G1 Focusing

Powershot G1 Focusing
Crab, crab, crab

A number of people have asked (and flamed) me about problems involving the G1 focus and flash. If the problems were isolated to me as a single user, that would be one thing — but sadly they're not, and they reveal what to me are the biggest problems with the G1's design, problems that have been much-improved in the later G2 and G3.

Autofocus

The G1 appears to use a contrast-based AF system. It also appear to use the entire frame to measure contrast. In other words, the contrast of pixels along the edges and in the corners are given just as much importance by the AF system as pixels near the center.

The G1's uncentered approach has serious consequences for autofocus use on real scenes. While it's fine for landscapes and may even do well for group shots, what about a head-and-shoulders portrait?

Typical G1 AF failure --
camera focused on the background

Only about 34% of the pixels
are part of the subject

Here's a typical example, shot with strobe.. The boy is more than 1m away from the camera, so it's not a "macro" shot — but he only covers about 34% of the frame. Centered or uncentered, the G1's AF will focus not on the boy, but the furniture behind him.

Canon's G1 manual mentions "autofocus crosshairs" on page 38, but this is simply wrong — they're in the optical finder and clearly have nothing to do with the Autofocus. What's more, they may give you the impression that the AF is concentrating on the area of the crosshairs (like the "target marks" did on the previous Canon design, the Pro 70) — and that's simply not true.

Likewise, you might think that turning on spot metering would affect the area considered by the autofocus — you might think that, but... you'd be wrong. It only affects the metering, not the focus.

The Pro 90 also has a "target bracket" area, which might actually do something (it's part of the EVF and LCD, not the optical finder). But both the G1 and Pro 90 manuals claim weakness to "Subjects with extremely low contrast to the surroundings." Even the A20 has AF brackets — why does the G1 have this crippled system? Is it some failed prototype of the A20's AiAF?

Manual Focus

Of course, if the AF is cantankerous, you can always use manual focus. But there's no way to know if you're really in focus or not — no zoom-in feature (standard on all the competition) is provided, so you're left guessing.

Fortunately, there's a partial workaround — use the digital zoom to expand the center pixels, focus, and then turn off the digital zoom. Great, but...

You can't use RAW
Digital zoom is only offered in the JPEG modes. When you select RAW storage, digital zoom isn't available. So if you want crucially-sharp focus, you'll have to compromise on image quality. Or compromise on the time it will take to flip back and forth through the menu system to switch from RAW to JPEG and back again while focusing.
You don't really see more detail
The pixels are blown up — so you won't really be seeing a closer view of the middle of the CCD. Bigger pixels will make it easier to see contrast, but not detail.
Manual Focus turns itself off at annoying times
Those times include any time the display is turned off by rotating or the DISP button, or whenever you try to turn the LCD to face forward. Another "gotcha" is trying to flip quickly to playback mode to review images — when you turn the camera back on, the AF will kick in for a sec, erasing your previous MF settings.
It sure is a lot of work for a simple operation
To use the digital zoom from RAW mode (if in JPEG mode, ignore the parts marked in blue) (and iterate the step marked in red until the shot is satisfactorily focused):
1. Press MENU
2. Press Down
3. Press Right
4. Press MENU
5. Press and hold SET
6. Jog the Zoom lever right and release
7. Jog the Zoom lever right and release again
8. Release SET
9. Press and hold the MF button while using up and down arrows until focused
10. Press and hold SET
11. Jog the Zoom lever left and release
12. Jog the Zoom lever left and release again
13. Release SET
14. Press MENU
15. Press Down
16. Press Down
17. Press Down
18. Press Left
19. Press MENU
20. Shoot
That's a lot of extra button pressing! Hope your subject is a patient one.

step number nine,

one hand?

right

Workaround #2

One workaround, though also with some peril, is to just keep a +1 (or even +2) closeup diopter on the camera when shooting close portraits.

Downsides: it takes time to thread and unthread the diopter; you are interfering with the overall optical quality; you are reducing depth of field; and you can't focus on faraway objects.

Upside: you can't focus on faraway objects, so you have a better chance on getting a shot at the near objects you want.

Flash

Critical focusing could be ameliorated by using a higher f/stop. Unfortunately, this too causes problems, and often doesn't work at all.

For whatever reasons, the Powershots exhibit strong chromatic aberration with "black body" light sources such as incandescent bulbs and sunlight. Most of these aberrations go away with flash — the difference is so strong that if you really care about color from a Powershot, especially skintones, you will always use flash illumination. But:

For whatever reasons, Canon has taken the attitude that the G1 doesn't really support flash correctly, and that only synch with Canon's own flash units is important. But:

For whatever reasons, Canon's own flash units work only with the lens wide open, and multiflash and ratio control are not supported (the infamous f/8 flash trick is truly a limited-application "trick," of very limited usefulness without multiple high-powered strobe heads, which are unsupported). So:

To get good color, you must use the settings that you really should not — settings that Canon deliberately appears to be going out of their way to prevent you from using (while denying that there's any problem with Powershot focussing or flash design), even as they advertise the cameras as the epitome of user control.

Hot Pixels

Lots of folks have trouble with their G1 CCDs. This is a manufacturing problem that's probably as much to blame on the CCD manufacturer (Sony, as I recall) as Canon. It's hard to say whether hot pixels have any effect on the focus or exposure calculations done by the cameras auto systems.

Color Control: RAW versus JPEG

The last major problem with the Powershots is color control. If you regularly shoot in RAW mode, you may never notice this — but if you shoot in JPEG, you may well have been plagued by "magenta shift." This isn't the typical magenta fringing around the highlights, due to chromatic aberration, and which is common in all digital cameras. Rather, it's the fact that when JPEG images are imported from the camera, to your computer, they are tinted magenta. This tint apparently comes from the camera's DSP itself, during JPEG compression.

The magenta shift is not visible in the thumbnail displayed in ImageBrowser/ZoomBrowser, nor in the playback image in the camera (same thumbnail). It's not visible in RAW display. Only if you shoot JPEG, when you click on the downloaded image in the viewer, will you notice that the large image is not the color you see in the preview!

Strange and mysterious? Yes. Appropriate for a camera whose marketing trumpets it as top-level and with lots of user control?

Canon at least gives the user RAW format as an option. It may be heavy and slow to work with, but at least it's there. There is another screwup with regard to RAW, however — at least for the Macintosh version of the TWAIN software. The TWAIN driver provided for use in Photoshop can read RAW images only directly from the camera. If you download the RAW images using ImageBrowser, and then try to read them from Canon's own Photoshop import module, it won't load. It won't even acknowledge that the images exist. What's the point of that?

Canon

Every camera has its own idiocyncracies. And not every camera can be top-of-the-line. But these are issues that are fundamentally broken, on a camera that was heavily marketed as a digicam that could be used by consumers and pros with high standards. Canon's attitude has been either to say "this is a camera for regular consumers, so we can't be expected to make it work correctly," to deny any problems exist, or to simply ignore all comments. It's truly sad, at least for me — it's lead to a deep disillusionment with the company. Years ago, I traded my Nikon F's for Canons, believing that they were the way to go. At the time, Canon worked hard for that kind of respect from customers. It's tragic that now Canon seems to rely on inertia and market presence, rather than quality and customer awareness, to keep them in the forefront. I've been sticking with Canon for over twenty years, and they've thrown away my sense of brand loyalty. Guess it's not worth much to them, which is why now I'm shopping Fuji, Olympus, and Nikon.