urgent question regarding CPU contacts

[richardHaw]

to those gifted with the talents for electronics, is there a simple way to tell the camera that the lens you have mounted is an AF lens? I want to activate the camera's screw AF motor and have that drive a lens that I am currently building. It has no electronics inside but it doesn have the gears for AF there. Should the camera also require other information in order for it to activate the AF motor? I hope that I can just short the ground and the pin that enables this and call it a day  help appreciated!

[Øivind Tøien]

I would think that all you need is one of Bjørn's chips (programmed as non-G) or a chip from an AF lens and when the lens does not push the screw in when mounted like a chipped manual focus lens would do, the screwdriver AF would engage? A question is then if the AF will be accurately tuned though.

[Bjørn Rørslett]

If the lens has the gears inside to make it an AF (screwdriver type) lens, and there are no matching CPU chip in the lens, a factory chip matching the lens specifications has to be added. This is entails far more than just shorting a pin or two. In fact, try avoiding a short at all costs as the chances the short-circuit will kill the camera electronics is are significant.

What lens is this? I might be able to get the factory chip for you if it is still on the inventory of Nikon Europe. You would also need the repair manual for that lens.

[richardHaw]

I have spare contacts here from junks 

[richardHaw]

If the lens has the gears inside to make it an AF (screwdriver type) lens, and there are no matching CPU chip in the lens, a factory chip matching the lens specifications has to be added. This is entails far more than just shorting a pin or two. In fact, try avoiding a short at all costs as the chances the short-circuit will kill the camera electronics is are significant.

What lens is this? I might be able to get the factory chip for you if it is still on the inventory of Nikon Europe. You would also need the repair manual for that lens.

I still have the chip with me. its a 35-70mm 

[Akira]

I have a mount part of the non-D AF35/2.0.  The mount still has the contact block and the original FPC with the chips.  There is no residual connector or soldiered cables that would have been connected to some other (F)PC boards inside the lens.  So, all of the electronic parts in the lens seems to be fully intact.

I tentatively mounted it onto my D750.  The camera appears to try to focus, but the AF screw won't rotate.  I don't know what else would be necessary...

[Bern]

I still have the chip with me. its a 35-70mm 

Just some side thoughts, can a cpu from another lens be reprogramed and used for modifying a MF nikkor? Thanks.

[Bjørn Rørslett]

The factory CPU cannot be "reprogrammed" as such. However, it can be recycled for use in other lenses if there is a match between the aperture (and range). Focal length(s) and exit pupil data will of course be wrong, so exposure accuracy will suffer. This assumes the CPU print can be implanted into the new host lens, which is often near impossible due to space limitations. The factory prints often are massive in size.

I initially commenced my F-mount CPU project (early 00's) by doing exactly this; getting prints from junk lenses and recycling them. The limited usefulness quickly forced me into the  next approach which was the special production of much smaller, reprogrammable CPU prints. My connections with Nikon allowed me to purchase the additional parts required, such as contact blocks, fixture screws, and contact pins. Thus I now have virtually all (>99.9%) of my F-mount lenses Nikkors or third-party items, CPU-modified. Many hundreds of lenses for others also have been modified over the last decade.

Strongly increasing prices of Nikon spare parts combined with reduced interest from other photographers of having their lenses modified have brought the product to a stand-still though. I have sold off nearly all my remaining inventory at present and am not likely to initiate a new production batch with all the associated costs.

[Erik Lund]

I would think it was not possible to use an AF CPU designed for another AF lens, not for achieving focus that is,,,

They are calibrated for the actual lens they sit in,,,

I have never tried it though,,,

As Bjørn states, we used to recycle AF CPU's for the manual focus lenses when chipping, worked fine and one could sometimes hear the screwdriver AF motor running trying to achieve focus, to no avail of course,,,

Trick was to for instance use the CPU from a 35-70mm f/3.3-f/4.5 AF and use it in a 55mm f/3.5 Micro Nikkor - Short circuit the CPU at 55mm zoom setting and it would read 55mm f/3.5 - Worked perfectly fine on F4 and F5 for Matrix Metering etc.

You don't state what 35-70mm or what you are actually 'building',,, a signed NDA?

I can confirm that shorting the contacts is not recommended, the cameras power supply will often die, no fuses,,,

[Hugh_3170]

I notice that Bjørn's CPU prints (aka PCBs) have high value series protection resistors (~100kΩ IIRC) in each of the three signal lines. 

During normal operation (and when attaching lenses without the precaution of the camera being first switched off), these resistors will ensure that the CPU chip does not cause excessive current draw from the camera.  In the extremely unlikely event that the CPU chip itself dies and creates a short, then these resistors will still limit current draw from the camera to safe levels.  (Another safety feature is that the last pin to engage when the lens is being mounted onto the camera is the pin that supplies voltage to the the CPU - a good example of Nikon's defensive design of the lens mount contact order.)

Don't confuse dropping a signal line to a "logical low" value with actually shorting it out and do not do so if you do not have explicit knowledge of the camera circuitry that lies beyond the contacts in the lens mount on its body.  It may or may not have protection built in on all of the contacts.  Best to err on the side of caution.

[Bjørn Rørslett]

Just to underscore the precautions Nikon built into their circuitry might be of value. I once had a customer that complained the lens he had CPU-modified with one of my chips didn't work. In fact, the camera went dead immediately when the modified lens was mounted and he was pretty unhappy about the state of affairs, needless to say. I asked for the entire CPU assembly with contact block and all be returned to have a look. When I received the allegedly faulty CPU, the print had by him been mounted flipped over then upside down in the contact block thus efficiently shorting out the camera while redirecting the current back into the camera circuitry... My oh my.

I reassembled the block correctly, put the mounted block on a dummy lens and voila! all was well. Returned the parts in their correctly assembled state and told him to try again. Now his previously dead camera happily reasserted itself.

There are some pertinent adages to come up with here but I'll refrain. Suffice it to say that even this nasty shock treatment of the camera electronics hadn't fried the motherboard.

[Bern]

It sounds complicated...having so little knowledge on electronics and stuff. I will just have to leave my MF lenses in their current state and keep enjoying them as such. But the information discussed gives a clear view of how the design for safety is incorporated in our Nikons.

I dont want to risk to short the electronics of my Nikons.