Full mechanical re-housing of LOMO anamorphic square front lenses as supplied by Van Diemen Films Ltd, with taking lenses from Cooke or the original Lomo prime optic. Baush & Lomb taking lenses are currently in the design phase of the manufacturing process.
Why are LOMO anamorphic total conversions a challenge to manufacture?
The challenge for square fronts is that they have two critical synchronised focus movements, one for the spherical taking lens and one for the focusing cylindrical lens. The focusing lens movement when in PL has to happen inside the PL mount and behind it this is mechanically difficult.
Why not rebuild the lenses using the original LOMO mechanical design?
The reason for re-housing is to overcome the inherent mechanical design short comings of the original square front anamorphics that resulted in undesirable performance problems, such as image shift and focus backlash. The original design for the LOMO focusing cylindrical works on a cam for the carrier, the carrier travels along two rods driven on one side only. This inevitably results in some degree of play resulting in image shift and focus backlash. As the focusing element is anamorphic in essence any play is augmented by the anamorphic compression expansion. The Van Diemen total conversion addresses these problems by full mechanical re-housing incorporating an entirely new helical thread focus movement for the taking lens with a Van Diemen patented Wireform™ movement for the focusing cylindrical lens. In comparison to the original design of a carrier of two rods driven by a cam on only one side, the Van Diemen system rides on three rods balanced by two Wireform™ carriers.
Complicating the matter further, many of the original square fronts have experienced wear due to use, damage due to less than suitable mount conversion attempts and service/adjustment, rusty steel or paper shims and the variable quality of the original LOMO mechanical parts.
Why is it recommended that I don’t shim my square front anamorphic?
During the Van Diemen re-house process all square front lenses are adjusted for optimum sharpness. Unlike spherical lenses which you can add or remove shims to achieve accurate focus marks square front anamorphics require critical adjustment of their flange distance to achieve optimum performance. Attempts to shim a square front anamorphic would likely result in softening of the image. Infinity focus is typically evaluated on a collimator, which does not account for the filter stack employed in modern cinema cameras. This leads to the next often asked question……..
Why do my focus marks appear to read slightly differently dependent on which camera I’m using?
Modern cinema cameras incorporate digital imaging sensors which are particularly sensitive to infra-red and ultra-violet light frequencies. To correct for this and other undesirable effects such as Moire these digital sensors require a filter stack which serves as a filter for the unwanted effects. Due to the placement of this filter stack between the rear of the lens and the sensor, the focal plane is essentially lengthened by approximately one-third the thickness of the filter stack. Different cameras, employing various sensors, require filter stacks of varying degrees thus affecting the thickness of the filter stack. Therefore, the effect of lengthening the focal plane is variable from camera to camera. This can result in slight drift of focus marks between cameras. Van Diemen use a combination of cameras, lens projector and collimator during scaling of focus marks to anticipate use with a broad range of digital cinema cameras as well as conventional film cameras. It is possible to optimise focus scales to suit a specific camera filter combination.
Why does my focus ring rotate go past infinity?
Upon assembly and adjustment, Van Diemen builds in a bit of headroom past infinity to permit infinity focus on the broadest range of cameras.