Autofocus Doesn't Work at Far Distances
I have a D300 and a 18-70mm/f3.5-4.5 G ED AF-S lens.
I just noticed that when photographing objects at great distance (distant mountains, etc.), the autofocus won't focus at a very wide angle (from about 24mm to the minimum 18mm). I think this is a new problem. This is true even when photograping a very contrasty subject, such as a dark mountain ridge against a bright sky.
This problem is most severe when the camera is held horizontally (landscape). When the camera is held vertically (portrait), it usually focuses.
Sometimes the lensmakes a bit of noise but doesn't "beep" to indicate focus, and sometimes the lens simply does nothing.
From about 25mm to 70mm, there is no problem - even in low light or when the subject is of low contrast and has no distinct borders.
Is this a lens problem or a camera problem? Would the warranty cover the fix? The lens is from Aug 2006, and the camera is from Mar. 2008.
TIA for any responses. I am generally very satisfied with lens, and this is driving me nuts.
#1. "RE: Autofocus Doesn't Work at Far Distances" | In response to Reply # 0CharlieS Registered since 29th Aug 2007Fri 12-Feb-10 07:38 PM
strange behavior indeed. I seem to recall reading about some problems with the 18-70 having some focus motor issues, but couldnt locate the article in question.
If your lens is making an abnormal noise and not functioning properly its probably due for some repair work.
Trying your lens on another camera, if possible, as well as trying a different lens on your body would help isolate the problem.
When no one is looking, Pigs can walk on they're hind legs
#2. "RE: Autofocus Doesn't Work at Far Distances" | In response to Reply # 0rasworth Basic MemberFri 12-Feb-10 07:47 PM
Have you verified that the actual images taken are out of focus?
Objects near infinity are generally going to be considered in-focus over a relatively large range of lens distance settings at wide angles as far as the af system is concerned.
#3. "RE: Autofocus Doesn't Work at Far Distances" | In response to Reply # 0Len Shepherd Nikonian since 09th Mar 2003Sat 13-Feb-10 06:05 AM
>I just noticed that when photographing objects at great distance (distant mountains, etc.), the autofocus won't focus
>at a very wide angle (from about 24mm to the minimum 18mm).
>This problem is most severe when the camera is held
>horizontally (landscape). When the camera is held vertically (portrait), it usually focuses.
>Sometimes the lens makes a bit of noise but doesn't "beep" to indicate focus, and sometimes the lens
>simply does nothing.
You are accurately describing an in camera AF limitation mentioned on page 70 of your D300 instruction book - and at http://nikoneurope-en.custhelp.com/app/answers/detail/a_id/4585
Your camera is showing common behavior for what you are trying to use it for.
In camera AF has difficulty in reading either low contrast (example 1 in the Nikon guidance) or very fine detail (example 6).
Distant mountains are often low contrast and wider angles make the detail smaller - which is why you get the majority of issues with distant mountains and wider than 24mm.
The outer AF points on the D300 are single line reading top to bottom of the viewfinder - and are more likely to find good for focusing detail when the camera is held vertically.
Digressing the "extra AF difficulties" with wider angles are mentioned in lens instruction for DX lenses going to 18mm or wider.
The common work around when AF cannot detect the subject is to switch to manual focus and for distant mountains to set the focus ring a little closer than infinity distance.
Photography is a bit like archery. A technically better camera, lens or arrow may not hit the target as often as it could if the photographer or archer does not practice enough.
#4. "RE: Autofocus Doesn't Work at Far Distances" | In response to Reply # 3lavie Registered since 27th Feb 2007Sun 14-Feb-10 01:11 PM
Thanks for the detailed reply!
I think that my situation may not quite match the conditions you describe:
1) I *think* this worked in the past, but am not sure.
2) I was shooting a mountain ridge square in the middle of the picture. I have focusing set to a single area in the middle of the picture, so the square wuld have contained a dark mountain bordering a bright scky - which should cause very high contrast.
3) With focusing set to a single dot in the middle, I wouldn't expect holding the camera horizontally or vertically to make any difference.
TIA for any further comments.