"Play" in focusing - Nikon 50mm F1.4

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Nobody - 31 Oct 2006 00:47 GMT

Hello,

I purchased a 50mm F1.4 AF lens for use with a D200. I notice that
there seems to be a fraction of an inch (maybe 1/16th) play in the
focusing ring after the autofocus has done it work. Is this normal?
I have just moved to autofocus and digital.

Regards.

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Jeremy Nixon - 31 Oct 2006 04:04 GMT

> I purchased a 50mm F1.4 AF lens for use with a D200. I notice that
> there seems to be a fraction of an inch (maybe 1/16th) play in the
> focusing ring after the autofocus has done it work. Is this normal?

Mine does it too. It's slight and inconsequential, and it's normal,
but I just did a side-by-side comparison and my 50/1.4 seems to do it
more than other (non-AFS) lenses. I'd never noticed the difference
before. I don't think it's anything to worry about, though.

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Colin_D - 31 Oct 2006 04:44 GMT

> Hello,
>
[quoted text clipped - 4 lines]
>
> Regards.

My Canon lenses have the same looseness. I gather it's to minimize the
drag on the focusing motor, specially with lenses where the front
element rotates. Perceptible stiffness would raise the current drain
from the battery while focusing, and may prevent the focus from being
precise, maybe even stalling the motor before focus is reached.

Colin D.

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Wolfgang Weisselberg - 31 Oct 2006 22:18 GMT

> My Canon lenses have the same looseness. I gather it's to minimize the
> drag on the focusing motor, specially with lenses where the front
> element rotates. Perceptible stiffness would raise the current drain
> from the battery while focusing, and may prevent the focus from being
> precise, maybe even stalling the motor before focus is reached.

It may cause slow focussing. It may cause a lot more power use.
But then the motor is matched to the very lens it sits within.
(Are your lenses FTM-capable, btw?)

It won't degrade focus accuracy: Canons AF checks the lens' focus
setting and corrects it until it's within the stated tolerances.

On the other hand, there is no measure-check-redo loop for the
AF one-shot setting.

-Wolfgang

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Colin_D - 31 Oct 2006 23:40 GMT

>> My Canon lenses have the same looseness. I gather it's to minimize the
>> drag on the focusing motor, specially with lenses where the front
[quoted text clipped - 5 lines]
> But then the motor is matched to the very lens it sits within.
> (Are your lenses FTM-capable, btw?)

Yes, ring-motor ftm. And the motor is matched to the lens for the
amount of friction built-in to the particular lens design, and may well
not have enough grunt to drive a stiffer lens, if one attempts to reduce
the looseness.

> It won't degrade focus accuracy: Canons AF checks the lens' focus
> setting and corrects it until it's within the stated tolerances.

If the setting is not correct because of stiffness, the camera won't fire.

> On the other hand, there is no measure-check-redo loop for the
> AF one-shot setting.
>
> -Wolfgang

Colin D.

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Wolfgang Weisselberg - 05 Nov 2006 12:58 GMT

>> It won't degrade focus accuracy: Canons AF checks the lens' focus
>> setting and corrects it until it's within the stated tolerances.

> If the setting is not correct because of stiffness, the camera won't fire.

If the camera is still trying to focus the lens, it will not fire
_in one-shot AF modus_. It _will_ fire in Servo AF mode. Important
difference.

-Wolfgang

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Sheldon - 03 Nov 2006 05:37 GMT

> Hello,
>
[quoted text clipped - 4 lines]
>
> Regards.

My understanding is that the play is there because the manufacturers use
little if any lubrication to free up and speed up the autofocus. Most AF
lenses not only feel loose but rattle if you shake them.

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