Apertures can be de-oiled, and de-greased, rebuilt and even converted to round ‘perfect bokeh’ apertures.
Many classic rangefinder lenses suffer from some focus shift. Often, it’s not too noticeable. Specific designs, like the 50mm Sonnar and 35mm ASPH Summilux V1, it’s so pronounced, it can be annoying unless the user knows how to compensate for this.
We can calibrate lenses that have noticeable focus shift, to a particular aperture for you. On Sonnar lenses, f/2.8 calibration allows for the smaller apertures down to f/16-22, to all be in focus. However, f/1.5 and f/2 become front focused then. Choosing f/1.5 instead causes f/4 and f/5.6 to be back focused. With f/1.5 Sonnars, we’ve had a lot of luck choosing f/2.2 as the calibration point.
This causes f/1.5 to be sharper than the f/2.8 calibration, but then also causes f/4-5.6 to be sharper than the f/1.5 calibration, almost a happy compromise. Equally, we can do f/1.5 or f/2.8, which are the classic calibrations also if you prefer.
Aperture blade modification and complete aperture change is something we plan on offering in the future.
To prevent rangefinder lenses from having too dramatic of a focus shift, manufacturers often utilise what is termed ‘ninja star apertures’ at the mid aperture zones, from about f/2.8 through f/8. This ninja star pattern, allows the lens to drop in light transmission to achieve its next f/stop rating. However, the pointed stars on the aperture also cause the natural aberrations of the lens not to be reduced as much. Almost as if the lens had utilised a perfectly round aperture.
This purposeful leaving of the aberrations partially present until the depth of field can overtake the focus shift is the reason many classic rangefinder lenses have these type of apertures.
While the ninja star pattern reduces focus shift, it causes the bokeh balls and bokeh definition to take on the ninja star pattern as well! For customers who are willing to trade off inducing more focus shift in their lens in exchange for a more pleasant bokeh and rounder bokeh balls, we plan on offering a 10-bladed custom aperture for certain popular rangefinder lenses in the future. The aperture is being designed in a way that from wide open to about f/5.6, the 10 blades maintain as circular of an appearance as possible, thereby improving the bokeh. At f/8, we plan to have them immediately jump to straight, as this is roughly where photographers begin to care less about the bokeh structure and more about potential landscape qualities of a lens, in Sunstar definition. Thus, a decagon becomes desired to purposely induce 10-pointed light source stars which are considered more aesthetically pleasing over the light blob that occurs typically on the round aperture. The aperture currently is in development targeting classic f/1.5 Sonnars (ZM C-Sonnar and Zeiss-Opton) and classic (pre-ASPH) f/1.4 Summilux’s and might be ready at the beginning of 2021. It is a drop-in replacement and will require the lens to be dismantled at the optical block level at our workshop in Warwickshire, England, for proper installation.
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