Canon 1000D vs 450d

Started Feb 10, 2009 | Discussions thread
NumberOne Veteran Member • Posts: 4,064
Re: Thanks for the correction! ...

David Chin wrote:
I honestly don't know how that one slipped by - I've removed the
offending section.

WilbaW wrote:

This doesn't sound right to me -

"On the Canon XS, the center AF (autofocus) point is of a cross-type
sensor that is rated at f/5.6, meaning, if the lens mounted on the
camera has a wide-open aperture of f/5.6 or larger, you get to enjoy
the higher focus accuracy that comes with cross-type sensors. On the
XSi, you'd have to mount lenses with wide-open apertures of f/2.8
(more often than not, these lenses are pricey) or larger in order to
get the same benefits."

My understanding is that the XSi sensor is a cross-type, like the XS,
but with enhanced accuracy for f/2.8 or better.

I wouldn't say a cross-type sensor is more accurate, it's just able
to work with horizontal and vertical lines at the same time.

To clarify this matter regarding Canon cameras:

A - If the cross-type sensor is f/2.8 sensitive it means that when used in conjunction with lenses whose luminosity is equal or bigger/better than 2.8 (1.4, 1.8, 2.0) it will AF in between the 1/3 DOF of the lens widest aperture, regardless of the used/chosen aperture.

B - If the cross-type sensor is not f/2.8 sensitive it means that when used in conjunction with lenses whose luminosity is equal or bigger/better than 5.6 (3.2, 4.0) it will AF in between the DOF of the lens widest aperture, regardless of the used/chosen aperture.

C - Keep in mind, that except in the professional line (1D...), Canon AF will not work accurately with lenses whose luminosity is smaller/worst than f/5.6...

So, generally speaking, you can say that f/2.8 sensitive cross-type sensors are 3 times more accurate than their f/5.6 siblings, when used with the appropriate lenses (f/2.8 or better/more luminous)...

Hope this helps.

Best regards,
Pedro

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