1

To quote the source, the following sites claim that the Nikons: D90, D5200, D3200 and so on will not meter with AI lenses.

http://www.aiconversions.com/compatibilitytable.htm

http://www.kenrockwell.com/nikon/compatibility-lens.htm

From my understanding there must be some kind of sensor inside of the camera that measures the amount of light that comes in (kind of photoresistor). If that were true, all Nikons will meter with basically all lenses, so what is different that it doesn't work?

And why the AI lenses work with high-end models: D7100, D200,... etc. ?

2

You can divide Nikon lenses in basically three categories (as far as metering goes):

  • pre-AI: no metering functionality, mounting them on a modern camera might break the metering system for old lenses. Interestingly they can usually be mounted without risk of damage on low end cameras because they lack the metering system for old lenses in the first place (bear in mind that officially Nikon denies this, however).
  • AI, AI-S: they communicate the selected aperture, maximum available aperture, etc. using mechanical prongs. They require mechanical prongs on the camera side to get these informations. High end models have these prongs.
  • AI-P, AF: they communicate the selected aperture, maximum available aperture and eventually more data using electronic contacts. This is the only interface supported on low end models.
  • No, pre-AI lenses have a meter coupling prong that connects to the meter on the body. All old Nikkor/Nikon lenses have the coupling prong. Modern consumer Nikon DSLRs will not mount these lenses as the coupling prong will contact the extended pentaprism of the DSLR. While the F-mount has not changed, there are many F-mount lenses that won't mount on modern F-mount cameras. I can't imagine how a modern camera would "break the metering" if you can get it to mount without force. – Pat Farrell Nov 30 '13 at 17:47
  • In fact some bodies (like D300) can be destroyed by trying to mount a pre-AI lense (if there are not converted). Tis because there is an external AI ring on that camera to turn in the same time as the aperture ring. For entry level camera such ring does not exists because no compatibility with AI(s) lenses, then no risk. – рüффп Dec 4 '13 at 20:43
  • Note as well I have a PB-4 belows, and even they state it is a pre-AI, the mount looks more like a AI (the ring on the camera is not touched by the belows mount) – рüффп Dec 4 '13 at 20:45
  • @ruffp: That's exactly what I wrote: "mounting them on a modern camera might break the metering system for old lenses" -> mounting them on a D300 might break the external AI ring of the D300. No problems on a D3x00/D5x00. – Marco Mp Dec 5 '13 at 10:22
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    @Marco Mp, yes I totally agree with your answer, I just commented to give more details like Pat Farrell. The D5x00 and D3x00 are still modern cameras but cannot be broken. – рüффп Dec 6 '13 at 16:36
2

The details you are looking for are provided in the note on the first link you gave. The camera bodies require that the microprocessor in the lens inform them of the aperture information (and possibly other information as well). The problem isn't the light sensor, but rather that without knowing the current aperture of the lens, it isn't possible to tell how much light there actually is, so it can't make automatic adjustments.

That information was previously communicated with a mechanical linkage and the higher end Nikon bodies still have the hardware necessary to interact with that mechanical linkage while the cheaper bodies have dropped it for cost savings and thus rely on the microprocessor.

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