Wednesday, 21 May 2008

Canon 100-400mm bokeh

I was going to go and see what this is all about, but turned out the hole in the road was so unremarkable it didn't even deserve taking the camera out of the bag. So I went to the harbour instead and as it was such a lovely, glittering day on the sea surface, decided to test what the bokeh of Canon telephoto zoom lens 100-400mm f/4.5-5.6 L IS USM looks like. The lens has eight diaphragm blades, so the out-of-focus highlights are octagon shaped, but pretty close to a nice circle, really.

Well, this lead me to read again what bokeh really means. Here is one explanation: Ken Rockwell on the case. We learn that good bokeh is the kind of bokeh where the "disk" of out-of-focus highlight is brighter in the middle and fades away towards the edges of it, i.e. one that doesn't have a hard edge to it. And definitely not looking like a bright doughnut. (Is that an oxymoron?) Hmm, I can see that the edges of the OOF highlights in my gull photo are well defined, so does that mean that this lens's bokeh is not very good, but only "neutral"?

There is something else I learned from the article that I had never thought of before:
Odd numbers of blades will give diffraction and reflection stars around very bright points of light that have double the number of points as the number of blades. For instance, a seven-blade diaphragm will give a lovely 14-pointed star. Even numbers of blades will give stars with the same number of points as you have blades. An eight-bladed diaphragm will give a boring eight pointed star.

Interesting! (I think I just found an example of a nine bladed one!)

Here are very illustrative examples of different qualities of bokeh: Rick Tenney's take on bokeh.

Now I want to go and test all my other lenses!


Josh Mullenite said...

You posted a link to a photo of mine at the bottom of your post here, the lens used is in fact a 9-blade diaphragm.

Katariina Järvinen said...

Hi Josh,

Thanks for confirming! What make is your lens, if you don't mind me asking?

Josh Mullenite said...

It's a Nikon 85mm 1.8D