D300s and inconsistent focusing.

wheelhot

macrumors 68020
Original poster
Nov 23, 2007
2,080
249
Hi, recently I got my D300s + Sigma 18-50 f/2.8 (and a few other accessories). I owned the camera for about 2 weeks and have been testing it in varied conditions. Usually the focusing was top notch and accurate but I recently put the camera to a real test when I use it to photograph a wedding.

While most of the photos turn out good, I do encounter a problem that are causing me problems during times where I need to get key shots. The focusing seemed off, even-though I double checked to ensure the focusing point is where I wanted (note that I am using single AF point focus)

I tried stopping down from f/2.8 to f/4 - f/5.6 thinking it was just the lens softness issue at f/2.8 but turns out I was wrong, cause the problem still exists. Some scenes, I asked to have a retake cause of the focusing problem and I still cant get the image to focus properly, so for those photos, I will need to find a solution to make it acceptable.

Anyone care to help me on this? And I thought it has something to do with Nikon contrast based AF system causing it not to be able to focus accurately on certain scenes, but that's just my guess. I'm not sure why my camera is not being able to focus properly.

Help pls :rolleyes:
 

pdxflint

macrumors 68020
Aug 25, 2006
2,407
14
Oregon coast
The D300s only uses contrast detect AF in "live view." Anyway, the D300 and D300s have great AF systems, but there are a lot of options of how to set it up for different uses - so it might take a bit of experimenting to find out which settings will yield more 'in focus' keepers for each type of shooting style you use. I know this doesn't help a lot, but I'm still learning myself, how to master the D300 AF system, and the huge customization in the various settings menus that can be assigned in the shooting banks and settings banks, as well as the 'my menu' custom settings. It's practice, practice, practice.

Here's a snippet from DPReview's review of the D300s discussing the AF:
The D300S has one of the most sophisticated AF systems on the market - not just in terms of the number of AF points (51, 15 of which are of the cross type that are sensitive in both the vertical and horizontal axis), but also in terms of its ability to select the active point and track with a subject.

The result is an AF system that you'll need to learn how to use, rather than one you can just take out of the box and expect to deliver. Which isn't to say it's overly complex - we're not sports photographers (nor do we claim to be), but with a little time spent getting used to its behavior, we were impressed by its ability to return a sequence of in-focus images, even in the hands of an inexperienced shooter.

The contrast detect AF in live view and movie mode is a fraction faster than we've seen on most DSLRs up until now, when using the 16-85 VR, at least, but it's still nowhere near the speed of a system designed around its use (such as compact cameras or Panasonic's G series). It's really only of use for stationary subjects but it's nice to have in studio settings.
Also, here's a link to John Cazolis blog on Nikon gear where he discusses the D300 AF. Actually the entire blog and all the D300 posts, (also applicable to the D300s) especially about how he sets up his camera for different purposes via the shooting and settings banks, make for a good discussion on some various Nikon gear this guy uses. I found it very useful, and more practical than a lot of other "reviews" I've read out there.

Good luck, and happy shooting!
 
Comment

wheelhot

macrumors 68020
Original poster
Nov 23, 2007
2,080
249
Thanks for the link. It was really useful.

Right now, I'm thinking of doing a focus check on the lens cause I heard that 3rd party lens is susceptible to focusing problems.
 
Comment

cr2sh

macrumors 68030
May 28, 2002
2,554
3
downtown
I've found that many Sigma lenses that I've owned have had poor focusing performance, especially in low light... I don't buy them anymore because of it.

Here's a review of that lens noting similar focusing problems.

AF speed is on the slow side of average. AF accuracy was also on the low side of average. When shooting the very well-lit ideal focus point on ISO 12233 chart tests using AF, every other image was completely out of focus at 18mm f/2.8 and AF was inconsistent at 24mm. In real world use, I missed a noticeably higher number of shots than I should have. AF performance was especially poor in low light (where focus hunting is frequent). Results were also poor in AI Servo mode.
 
Comment

wheelhot

macrumors 68020
Original poster
Nov 23, 2007
2,080
249
thanks, I've read that too. Too bad I cant find any more similar problems.

I hope this problem can be fixed though :(

Damn this sucks, whats the point of getting the lens sharp but cant achieve proper consistent focusing =.=
 
Comment

wheelhot

macrumors 68020
Original poster
Nov 23, 2007
2,080
249
I was going to comment I would look at the lense first before the camera. I don't have any experience with Sigma lenses thou.
Aah, but hmm, I never did any focus test before, anyone care to explain how is the correct technique to measure focusing accuracy (the positioning, aperture settings, does shutter speed make a difference?)? Cause like I said, sometimes it's in focus and some time it's not in focus (but the camera says it's in focus).

Oh and how far does AF Fine Tune able to...fine tune?
 
Comment

Rondue

macrumors regular
Jul 30, 2008
162
0
PA
Love mine

I am a new D300s owner and photo n00b I have not had any issues with focusing unless I'm in way to close with my 35mm 1.8 Nikon. I haven't any non nikon lenses though.
 
Comment

wheelhot

macrumors 68020
Original poster
Nov 23, 2007
2,080
249
I am a new D300s owner and photo n00b I have not had any issues with focusing unless I'm in way to close with my 35mm 1.8 Nikon. I haven't any non nikon lenses though.
Good for you, well I remember using my friend Nikkor 24-70 f/2.8 and didn't have any problems with it (well that was my initial test, haven't tried it in real tests) except that it shows more details at higher ISO then my Sigma 18-50! :eek:

Despite the focusing issue, the D300s performed admirably during the wedding session.
 
Comment
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.