• site home
  • blog home
  • galleries
  • contact
  • underwater
  • the bleeding edge

the last word

Photography meets digital computer technology. Photography wins -- most of the time.

You are here: Home / Technical / Focusing, part 3

Focusing, part 3

February 14, 2011 JimK 2 Comments

OK, so your autofocus works under controlled conditions, but you’re still getting some misfocused pictures. The camera thinks it’s focusing properly, but it’s not focusing on what you want.

If it’s really dark, most likely that’s just the way it is; take comfort in the knowledge that, with modern DSLRs, the AF can focus in situations too dark for you to focus manually.

  • If what you’re focusing on is of low contrast, and there’s something of high contrast on which the camera wants to focus, try moving the focus point away from the high contrast thing to a similarly far away point on the low contrast thing, and use focus lock.
  • Your camera probably has several different AF sensors. They probably don’t all have the same capabilities. Try using the center one and focus lock.
  • Focus on something else, and then refocus. Take a picture. Do that several times and hope one is correctly focused.

Do these suggestions sound lame? Well, they are. When AF is off a lot, you can often find a way around the problem, and you’ll know it’s a problem right away. When it’s off a little, you’ll have no clue that it’s off until you hit playback and zoom in on the subject, or bring up the images later in your favorite photo editor.

There’s a way around all these AF problems. It doesn’t work if your subject is moving. It is awkward unless your camera is on a tripod. It’s available on most newer high end DSLRs. It’s called live view. When you turn on live view, the screen on the back of your camera shows you information taken right off the main sensor. You can zoom in to your subject and focus. No AF errors. No dim light problems. No lens-dependent misfocusing.  No misalignment between the ground glass and the sensor.

If you’re outdoors, you’ll need something to keep the light off the screen. You can go traditional and pull out your old dark cloth, but I recommend this, or something like it:

shade

Once you are set up to see the screen well, the basic operation for picture taking is: turn live view on, let the AF focus on what you most want sharp, frame the picture, zoom in on the area you want in critical focus, tweak the focus ring until it’s nice and crisp (if you’re using a typical AF lens, swear at the crappy focusing feel), and trip the shutter.

Using the AF to pre-focus is more than just a convenience. If you can’t improve the focus over what the AF did, which happens a lot if you’ve got things set up right, you’ve just learned that you can trust the AF in that particular situation, and you don’t have to mess with live view.

You old view camera users may be thinking that live view is just the thing to use with a tilt/shift lens. You’re right, but live view (on the Nikons, anyway) wasn’t designed with that in mind. To take advantage of the Schleimpflug (love that word) effect, you usually want to pick two points that define the plane of sharp focus and, through a combination of tilting and focusing, make them both sharp. Live view only lets you zoom in on one point at a time, and it’s not either quick or simple to toggle back and forth between two points. This cries out for a fix from the camera manufacturers.

There are many high end DSLRs that don’t offer live view: Hasselblad and Leica are two prominent examples. Leica doesn’t offer it on the M9, where it would even be more useful. What these cameras have in common is that they use CCD sensors instead of the CMOS ones in the cameras that do support live view. Some people have said that there’s an inherent limitation of CCD technology that doesn’t allow live view. I don’t buy that, and offer as a counterexample all the video cameras whose electronic finders are essentially the same thing. It is possible that all of the CCD sensors used in still cameras happen not to support live view.

There is serious question about whether, in the absence of live view, cameras with 20 megapixel and larger sensors can consistently deliver in the field all the image quality inherent in their sensors and lenses.

Technical

← Focusing, part 2 Controlling resampling in the Epson driver →

Comments

  1. Brooks Jensen says

    February 15, 2011 at 7:12 am

    And then there is the radical idea of using manual focus. Worked for me for 40 years. 🙂

    Reply
  2. Jim says

    February 15, 2011 at 7:43 am

    Ah yes, but that’s not so easy these days. Modern focusing screens are missing split image and microprism aids, and the tooth of the ground glass is optimized for a bright image at the expense of focusing. High-resolution sensors mean that focusing accuracy is more important, and drive you to wider f/ stops to avoid diffraction degradation. Manual focusing with most AF lenses (at least the shorter ones) is difficult because the manual focusing action is poor. And I don’t know about you, but I’m getting older.

