From Canon to Nikon: Focusing

On September 2, 2008, in Photo, by peterb

(Part 1 of this article explains my rationale for answering the question “How hard is it for a Canon shooter to go Nikon?” After a month with a D300, I’m ready to answer that question. If you buy equipment from Amazon via links on this page, or click on the ads, we get a little cash, which helps us maintain this site.)


Nikon’s auto-focus system UI differs from Canon’s in the particulars. In its default mode, the Canon focus system tries its best to focus, and then lets you take the photo. The D300 in “S” (“single-servo AF”) mode will refuse to take a photo if it thinks it isn’t focused. The camera goes to great lengths to make sure that you, as a photographer, know what’s going on with the focus system. In “S” mode (which I think of as equivalent to Canon’s “one shot AF” mode), half-pressing the shutter causes the lens to focus, the selected focus sensor to flash in the viewfinder, the camera to beep (unless you tell it not to), and a small dot to appear in the viewfinder, which means the camera believes it is focused on something. Squeezing the shutter release the rest of the way takes the photo.
Overall, I found D300′s focusing to be superbly accurate, but slightly slower than Canon’s. We’re not talking a huge difference here. Subjectively, it feels like about a hundred-millisecond difference. For most non-sports situations, that’s enough that you notice, but not enough that you miss the shot. For my money, this is a good tradeoff: when the focus system works, which is most of the time, you get superb accuracy and tack-sharp results. That means more keepers.


Now, it’s worth noting that I wasn’t using the kit lens, but the superb 17-55 f/2.8 designed for DX cameras. The difference in contrast and color reproduction between this lens and some of the others I tried was nothing short of dramatic. On the one hand, as someone who doesn’t sell photos for a living, $1200 for a lens seems like a lot of money. On the other hand, given the month of shooting I’ve just had, I’m not sure it’s a lot of money for this lens.

If I may digress for a moment, I should note that I’m well aware some will think I’m comparing apples to oranges here; after all, I’m using what by reputation is one of Nikon’s best lenses, and the Canon lenses I have shot with are, comparatively, low rent. While that does speak to certain image qualities such as color and contrast, and probably also to focusing speed and accuracy, it’s worth keeping in mind that what impresses me most about the D300 are the excellent viewfinder and its intelligence in choosing exposures, which should be the same across all lenses of a given aperture. It’s worth remembering, though, that what I’m actually reviewing here is the combination of those two pieces of equipment.

The D300 has two ways to switch to manual focus. First, most autofocus lenses will have a small switch that changes them from automatic to full-time manual focusing. The body also has a small three-way switch that lets you choose between “S” mode (the camera will insist on focusing before allowing the shutter to be released), “C” mode (for quickly moving subjects, the camera tries to anticipate the best focus point and lets you release the shutter at any time) and “M” mode (manual focus).

detail d300

My nemesis.

This switch is located just to the lower-left of the lens (from the perspective of the photographer). In other words, the switch is located in a place where I am likely to brush against it with the heel of my left hand while manipulating the focus ring or zoom ring on the lens. When shooting with the D300 I accidentally flipped this switch, without realizing it, more than once. Usually I would knock it from “S” into “C” — continuous — mode. That’s not the end of the world. In the midst of a carefully planed shoot, however, I accidentally flipped the camera into “M” mode. There’s nothing more frustrating than having the perfect light and realizing that you haven’t been correctly focusing for the past 20 shots.

Missed opportunity courtesy of the S/C/M switch.

“C” focus mode is meant to be used for quickly-moving subjects, the equivalent of Canon’s “AI SERVO” mode. The accuracy of focus here was noticeably less perfect than in “S” mode, but then tracking moving subjects is a much more difficult task. From a practical perspective, I stopped thinking of it in terms of its intended function, and just started treating it as a “focus faster, I don’t mind if I miss a few” switch.


Jump! f/4, 1/800, ISO 500

Something that must frustrate camera designers is that many photographers don’t use the more advanced features of their autofocus systems. A traditional issue with SLRs is that the focus sensors in the center of the frame are more accurate than those on the edges. So after getting burned by missing photo when using all the sensors, some of us — and I’ve certainly done this at times — resort to what’s called “focus and recompose”: you lock the focus by pointing the center of the frame at what you want in focus, then you reorient the camera while holding the shutter half-pressed.

For most of my time with the D300, I left it in its magic autofocus mode, where it dynamically decides what parts of the scene I probably want in focus. It then flashes those sensors so you know what it thinks it is focusing on. If it gets it wrong, you can release the shutter and half-press it again, or you can switch to a center-weighted focus mode, or you can specify a single focus sensor to use. The dynamic full-frame focus mode worked great for about 90% of my shots. This worked in part for one reason: the wonderful viewfinder. With a nice large viewfinder, you can immediately tell when the camera has focused on the wrong thing. This, more than anything, is why I’m OK with carrying around a camera this large. The viewfinder is clear, bright, and covers 100% of the sensor area. When I compose a shot in the D300′s finder, I know exactly what composition I’m going to get in the final frame. I used to think that this didn’t matter, but now that I’ve lived with it for a while, I have no idea how I’m going to go back to anything less.

Our next section focuses on performance in low light.


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