DIY Apodization Filter replace the aperture.

vfan wrote:

ProfHankD wrote:

Interesting way to make the apodization filter....

I wouldn't have expected that to be optically ok, but it seems fine and smoother tonally than simpler methods (e.g., laser printing on transparency material).

I had the laser printing version. It is bad optically of image.

You're getting quite a bit worse for your lasered filter than I got for the laser-printed filter, but that's probably because I prefer to put the apodizing filter in front of the lens -- which means the area is larger and thus the laser dots are effectively smaller. I never got any of the obvious diffraction patterns you got, but I agree optical quality isn't very good.

Inkjet printing on transparency material gives better tonality than laser, but the transparency material is coated to accept the ink, and that coating acts as a bit of a diffuser. Laser-cut or programmable paper cutter "sink strainer" designs I made had very heavy textures in the bokeh. You can do quite a bit better exposing and processing B&W film to make the filter (I tried 6x6cm film), but it's a pain. I also built a homemade sputtering machine to coat filters with a controlled optical density gradient; it produced very good quality, but it was a nasty hack and hard to use (although I've often thought about making a better sputterer now -- the one I made was many years ago, before I had a 3D printer, etc., to make the parts).

Your approach seems to produce a filter very much like the original Minolta STF 135mm's apodizing filter. So, how easy was it to produce a controlled gradient? Any fabrication tricks? Any optical problems with the significant thickness of your filter?

BTW, the other trick one can use is a variant of what Minolta did in the Maxxum 7's STF (Smooth Trans Focus) simulation mode: vary the aperture during exposure. They actually did it as a multiple exposure with different aperture and exposure time settings to approximate the desired apodization function, and that obviously can also be done in post with just about any digital camera combining aperture-bracketed exposures. No filter needed, but you need to be able to automate aperture control... which isn't as easy with most manual lenses. It was easy for me to implement in-camera using Canon PowerShots under CHDK (although most current PowerShots don't have a controllable aperture).