Is it just me, or does the D50 occaisionally (I have trouble spelling that word) focus slightly behind the subject. I have a number of pictures where, for instance, I have focused on a persons eyes/nose but when I view the images during post processing I find that the ear lobes are actually sharper. Anyone else had or having this problem?
#3. "RE: Focus Errors????" In response to Reply # 0
I've noticed I really have to pay attention to the "focus square" I see in the lense. Several times the camera has chosen something I did not want. If I'm in Auto mode, I change my view a little and then press half-way down and see which square lights up, then I re-compose if necessary.
#4. "RE: Focus Errors????" In response to Reply # 3
If back/front focus problems are not constant there is nothing wrong. It is possible that the AF has just focused to slightly different place than you intended. In order to test focus issues i recommend doing some tests with D70 focus chart.
#5. "RE: Focus Errors????" In response to Reply # 0
Okay - I dug this up when the D70 first hit.
1. Background on the AF module
The CAM900 AF module (D100, D70/S, D50) has a five sensor array. Of the five, the center sensor is a cross and the other four are slight canted vertical lines . The center sensor is the most reliable - because of it's cross-configuration, it's able to pick out the contrast/orientation of the subject more accurately than any of the others.
The sensor ovals on your viewfinder are not 100% accurate - the individual sensor's sensitivity actually extends beyond the edges of those markings and may not be perfectly aligned. This varies by camera, and can be determined using a variety of test targets and the camera mounted on a sturdy tripod.
2. What is your AF-Area setting?
Traditionally, Nikon bodies equipped with a five-area AF module operate in several modes - Single-Area AF where the photographer controls the selection of the AF sensor using the rear control pad; And Dynamic-Area AF where the photographer can choose the initial sensor, but the camera can override that selection depending upon what it perceives to be the subject's movement and contrast. Either of those settings can be combined with Closest-Subject Priority (CSP), which defaults the focus point to what the camera perceives to be the closest subject in the composition.
Single-Area is the most reliable method for gaining lock along with the selection of the center sensor. Despite the ability to pick the initial sensor to base focus upon, the photographer has NO control over Dynamic AF - the camera picks the selection. What is really bad about Dynamic AF is that the camera will not tell you, a)that it has moved the sensor of interest from the one you started with to another sensor and b) gives no visual feedback on the actual sensor currently in use at the time of the photo being taken (i.e., it doesn't highlight the sensor in use like Single-Area - the fact that the sensor you picked is still highlighted means nothing - it's a false positive). Use of CSP is not recommended in most cases - it may inadvertently lead the camera to decide the daisy sitting right in front of your dog's face is the desired subject.
3. What is your Servo Setting?
On the D50, Servo can be set to AF-S (Single), AF-C (Continuous) or in a new twist (the D100 and 70 did not have this setting) AF-A (Auto - which lets the camera decide which one to use).
Let's step through each of the servo settings:
Single - the shutter button will not "fire" until the camera believes it's achieved a focus lock - a.k.a., focus-priority.
Continuous - the shutter button will "fire" even if focus is not achieved - a.k.a., release-priority.
Auto - camera decides on AF-S or AF-C - either way, expect some delay if it picks AF-S or an immediate response if it picks AF-C. I don't like this setting because it takes control away from the photographer - you're at the mercy of the camera and may miss "the moment" because it interpreted the shooting situation incorrectly.
The most reliable setting to ensure in-focus shots is, of course, AF-S. AF-C is fine if you're in a sports or fast-moving situation and feel that AF-S may not respond sufficiently to let you capture the moment.
4. What effect do these settings have when using the Digital Vari-Program Settings (i.e., Child, Sports, Portrait)?
The camera takes control of all these options and gives you NO control over the settings. When using Vari-Program, the camera is pre-programmed to set certain things in order to achieve the desired effect.
You will have control over the focusing settings if you use one of the PSAM modes - Program, Aperture-Priority, Shutter Priority or full Manual.
So what does this have to do with the OP (original poster's) question? Well, let's review - were you in a Vari-Program, Auto or one of the PSAM shooting modes when you took the photo? If PSAM, what were your focus settings?
The key point here is that the most reliable focus setting for static or relatively slow-moving subjects is AF-S (single servo) with Single-Area AF (center sensor selected) and CSP off.
Initial thoughts - it seems that the AF chose to focus not on the subject's eyes as you selected, but rather some other prominent feature that it decided had better contrast or orientation. This sounds like Dynamic AF, but it's only a guess. Can you provide the exact shooting settings at the time of the photo? If you view the photo in PictureProject or Nikon View, it will give more information....
#6. "RE: Focus Errors????" In response to Reply # 5
There's just one difference (that I know of) with the D50 from the above. The D50 in AF-C won't fire unless it's achieved a focus lock. This does mean the camera did get a focus on something and it likely was that the camera was allowed to make the choice.
#7. "RE: Focus Errors????" In response to Reply # 6
That's not how AF-C works. AF-C is supposed to allow shutter release before AF-lock is achieved - this is why you'll hear the lens constantly refocusing (if using a screwdrive lens) - it's trying to get as close as possible to the focus point without neccessarily imposing an additional lag penalty before the shutter fires. While it is getting close to the lock, it does not neccessarily mean that it has acheieved a perfect lock. You can use the AF-L/AE-L button to lock focus during AF-C use, but this assumes you can anticipate "the moment" that you're seeking to photograph...
#8. "RE: Focus Errors????" In response to Reply # 7
I can only suggest you try it Armando. Set it on AF-C, burst mode and start shooting and moving the camera to wildly different focal lengths, you'll find it will not trigger the shutter until it's locked the focus. I'm talking about when you keep the shutter down of course
I've been finding it quite useful trying to get some fairly close shots of gulls flying around, I can press the shutter right down and know that at least it has focused when it fires. (I use closest focus mode for this so I don't get some nice sharp shots of the background).
As you say you can lock it yourself with the AF-L button if you want that focus point or you must have a shot whether its focused or not. I take enough lousy photos without adding badly focused ones to the mix
#9. "RE: Focus Errors????" In response to Reply # 8
Thanks for the tips guys. Just to clarify the settings they are as follows. AF-C, 18-55 kit lens, centre weighted (if that has any bearing on focus) single area AF (always the centre)AF assist on, manual ISO, auto wb. It does not happen all the time, which is probably worse when I think about it) Just a side note, I find it really easy to accidentally change the AF area but I know this is not the problem because the focus is not that far out.
#10. "RE: Focus Errors????" In response to Reply # 7
Actually Armando, with the D50 and the D2X, AF-C is focus priority also. Why the change, I don't know. On the D2X, I believe you can switch it back to release priority via custom setting, not so on the D50.