    I was thinking about doing a post on finder magnifiers, but those I’ve found only help a little.

    I use the optically great Zeiss manual-focus-only lenses on my Nikons, and they are really nice. but I have a heckuva time knowing when the subject’s critically sharp sometimes.

    Thanks, Brooks.

    Jim

    Reply

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

May 2025
S M T W T F S
 123
45678910
11121314151617
18192021222324
25262728293031
« Apr    

Articles

  • About
    • Patents and papers about color
    • Who am I?
  • How to…
    • Backing up photographic images
    • How to change email providers
    • How to shoot slanted edge images for me
  • Lens screening testing
    • Equipment and Software
    • Examples
      • Bad and OK 200-600 at 600
      • Excellent 180-400 zoom
      • Fair 14-30mm zoom
      • Good 100-200 mm MF zoom
      • Good 100-400 zoom
      • Good 100mm lens on P1 P45+
      • Good 120mm MF lens
      • Good 18mm FF lens
      • Good 24-105 mm FF lens
      • Good 24-70 FF zoom
      • Good 35 mm FF lens
      • Good 35-70 MF lens
      • Good 60 mm lens on IQ3-100
      • Good 63 mm MF lens
      • Good 65 mm FF lens
      • Good 85 mm FF lens
      • Good and bad 25mm FF lenses
      • Good zoom at 24 mm
      • Marginal 18mm lens
      • Marginal 35mm FF lens
      • Mildly problematic 55 mm FF lens
      • OK 16-35mm zoom
      • OK 60mm lens on P1 P45+
      • OK Sony 600mm f/4
      • Pretty good 16-35 FF zoom
      • Pretty good 90mm FF lens
      • Problematic 400 mm FF lens
      • Tilted 20 mm f/1.8 FF lens
      • Tilted 30 mm MF lens
      • Tilted 50 mm FF lens
      • Two 15mm FF lenses
    • Found a problem – now what?
    • Goals for this test
    • Minimum target distances
      • MFT
      • APS-C
      • Full frame
      • Small medium format
    • Printable Siemens Star targets
    • Target size on sensor
      • MFT
      • APS-C
      • Full frame
      • Small medium format
    • Test instructions — postproduction
    • Test instructions — reading the images
    • Test instructions – capture
    • Theory of the test
    • What’s wrong with conventional lens screening?
  • Previsualization heresy
  • Privacy Policy
  • Recommended photographic web sites
  • Using in-camera histograms for ETTR
    • Acknowledgments
    • Why ETTR?
    • Normal in-camera histograms
    • Image processing for in-camera histograms
    • Making the in-camera histogram closely represent the raw histogram
    • Shortcuts to UniWB
    • Preparing for monitor-based UniWB
    • A one-step UniWB procedure
    • The math behind the one-step method
    • Iteration using Newton’s Method

Category List

Recent Comments

  • bob lozano on The 16-Bit Fallacy: Why More Isn’t Always Better in Medium Format Cameras
  • JimK on Goldilocks and the three flashes
  • DC Wedding Photographer on Goldilocks and the three flashes
  • Wedding Photographer in DC on The 16-Bit Fallacy: Why More Isn’t Always Better in Medium Format Cameras
  • JimK on Fujifilm GFX 100S II precision
  • Renjie Zhu on Fujifilm GFX 100S II precision
  • JimK on Fuji 20-35/4 landscape field curvature at 23mm vs 23/4 GF
  • Ivo de Man on Fuji 20-35/4 landscape field curvature at 23mm vs 23/4 GF
  • JimK on Fuji 20-35/4 landscape field curvature at 23mm vs 23/4 GF
  • JimK on Fuji 20-35/4 landscape field curvature at 23mm vs 23/4 GF

Archives

Copyright © 2025 · Daily Dish Pro On Genesis Framework · WordPress · Log in

Unless otherwise noted, all images copyright Jim Kasson.