D70s & 18-200 Focus Issue

[jeryang]

I was shooting at the zoo this past weekend. I was using my d70s and 18-200 lens. When zoomed out to 200 I could not get the camera to focus on the animal.

In particular I noticed this when I was shooting a bear. The camera kept trying to focus but was just not getting it. I finally shut off the auto focus and did it myself with poor results.

This happened again when I was shooting a tiger. Same thing: camera kept trying to focus, but no good. Again, I shut off auto focus, but the results were not good.

Any idea why this would happen? Thanks for your input.

[K1W1]

How much contrast was in the scene, specifically in the area you were focussing on? Were you trying to shoot through glass?
It's not uncommon for zooms to struggle a bit focussing at the far end of their range so try focusing on something with really good contrast at 200mm (a black line on a white wall or something) and see what happens.

[Dread Pirate Roberts]

Try focussing on a line.

Sometimes hair and faces (skin) don't have enough contrast for it to detect an edge and focus. For faces I often pick an eyebrow or something that forms a line. Hair can sometimes work for people but for shiny animals it often isn't good enough and somewhere where the fur changes colour or an eye can work.

I think you can adjust the size of the focus area if you're using spot focusing and that might help but you'd have to read the manual as I'm guessing wildly now.

[K1W1]

I think you can adjust the size of the focus area if you're using spot focusing and that might help but you'd have to read the manual as I'm guessing wildly now.

On the D70S you can adjust the size of the metering area for centre weighted metering but not the size of the focus area.
Can you adjust the focus area size on any Nikon? I'm not talking about select more or less focus points but adjusting the size of any particular point.

[Dread Pirate Roberts]

You're right, I was full of S when I thought the focus sensor size could be adjusted. Those manuals takes some reading.;)

[XaiLo]

Yeah that contrast issue will do it every time! when this happens if all else fails and time permitting I try to focus on something else on the same focus plane and employ focus lock recompose and pray. :)

[jeryang]

Thanks all. The brown bear was against a light brown (fake rock) background. That might have done it. I'll try again soon.

[Dread Pirate Roberts]

We've all assumed your 18-200 is a Nikkor 18-200VR. If it's not the advice might change. If it is the 18-200VR then you can always just tweak the focus ring to get manual overide.

[jeryang]

I was in a gym while my son was playing "basketball". He is 3, so playing "basketball" is a bit generous. His teammates and his coach were huddled at the midcourt line. I was at the baseline about 40 feet away. The lens would absolutely not focus. No matter what I did, the lens would not focus.

I noticed this again while shooting some mountain biking this weekend. I was out on the course and could not shoot riders who were farther away. I had to wait until they were close by and then shoot. When I tried shooting riders (and their bright colored jerseys against a dirt brown background) who were far away, the lens would just stop trying to focus. It seemed to have given up. When I grabbed the manual focus ring, nothing happened. I couldn't get things into sharper focus.

I have had this lens, the Nikon 18-200 Vr, for about a year and it was fine until a couple of weeks ago when I noticed some focusing issues. Is there something I'm doing wrong? What can I do short of sending it to Nikon?

I don't seem to have this issue when I'm shooting things closer in. Within about 15 feet, I'm fine. I haven't found the exact point where it stops focusing, but it seems to be a problem with distance, not zoom length. And grabbing the focusing ring is not a solution for a manual override is not the solution as this doesn't help.

I'm trying to determine if it is an slr issue or a lens issue. I'm going to swap the lens on to another person's Nikon to test it out to see if the problem persists. I don't know if I'd rather the body have an issue or the lens...

Also, my 50 1.8 works fine on the d70s. No issues at all with focusing, although I tend not to focus too far with the 50.

Thanks for your input.

[Dread Pirate Roberts]

A big errm no idea from me. Sounds like a logical problem solving approach though trying a different body. So it's just not getting near infinity focus is that right but manages within 15 feet?

[jeryang]

A big errm no idea from me. Sounds like a logical problem solving approach though trying a different body. So it's just not getting near infinity focus is that right but manages within 15 feet?

Thanks for the response.
You're exactly right. Everything focuses within about 15 to 20 feet. Haven't had a chance to swap lenses to another body yet but I plan on doing this soon!