Focus - Am I expecting too much?

KellyC

http://mxlens.smugmug.com/gallery/8350359_3aTCy#562736733_zQP9q-O-LB

The truck (middle far right) seems slightly out of focus to me, I think there may be a problem with my camera... I have had a fair amount of my pictures seem soft or the focal point does not match where the I have it set. In this picture the focal point was set as far to the right as I could get it on the camera (probably aligned with the back of the door) when the picture was snapped. (I know it is a bad picture, it was taken this way for testing purposes.)

I have a Nikon D90, using a Nikkor 70-200VR on this picture.
Lens set to active VR - does not change if I turn the VR off
ISO 200
f2.8
shutter 1/800
116mm
camera set to aperture mode

Sometimes I get those pictures that just pop and you can tell you nailed it, but about 1/3 - 1/2 of the time it seems like I missed it... not by much, but just not quite there. It does not matter if the shutter speed is pushing 1/2000+ still seem to have the same problem.

Thanks for you help in advance.
Kelly

jfriend

First off, is this truck stopped? Are you on a tripod? What focus settings did you use? Why are you using Active VR?

Second, do you realize that the depth of field at f/2.8 is pretty narrow and the lens probably doesn't have a perfectly flat field of focus at the edges (e.g. the plane of best focus is curved a bit).

Third, do you realize that most lenses show some degradation in sharpness when wide open as you get to the edges? Look at any performance chart for pretty much any lens and you will see better performance in the center than the edges, particularly at wide apertures. Better edge performance usually comes by stopping down one or two stops from max aperture.

KellyC

jfriend wrote:

First off, is this truck stopped? Are you on a tripod? What focus settings did you use? Why are you using Active VR?

Second, do you realize that the depth of field at f/2.8 is pretty narrow and the lens probably doesn't have a perfectly flat field of focus at the edges (e.g. the plane of best focus is curved a bit).

Third, do you realize that most lenses show some degradation in sharpness when wide open as you get to the edges? Look at any performance chart for pretty much any lens and you will see better performance in the center than the edges, particularly at wide apertures. Better edge performance usually comes by stopping down one or two stops from max aperture.

I am new to all this stuff... This is my first DSLR camera. The truck is doing about 50 mph, hand held I should have said NORMAL instead of active. I do realize that f2.8 is pretty narrow. I have the same problem when the subject is centered in the picture.

Here is another picture (cropped) that I took this afternoon, the focal point is the face, but it seems the ball is more in focus than the face and hair. The top of the head is about 1/4 the way down in the original picture.

ISO 200
f3 autofocus
shutter 1/320
105mm
camera set to Aperture mode
AF-area: single point, normal zone
hand held
AF-C

Thanks,
Kelly

jfriend

KellyC wrote:

I am new to all this stuff... This is my first DSLR camera. The truck is doing about 50 mph, hand held I should have said NORMAL instead of active. I do realize that f2.8 is pretty narrow. I have the same problem when the subject is centered in the picture.

Here is another picture (cropped) that I took this afternoon, the focal point is the face, but it seems the ball is more in focus than the face and hair. The top of the head is about 1/4 the way down in the original picture.

ISO 200
f3 autofocus
shutter 1/320
105mm
camera set to Aperture mode
AF-area: single point, normal zone
hand held
AF-C

Thanks,
Kelly

With the truck doing 50mph, it takes really good technique to nail focus.


Though I could tell better if I could see the full res, uncropped shot, this looks to me like the ball is sharp and the rest of the image is suffering from narrow depth of field. At 105mm, f/3 and a subject distance of 10 feet (I'm just guessing), you only get 1.8" of good focus on either side of your focus point. That is not enough depth for this kind of subject. If you had focused on the girl's eyes and locked focus there, you might have made the image work (though other parts of her would have not been sharp). If you want the whole depth of your subject in focus, then you need to shoot these types of shots at f/5.6 or f/8. It sounds like you need to learn the basics of depth of field and how your aperture, subject distance and focal length affect it. You can play with this depth of field calculator to see how they parameters are related.

I'd suggest you only shoot wide open on your lens when you have to (there just isn't enough light) or when you are doing so on purpose to create a narrow depth of field. You will get more keepers at f/5.6 or f/8 and as you get more of a feel for when to use what aperture, you can start using wider apertures (like f/4 or f/2.8) at appropriate times.

Remember, you can raise your ISO up to 400 or 640 if you need to in order to maintain a desired shutter speed and not really lose much image quality as long as you don't underexpose the image.

TonyCooper

Just a thought here...most Nikon dslrs have the option of setting the focus at "closest subject", "dynamic area, or "single area". The choice is made in the menu Custom Setting Menu>AF - Area Mode> then choose. I always set my Nikon to "Single Area", but it reverts to "closest subject" when you turn the camera off or change modes.

It doesn't make a difference where the brackets are placed if the setting is "closest subject". The brackets may be on the face, but the camera sees the ball as the point of focus.

