Fitting a Vectis 80-240mm to the NEX
OVER the past few days I’ve been looking at the NEX-5 and a range of lenses and optical systems. I’ve got adaptors for C-mount (16mm/TV/CCTV) lenses, Leica 39mm screw, Minolta MD and the LA-EA1 for Alpha A-mount. The NEX-5 has proved able to provide a surprisingly bright focusing image through a classic German microscope:
It also proved very competent with the Sigma 70-300mm f/4-5.6 OS lens, the adaptor providing power for the OS which is fully functional, and also for auto exposure, leaving only manual magnified focusing to tackle. The OS Sigma has an internal motor for focusing on Alpha, not screw drive though it sounds and feels like it. It’s not HSM and almost certainly won’t be friends with any AF enabling update of the NEX/Lens Mount Adaptor firmware.
One lens I have obtained a coupled of sample of to experiment with, even if it means dismantling one. That is the Minolta Vectis 80-240mm f/4.5-5.6 APO, a miniature version of the 100-300mm APO made for 35mm, in the APS Vectis mount. This mount is all-electronic like the Vectis, but probably very different in the voltages required and the command protocol. But who knows? Maybe an AE adaptor with power for manual focus might be possible.
Using a Zenith 39mm (Leica type SLR) thread T-mount the Vectis 80-240mm nearly focused OK attached to the Leica adaptor of the NEX, but the bayonet was only just able to fit in a doctored T-mount and the combination with the NEX Leica screw adaptor was clearly a little too thick.
Using a Leica thread lens reversing ring (don’t ask, from my box of miscellaneous old rings and things – 49mm filter to Leica screw!) and duct tape, I was able to fit one of my two 80-240mm APO guinea-pigs to the mount within 1mm or so of correct register (38mm). It’s only taped, but solid enough. I do not want to cement the bits together at this stage.
Effectively it’s got a Leica screw mount taped as close to the Vectis lens mount as anything will allow. There is plenty of room to make a proper Vectis adaptor, with or without contact arrays at both ends and a chip to convert the signals. Without that, the lens is stuck forever at full aperture. If power could be supplied to the correct pins to enable the focus-by-wire action, that would complete the job with this Vectis lens – but other Vectis lenses don’t even have a manual electronic focusing option. As it is, wrenching the front tube round focuses the lens. Just like it did when you were fitting or removing the lens hood, a frustrating rotating front unit.
As it stands, the 80-240mm Vectis APO f/4.5-5.6 is a really neat size of lens for the NEX and Sony could do far worse than remake this in an OS version for NEX. At full aperture, performance up to 200mm is very good but a familiar softness (like the 100-300mm APO D at 300mm etc) creeps in at 240mm. For 1996, the lens is pretty amazing.
80mm wide open, http://www.pbase.com/davidkilpatrick/image/127009628/original.jpg for original
240mm wide open – http://www.pbase.com/davidkilpatrick/image/127009627/original.jpg
Close focus at around 135mm wide open (because the lens can not be stopped down):
Around 100mm, same conditions apply:
And at 240mm close focus again:
This lens has some really good qualities, considering it is not even mounted correctly and is definitely not correctly set up for register, which alters the way the zoom/focus correction functions. It could no doubt be made to look better by picking a flat target and a medium distance, rather than homing in on garden close-ups with too much depth for the wide-open setting.
But the bokeh effects are not too bad, the point of focus is well defined, and the lens has few vices considering the imprecision of its mounting!
– David Kilpatrick