Surprised at autofocus


Mike_Young Plus
13 21 9 United Kingdom
29 Aug 2018 10:15AM
Hi all,
I use a Nikon D7200 camera and recently splashed out on a Nikon 200-500 F5.6 VR zoom lens. I already own a Nikon 1.7 TC 2 converter.
Reading all the paper work re compatibility is says that Autofocus is not supported using this combo.
Tried it out this morning in very low light conditions to find that it does in fact autofocus albeit at bit slow !
Anyone had a similar experience, or is there someone out there who is a technical buff care to comment.

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Railcam 13 776 2 Scotland
29 Aug 2018 12:22PM
I think the D7200 requires lenses with a maximum aperture of f5.6 or wider to guarantee autofocus. Adding a 1.7 Converter reduces the maximum aperture of the 200-500/f5.6 zoom to worse than f8 so Nikon cannot guarantee it will work. The fact that you have got it to work (albeit slowly) is merely a bonus.

Some higher end Nikon bodies will A/F at f8, but usually on the centre focus point only..

I hopet this clarifies.
Mike_Young Plus
13 21 9 United Kingdom
29 Aug 2018 12:54PM

Quote:I think the D7200 requires lenses with a maximum aperture of f5.6 or wider to guarantee autofocus. Adding a 1.7 Converter reduces the maximum aperture of the 200-500/f5.6 zoom to worse than f8 so Nikon cannot guarantee it will work. The fact that you have got it to work (albeit slowly) is merely a bonus.

Some higher end Nikon bodies will A/F at f8, but usually on the centre focus point only..

I hopet this clarifies.



Thanks Keith that does indeed help, I had a suspicion that was the case, I don't mind if it has certain shortcomings, its not a combo I'd be using very often anyway.
LenShepherd 11 4.0k United Kingdom
30 Aug 2018 11:57AM
Nikon is well known for fast focus tracking and seems to take focus tracking speed into account when giving AF guidance.

Clarifying two "not accurate" replies, not only does the D7200 have f8 AF capability, just about every AF point on every pre f8 AF pro and semi-pro Nikon DSLR going back to the F5 and F100 from last century have some AF f8 ability in good light with a static subject.

Having been advised (by Moose Peterson) of the f8 AF ability, it was the primary reason why I chose Nikon and not Canon when I switched from the Olympus OM 4 system in 1999

My experience is a DX body can sometimes AF with slightly lower "working apertures" than FX.
I agree there is some limited AF ability as you describe at effective f9.5.
I just tried it again on a low contrast subject with the centre AF point.
I needed a medium contrast subject to get a far outer AF point to work.
I cannot get any AF response at f9.5 with an FX body.

On the recent 153 AF point bodies there are some significant limits as to how many AF points work with an f8 combination or f9.5 on DX.

Some seem to have misconceptions about the limited to static subject Nikon AF ability at small effective apertures.

LenShepherd 11 4.0k United Kingdom
17 Oct 2018 9:09PM
Not directly relevant, the Nikon ML Z7 has reasonable AF with an f11 lens such as your zoom with a 2x converter.
Using the Z7 function button MF2 as a dof preview button you still have a bright viewfinder even stopped down to f32.


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