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It's possible to build a simple lens with very few elements:
This lens costs less than a soft filter and the results are spectacular.
A low magnification factor gives a longer lens and a wider glass gives a wider aperture and a stronger effect.
The sample described is roughly a 150mm f/2.4. The principle being a "long lens", the length between the center of the loupe and the film plane is the focal length. Diaphragm was evaluated by comparing with a classic lens.
Focus is done by sliding the tube to vary the loupe-film distance and exposure is done at full aperture as there is no diaphragm.
This kind of lens has probably the complete set of aberrations known on earth ...
Spherical aberration gives a strong soft focus and chromatic aberration gives a pretty original color shading.
Well, we're pretty close to David Hamilton but with some differences ...
The results ? Here are some examples:
Some pictures of the lens:
Front view of the two tubes, the lens is a simple stamp collector loupe, the diameter difference between the extension tube and the loupe is compensated by several layers of black cardboard maintained with adhesive tape.
Back view of the two tubes and the extension tube acting as support.
You can easily slide off the extension tube for a more classic work.
In action on a ... F5.
Light metering switches to weighted metering and the built-in focusing system indicates you when you're right in focus despite of the strong unsharpness !!!