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Variable Bokeh with modified projection lens
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PostPosted: Fri Jul 22, 2022 8:04 pm    Post subject: Variable Bokeh with modified projection lens Reply with quote

I was inspired by the Correlar 80mm f/2.8 lens, a triplet developed from a Dacora Digna 6x9 camera.
The correlar has a distance setting by shifting the front lens group, consisting of lens 1 and 2, in relation to the 3rd lens. In between is/was the aperture and shutter. The aperture slats were hanging out, of the original 10 I reinstalled 5 for the time being. I removed the clasp. The rest of the camera ditto.
I disassembled the Ennagon, also a triplet, cut it up and machined it with the lathe. The front part with lenses 1 and 2 fits quite well in a 17-31mm M42 helicoid. I glued the 3rd lens with its edited mount to the camera end of the helicoid. The original distance between lens 2 and 3 was about 8mm, I think the projection lens was optimized to 2-3m.
The helicoid now allows the distance to be changed between 0 and approx. 15mm. The bokeh (bubbles) is strongest at zero and the most indistinct at 15mm. Theoretically, zero would be infinity, 15 mm approx. 0.5 m.
For focusing, I use another helicoid with a thin Nex adapter.
The whole thing is a prototype with no claim to completeness (I would like to have a variable aperture) and elegance and only serves to prove that the functionality of the Correlar is reproducible.


Last edited by hansgru on Sat Jul 23, 2022 1:56 pm; edited 1 time in total


PostPosted: Sat Jul 23, 2022 12:08 pm    Post subject: Reply with quote

Sounds interesting. Unfortunately you facebook page is unavailable without login. Would you mind republishing here some of your samples?


PostPosted: Sat Jul 23, 2022 1:49 pm    Post subject: Reply with quote

alex ph wrote:
Sounds interesting. Unfortunately you facebook page is unavailable without login. Would you mind republishing here some of your samples?

I have already tried to upload pictures, until now I failed. I will try it again.
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PostPosted: Sat Jul 23, 2022 1:55 pm    Post subject: Reply with quote

Sample pictures:


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PostPosted: Sat Jul 23, 2022 5:09 pm    Post subject: Reply with quote

Thank you for the lens shots and samples. That is a really interesting and informative experiment. The resulting images are a bit too soft to my taste. But it might be used on purpose. And OOF differences and peripherial swirl worth a play.

What might be a good complement to your experiment: a discussion we had in another thread about IQ effects of screwing off the front element of four-glass lenses. Even though the inter-glass distance is less than in your case and limited to 0.5-3mm.

P.S. You could not publish images in your first post (an antispam measure), and since then everything would work fine.


PostPosted: Sat Jul 23, 2022 6:17 pm    Post subject: Reply with quote

alex ph wrote:
Thank you for the lens shots and samples. That is a really interesting and informative experiment. The resulting images are a bit too soft to my taste. But it might be used on purpose. And OOF differences and peripherial swirl worth a play.

What might be a good complement to your experiment: a discussion we had in another thread about IQ effects of screwing off the front element of four-glass lenses. Even though the inter-glass distance is less than in your case and limited to 0.5-3mm.

P.S. You could not publish images in your first post (an antispam measure), and since then everything would work fine.


Thank You very much, Alex.


PostPosted: Sat Jul 23, 2022 6:24 pm    Post subject: Reply with quote

hansgru wrote:
alex ph wrote:
Thank you for the lens shots and samples. That is a really interesting and informative experiment. The resulting images are a bit too soft to my taste. But it might be used on purpose. And OOF differences and peripherial swirl worth a play.

What might be a good complement to your experiment: a discussion we had in another thread about IQ effects of screwing off the front element of four-glass lenses. Even though the inter-glass distance is less than in your case and limited to 0.5-3mm.

P.S. You could not publish images in your first post (an antispam measure), and since then everything would work fine.


Thank you very much, Alex. Your advice is very helpful.


The Correlar pictures are similar, also rather soft. The first is 1m, the second is 6m.

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PostPosted: Sat Jul 23, 2022 6:43 pm    Post subject: Reply with quote

Very interesting!


PostPosted: Wed Aug 24, 2022 11:35 am    Post subject: More modifications Reply with quote

When I change the difference between front lens and the others of the Ennagon AND the distance to the back lens there are more interesting results.
All pictures are softer than with the unchanged Ennagon because of dirt between the lenses and reflections in the tube of my test setup.

#2 is the standard configuration.
#3 is a slightly larger distance of the front lens
#4 is distance of front lens zero, back lens 3mm more than standard. Soft and swirly.
#1 is distance of front lens zero, back lens standard. No swirl, but soap bubbles.

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PostPosted: Fri Sep 23, 2022 4:05 pm    Post subject: Reply with quote

Interesting project. Photos are soft glowy and lack contrast, but interesting bokeh. Might be good for a artistic portrait set. Especially in B&W.