Wednesday, January 17, 2018

Manual Focusing: Thoughts and Tips - Part 1(Guest Article)

I'm happy to present another guest article today. It's a comprehensive look at manual focusing by Chuck, who some time ago reviewed the Nikon AF Nikkor 28-70mm f/3.5-4.5D lens

Guest writer Chuck here. Today, I present some thoughts on the subject of manual focus, and a few tips on how to do it better.

Why Focus Manually?

Why, indeed? Autofocus is so much more convenient. Push a button, and something — hopefully your subject — pops into focus. Take the picture.

Autofocus is fast and accurate. Given enough light and contrast, any decent AF camera/lens combination can achieve focus in under a second — even if it has to go from infinity all the way to minimum distance. In typical situations, the time needed can be closer to one-tenth of a second. With speed like that, you can magically keep a moving subject in focus with no more effort than it takes to keep your eye on it. Technology is wonderful.

In contrast, a human who is particularly quick at manual focusing may be able to bring a subject more-or-less into focus in about one second. That doesn't sound too bad — but it is. The problem is accuracy and rates thereof. If you take only one second to focus each of a series of shots, you will be lucky to achieve accurate focus one time out of ten. The other nine times, you will have something that is more or less out of focus. Compare that to a good autofocus setup, which can achieve an accurate-focus rate more like eight or nine times out of ten, and will do so taking far less than a second each time.

D800, Nikkor 135mm 2.8 AI-s @ f/4

Defining Accurate Focus

As an aside, here's a completely arbitrary definition of accurate focus: A photo is accurately focused if, when viewed on a 27-inch, 16:9 display, scaled such that the height of the photo matches the height of the screen, the focus error is no more than about one tenth of a millimeter. By focus error I mean the additional blur radius compared to a photo that is focused as well as possible, all else being equal. Take a photo of the night sky. Given very precise equipment and excellent shooting conditions, let's assume the diameter of a star viewed on that display is two-tenths of a millimeter when the photo is focused as well as possible. Now, if, in the actual photo, the star's diameter is four tenths of a millimeter, you have a focus error of 0.1mm — the difference in radius between the perfectly-focused star and the imperfectly-focused one. On a 218-dpi Retina iMac display like the one in front of me, a single hardware pixel is about 0.12mm wide. So, a focus error of 0.1mm is a little less than one pixel wide on such a monitor. This is a fairly stringent definition of accurate focus.

Unless you are unusually good at it, speedy manual focusing is a bad idea. You get much better results when you slow down and take your time. I, for one, need anywhere from six to ten seconds to focus well. At this speed, I'll get a result that meets the above definition of good focus in about seven out of ten tries. That approaches the accuracy rate of AF, although at a much slower pace.

But I still haven't answered the question. Why focus manually? I have three reasons: greater control, old lenses, and because it feels good.

Manually focusing a camera is a lot driving a car with manual transmission. When you shift gears manually, you decide when to shift, and by how many gears to shift. You have greater control over what your car is doing. You have more immediacy, a greater sense of connection with the car and with the road. And it just plain feels good to use your hands, because hands are for using.

It's the same when you focus manually. You choose where to focus — and you don't have to fiddle with a d-pad or a joystick to move a focus point to that spot; you just look at it. Want to focus on something in the corner of the frame, where your fancy DSLR has no focus point? Go right ahead. Manual focus frees you from the tyranny of the focus point, and that feels good.

Thoughts on Composition and Equipment

It's been said that focusing manually forces you to slow down and really think about the photo you are taking. That's not true: it may encourage you to do that, but it doesn't require you to. It's possible to become so preoccupied with precise focusing that you actually forget to think about light, about composition...about what you are shooting in the first place and why you are shooting it.

D800, Nikkor 28mm 2.8 AI-s @ f/2.8

What I find manual focusing does for me is, simply, it makes the process of taking pictures more enjoyable. It feels good to fiddle with the focusing ring. It feels good when your subject snaps into focus through your direct, physical manipulation of the lens. And it feels really good when, after you hit the shutter release, you see that you've nailed focus — and the camera didn't do it for you.

Something that very much enhances the tactile pleasure of focusing manually is the use of old, manual-focus lenses. If you've ever handled a Nikkor AI, AI-s, or even older manual-focus lens, you probably know what I mean. They are exquisitely well made. Being made mostly of metal and glass and with less empty space in them than the latest technical marvels, these lenses feel solid in the hand — dense and weighty. And the focus action is amazing. When the helicoids are in good shape and perfectly damped, turning the focus ring feels wonderful.

The old lenses also have unique optical signatures that are quite different from those of modern glass. They are often less sharp in the corners than newer lenses, even when center sharpness is just as good or better. Some examples have lower contrast, more flare, and more coma. That's only a problem if you think every photograph should be technically perfect.

Make sure to check the second part of the article, where Chuck gives some detailed, useful tips on perfecting your manual focus technique.

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