AIS lenses can they be used on D40, D50?

Started Jan 1, 2007 | Discussions thread
Helen
Helen Veteran Member • Posts: 5,399
Re: Cheap D200

Jim5k wrote:

We're getting in a little over my head. I don't even grasp what the
S in AIS does. I simply want to focus wide open and have the
aperture snap down when I push the button. I just assumed the D-40
does that. Or do the new lenses do that using a less expensive
method? Maybe I don't give the FM-2 enough credit, but a digital
FM-2 (dFM-2?) doesn't sound like a complicated or expensive
venture. (But I've been wrong before.)

Nikon have used the same physical lens mount design since 1959 (it came in with the Nikon F) but the linkage between camera and lens has evolved. They were always full aperture metering lenses with automatic stopdown on taking the shot. You might have noticed that Nikon lenses used to have a metal claw or fork ("rabbit ears") sticking up from the aperture ring? This was the first way of connecting the lens to the camera's metering system, so it could meter at full aperture. The meter was in certain interchangeable prisms for the F - the user would set the lens to f5.6 prior to fitting it, then pull down a coupler from the prism so it fitted in the fork before twisting the lens onto the camera, and would THEN twist the aperture ring smartly to and fro (minimum aperture to maximum aperture, I believe) - so that the camera "knew" the range of the lens fitted. Quite some work, but I understand most Nikon users did it automatically! With some cameras, the act of setting a lens to f5.6 when removing it would leave the camera's peg in the right place for a new lens at f5.6 to mesh but you still needed to do the to and fro trick with the aperture ring after mounting the lens. You can recognise such pre-AI lenses by the fact that their forks look like a solid semicircle with just a central slot. Because the later systems (AI, AIS etc.) involved some cutouts to the rear of the aperture ring, these old lenses can damage newer bodies in some cases, by crushing up against couplings that didn't exist when they were designed.

In the mid seventies, they introduced AI lenses (auto-indexing, or aperture indexing if you like) which still had the fork so they'd work on older cameras, but which didn't require these shenanigans with new AI-compatible cameras. Instead, a spring loaded tab on the outside of the camera's bayonet mount automatically matched up with the lens and the camera "knew" automatically what the aperture range was. This was pretty much the same as competing manufacturers were already doing. Whilst they were about it, Nikon introduced a feature called ADR (aperture direct readout) so that a window in the finder of suitably-equipped cameras could show what the lens aperture was set to. This required a tiny additional scale behind the main one, and is the reason that the fork on AI and later lenses has a little hole on either side of the central slot, so it doesn't block the light onto this scale. For quite some time, Nikon offered a service to "AI" the older lenses, and independent repairmen did it too. Earlier AI cameras like the FM and FE allowed their AI couplings to be folded back so that pre-AI lenses could be used (in stopdown metering mode, I presume), but the FM2 and FE2 didn't and could have the couplings broken by those older lenses.

AIS was the next evolution, and was so that the FA camera's multi-program modes could work efficiently (the cheaper FG didn't need AIS but any AI camera could use AIS with no problems). It gave the camera a way of (mechanically) knowing the specs of the lens (such as its focal length, roughly) via an arc-shaped cutout in the metal of the lens mount, and also the mechanics were revised so that the intervals between which aperture setting on the aperture ring were precisely geometrically regular (previously they may have varied a bit through the range). AIS lenses should always have an orange minimum aperture to help identify them, as otherwise they don't look any different from AI unless you look for the milled cutout in the mount. The more affordable Series E lenses introduced for the EM were actually the first to have the AIS feature, and they were also the first not to have the "fork", which was eventually left off the AIS lenses too (but could be retrofitted if required).

All the above lenses were manual focus only, and only communicated mechanically with the camera. Electronic communication between the camera body and the lens came in with AF Nikkors, but the earlier AF cameras (and the most expensive digital SLRs) retained the mechanical couplings too. It's the mechanical couplings for telling the camera what aperture the lens is set to, etc. that have been removed in more recent film SLRs and DSLRs at the more affordable end of the range, resulting in the situation that they will not meter with manual lenses - they must be used in manual exposure mode, with no in-camera metering at all. But they should still operate at full aperture for manual focusing and will stop down on taking the shot. Hope that helps (I've skipped some minor details but I hope that's generally complete. There are of course evolutions that happened after AF too, briefly that D lenses include chippery to tell the camera the distance the lens is set to, to include in metering calculations, and G lenses are the same but lack physical aperture rings - they're designed for use only on cameras that set the aperture from the body controls).

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