Bokeh: 50mm 1.4 with 12mm extender

DavidTO

I picked up my camera for the first time in months (nearly a year) and had a great time shooting the SoCal wildflowers.

I'm noticing some funkiness in the bokeh in some of the shots, and I'm wondering if anyone knows if the use of an extender affects the quality of the bokeh. I know that it decreases the DOF, so that you get more of your image OOF, but aside from giving you more, how does it affect the quality?

Click for EXIF


Some seem better than others:

craig_d

Just to be clear, when you write "12mm extender" you mean an extension tube with no optics inside, right? In Canon's nomenclature, an "extender" is a teleconverter, not an extension tube, but TCs are normally described in terms of magnification (1.4x or whatever), while extension tubes are described in terms of length.

A teleconverter, since it contains optics, can affect the image in all sorts of ways. Typically, they add some barrel distortion and CA.

With an extension tube, you are simply moving the lens farther away from the sensor or film. Fundamentally, this is no different from what many lenses do when focusing closer than infinity, but extension tubes let you move the lens farther from the sensor than the lens is able to do by itself. This effectively reduces the lens' minimum focus distance, thereby increasing its maximum magnification, at the cost of losing the ability to focus to infinity.

One thing to consider, though, is that when using an extension tube to focus more closely than the lens would normally allow, you are operating outside the lens' design parameters. Because of this, I would not think that it could be guaranteed that image quality will be maintained. It's not unreasonable to think that the quality of OOF areas may change, or that the image may soften. The effect of this will tend to increase with longer extension tubes, and will probably vary between different lenses, especially those designed with different optical formulas.

I kind of like the quality of the background blur in your first shot; it has a sort of impressionistic quality. I agree that it isn't what I would expect from the Canon EF 50mm f/1.4, but it's kind of cool.

DavidTO

Thanks! Yes, I meant an extension tube with no optics inside.

Thanks for the info!