Depth of Field Adapter on Steroids

ProfHankD wrote:

Eggplantt wrote:

I was going to say even the lenses I had in mind aren't cheap/common enough, but then I remembered the plethora of extremely fast (f1.2 or faster) projection TV lenses that could work here, that cover 4x5.

This is perhaps the only common and sub $30 option out there.

That's not what Faboky uses. The lens for it costs $2.20 new.

OK. In the interest of keeping people from spending lots of money on lousy-but-fast lenses, I'll spill the beans and tell you the "F" in Faboky stands for Fresnel. That's how you can buy a very cheap (but comparably lousy) huge aperture lens for $2.20 and have it be very lightweight. It's a 7" diameter circle cut from a full-sheet Fresnel magnifier. Faboky stands for Fresnel Apodized Bokeh Obscura from KentuckY. With it coming from me, you should have known there'd be at least a couple of tech tricks inside.

The absolute line pairs per mm resolution of a cheap Fresnel lens is pretty bad, but coverage is huge -- after all, vignetting is usually associated with thickness of the lens system, and you can't get thinner than a Fresnel element. That combination makes an obscura the ideal way to use a Fresnel optic, because you get to "condense" the resolution into a smaller format.

Screen size is limited by portability and ease of build. I've tried 3 different rear-projection screen materials so far (from about 30 I had tested for earlier obscuras ), and I'm not seeing a heavy texture with two of them, but neither am I seeing the same resolution I see with front projection. So, I'm close to settling on this rear-projection design and throwing-together a front-projection version (which would have far less 3D-printed material in it because the size gets a bit larger and it wouldn't fit on the bed of most 3D printers).

PS: Years ago, I actually managed to 3D print Fresnel optics on a standard FDM printer. They were truly terrible, resolving no more than 1-2 lp/mm... so don't bother trying that. Cheap commercial Fresnels like I'm using in Faboky seem to peak closer to 20 lp/mm, although they still have quite low contrast.

Fresnel Apodized Bokeh Obscura from KentuckY

I was wondering this and couldn't figure out the fresnel part, and should but didn't get the Kentuky part either....F-. Regarding this not being a researchy project, it's a fun basic project that can get some people enthusiastic about 3D printing, etc.