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Monday, August 28, 2006
6:11 PM      

I just heard that John Mark Karr will not be charged in the Ramsey case. I could smell this coming for several days, and I even sensed a few in the press trying to hedge their position. Jack Cafferty said the press was ‘played like a tin drum’ on this case. I say they did it to themselves, once again.

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5:48 PM      

I'm sure [that right] after Alexander Graham Bell said ‘Watson come in here. I need you,’ he said ‘What are you wearing?’

A funny and poignant observation by Jon Stewart about how changing technology alters the norms of decency.


Early in my exploration of photography, I learned about the relationship between aperture (ƒ-stop) and depth of field — the phenomenon that describes how much of the image taken in by the lens is drawn in sharp detail. I've recently discovered, though, that there are interesting nuances to this distinction.

[With a shallow depth of field, only a narrow plane of view is sharp, while things in front of or behind that plane are rendered out of focus or ‘soft.’ In a photo with a deep depth of field, virtually everything in the scene can be sharply in focus. Apertures like ƒ/2.8 give a shallow depth of field — isolating the face of one person in the foreground from a crowd standing behind, for example; while apertures like ƒ/16 or higher offer a high depth of field, and might well record everything in a landscape sharply.]

The first nuance is bokeh, which describes how the lens handles the part of the image that is outside the depth of field. There is such a thing as bad bokeh, and good bokeh has to be designed into a lens. Bad bokeh puts hard edges around out-of-focus elements. Ken Rockwell has a good discussion of this. How can you gauge the bokeh in your lens? Ken says:

Find a point of light in the distance. You can do this easily at night by finding a distant point streetlight, or you can do it indoors by taking the reflector off of a Mag-Light flashlight and just setting it up on the other side of the room.

Now look at the ground glass as you focus. If you see perfect round disks your lens has neutral bokeh, if you see soft-edged shapes you have good bokeh, and if you see doughnuts you have bad bokeh.

I began to find out about this issue when I was researching the new Zeiss lenses for Nikon mount. A cryptic message on a discussion board said ‘the bokeh will suck.’ As I looked further into it, I found out that while the legendary Zeiss name connotes the pinnacle of German optics and a history that dates back to 1846, many Zeiss lenses are manufactured under license in Asia, and many of the Zeiss design patents have expired, so lots of companies can make more or less the same lenses (Think off-brand low-cost lenses that boast incredible performance). Of course, the quality of the glass and the components used can vary greatly.

More interesting, the Zeiss lenses for Nikon mount are being brought to market first and foremost because Kyocera has killed the Contax camera line — once an important outlet for Zeiss photographic lenses. Zeiss has responded by marketing some of their best-known lenses in Nikon F-mount format, and by increasing their partnership activity with companies like Sony, who market the Alpha D-SLR.

The Zeiss ZF lenses are manual focus lenses, and offer what is essentially only a physical compatibility with my Nikon body. The prospect is not exciting. What is exciting is that the Nikkor 85mm ƒ/1.8 is a really nice, light, fast lens, perhaps the perfect portrait lens for me, and it's not so expensive. [I think it's the next lens to get.] The 85mm ƒ/1.4 is an even more impressive lens, but it weighs about a pound, it costs more than triple the price, and its performance characteristics are only marginally better. Yeah, when I get a really nice windfall, I might think about it again, but maybe not — there's always more kit to get when you're doing photography.

Now for the second nuance. In 1932, 11 West Coast photographers (Ansel Adams, Imogen Cunningham and the Westons among them) dubbed themselves Group ƒ/64. The name comes from the smallest available aperture for a large-format view camera at the time. It was an aperture that provided infinite depth of field, making it very useful for landscape photography.

35mm camera lenses can't stop down to ƒ/64m but they often go down to ƒ/22, and for some time I've heard that the smaller the aperture, the greater the depth of field. Why do we care? With a great enough depth of field, focusing becomes a non-issue, which is a boon to street photographers, and even event photographers who need to shoot fast.

When I was shooting with my D100 last summer, I started to notice that some of my landscape shots seemed to be coming out soft, even though I was intentionally pushing the aperture to ƒ/22. I thought it was some weird focusing problem, but it turns out that I had bumped into an optical limitation of the system. The small aperture causes a diffraction effect, which substantially degrades sharpness. You might want to think twice about using ƒ/22, especially if you're shooting digital.

What causes the problem? An incompatibility between the size of the photosites on the camera's sensor and the size of the circles of confusion produced by the lens when it's stopped down to such a small aperture. Depending on your camera, this effect could kick in at apertures as moderate as ƒ/5 or so. Most mid-range and high-end digital cameras won't show the effect until you pass ƒ/11- ƒ/16. Here's a link, if you want more detail on this.

There's actually another reason to think twice about stopping down [setting a high ƒ-stop #] (or opening up [setting a low ƒ-stop#]) too much: many lenses, and especially zoom lenses, only exhibit optimal sharpness through several stops in the middle of their range of apertures. You'll lose sharpness in your image if the lens is wide open, or if it's closed down too much.

For me, that means I don't plan to stop down beyond ƒ/11-16, and I might think twice about using ƒ/3.5-4.5. ƒ/8-9 is starting to sound like a real good range to aim for.

[ link | e-me ]
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