I've lost many a shot because I forgot to change the setting to "single area" when shooting with a fairly wide-open aperture.

KellyC

Thanks jfriend I will look in to the depth of field more, I appreciate the information. Off to do more reading.

Kelly

jfriend

TonyCooper wrote:

Just a thought here...most Nikon dslrs have the option of setting the focus at "closest subject", "dynamic area, or "single area". The choice is made in the menu Custom Setting Menu>AF - Area Mode> then choose. I always set my Nikon to "Single Area", but it reverts to "closest subject" when you turn the camera off or change modes.

It doesn't make a difference where the brackets are placed if the setting is "closest subject". The brackets may be on the face, but the camera sees the ball as the point of focus.

I've lost many a shot because I forgot to change the setting to "single area" when shooting with a fairly wide-open aperture.

You don't say what camera you're using, but I think it only defaults to closest subject if you set your default to that or you have it set to some scene modes (like portrait). If you don't want it to default to closest subject, then perhaps you could change scene modes.

FYI, the D300 got rid of the closest subject focus option because it can be so problematic. I never used it on my D2X for that reason.

angevin1

ISO 200
f3 autofocus
shutter 1/320
105mm
camera set to Aperture mode
AF-area: single point, normal zone
hand held
AF-C

Kelly,

Based on those settings listed.

1. ISO 200 is probably a bit low: I use ISO to drive my Shutter speed.
2. f3 is fine if you want a shallow field of focus.
3. Shutter speed can be too slow for a child, or really anyone moving about.
4. 105mm is a good focal distance.
5. Aperture priority means the camera will adjust to keep your preferred priority. meaning you have less control over shutter speed.
6. Single point is a good idea.
7. Hand held is normal for kids and moving objects, but most times requires more shutter speed: 600 and above.
8. AFC! Constant adjustment of what you intended to be in focus. I do use AFC, but can count on one hand the times I have. If her head was wiggle-waggling along as most childrens do, she could've been on the waggle end of focus and the photo could've been snapped while the lens was readjusting to that movement. Or if you moved the focus reticule even a smidge, it would see the smidge and adjust accordingly. AFS wouldn't have helped perhaps, but the lens also wouldn't have had to find its target.

Suggestions for this scene.

readjust ISO to give a shutter speed at 600 or above.
or
Use shutter priority and set the shutter speed you wish.
and
click off about ten frames on this shot to ensure you got one or two that are what you intended.

my settings for this shot:

iso as low as I can get it to give me a 1250 shutter speed.
Manual mode, AFS, f2.8-f5.6 or maybe 6.3, handheld and 8-10 frames.

cheers, and enjoy your lovely model!

TonyCooper

jfriend wrote:

You don't say what camera you're using, but I think it only defaults to closest subject if you set your default to that or you have it set to some scene modes (like portrait). If you don't want it to default to closest subject, then perhaps you could change scene modes.

FYI, the D300 got rid of the closest subject focus option because it can be so problematic. I never used it on my D2X for that reason.

I have a Nikon D40. I've never used any of the scene modes. The choice is in Custom Setting Menu>AF-Area Mode>closest subject, dynamic area, or single area. I always shoot "single area", but the camera reverts to "closest subject" if I change modes (Auto to Aperture, Aperture to Shutter, etc.) and often when I turn the camera off.

Art Scott

After reading the thread i can't offer any better advice than already given......I always try to shoot in the realm of f5.6-11.....unless it is impossible to do because of lighting conditions.....f4-2.8 is reserved for very dark times.

renay johnson

I use to complain about my lenses and whether or not they were sharp and a guy told me "just because you can shoot at f2.8 doesn't mean you should". I echo the response regarding shooting at such a wide aperture and images will suffer some degredation. Don't get me wrong, all of my lenses are f2.8 but some images tend to not look tack sharp to me. f2.8 does it job You got some good advice because I had the same questions.

KellyC

Thanks everyone, I appreciate the advice and will put it to use.

Kelly

wadesworld

Not an expert by any means, but don't overlook the suggestion to use AF-S instead of AF-C. AF-C is typically used for fast action shooting, such as sports.

amp'd

I think the problem lies in your aperture. I usually only use wide open aps if I am going for a great eye shot or after something small in a picture I want to be sharp and the rest to slowly start to melt away like butter. For the car/truck shot stop down and bump up your shutter speed and you should get a nice crisp photo.

Also when you throw your aperture that wide, you need to make sure you know exactly what you want in focus and nail it- and using burst mode really helps with that creepy crawly auto focus setting. It takes seconds to capture a couple extra shots of a moving target and a few extra seconds to dump them later when you view them on your computer and (imo) worth those few extra seconds. Usually the 2nd or 3rd shot for me is nice and sharp. I chase toddlers around all day so I am constantly moving settings around to capture those little people!

Altho I am no expert, still meandering my way around all this stuff! Good luck!