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DPChallenge Forums >> Tips, Tricks, and Q&A >> Focusing and Zones
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Showing posts 1 - 14 of 14, (reverse)
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 01/29/2011 05:03:49 PM · #1
I am doing baby photography which involves close ups and shots taken from around 2-3 feet away. I'm using their Canon 40D and the 18-55mm at around 3.5.

The camera and lens are set to auto-focus. (I've tried in the camera, One-Shot and AF Focus modes.) Various of the 9 AF points flash and I have a hard time getting it to focus on what I need. It gets doubley worse when I don't notice it's *slightly* out of focus until I've finished with the client and am editing on a full screen.

Which brings on my question about AF points. I read the manual and maybe I'm over-complicating things, but I am trying to get the center dot to be the point of focus. Do I just need to select the center point as the AF point and stop having it "choose" on its own?

I read somewhere in the manual that the camera wants to choose whatever is closest as the focus point. Did I just figure out what to do while I was typing this? :-D
 01/29/2011 05:13:58 PM · #2
Yes, select the center focus point as the focus point. The only downside to this is that if you want an off-center composition, you would need to focus & recompose, incurring the risk that you move during recomposing, changing the focus.
You say you are using the 18-55 at or near f/3.5? This seems to imply you are shooting near the wide end, which does not seem optimal for portraiture. Also, the 18-55 shot wide open doesn't seem like it would be all that sharp, but I could be wrong.
01/29/2011 05:29:58 PM · #3
No, I think you are right. Some shots are...lackluster in the sharpness department.

What's a decent zoom for that lens? I am sticking towards the wide end just because of the setting (hospital room), but if there is a point I need to avoid going past, I'd love to know it!
 01/29/2011 07:55:48 PM · #4
That's also a really shallow dof, especially for a moving, squirmy target, and may result in a flattening of your subjects.
 01/29/2011 08:07:48 PM · #5
I think I am learning what this means in practice, as opposed to in theory.

I thought a shallow DOF might be good because the plane of focus is on the child. So are you guys saying the plane of focus itself won't be as sharp at a shallow DOF? I have no idea why that would be that way.
 01/29/2011 08:55:46 PM · #6
Originally posted by adigitalromance:
I think I am learning what this means in practice, as opposed to in theory.

I thought a shallow DOF might be good because the plane of focus is on the child. So are you guys saying the plane of focus itself won't be as sharp at a shallow DOF? I have no idea why that would be that way.


The actual plane of focus should be reasonably sharp regardless of the aperture. That lens is probably slightly sharper at f/8 than it is at f/3.5, but the difference won't be extreme. The problem is, with a 3-dimensional subject (baby) shot at an angle (feet closer to camera than head, left side closer than right side, whatever, it's almost unavoidable) there may not BE much of the baby actually located ON the plane of focus, see? So you probably need more DOF. Certainly if you're having these problems, you do.

Shallow-DOF portraiture, especially of pets and babies, who are not all that controllable, takes a LOT of experience to pull off really well.

R.
 01/29/2011 11:21:42 PM · #7
What he said. That's what I meant.
 01/30/2011 02:59:52 AM · #8
This is something I need to work on... I love my shallow DOF, but it often results in getting my images back to the computer and realizing they're slightly out of focus :( I need to play around and get a "feel" for when it's appropriate to use a wide open aperature and when I should crank it down to increase the plane of focus.
 01/30/2011 09:21:32 AM · #9
Originally posted by Ductyl:
This is something I need to work on... I love my shallow DOF, but it often results in getting my images back to the computer and realizing they're slightly out of focus :( I need to play around and get a "feel" for when it's appropriate to use a wide open aperature and when I should crank it down to increase the plane of focus.


What you NEED, actually, is to get in the habit of shooting f/8 "safety shots" whenever you are doing work on the razor's edge of wide open. Because those edgy shots are gonna have a very high failure rate, and if you're being paid to do the work, complete failure is not a viable option.

R.
 01/30/2011 12:42:40 PM · #10
Today I switched to the center point on AF and shot at 7.1 and noticed a lot of difference in sharpness and focus.

I agree with the "safety" thing, and I'll continue to learn on my free time and be safe when money is involved!
 01/30/2011 04:29:29 PM · #11
Originally posted by Bear_Music:
Originally posted by Ductyl:
This is something I need to work on... I love my shallow DOF, but it often results in getting my images back to the computer and realizing they're slightly out of focus :( I need to play around and get a "feel" for when it's appropriate to use a wide open aperature and when I should crank it down to increase the plane of focus.


What you NEED, actually, is to get in the habit of shooting f/8 "safety shots" whenever you are doing work on the razor's edge of wide open. Because those edgy shots are gonna have a very high failure rate, and if you're being paid to do the work, complete failure is not a viable option.

R.


Sound advice, I'm no where near getting paid to shoot anything, but it's a tip that I'll start using to save myself much aggravation.
 01/30/2011 08:50:19 PM · #12
I almost always use one focus point. For years it was the center point, and I just recomposed (better than decomposed :)

Now I use one focus point, but I switch it to where I want it to be. It only takes a second, and then I don't have to worry about losing the focus when recomposing the shot.

The 7D has focus zones. I'll use those when trying for birds in flight. The one focus point is too slow to respond for fast moving birds, and I miss more shots. Could be user error, but I find the zones helpful at that point.
 01/31/2011 02:05:02 AM · #13
if your camera supports back-button auto-focus, i'd suggest you not only give it a try, but learn to love it. then practice like crazy moving a single focus point while shooting. handling a camera is no different than playing music and learning 100s and 100s of songs: it takes TONS of practice for your hands to develop the muscle memory necessary to make all the camera adjustments required to capture fluid situations.
 01/31/2011 07:46:02 AM · #14
I can't agree enough about the DOF issue - I was trying to catch some shots of my 11 week old with a 17-55, mostly sitting between about 20mm and 40mm, at a range of about 60cm or so. I plugged the data into my phone's DOF calculator and reckoned that I had about 4cm DOF with aperture at f5! With a squirming baby, it's not a lot to play with!

...I switched to f8 and used some flash... ;o)
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