slow auto focus. body or lens?

babygodzilla

i use my Nikon 18-200mm on my D5000 often, and I just feel the auto focusing is slow. is this the body's or the lens' fault? if im not mistaken, the AF is on the lens, right? so it's the lens' fault? what can i do about it?

thanks

ABCL

I'm not familiar with Nikon's lenses, but AF performance steadily increases with the price of the lens. You could try manual focus, like the good ol days

babygodzilla

haha im not that great with manual focus...

ziggy53

The Nikon D5000 lacks a sophisticated AF section and the Nikkor 18-200mm, f3.5-f5.6 G ED-IF AF-S VR DX aperture gets slow pretty quickly.

A modern dSLR AF uses:

An AF sensor, located inside the camera body, behind and under the main mirror.
The AF motor of the lens (in the case of the D5000).
The image processor of the camera to interpret the data from the AF sensor and use that to guide the AF motor of the lens.

The AF sensor uses a type of "electronic rangefinder" to determine whether prime focus should be forward or backward from the current focus position. The most sensitive and accurate portion of the AF sensor is the very center. The sensor is more sensitive in both higher light levels and with subjects which have both high contrast and sharply defined edges.

For indoor shoots use a flash that has an AF assist light and use the center AF dot of the camera. (For the Nikon D5000, Custom Menu a1 and select "Single Point" then use the controller to select the center point, if not already selected.) The AF assist light of the flash generally projects a "pattern" which, when projected onto a plain surface or subject with little definition, gives the AF sensor more information from which to determine prime focus. It also provides illumination which the AF sensor needs for proper signal strength.

Try not to "focus and recompose" too much if you are shooting close to the subject. That will throw off the geometry of the focus acquisition and lead to either front-focus or back-focus.

babygodzilla

wow @_@ a lot of techno babble. so basically you're saying the AF inside the D5000 sucks?

if i replace the 18-200 with a faster lens, say the 17-55 f/2.8, would it help? I'm looking to replace my 18-200 with something faster. i dont use the tele end of that lens that much... however, the 17-55 is actually as heavy if not heavier than the 18-200.. @_@

what would you recommend as a replacement to the 18-200? i mostly shoot people and objects at wide to normal range. sometimes in tele, but not that much.

I currently have an 18-200 f/3.5 and a 35mm f/1.8. I rarely ever use my 35mm, but it's got a very nice bokeh, it's light, and it didnt cost that much ($250-300ish) I think I'll just keep it.

suggestions for replacement lens? thanks

ziggy53

babygodzilla wrote: »

... so basically you're saying the AF inside the D5000 sucks? ...

Not at all. Used within its design limits it works quite well. It would be true to say that one of the D3 series cameras has a much better AF section however.

babygodzilla wrote: »

... if i replace the 18-200 with a faster lens, say the 17-55 f/2.8, would it help? I'm looking to replace my 18-200 with something faster. i dont use the tele end of that lens that much... however, the 17-55 is actually as heavy if not heavier than the 18-200.. @_@

what would you recommend as a replacement to the 18-200? i mostly shoot people and objects at wide to normal range. sometimes in tele, but not that much.

I currently have an 18-200 f/3.5 and a 35mm f/1.8. I rarely ever use my 35mm, but it's got a very nice bokeh, it's light, and it didnt cost that much ($250-300ish) I think I'll just keep it.

suggestions for replacement lens? thanks

The Nikkor 17-55mm, f2.8G ED-IF AF-S DX is indeed a very nice lens and it would probably out perform your current 18-200mm VR zoom. You would still probably need the flash with an AF assist light for it too. There would still be some limitations even with the very best of everything.

I would recommend starting with the flash and center focus dot only, and see if that doesn't help your situation. A flash, used properly and with a appropriate flash modifier, will also add considerably to the image quality.

babygodzilla

i have an SB900, and i do use the AF assist on it. i still feel like replacing the 18-200 tho... no $$$ tho...