Autofocus issue or user error? Help!

mofo83 · Feb 1, 2013

Hi all,

I just picked up a used Nikon D200 body to replace my beloved Nikon D50.

With my D50, I could almost always trust the autofocus to be spot-on, even hand-held in not-so-ideal light at f/1.8. Whatever I wanted to be in focus was usuallyin focus.

So far, with the D200, I'm noticing that it's much more difficult to take pictures that have the subject in focus when using wide-open apertures. When I review the photos I've taken and "zoom" in on the subject (say, a person's face), more often than not, something a few inches in front or a few inches behind the subject is much sharper, and the face is a little soft.

I'm wondering what might be causing this? Is the D200's autofocus known to be poor in lower light? Am I doing something wrong? Is my new(old) D200 defective?

Just FYI, I have used a blower brush (not the brush, just the blower) to try and clean out the AF area.

Any advice is appreciated. Just trying to make sure this D200 is okay.

Thanks

gsgary · Feb 1, 2013

How long has the D200 had a bigger sensor than the D50 ? you must have picked up a very rare full frame D200 it will be worth a lot of money on Ebay

tevo · Feb 1, 2013

Sounds like a back focus issue to me.

mofo83 · Feb 1, 2013

HA. Thanks gsgary. I knew it wasn't full-frame. I guess I somehow thought that the D50 had a smaller sensor than the D200... didn't think about the fact that all DX format cameras have same sensor size (right?) I've edited the original post so that further advice focuses on actual probable problems.

KmH · Feb 1, 2013

The D50 and the D200 both use the same size APS-C image sensor.

Part of what is different is the aggressiveness of the anti-aliasing (AA) filter in front of each models image sensor.
The AA filter effects focus sharpness.

mofo83 · Feb 1, 2013

But, KmH, parts of the picture are as sharp as the D50... just not the subject I was aiming to have in focus! So doesn't this eliminate the AA filter as a culprit? Or does the AA filter actually effect WHAT is in focus?

And Tevo, that is also where my mind went first (backfocus issue) but it seems like most backfocus issues end up being explained (at least online) by user error, a dusty camera, etc.

mofo83 · Feb 1, 2013

Wow, I just noticed this discussion on Flickr. It sounds EXACTLY like what I'm going through. Sounds like I may need to have it repaired

Flickr: Discussing Another D200 focus problem... in Nikon D200/D300 Users

I'll try to blow off the AF sensor area again one more time, hopefully that helps. If not... maybe I'll get a repair quote. If it's too much, you may see this body on eBay as "repair needed"!

It may seem like I'm jumping to conclusions a bit, but I should be able to grab this camera and trust it to take as good of images as my D50... if not, something is wrong.

ph0enix · Feb 1, 2013

mofo83 said:
HA. Thanks gsgary. I knew it wasn't full-frame. I guess I somehow thought that the D50 had a smaller sensor than the D200... didn't think about the fact that all DX format cameras have same sensor size (right?) I've edited the original post so that further advice focuses on actual probable problems.

200/50 = 4. This would mean the D200's sensor is 4 times larger than the D50's. Makes perfect sense!

mofo83 · Feb 1, 2013

Ha. Yes Ph0enix, I'm not that confused after all!

An update: I called the only Nikon-approved repair place for D200s nearby (Portland) and the helpful guy there said that it's probably either dust inside the body... OR I'm basically screwed because it will cost more to fix than I paid for it.

For future reference of others who are at my level... there is a small mirror behind the main mirror - this is what needs to be cleaned to help the autofocus function better. You can gently push the main mirror up part way (not touching the mirrored surface, of course), and then blow off the little mirror behind it, hopefully knocking any dust/debris out of the camera.

I'm going to try it tonight...

Thanks

Garbz · Feb 2, 2013

That's usually the least of your problems. The dust on the rear mirror will likely fall off quite easily ... straight into the autofocus mechanism in the bottom of the camera. On the D200 the autofocus system has a small screen on it with cutouts for where the AF points are. This screen is great for trapping dust and hard to clear.

If the camera is consistently front or back focusing then you can use the small eccentric hex nuts in the mirror housing to adjust the mirror position. One nut does the focusing screen and the auto focus, and the other nut does the autofocus independently.

greybeard · Feb 2, 2013

To the OP, it sounds as though you are having back focusing issues. Stretch out a tape measure on a table, mount the camera on a tripod and point it at the tape at a 45 degree angle maybe 12" away. Focus on a particular spot and snap away ad some different f stops. Make sure to write down the point you are focusing on. These shots should tell you just what is going on with the focusing. I'm not sure but the D200 probably has a function to let you fine tune the auto focus for each lens, I know the D7000 does.

http://www.slagermanphoto.com/blog/2009/01/08/nikon-autofocus-fine-tuning/

TCampbell · Feb 2, 2013

You can buy a commercial focus test chart (such as the Spyder LensCal by Datacolor) or you can make your own (for a lot less).

