Why does my Nikon D40 require the aperture ring on an AF Nikkor lens to be locked at the smallest aperture?
Asked 2/4/2011
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I'm using a Nikon 50mm f/1.8 AF lens on a Nikon D40. It meters fine, though I have to focus manually, which is okay for portraits. However, the camera seems to require the lens aperture ring to be set and locked at the smallest aperture before I can shoot properly, even when using Manual exposure mode. Why does the D40 work this way, and how is the aperture actually controlled?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
15y ago
2 Answers
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The 50mm f/1.8 AF will meter on the D40, it does have a chip. But it will not AF.
You have to set all[1] Nikkor lenses with aperture rings to the smallest aperture in order for Program and Shutter priority modes to work. The reason is that the camera body will set the aperture at the moment of taking the shot in these modes, and the aperture has to be in a "known state" for this to work.
The lock is simply a convenience to avoid the aperture ring moving accidentally.
If you look at Nikon's G lenses - the ones without an aperture ring - you'll notice the aperture blades are stopped down all the way when the lens is unmounted. This is the same principle at work.
It's been a while since I used the D40 but I do think you have to set the aperture on the camera body - press and hold the exposure compensation button and move the thumbwheel.
[1] all lenses confirming to the AI-s spec (including AF lenses)
Originally by user3114. Source · Licensed CC BY-SA 4.0
user3114
15y ago
0
Generated from our catalog & community — verify before relying on it.
On the D40, AF Nikkor lenses with an aperture ring are meant to be used with the ring set to the smallest aperture (highest f-number) and locked there. That puts the lens in a known starting position so the camera body can control the aperture correctly at the moment of exposure.
This is especially necessary for modes where the camera sets aperture for you, but many Nikon bodies also expect this setup in Manual mode when using compatible CPU lenses like the 50mm f/1.8 AF. You then change aperture using the camera controls, not the ring.
The lock is mainly there to prevent the ring from being moved accidentally.
Your 50mm AF lens meters on the D40 because it has CPU contacts, but it will not autofocus because the D40 lacks the in-body focus motor needed by older AF/AF-D lenses. So: manual focus is normal, but aperture should still be controlled from the camera body with the ring locked at minimum aperture.
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