Friday, June 27, 2008

G9: Focusing Indoors

As previously noted, although the G9 has five automatic focusing modes, I almost always choose the small Flexizone frame centered in the LCD. I place the focus frame on the subject of interest, push the shutter button halfway, think “focus”, check for the frame to turn green, recompose the scene and finish pressing the shutter. To get additional shots from the same vantage point, I then switch to manual focus and keep the previous focus distance. This method almost always works well even if it is a bit slow and methodical.

Without recomposing, the small Flexizone frame may not detect enough contrast to obtain focus. Also, without recomposing, the small Flexizone frame may focus on the wrong object. This is particularly a problem when photographing indoors. To illustrate this problem, I set up my G9 on a tripod and tried the various focusing methods indoors.

In this scene, the G9 was set for the widest angle, 7.4mm; the aperture was f4.5 (the “Sweet Aperture”) . The image shown was downsized from the in-camera JPEG. The focus distance, as determined by the small Flexizone frame was 15 feet but the large Flexizone frame determined the focus to be 8 feet! This discrepancy occurred because the small frame fell on a photo on the opposite wall but the large frame included a chair. The focus distance, as determined by the small AiAF matrix was 12 feet. The large AiAF matrix also determined the focus to be 12 feet. Interestingly, the large AiAF matrix did not always lock onto the same object even though the G9 was on a tripod. I had suspected that the different focus methods would lock onto different objects and I was correct.

Using manual focus, I dialed in 5 feet and took another shot. Later, to my surprise, all the pictures look essentially the same. Why? Of course, the explanation is hyperfocal distance. For the 7.4mm zoom focal length and f4.5 aperture, everything from about 4 feet to infinity is in acceptable focus. In setting up my test, I’d forgotten about the hyperfocal distance. Chalk one up for the G9.

Since this humbling experience, I’ve toyed with the various focus modes quite a bit. My basic hypothesis was correct: With any focus mode other than the small Flexizone frame, I cannot be certain of getting the exact focus point that I want. Fortunately, often it just doesn’t matter.

But sometimes it does .... (more later)

Thursday, June 12, 2008

G9: Focusing with a Polarizing Filter

The title of this post is somewhat misleading. When the G9 is fitted with a polarizing filter, the focusing process does not change. Also, either linear or circular polarizing filters can be used on the G9. In fact, this is the entire point of this post.

Although filters were extensively used in film based photography, digital editing has significantly reduced the need and use of filters. Even so, a polarizing filter can be a great asset. This filter can pump up the colors, make the sky more blue, knock out the glare, etc. Many believe that a polarizing filter provides the only effect that cannot be simulated in the digital editing process. In a previous postings, the effects of a polarizing filter, graduated neutral density filter and various post processing effects, including HDR, were compared.

A polarizing filter was the second filter I ever bought (the first one was a clear, protective filter). Although I didn’t know it at the time, that polarizing filter was a linear type. Years later, my auto focusing (film) SLR required a circular polarizer. That was the first I’d heard of a circular polarizer. For a long time, I thought all auto focusing cameras needed a circular polarizer. A few years ago, I bought a circular polarizer for my Canon G3. For my G9, I still use that circular polarizer but I’ve since learned that a linear polarizer also works on the G9.

Once again, Wikipedia to the rescue for the details about polarization but be sure to scroll towards the end of the highly technical article. Also, that article does not really cover linear vs circular for photography.

It turns out that DSLR cameras and digicams like the G9 use different focusing systems. As mentioned previously, the G9 (and, I think, most digicams) use contrast detection as the basis for focusing whereas DSLRs use phase detection. As a result, the G9 can use a linear polarizer but DSLRs require a circular polarizer. This differentiation is often confused. The linear polarizer is less expensive but if you have, or intend to buy, a DSLR, the circular polarizer is more versatile.

To fit any filter to the G9, an adapter is needed (well, you can actually just hold the filter in front of the lens). In addition to selling the adapter, Lensmate sells polarizing filters and notes that either linear or circular types will work with the G9.

As final proof, I compared my 40 year old linear polarizing filter to my newer circular polarizing filter and found no obvious differences. The G9 worked fine with either. Nothing like a simple test to prove something to yourself!

Friday, June 6, 2008

G9: Can’t Focus

Sometimes the G9 can’t focus. When the G9 has acquired focus, it beeps twice (very quickly) and the AF frame on the LCD turns green. If the G9 is confused about the focus, it only beeps once and the AF frame turns yellow. That (yellow frame) was the case for this uncropped image. For this composition – as attractive as it is – the small AF frame did not include any details and the G9 could not focus. I pressed the shutter button anyway and got an out-of-focus picture.

Switching to manual focus immediately after the shot, I found that the G9 decided to focus at infinity instead of the true distance of about nine feet. Had I selected the nine large frame AiAF focus method, the G9 would have focused correctly because some of the frames would have included the plaques (tested and proven).

As noted previously, I almost always use the small Flexizone frame for focusing. I even leave the frame centered; that is, I focus, recompose and shoot. But sometimes, especially when in a hurry, this is not the best method and it definitely is not the best method without recomposing.

The G9 focuses by means of contrast detection and tends to select the closest object. When using the small AF frame to focus, make certain that the focus frame includes an edge, some sort of pattern, different colors, different lighting, etc. In fact, when using the large frame or the multiple AiAF frames, keep in mind that the focus point will be selected on the basis of proximity and contrast.

And watch for that frame to turn green!