Soft focus v2
By Mario-Cezar Popescu
29 May 2009
While trying to make some diffusion disks to match my monocle, i've accidentally used this "filter" with a modern lens, well corrected for aberrations. If I remember correctly it was a Nikkor 18-135mm f3.5-5.6 lens. The result puzzled me, it gives the out of focus portion of the photographs a whirl that does not resemble the bokeh of a Helios-40, being more mechanical and predictable but still different. Used on a less corrected lens it blows the highlights into glows, so i can diminish to some extent my lust for a Rodenstock Imagon till i can afford one. I've made this diffusion disk with a monocle (that's a lens with a single meniscus element) in mind, Sima Soft Focus 100mm f2.8. I've chosen this lens because it's extremely nice to work with, being light and easy to focus. Also it came with a f-mount so does not require additional modification when used on my Nikon camera.
Anyways, the contraption was simple. I started with thin aluminum cut square, i've marked the location of the holes and drilled them, the big one first then the first concentric series of holes, the the smaller ones. Because i was thinking to use this filter together with a Sima lens, which has 100mm focal lenght, it was easy to calculate the diameter of the big hole to match a desired f8 diaphragm. The dimensions and location of the smaller hole were pure guess.
After i've finished drilling i've painted both sides with matte black car paint and i've mounted the diffusion disk on a broken uv filter, using only the metal round parts.
A word about the v2 part of the title: as you can imagine, this is my second attempt to make this diffusion disk, the first one was really crappy, mostly due to lack of proper tools.
4 responses
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Nathan Regener said (5 Jun 2009):
I really love the results of the filter, but the story could have used some more helpful information, such as how to calculate the diameter of the big hole, and why you chose that pattern of holes. Thanks!
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Mario-Cezar Popescu said (10 Jun 2009):
Hihi, i used it to smoother the edges of the holes, nothing else :)
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Janice Eddington said (3 Jul 2009):
How do you calculate the center hole? I don't even know where to begin?
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Mario-Cezar Popescu said (4 Jul 2009):
Prior to start calculating the center hole diameter you need to know some stuff: you have to decide which lens you are building the filter for. You need to know mainly the focal length of that lens - usually it's engraved on it. After that it's simple math: the diameter of the hole it's just the result of focal length divided by required f-stop.
Bear in mind that the amount of light that will pass through the filter will be slightly larger that one related to desired f-stop due to small adjacent holes, so you have to compensate for this by making the central hole a little bit smaller that the calculated diameter. It's not an exact process, it's more like trial end error.
If you have more questions please contact me directly on ym at popescumariocezar — i'll be more than happy to help you out.
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