The latest discoveries with the Steenbeck ST1600 are
My original static tests in a jig with the SI2K camera suggested that the Fujian 50mm lens, used as a projector lens yielded sharpest results. However, that was without the Steenbeck's polygon prism shutter in the optical path.
The Fujian lens was chosen, not because it is inexpensive but it is the only one I could find which would fit into the available space on the metal deck of the Steenbeck film transport without requiring milling or cutting of the deck. The lens has to be stripped down to its block or core. The C-mount remains in place.
I have since found that the lens work best when set up as a camera lens, facing correctly mount-end towards the camera with a huge macro offset forward of the camera with the prism shutter in place. The projection lens arrangement may still work best for film direct-to-camera without the prism in place.
Colour rendition when using the Steenbeck's original projection lamp and 90degree prism/condensor is vastly improved when an IR-750 filter and Lee "Big Stopper ND" filter were added into the optical path. The "Big Stopper" is extreme. With its 10 stops of ND in action, I had to set 3db of gain on the camera. A ND1.2 or ND1.8 would probably be adequate for the SI2K with its real-world practical ISO of about daylight 160-200.
Moving grain structure was softly visible. The image sharpness numbers registered by the SI2K from film were best at 32. When compared with direct-to-camera imaging of a subject, it is not great. However this is what the film emulsion itself is yielding of the original image which fell upon it.
The sharpness numbers when the lens was used front-to-camera as a projection lens were at best 12.
More of the film image appears to the camera without edge interference from the prism. I really don't know what is going on there except that the prism vignettes the sides more noticeably in the projection arrangement. Edge-to-edge, the Fujian lens seems to yield adequate image sharpness into the corners in both arrangements.
With the Steenbeck's prism-condenser in place, scratches in the film are more apparent and darker than if a diffuse source of reflected light is used by swapping the prism for a matte-finished white reflector. This turned out to be less than ideal because the unfocused light from the lamp filament is not optically corrected. A faint dark band occurs down one side of the image. You can see that darker area on the left side of the family images linked in the preceding post. This would be hopeless for negative scanning because the inversion process amplifies contrast.
If a substitute deck-mounted diffused LED light is substituted, the lamp circuit within the Steenbeck supplies its miniature halogen globe with 12 volts and is conveniently close to tap into. There is limited workspace to install a diffused LED setup as the optical centre is approx 12mm above the deck surface.
Due to bits and pieces obstructing access, I am not able to measure precisely the forward offset of the lens and the corrssponing distance from front of lens to the film plane. I am going to buy in a stack of CS-Mount to C-Mount spacers which add increments of 5mm and dress one down until best focus is achieved.
With the Steenbeck's polygon prism shutter in place, a Super16mm image can be seen but approximately 1mm of the the right side of the image falls into the prism vignette. For the film frame to be effectively zoomed larger to fit a 16:9 sensor image with the top and bottom of the 4:3 frame cropped optically, both the camera and lens have to be repositioned. However the zone of movement of both is very small.
For most 16mm projector-based telecine/scanner builds, I would expect the Fujian lens with its focus and aperture control rings would fit inside the projector's own lens mount space. With a custom adaptor in place of the original projection lens, with a focusing spiral machined into the barrel, tghe projector's own focus mechanism may remain conveniently usable for focus trims when the iintial focus has been set in the construction. Most 16mm projector lenses are themselves of 50mm focal length. However they have no aperture control. Optically I have found them to be inferior to camera lenses.
The old Taylor, Taylor and Hobson ( think Cooke optics ) lenses for the older Bell and Howell 16mm projectors were sharper projection than the later and larger diameter lenses which were unbranded.