Here's a good site: Jeffrey Friedl's Blog » Jeffrey?s Autofocus Test Chart

Read the full article before you get started. For the chart to work well, you need to KNOW that the camera's focus target was at the chart's center distance. But since the chart is on a diagonal (so that there are both nearer and farther focus areas that you can visually see to detect if your camera is front or back-focusing) you can't necessarily be certain the focus point the camera picked was the point that you intended. Commercial charts like the Spyder LensCal solve this by having a large focus target which is parallel to the sensor plane and you point your cameras AF point at that flat (not diagonal) part of the target. When you make your own test targets you generally lay them on a 45º angle to the camera and that means there's no single "flat" point to lock focus. You can still use the DIY focus charts but you have to think carefully about how they work to make sure you use them correctly.

On the Lenscal chart, there's a scale laying at a 45º angle. The scale actually measures centimeters but they're stretched so that they if you hover above the chart and look straight down, they'll measure centimeters front to back (but the scale is on a 45º angle so they need to be stretched a bit.... Pythagorean triangle math. Each centimeter is actually stretched to 1.4 centimeters.) The idea is that the 0 point should be in focus. But if the 2 above the 0 on the scale is actually in sharp focus then means your camera is back-focusing by 2 centimeters on THAT lens (each lens can be different.)

On the website above (where you make your own chart) he prints the chart so that there's a strong bold high-contrast focus target at the center. BUT... the pattern near that center line is very pale... so pale that the AF sensor shouldn't be able to get enough contrast to lock onto it. That's done intentionally... so that the AF point *should* hopefully lock on the intended point (which is bold and has high contrast), but you can still read the chart clearly enough to see if you've got a front focus vs. back-focus problem.

ALSO... run the focus ring on your lens all the way in minimum distance, let the camera auto-focus and take a test shot. Run it all the way in again. Let it focus again. Take another test shot. Do this a half dozen times.

THEN run the focus all the way OUT... do that test a half dozen times.

You're trying to determine if it's a mechanical issue here. Does the camera have some "slop" in focus such that it only back focuses when, say, it was focusing from back to front, but it doesn't have the same focus error if it ran the focus front front to back? And of course you take LOTS of shots so that, should one shot be an anomaly, you wouldn't want to adjust the camera based on an anomaly.

Start with prime lenses. They should be the most consistent. Zoom lenses can actually have focus errors which are different depending on the focal length on the zoom. It can be trickier to test a zoom.

Good luck!

mofo83 · Feb 4, 2013

Thanks for the info everyone! Much appreciated.

Garbz... I had attempted to clear out that autofocus mechanism on the bottom, maybe I didn't get everything out. It's hard to even see if there's anything in there - I need a dentists mirror or something! I'll try it again. Now, about adjusting those hex nuts... that sounds like something that could get me into trouble pretty quickly? Is it fairly easy to "mess up" and put the whole focusing system totally out of whack?

TCampbell... thanks for all the details on how to identify a backfocus problem. My question is... once I do identify the problem (which sounds tricky... especially since every lens is different!) is there an easy way to fix it (that costs less than $175, which is what I could buy a new body for off CL?) If not... maybe I won't even spend the time identifying it, and cut my losses, honestly.

Greybeard... I do not believe that the D200 has a focus fine-adjust setting, unfortunately.

Overall, I'd say I'm a bit overwhelmed by all this. It seems like there are so many possible culprits, so many variables, and so few "easy/cheap" ways to fix the possible issues, that I may just sell this as "focusing issues" on eBay, and start fresh with another used body (luckily, I got this body extremely cheap.) Because, as I'm realizing, it's important to trust your camera, and I'm not sure I trust this one...

Thanks again.

TCampbell · Feb 4, 2013

mofo83 said:
My question is... once I do identify the problem (which sounds tricky... especially since every lens is different!) is there an easy way to fix it (that costs less than $175, which is what I could buy a new body for off CL?) If not... maybe I won't even spend the time identifying it, and cut my losses, honestly.

Some camera bodies have an AF micro-adjustment menu which lets you enter a compensation amount. I'm a Canon shooter and my current bodies have this, my old bodies did not, and I know some Nikon bodies have the feature but I don't know the Nikon line well enough to know which bodies have the feature.

Perhaps someone heavily experienced with Nikon bodies can chime in. Otherwise you may have to call Nikon and ask them.

Also keep in mind that the focus error is usually only noticeable at shallow depth of field amounts. When DoF is heavy, the focus error wont be great enough to be beyond the limits of the DoF.

If your camera also supports a "live view" mode, then you can switch to live view when focusing at shallow DoF since this uses contrast-detect AF and not phase-detect AF. That means the contrast detect AF (although slower and it consumers more battery power) will generally overcome any focus error issues.

mofo83 · Feb 4, 2013

Thanks again Tim. As far as I can tell, the D200 does not have the AF micro adjustment menu (the D300 does.) And, I don't have the live-view option.

Good point about the shallow DOF... unfortunately, I really like using shallow DOF often! Plus, sometimes I'm shooting indoors in low light without flash, so it's not so much a choice as the best available option.

I am trying to avoid "just dealing with it" as an option, considering the fact that I still have a capable D50 body that performs flawlessly, and that another used D200 body can be had cheaply.