Background in focus, subject not in focus.
Click for a larger full frame version.
Probably the weakest feature on the G1 is its focusing system. In most brightly lit conditions, the autofocus (AF) system does a fine job, but when the apertures get big, and the subject gets tricky, the G1 falls flat on its face. Canon is well aware of the problems. Here's a quote from the G1 manual:
"The autofocus may not work well on the following types of subject.
- Subjects with extremely low contrast [compared] to the surroundings
- Subjects mixing close and far objects
- Subjects with extremely bright objects at the center of the composition
- Subjects that are moving quickly
To shoot these subjects, first aim the camera at an object at a similar distance, lock the
focus and recompose the image with the desired subject, or use the manual focus."
"Subjects with extremely low contrast to the surroundings" is the case where the AF focuses on the background instead of the subject. "Subjects mixing close and far objects" is a perfect description of when the G1's AF is most challenging to use. Bright objects in the center and motion are classic problems for all AF systems.
The Olympus digicams zoom in the LCD preview when you go to manual focus mode so you can see exactly what you are focusing on, and whether or not it is in focus. The Nikon digicams sharpen the preview so the portion that is in focus is very clear. The Canon G1 offers no focusing aids at all. You can digital zoom by 2x and 4x, but unlike the Olympus digicams, this digital zoom gives no additional detail in the LCD. Instead the display just becomes blocky.
In tricky focusing situations, your only option is to check the results in playback mode zoomed all the way in. Or check the results on a computer monitor. Although the LCD works well in bright sunlight, it is easier to judge focus in less bright conditions. Move to the shade to check focus on the LCD in playback mode.
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Background in focus, subject not in focus. Click for a larger full frame version. |
The G1's autofocus (AF) system is rather mysterious. The documentation doesn't describe what kind of AF it is, it only says "TTL". It certainly isn't spot, since it doesn't always focus on what is in the center of the frame. Click here for a typical example. Instead it behaves as if it is entire frame contrast detecting AF. It looks for the most contrasty thing anywhere in the entire frame, and focuses on that. Depending on subject lighting, contrast, and size, the G1 might focus on anything in the frame. Add to this the lack of any sort of focusing aids, and you quickly realize that focusing with the G1 can be a real challenge.
The G1's AF system is particularly difficult to control when shooting at the near macro distances. If your subject isn't completely flat, the G1 will pick all sorts of interesting distances to focus on. Shooting a dollar bill is very easy. Shooting small flowers scattered about at various distances is not easy.
Here are some example macro images taken mostly in continuous AF mode. All were done at full wide angle, which is definitely a factor in the AF equation. Next year I'll go with full telephoto and see how I fare. Also note that it was windy when I was shooting, so these flower clusters were moving a bit. All AF systems have trouble with moving subjects. So the problems you see here might be attributed completely to motion caused by wind. However, I have shot in windless conditions and had problems similar to those seen here.
Image 1 - This image shows AF not on close flower cluster in center. Spot metering was on to test "spot AF" theory. (Canon has already said that Spot Metering does not mean Spot AF on the G1) The bigger, more contrasty background is in focus.
Image 2 - This image shows that filling the frame more with the cluster gets the desired effect. It appears that at this point the cluster fills enough of the frame to be noticed.
Image 3 - This image shows that the G1 would much rather focus on the more contrasty sky and branches than on the very close flowers. This was taken in Macro mode. Apparently with f/5.6 at 7.0mm you can focus out to infinity even in Macro mode. Talk about DOF!
Image 4 - For this image, I gave up and switched to manual focus. Still pretty tricky to get right.
Users of Canon's XL-1 video camera have similar complaints about AF, which has led some to suspect that the G1 uses the same algorithm.
Manual focus with the G1 is incredibly difficult. The lens moves in steps and getting confidently from one step to another isn't easy. If you hold the up or down control a little bit too long, you'll overshoot one or two focusing steps. The LCD is much too small to tell whether you are really in focus. When doing macro work, you'll find yourself moving the camera in and out more than adjusting the manual focus. Even then the LCD doesn't really tell you whether you are in focus. Be prepared to do a lot of reshooting after examining the results on a big screen.
I've noticed that if the autofocus system is completely baffled by what it sees, it will switch to infinity and set the Focal Length in the Exif information to 0. One way to test this is to pan the camera while it is auto focusing. If you customarily examine your Exif info to figure out why a shot turned out poorly, this is good to know.
