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Auto-focus question

I went browsing for a new lens in one of the photographic stores near my home the other day and I'm hoping someone here can clarify something for me. One of the things I wanted to know when comparing two lenses I'm considering is how good their auto-focus is in low light. I've got terrible night vision so I'm heavily reliant on auto-focus when I'm shooting in low light conditions, and the salesdude suggested that the sharpness of the autofocus would come down mostly to the camera body over the lens. I'm currently shooting on a Canon 450D but I'm thinking of upgrading to a 5D MkII when I find a money tree, and he said the 450D is accurate to 'within half a depth of field'.

Is this a spec which I could find listed somewhere? Is this actually correct, or is he just trying to upsell me a camera body with the new lens? It sounds plausible, but I'm interested to hear other opinions.

Comments

( 5 comments — Leave a comment )
anywhereanyone
Jul. 4th, 2011 07:33 pm (UTC)
Half a depth of field? WTF is half a depth of field? I would agree that it comes down more to a camera body than a lens, but his terminology sounds ludicrous.
zqfmbg
Jul. 4th, 2011 08:33 pm (UTC)
2nded. While he (the salesman) is at it, there's an advanced fribblefram inside there that nobody else has that will make you magically compose better. :)

I'm only familiar with differences in how quickly things do AF. IM(not-so-well-informed)O, camera bodies all hit about the same level of accuracy. AF speed depends on both the body and the lens; the more expensive cameras may be a bit faster, but the AF motors in the lenses are the primary determinant there.

One big thing to keep in mind: your 450D has a smaller sensor than the 5Dmk2. (5Dmk2 is the area of a 35mm film frame while 450D is smaller... I don't remember how much; I shoot Nikon.) If you have any EF-S lenses (and I bet you do), you won't be able to mount them on the 5Dmk2, meaning that you might have to track down their EF equivalents. It is not as simple as just switching the camera body, I'm afraid. (Wikipedia says that EF-S lenses project a smaller image and also are designed a smaller distance from the rear element to the sensor, which would mean that if you could mount them on a full-frame camera, you'd have the mirror slapping into the back of the lens, which is obviously not good. So I highly expect you are physically blocked from mounting them.)
bobbinsgalore
Jul. 5th, 2011 12:35 am (UTC)
Cheers, I appreciate the input :) I'm glad to hear another opinion because my experience is pretty slim. And yep, def. looking at EF lenses since they'll fit both my 450D and any future full frame cameras (I can dream!) I get.
bobbinsgalore
Jul. 5th, 2011 12:34 am (UTC)
Haha, I also wondered what this hitherto-unknown measurement was but I didn't want to look like a dunce if it turned out to be an actual thing ;)
anywhereanyone
Jul. 5th, 2011 12:40 am (UTC)
In my experience photographers who throw around the most weird terminology tend to suck at photography and work in camera stores. Not saying all camera store employees are lousy photographers, but it's just something I've noticed. By the way, that back tattoo is amazing. Come to America so I can photograph it.
( 5 comments — Leave a comment )

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