CPU Contacts

paul_garland · December 16, 2008

<p >I have a couple of old Nikon 35mm film SLRs which are pretty much manual, and two somewhat newer Nikon film SLRs which automatically adjust shutter speed and aperture and which do perform autofocus. I also have two Nikon digital SLRs. I have a bunch of old and newer Nikkor lens too, some which are non-CPU and many of which do have CPU contacts.</p>

<p >Looking at the cameras the N6006/F601, the N60, and the D40X both have seven (7) internal contacts through which the camera and the lens communicate. The D300 has eight (8) of these internal contacts.</p>

<p >Many of my older CPU lenses have what I call the 4 + 1 format of contacts for a total of five (5) contacts. Some of the newer lenses have seven (7) contacts, and my favorite macro lens has ten (10) contacts!</p>

<p >I find this both interesting and a bit confusing, all at the same time. I’m intrigued and I sure wish some technical wizard with Nikon could explain this to me.</p>

<p ><a href="http://hpgarland.blogspot.com/2008/12/nikon-cpu-contacts.html">http://hpgarland.blogspot.com/2008/12/nikon-cpu-contacts.html</a></p>

ellis_vener_photography · December 16, 2008

<p>Have you tried reading yor D300 manual?</p>

paul_garland · December 16, 2008

<p>Are you always this rude? Of course I have read the D300 manual jerk.</p>

bjørn rørslett · December 16, 2008

<p>The number of contacts will depend on the features supported by the lens. The minimum is 5 and allows the basic communication between lens and camera (communicating lens focal length, aperture, distance, exit pupil location). AFS and VR adds more contacts. The "E" teleconverters have pins to communicate the new focal length of the master lens + TC to name one feature.</p>

photo5 · December 16, 2008

<p>Bjorn is right, the eighth contact has to do with AFS and VR, which isn't supported on film bodies older than the F100. The macro lens having 10 contacts is a mystery though, if the D300 only has eight contacts, what would the extra 2 be for?</p>

User_276104 · December 16, 2008

<p>My 17-35mm f/2.8D has 10 pin contacts, and that lens has been around for nearly 10 years now.</p>

<p>I bought my 17-35mm in early 2001 and recall wondering about all those pins once. Camera manuals don't tell you how many CPU contacts it takes to use various lens features.</p>

joseph_wisniewski · December 16, 2008

<ol>

<li>The five contact interface is actually 7 contacts wide, with a 2 contact gap. 2 contacts are power and ground, three more are a serial data interface (clock, data, and read/write). They do pretty much what Bjorn said, communicate lens data back to the camera, and communicate commands like "start VR" to the lens. </li>

<li>The gap is because Nikon originally designed an entirely different AF system for the F3-AF. This system had 7 contacts, and a motor in the lens, and the camera would drive the lens motor through two high power contacts: "near to far" and "far to near". There was no serial communication, just power and limit switches. When Nikon made the new "screwdriver" system for the N2020 camera, they avoided using those two contacts, to keep old F3-AF cameras from frying the new "digital interface" lenses. Nikon F4 (aside from being the ugliest Nikon ever designed) actually had the circuitry to drive either the F3-AF lenses or the new AF Nikkors.</li>

<li>AF-S and AF-I lenses need 8 contacts to function properly. They add an additional high power line so that the lens motor could suck power directly from the camera battery. A pair of additional motion detection lines allow the camera to track the direction and speed of lens movement. Nikon "recycled" the contacts from the "gap" in the second AF system. This tracking function is only used by high end bodies like D2X, D3, F100, F5, so those bodies have 8 contacts. Lesser bodies like D100 or N80 have 7 contacts. I don't know about some of the newer low end bodies.</li>

<li>Although cameras have 7 or 8 contacts, Nikon AF-S (and older AF-I) lenses have 10 contacts. Two of these are for use with teleconverters. AF-S teleconverters have 10 contacts on the front (lens side), and 8 on the camera side. The two contacts let the converter send a "hi, I'm a 1.4x teleconverter" message to the lens. This allows the lens to send a "I'm not really a 105mm f2.8 macro, I'm really a 147mm f4 macro" to the camera. Even AF-S lenses that aren't normally used with teleconverters, like the 12-24mm f4 DX, have 10 pins, and often work properly on Kenko teleconverters.</li>

<li>I'm not sure why a lens would have 7 contacts, unless it's a low end AF-S lens designed only to exploit the features of a low end body, leaving off the motion detection. Which lenses have you seen with 7 contacts.</li>

