What size hole do I use to make differently shaped bokeh?

Question

This is my question in one huge breath:

What would be the correct size of an elliptic bokeh filter be to create a fake anamorphic distorted bokeh effect with a regular Canon 50mm f/1.8 II lens with a Canon EOS 550D (crop sensor of 1.6x, AF-S)?

Say what, elliptic bokeh, fake anamorphic?

Check this video to see an example of the fake bokeh. Notice the bokeh appears to be stretched vertically.

How can you make one?

Check this video for an example. The actual filter is shown at 0:36.
The basis is to draw an elliptic "slit" on the filter. I'd take it a step further in cutting some vinyl and taping it to the filter, to get a clean edge and no leaking light.

Why do I need you in this process?

I have no clue on what the best dimensions of this ellipse would be. Trial and error could work, but to what extent? It's optics, can't this be calculated?

You expect me to solve that just for you there?!

That would, of course, be great! Yet, I'm just as grateful for any and all pointers in the correct directions!

Asked by n/a

Answer

• Well "best" is an extremely subjective term and will largely be determined by individual taste.
• In general, what you're describing sounds alot like a Bokeh Master
• Your cutout must be at least smaller than the real aperture you'll be shooting at (shooting at, not the maximum for your lens). This is because you need it to become effectively the new aperture shape. If you're shooting at 50mm f/2 - then it must be at least smaller than 25mm across. If you have a 50mm f/1.8 and are shooting wide open, all the time - then its 50/1.8. If you have a 50mm f/1.8 lens and are shooting around f/2.8, then its 50/2.8. In order to keep as much light, you want it as large as possible without going over (focal length / f-stop).

Answered by rfusca

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