Switch to macro mode. Focusing on the background could be a sign that you should switch to macro mode. In macro mode the G1 can focus out to 8 feet or more(!) depending on the aperture setting. If the camera is focusing on the background it might be because the foreground is within macro focus range.
Try AF with digital zoom. This gives you a "poor man's" Spot AF. Hold down the "set" button then press the zoom lever two times to get the "4x" in the preview. Point at what you want to focus on, half press the shutter button and press the MF button to lock focus. Hold down the "set" button and press the zoom lever twice to get rid of the "4x" (and "2x"). Shoot. A lot of button pressing, but it does seem to work very well. You could also use the optical zoom to further isolate your focus point as explained in the next tip.
Zoom in, focus, zoom out. If you are doing a wide shot and need to focus on something specific, you can use the optical zoom to zoom in and isolate the portion of the subject you'd like to focus on. Half press the shutter to focus, then press the "MF" button to lock focus. Zoom back out, recompose, and shoot.
Shoot in the dark, or near dark. Unlike other digicams that can't focus at all in the dark, the G1's AF system actually works better in the dark. The assist light becomes your spot AF point.
Use digital zoom with manual focus. You can use the digital zoom to help manual focus a little bit. Press and hold the "Set" button while moving the zoom lever to activate the 2x and 4x levels of digital zoom. At 2x, you should be able to see the sharpness slightly better. 4x probably won't help much since there is no additional detail, just a lot of blockiness. Don't forget to turn off the zoom before you shoot. This digital zoom is not available when shooting in RAW format (switch to JPEG, focus, then switch back to RAW).
Use reading glasses. They might look a little funny, but they will help you get significantly closer to the LCD while you are shooting (no matter how old you are). This makes it easier to identify out-of-focus situations. Go for a diopter of +1.5 or more (experiment at the store with your camera). Make sure they are small enough that you can see over them when looking for a shot. As an added bonus, reading glasses reduce eye strain when looking at the LCD. You'll be able to shoot a lot more.
Focus on something else. The G1 manual suggests focusing on something that is at the same distance as your subject, locking focus with the MF button, then recomposing and shooting. For macro work, a business card is a very handy focus target.
Myth: Spot Metering = Spot AF. Spot Metering doesn't imply Spot AF. Don't switch to spot metering mode thinking the G1 will focus on what is in the spot. It won't. The exposure may affect the AF system to a certain extent, so you might be tricked into believing that spot metering mode has some sort of effect on AF. Canon has said that it doesn't, and my experience agrees with Canon.
One of the main reasons I chose the G1 was because it has a focus assist light that helps it focus in low light. It works really well as long as the ambient light doesn't start to compete with the assist light. Shining the assist light on a low contrast subject with a contrasty background that is slightly better lit causes the focus to be on the more contrasty/better lit background. Olivier's Foot Picture is the perfect example of this.
In complete darkness, the G1's AF works perfectly since all the distractions throughout the frame are gone. The AF system has only the focus assist light to go by, and it focuses with that.
The G1's "Single" focus mode is actually much faster than its "Continuous" focus mode. Normally continuous focus mode is intended to help the focus system be at the right place at the right time. In the G1's case, continuous focus just slows things down.
Single focus makes it a little bit easier to do focus lock. Since the AF won't keep hunting every second, you can half-press the shutter button to focus, and let go. Then, at your leisure, press the MF button to lock the focus.
There are a couple of disadvantges to single focus mode. First, the LCD preview freezes momentarily while focusing. This is probably because the AF system takes control of the CCD, and that's why it can be a lot faster. Second, if you are shooting with flash in manual mode, and you have the camera stopped down to where the LCD is black, Single focus mode won't let you see a brief glimpse of the preview when you half-press the shutter button. Continuous focus mode will give you that brief glimpse.
I strongly suggest switching to single focus when you first get a chance, and leaving it there. For the very few times when continuous focus would be useful, you can always switch back.
Careful reading of the manual yields an interesting tidbit. On page 38, the crosshairs are referred to as the "autofocus crosshairs". That gives you the impression that the G1's AF system is a spot AF system. Nowhere else does the manual mention spot AF or centering your subject for focusing.
With a lot of practice, you can become very adept at using the G1's focus system in many situations. It would have been nice if Canon had helped out a bit with a spot AF mode and a focusing aid or two.
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Copyright ©2001, Ted Felix
