Nikon cross-type sensor

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Bill - 17 Aug 2006 12:15 GMT

Here's something on which I can't seem to find anything conclusive. In
relation to the autofocus systems in several Nikon cameras:

"...the center AF sensor is cross-type, able to respond to subject
detail oriented either horizontally or vertically..."

I've seen this mentioned and I know exactly what it means and how it
improves autofocus performance.

But since I come from the Canon camp, I know that with Canon cameras the
high precision cross-type sensors are only useful with bright lenses,
specifically if you have an f/2.8 or better lense attached. The high
precision cross-type sensor does not help with kit lenses like the 18-55
f/4-5.6 or even L glass like the 17-40 f/4, although the regular sensor
does work up to f/5.6.

Does anyone know if Nikon follows the same rule or is their sensor the
same type and function at all f stops?

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Frank B - 17 Aug 2006 14:28 GMT

Bill,

I have a D50 and I have tested the center cross-type sensor against the
others with my f3.5/5.6 Nikon18-200 mm VR and it works in both
directions while the other sensors do not. I tested at 200 mm, f5.6
being the widest aperture at that focal length.

> Here's something on which I can't seem to find anything conclusive. In
> relation to the autofocus systems in several Nikon cameras:
[quoted text clipped - 14 lines]
> Does anyone know if Nikon follows the same rule or is their sensor the
> same type and function at all f stops?

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Bill - 17 Aug 2006 17:22 GMT

>Bill,
>
>I have a D50 and I have tested the center cross-type sensor against the
>others with my f3.5/5.6 Nikon18-200 mm VR and it works in both
>directions while the other sensors do not. I tested at 200 mm, f5.6
>being the widest aperture at that focal length.

Thanks for the quick response Frank.

I'll have to borrow my friends D70s and a couple of lenses on the
weekend and do a little testing myself. I'd borrow his D200, but the
pr!@k won't let me have it most of the time.

Imagine that...

:-)

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AaronW - 18 Aug 2006 22:47 GMT

> But since I come from the Canon camp, I know that with Canon cameras the
> high precision cross-type sensors are only useful with bright lenses,
> specifically if you have an f/2.8 or better lense attached. The high
> precision cross-type sensor does not help with kit lenses like the 18-55
> f/4-5.6 or even L glass like the 17-40 f/4, although the regular sensor
> does work up to f/5.6.

Does Canon have some web pages on AF?

http://digitcamera.tripod.com/#slr

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Bill - 18 Aug 2006 23:12 GMT

>> But since I come from the Canon camp, I know that with Canon cameras the
>> high precision cross-type sensors are only useful with bright lenses,
[quoted text clipped - 4 lines]
>
>Does Canon have some web pages on AF?

I don't recall seeing anything technical on Canon's site, just marketing
info mostly like this:

"Impressive 9-point Wide-area AF with a dual precision sensor at the
center"

"The EOS 30D has a high-precision, 9-point wide area AF system that uses
both normal and high-precision focus depending on the aperture and
available light."

Most of the info about their AF I found on various sites in reviews of
cameras.

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AaronW - 21 Aug 2006 02:31 GMT

> Here's something on which I can't seem to find anything conclusive. In
> relation to the autofocus systems in several Nikon cameras:
[quoted text clipped - 11 lines]
> f/4-5.6 or even L glass like the 17-40 f/4, although the regular sensor
> does work up to f/5.6.

I think with Canon, the side AF points need large aperture to enable 2D
high precision. The center AF point is always 2D high precision even
with f/5.6 lenses.

http://digitcamera.tripod.com/#slr

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Sheldon - 21 Aug 2006 04:36 GMT

I'm not sure what you mean by a cross-type sensor, but I've had no trouble
focusing with my D70 in any position with any lens using any of the focus
modes. I know in continuous mode the camera is supposed to try and figure
which direction the object is moving, and that can be a little tricky.

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Bill - 21 Aug 2006 13:26 GMT

>I'm not sure what you mean by a cross-type sensor,

An autofocus sensor that detects phase variance on both a vertical and
horizontal plane in the same area of a subject scene.

Some subjects may lack vertical or horizontal phase differences, and if
the focus point used is sensitive to just one plane, it may not acquire
focus accurately using that point.

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