D90 focusing question

[Tbini87]

Hey guys,
My wife and I did a family shoot today for some friends who have a 2 year old daughter and a 4month old son. We were using our D90 that is still relatively new to us, and we had a lot of shots that were soft (at least one person in the group of 4). I think we were shooting with too low an aperture (2.5ish give and take) with a 50mm prime. However, I am pretty confused on the AF system in the D90 since we have been using our D40 with what seems like a much different AF system for the last 2 years.
So my main question is what AF choice do you guys use in the D90 (for those of you that have owned or still own a D90). What AF choice is best for group shots? Do you use the same choice for a single person portrait as well? Do you think the problem was due to shooting at such a low aperture? Any guidance, recommendations, suggested readings, etc would be appreciated! You can also see some of the pics at albiniphotography.blogspot.com, though we trashed the images that were blatantly soft.

 

[Flatsfish b]

I Am far from a pro, but shooting at such a large aperture, it is going to be very difficult to keep 4 people sharp, I would try somewhere above f/4. But that's just me. Maybe there is a better way I'm curious to see. I own a d90 as well.

 

[Mbnmac]

As above, no pro here but yeah too low an aperture for that kind of shot, I think I've seen most info pointing at f8 being the sweet spot for sharpness depending on the lens, give a couple a go a see what turns out nice.

As far as the AF system on the D90, I've not really tooled around with it too much as most of my shots have been of relatively still things, so can't offer much info on that.

 

[ababysean]

I just got a D90 also. I had a D3000 and so the focus system is similar but I can not seem to get as crisp shots I think with my D90, and I don't know why.

That being said, I think the general rule is one Fstop for each person, so you should have shot above F4.

How close where you? That makes a big difference as well.

 

[Stradawhovious]

Sounds like a depth of field problem.......... ask me how I know.... Unless you're stanging 15 feet away, and your subjects are lined up perfectly in a straight line (i.e. all the same distance from the lens) f/2 probably isn't enough DOF.

If you have an Iphone, Ipod touch, or a computer (which I'm assuming you do from your post....) look into a program called DOF Master. It can be found here... Hyperfocal Distance and Depth of Field Calculator - DOFMaster.

That 50mm lens can be an awful lot of fun, but the shallow DOF wide open can get you in to trouble. That program will more than likely be a life saver. I just bought my 50mm lens a couple of weeks ago, and learning about the DOF the hard way isn't any fun.

To answer your question, I was told in a recent class to focus on one point, and rely on DOF for the rest. After doing this for a while, it really seems to make a lot of sense, and helps me concentrate on things other then the point of focus. Also, with my Nikon, when I have the 11 point focus on, the camera makes a best guess as to what I want in focus, and it isn't always right. With the single point focusing, that issue is eliminated.

 

[Tbini87]

Thanks for the responses guys. I could tell that we weren't shooting at a high enough f-number. I also need to do a lot more research on the different focusing options the D90 gives.

 

[rainking]

Make sure you are using the right focus mode for your type of shot. AF-S, AF-C and AF-A. Then you have to make sure you have the right AF area.

 

[timethief]

D40 doesn't have an internal focus drive motor, instead it only has CPU contacts which means it can only Auto Focus with AF-S and AF-I lenses (those with built-in focus motors)

So your problem was probably with your low aperture.

 

[rainking]

For group shots, I would use the AF-S since your subject is not moving around.

 

[KmH]

The D40 had the Multi-CAM 230 AF module, 3 focus points, none of them cross-type points.

The D90 has the Multi-CAM 1000 AF module, 11 focus points, the middle point being a cross-type focus point.

Cross-type focus points are more accurate than regular focus points.

You not only need to select a focus mode, you also need to select a focus area mode. Read your camera's users manual, pages 54 to 60.

As mentioned, your problem is likely more related to DOF, though it could also be related to shutter speed.

Without examples, no one can say for sure.

 

[Tbini87]

The D40 had the Multi-CAM 230 AF module, 3 focus points, none of them cross-type points.

The D90 has the Multi-CAM 1000 AF module, 11 focus points, the middle point being a cross-type focus point.

Cross-type focus points are more accurate than regular focus points.

You not only need to select a focus mode, you also need to select a focus area mode. Read your camera's users manual, pages 54 to 60.

As mentioned, your problem is likely more related to DOF, though it could also be related to shutter speed.

Without examples, no one can say for sure.

Do you mean the shutter speed being too slow, possibly letting the some motion blur into the image? I would have to check the data but I think using such a low aperture was letting us use a pretty fast shutter speed. I think it was probably a DOF problem, but I will certainly be researching the different focusing options and how they work. Thanks.

 

[Tbini87]

I read up today on the different focus modes and focus area modes. Still pretty confusing, but sounds like I will be using the AF-S for portraits. Should I be using the center focus point since it is the only cross type one and is better in general than the others?

 

[Light Artisan]

Use which ever one is on the subjects face, or move it so one is.

 

[Derrel]

One needs to allow a bit of a depth of field cushion when photographing a group of 4 people in normal group arrangements; with a 50mm lens at f/2.5, at distances of under 15 feet, focusing is absolutely critical. Check Online Depth of Field Calculator

for some calculation help and some good graphic representation of the DOF with a 50 at f/2.5. Stopping down a bit more would have most likely saved your bacon. Does anybody here remember the focus-and-recompose brouhahha of last week????? This is a good example of where the real world, and the rubber, meets the road in terms of achieving accurate, proper focus at wider apertures...at f/2.5, you have a VERY limited DOF band under 15 feet...a 6-inch error between the sides of the frame and the center AF point at 15 feet could potentially sink your ship...you need to have absolutely ALL of your ducks in a row when shooting at f/2.5 inside of 15 feet...everything...

 

[Tbini87]

Use which ever one is on the subjects face, or move it so one is.

If using the AF-S with the center point selected can't you focus on the subject's face in the middle of the frame, keep the shutter button pressed halfway, reframe the shot then shoot it and get the same result as selecting a different focus point? I know that wouldn't work with the AF-C option though.