...because I do not want you to know what happens inside my head except in the controlled circumstances under which I normally share. I don't need help "interpreting" my dreams, and the ones I remember generally explore aspects of my personality that you don't need to know about.

But this one was too weird not to say something about, and emotionally neutral enough that I can let it out. Not weird in the surreal sense, except to the extent that who thinks about that enough to dream about it all night long? Also it lets me put on my teacher hat, and I like showing off things that I know. :)

It was Monday night, after I got my new lens. Not too surprisingly, I dreamed about taking pictures with the new lens. But the dream did not focus (that there is a pun, you see immediately. What you do not see right off is that it is a pun *twice*) on the subject of my photography. Instead, it was about bokeh.

WTF is "bokeh"? you ask, and well you might. Bokeh is a Japanese term (alternately spelled boke, but adding the 'h' guides the reader closer to the correct pronunciation) which refers to the quality of the appearance of the unfocused area of a photograph. It does not, in my admittedly limited experience, get much attention in American teaching of the photographic arts.

Broadly, when a point source of light is not part of the area of sharp focus in a photograph, it is blurred into a small disc (we will discuss this as a "circle of confusion" in the Depth of Field article which I will someday write). The distribution of brightness in this disc determines bokeh. If the light is evenly distributed across the disc, this is considered "neutral" bokeh. If the light is concentrated toward the center of the disc, and fades away toward the edge of the disc, this is considered "good" bokeh. If the light is concentrated toward the edge of the disc and fades away toward the center, this is considered "bad" bokeh. These effects are going on with *every* unfocused point in the image, not just light sources, it's just that it's easier to see the effects with point sources of lights.

The reason why "good" bokeh is good is that the different points blend gently into their neighbors, providing smooth transitions between edges. "Bad" bokeh is bad because edges blend into each other discontinuously (because each edge appears as a double edge with a gap in between). At its worst, bad bokeh can make the out-of-focus areas of the image appear jagged and distract from the subject, just the opposite of the effect you're going for when you throw that area out of focus in the first place. The effects are generally very subtle, though, even if you are looking for them and know what you are about. I have never had a lens that allows for as much unfocused space in my images as my new lens will allow (also, as a shooter of landscapes, I tend to try to maximize the depth of field in my images and minimize the areas of unfocus), so I have never paid any attention at all to the bokeh in my images. I am aware of the phenomenon (obviously), but it's never been an issue or an interest for me.

So imagine my surprise when I dream me many dreams over the course of Monday night, all about me taking pictures in various situations with my new lens, and all focusing (and now you see why that is two puns for the price of one) on whether or not I was getting good bokeh out of the deal. Sometimes I was just holding the lens, with no camera attached, and evaluating the bokeh I was getting from it. Sometimes it was little fading-to-the-outside discs, and I was happy. Sometimes it looked like little rolled-up condoms, and I was annoyed.

I expect I will find out this weekend what kind of bokeh the lens actually has, and I will never have these dreams again. Though even for a given lens, bokeh can vary depending on whether the out-of-focus point is closer to or further from the camera than the field of sharp focus. I understand that some Nikon lenses, and formerly, some Minoltas (Minolta has gone bye-bye, and we are saddened), actually allow you to adjust the spherical aberration of the lens in order to change the bokeh effects, but boy, is *that* ever a topic for the Advanced Class. :)

ETA: Because spherical aberration in lenses is about the differential refraction of light waves, and while my math is probably up to it, my ability to *describe* the math is probably not, that's why.

Related topics (will add links when associated articles are written, or you can search on my “photography” tag):
Exposure
Focal lengths, f-stops, photon density, and autofocus
What the hell is "bokeh"?
Depth of Field
Camera shake and motion blur
Using the flash (Yeah, right! As soon as I figure it out myself…)
Film: Reciprocity failure
Expanding depth of field with Photoshop
Digital: The histogram is your friend
(Part 2 will have to wait until after the weekend.)

I knew it was going to be nice. I knew that, theoretically at least, the autofocus was going to be faster, quieter, and more accurate.

Digression the first: Focal lengths, f-stops, photon density, and autofocus.

This gets long, and there is a little math... )
The short story: Oh. My. God. What an *awesome* lens.

Related topics (will add links when associated articles are written, or you can search on my “photography” tag):
Exposure
Focal lengths, f-stops, photon density, and autofocus
What the hell is "bokeh"?
Depth of Field
Camera shake and motion blur
Using the flash (Yeah, right! As soon as I figure it out myself…)
Film: Reciprocity failure
Expanding depth of field with Photoshop
Digital: The histogram is your friend
.