<li>Yes, he usually is.</li>

</ol>

joseph_wisniewski · December 16, 2008

<p>The contacts are identified in Nikon service manuals (and on the circuit boards of cameras and lenses) as "A" through "J". "A" is the leftmost contact as you gaze lovingly into the lens mount of the camera. The names of the contacts vary depending on what manual you read. E and F are the "gap" contacts in older cameras.<br>

The first F3-AF interface:</p>

<tbody>

<td width="50" height="17">number</td>

</tr>

</tr>

<td >Limit switch</td>

</tr>

</tr>

</tr>

</tr>

<td >Relative Distance</td>

</tr>

</tr>

</tbody>

</table>

<p>The second AF interface, as used in 5 contact screwdriver lenses:</p>

<tbody>

<td width="50" height="17">number</td>

<td width="44">patent</td>

</tr>

</tr>

</tr>

</tr>

</tr>

</tr>

</tr>

</tr>

</tbody>

</table>

<p>The third AF interface, as used in cameras that support AF-S lenses:</p>

<tbody>

<td width="50" height="17">number</td>

<td width="44">patent</td>

</tr>

</tr>

</tr>

</tr>

</tr>

</tr>

</tr>

</tr>

</tbody>

</table>

<p>The full 10 pins from the 300mm f2.8 AF-I service manual:</p>

<tbody>

<td width="50" height="17">number</td>

<td width="110">protection</td>

</tr>

</tr>

<td >pull up and series</td>

</tr>

<td >Clock</td>

<td >series</td>

</tr>

</tr>

<td >Hotline, Pulse</td>

<td >pull up and series</td>

</tr>

<td >Power for Motor</td>

</tr>

<td >Motor GND</td>

</tr>

<td >Hotline, Pulse</td>

<td >pull up and series</td>

</tr>

<td >Reserve</td>

</tr>

<td >Reserve</td>

</tr>

<td height="17">Mount</td>

</tr>

</tbody>

</table>

<p>Wow, this new software lets you paste from an excell spreadsheet and get HTML tables. Way to go photo.net software guys!</p>

btmuir · December 16, 2008

<p>Thanks for that info Joseph. Appreciate it.</p>

paul_garland · December 16, 2008

<p>Joseph, thanks for the great reply!<br>

The lenses I have that have 7 contacts are the 55-200 VR lens and the 18-55 lens. Both are DX lenses. Pictures at: <a href="http://hpgarland.blogspot.com/2008/12/nikon-cpu-contacts.html">http://hpgarland.blogspot.com/2008/12/nikon-cpu-contacts.html</a></p>

richard_driscoll · December 17, 2008

<p>Some new lenses have electric diaphragm control. Does anyone know if these lenses, and the cameras that can use this feature, have extra contact(s)?</p>

bjørn rørslett · December 17, 2008

<p>A PC-E Nikkor has 10 contacts. Same number as an AFS VR lens.</p>

joseph_wisniewski · December 17, 2008

<p>Paul, thanks for the info. I think that means that these lenses have the AF-S and VR protocols without the contacts for enhanced focus speed sensing or teleconverter use. Which sort of makes sense, as the 55-200mm is a bit slow for teleconverters.</p>

<p>Richard, as Bjorn said, the PC-E lenses have the same number of contacts. (Odd that they have teleconverter support). You don't need extra contacts for electronic aperture, the AF-S contacts already provide enough power to drive big focusing motors, so little aperture motors are no challenge. What I can't understand is why it took them so long. Would you believe electronic aperture control has been part of the Nikon protocol for about 20 years, right back to the original patent? Which also makes me wonder why only D3, D300, D700, and D90 can control the aperture on the PC-E lenses.</p>

richard_driscoll · December 17, 2008

<p>Thanks for that Joseph. Canon EOS had electronic aperture control from the start and I'm sure I've read that the Nikon 'dead reckoning' system used in the G lenses and in the older lenses for P and S modes can result in errors of around 1/3 stop.</p>

<p>Do you know if the Nikon electronic system is open loop or closed loop. In other words does the camera send a command like "stop down to f/5.6" to the lens or does it signal the lens to start stopping down while monitoring a feedback signal from the lens?</p>

<p>Do you have the patent number for the Nikon system to which you referred?</p>

<p>Since you imply that the aperture control information is multiplexed along with other stuff, my guess is that it's only firmware that stops the electronic control being available on the older cameras.</p>

<p>Of course one trouble with patents is that there is no guarantee that the implementation follows the patent. For example the patent on the D lens operation without flash implies that the distance information should have a significant effect but people report little difference!</p>

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