geared for very fast focus, and many of these lens types also have specialized focus systems built into the lens (USM or Ultrasonic focus motors, Super Sonic Focus Motors, Silent Wave Focus Motors, etc., depending on the manufacturers term for it).

The degree of change needed also impacts AF speed. If you focus on something close, then focus on something far away next, the camera will take longer. But, if you are already focused on a subject, and focus again later, the lens mechanism won't have to move as far (if at all), so it's faster.

There are a lot of variables involved with AF speed, with the lens, subject type and amount of light being the three biggest ones.

The times you're looking at are only useful for comparing models timing them in identical conditions, using identical subjects with similar lenses. Your Autofocus times may be much faster, or much slower than you see reported, depending on the lens, subject and lighting.

As for startup speed, the memory card being used will have a big impact with most models.

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Old Jul 13, 2006, 7:53 AM   #3
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Don't kill yourself over focus speed and start up between these 3 cameras. They're all exceptional and will be plenty good enough for what you want to do. Any of the 3 will be an exceptional sports camera - they still don't stack up to the pro models - especially where focusing comes into play. But unless you're willing to step up to the Canon 1d Mk II N for $4000 then any of these 3 will more than meet your start up and focus speeds - again assuming you spend the money on the good glass necessary to maximize focusing.

For what it's worth, I still think the better high-ISO performance of the 20D/30D gives them and edge over the D200 as a sports camera although overall feature set and durability makes the D200 the better overall camera.

But, my point is the 2 aspects you're looking at are not the difference makers between these models.
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Old Jul 14, 2006, 9:26 PM   #4
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Is the difference between .1 sec. and .3 sec. important? It takes longer than that to lift the camera to your eye, let alone compose the shot.
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