A Soft Bokeh Experiment
with Schneider-Kreuznach Radionar 4.5/10.5cm,
front cell focus fixed at 1m, focusing with bellows

Veijo Vilva

(Page under Construction)

Mounting a front cell focusing lens on a bellows or a helicoid gives us a lens system with adjustable charasteristics depending on the front cell focus setting. Fixing the front cell focus at 1m or less results in an undercorrected lens which has a peaky background bokeh and a lot of glow due to spherical aberration, almost like a meniscus but with a better sharpness at focus and rather little coma. Sometimes the result is a wee bit extreme, but with practice it can be moderated at will using the front cell, setting the softness before focusing just like when working with an old-time soft portrait lens.
NB. most of the glow in the photos isn't lens flare but just spherical aberration as indicated by the dependence of the halo width on the distance, e.g., being in focus the white blouse at the lower edge of the photo #0564 causes quite negligible flare but those further off have a quite distinct, outwards thinning halo surrounding them. The foreground column and the background statue in #0527 also show this relationship very clearly. Correspondingly, the black roof and the other black structures in #0533 have a very distinct black halo, and #0556 has multi-colored smearing. The smearing can be discerned at the outlines but also affects the insides of larger objects lending them a glow which differs from the OOF behaviour of differently tuned lenses. This is the price which must be paid for the high quality bokeh, completely without the glow a bokeh can be neutral at best.
The focal length of the lens system depends on the front cell setting. If the FL is 105 mm at the infinity setting, it must drop to 95 mm at the 1 m setting in order to achieve focus in the original folder camera, which has a fixed lens-to-film distance and thus must resort to changing the focal length.

The background is undercorrected: a very good, Gaussian highlight bokeh.

The foreground is overcorrected: a bright edge highlight bokeh.

All shots at full aperture (f/4.5)









0561 (BW conversion using the blue filter style of LightZone)


0575 An Old Man Reminiscing

0602 Youth

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