Homemade soft focus filter

I have been reading some of the DIY lens building write-ups, and this one mentions a filter for the Leitz Thambar soft focus lens, which is sort of an inverse aperture - a black dot in the middle of a clear filter.

http://www.siskinphoto​.com …ine/zpdf/LensAs​sembly.pdf

Well, that sounded too easy to DIY to pass up. My thought was that it was blocking the sharper center of the lens, allowing only the widest outside radius of the lens to project the image, maximizing the aberrations that come with a wide open lens. Sort of the opposite of stopping down. I have a couple of old MF Olympus 50mm lenses, an f/1.8 MIJ and an even older silvernose f/1.4, which while sharp stopped down get soft wide open, I thought one of those might make a good candidate for my first experiment.

Below is a single picture collage of my initial testing with a few different sized dots - Mods, I hope this meets the spirit of a 1200x1200 pixel single image rule? If not, let me know and I'll remove it. Long term I should set up a Flicker account or similar for experiments like this I guess. EXIF will be missing due to GIMP - all of these are taken with my 60D 1.6x crop camera using the Zuiko 50 f/1.4 lens on an adapter at its minimum focus setting, hand-held, so focus will vary slightly.

From the lower left corner going clockwise:
LL corner is f/5.6, iso 400, 1/1600
Left center is f/2.0, iso 100, 1/3200
UL corner is f/1.4, iso 100, 1/5000
UR corner is f/1.4, iso 100, 1/4000, 15mm black paper dot in the middle of a 1A skylight filter
Right center is f/1.4, iso 100, 1/3200, 25mm black paper dot in the middle of a 1A skylight filter
LR corner is f/1.4, iso 800, 1/1600, 35mm black paper dot in the middle of a 1A skylight filter

Interessting results!
With the "normal" lenses like the Olympus 50mm/1.4 with a tensioned Double Gauss construction to get the free room for the mirror the entrance pupil is inside the lens. This results in strange effects with such a front kind of aperture.
Best would be to build such a filter in the aperture plane. There you really can block the central / sharpest image part, without getting the blackend center.
But there it is bad to insert a 2mm thick glass filter. I have used film for apodiszation filter tinkering.

I am not sure whether "modern" lenses like that Olympus have a bad enough border image quality. For sure you get some spherical aberration, but to get that sharp-unshap effect it would be probably best to have the border aperture rays + some central rays as well.

Instead of black opaque dots, why not use clear nail polish protectant to make tiny yet transparent raised dots?!...a homemade Softar!

ZoneV - Apodization, that's the word I was looking for...that's a very nice link, thanks. Yes, I was imagining a negative version of that. You are right that putting this sort of filter at the aperature location, like a Waterhouse Stop, is the right way to go about it, but I like this lens and I don't have the courage to disassemble it like the link did with their Helios. I think the strange effects in the background of the center-right photo are due to the poor placement of my filter in front of the lens as you say. I actually have an old set of opera glasses that are never used, whose objective lenses are a pair of 100mm FL cemented dual element (achromatic?) meniscus lenses of 25mm diameter that unscrew easily. With a body cap and some PVC tubing I could assemble something approaching a 100mm f/4 Chevalier landscape lens, which would let me put my "filter" in front of it at the normal aperture location, and that should give huge amounts of aberration. Or I could try to use the pair together in a RR setup for 50mm f/2, if my Canon's ~46mm flange distance will fit it in front of the mirror. But yet another 50mm lens? I think a landscape style 100mm lens would have a softer look anyway (I could stop it down a little if it's too soft, with sort of an apodization ring).

Wilt - I was thinking of that, but cutting out a circle of construction paper was just too easy not to try. Still, I'm going to keep playing. If I get anything significantly different I'll post it. Many years ago when I was a teenager, I took a photography class and the guy who was teaching it said that rather than spend money on soft focus filters, he just fogged up the lens by breathing on it. It has the advantage that you could take a few pictures as the fog went away, giving variable softness. I'll try that too when the snow/rain goes away (crazy Colorado spring weather) and I can get outdoors.

mfturner wrote in post #17520625
Many years ago when I was a teenager, I took a photography class and the guy who was teaching it said that rather than spend money on soft focus filters, he just fogged up the lens by breathing on it. It has the advantage that you could take a few pictures as the fog went away, giving variable softness.

I've done that in the studio & it worked OK, but it's hard to replicate the results if you should need to. This is a 12" Viking ship in a developing tray:

OK, 2/3rds of a year later, and I stumble on a youtube video disassembling the Zuiko 50f1.8 that I have with a bent filter ring, it looked pretty easy so I just had to play around some more. That lens, like it's f/1.4 sibling, is "artistic" when wide open and surprisingly sharp 2 stops down. I don't have any film set up for my filters, so I used a very thin cellophane plastic, maybe 40 mils, and a "Sharpie" brand permanent marker to fill in the area with crude big dots. At the aperture, it is maybe 2 cm when fully open. I drew up one filter filling in the center cm about 50%, another filter filling in the center 1.5 cm about 30%, and a third filling in the outer diameter fading into an open center, leaving the middle cm totally clear. I'm sure the cellophane on its own is a large part of this effect, I should test that too. This lens worked easily for this test, after removing the name ring I just had 3 screws to hold the front group in front of the aperture, so it was quick to swap things in and out.

It does what you might expect, specular highlights show the image of the "filter" really well, either of the center filled filters give a bit of a bright ring or donut image with nervous bokeh zoomed out, and the outer filled in filter smooths the out of focus highlights quite well. I need to build up some film filters next, I'll have to hunt down some slide film since negative film has problems (either that or develop it myself with a bleach step, hmm).

Apologies for lousy test shots, all were taken with a Canon 60D at 1/100th, ISO's between 800 and 3200, and with the Zuiko 50f1.8 wide open (but with various filters).

Here is a 2x3 collage of a fake candy-cane on a fake tree, with some surrounding lights, along with the amaryllis flower. The candy-cane from top left looking counter-clock-wise is bare lens (UL), center 1cm filled 50% (UR), outer edge filled (LR) and center 1.5cm filled 30% (LL). The flower is taken with a center-filled filter (left) and the outer edge filter (right), look at the flower stem and the horizontal window blinds to see the difference in the filters.

I like the cat! But I'm partial to cats.

Hair spray is another cheap way to make a soft filter. Apply to a UV filter of course, the cheaper the better.

Everyone loves that cat, even people allergic to cats, and he makes a very cooperative subject. Here's another in portrait mode to see the in-to-out-of-focus transition better, pretty much at the MFD of the 50mm lens and so it exaggerates the softness.

Back in the dark ages we just smeared vasoline on a uv filter. Pretty much the only good purpose for a uv filter in digital.

Wilt wrote in post #17519927
Instead of black opaque dots, why not use clear nail polish protectant to make tiny yet transparent raised dots?!...a homemade Softar!

I did that exact thing 'way back in the day. Worked just fine.

Stretch a piece of black net stocking on the front of the lens (or secure it inside of a filter ring on top of uv filter glass) for plain soft focus. Aperture will control the softness.

Try white stocking for a diffused dreamy (glow) look....

starlights wrote in post #18226083
Stretch a piece of black net stocking on the front of the lens (or secure it inside of a filter ring on top of uv filter glass) for plain soft focus. Aperture will control the softness.

Try white stocking for a diffused dreamy (glow) look....

Also try burning small holes in the stocking to "adjust" the sharpness.

Wow, I really like the idea of burning holes in it, I may need to experiment...