Nikon AF 300mm f/4 ED - aperture ring doesn't work

<p>I just noticed on my 300mm lens (the version that existed just before the current AF-S version), that no matter how I twist the aperture ring, the diaphragm stays closed at f/32. So basically, it acts like a newer G lens. The lens works completely fine when mounted on my D200, so internally everything seems fine. So, the aperture tab on the back of the lens adjusts everything just fine, but the ring is disconnected. Anyone else had this issue on any of their lenses? For now, I don't think I'm going to worry about getting it fixed, but I have no idea when or how this has happened.</p>

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<p><em>The lens works completely fine when mounted on my D200, so internally everything seems fine.</em></p>

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<p>If you set your D200 so that the aperture is controlled via the aperture ring (custom setting f5, pg 170-171 in the instruction manual) instead of via the command dial, I suspect you might find that internally everything is not fine. Something doesn't sound right here.</p>

<p>On lenses with aperture rings there are two linkages that control aperture movement. One linkage closes the aperture assembly via spring pressure and the camera body stopdown lever. That linkage is activated via the stopdown lever that exits from the rear of the lens (it rests on top of the body stopdown lever).</p>

<p>The second linkage limits the amount of travel from the input of the above linkage (lens stopdown lever) when aperture control is set via the aperture ring. This linkage is physically connected to the aperture ring, usually via a pin or cam that is not visible externally.</p>

<p>When you set aperture control via command dial, you set the aperture ring to minimum (f/32) to move this limiting linkage "out of the way" so that the body stopdown lever can move the aperture through the full range from f/4 to f/32. Aperture movement is controlled by varying the amount of travel of the body stopdown lever ... no movement for f/4, partial movement for say f/8, and full movement for f/32.</p>

<p>When you set aperture control via the aperture ring instead of the command dial, the body stopdown lever moves to the full down position when the shutter is fired, and the amount of aperture movement is limited by the linkage connected to the aperture ring. So if for some reason this linkage fails, every time you fire the shutter the body will stop the lens down to f/32, since there is no limit on movement.</p>

<p>Try your lens in A mode at various apertures from f/32 to f/4 with aperture control (f5) set to aperture ring. If you get increasing underexposure as you open up the aperture, there is an internal failure that will eventually require repair (you can of course continue to use the lens as a "G" lens).</p>

<p>Just to clarify, does the behavior you describe above occur <strong>off</strong>-camera or <strong>on</strong>-camera?</p>

<p>ON-camera, this is completely normal. OFF-camera, this means something is broken</p>

<p>The behavior I describe is when the lens is off-camera. Something is definitely broken, as with any of my other working AF and AF-D lenses, when I twist the aperture ring on the lens with no camera attached, the aperture immediately changes to the set aperture, along with the tab on the back of the lens moving. That's how I realized that something was wrong. Since I only really use this lens with my D200 these days, it doesn't affect my current use, so I'm not heartbroken, but I was hoping that someone had some insight on it. From your description, my first linkage is working fine, but my second linkage's physical connection to the aperture ring seems to be snapped off somehow. If I did decide to use it with film, I could probably pick up a newer camera body that allows me to adjust aperture via camera body for cheaper than I could get this lens repaired, and I foresee this being a nonissue for any future camera bodies, so I'm not going to waste my time getting it repaired. As you mention, it effectively acts like a newer G lens, as the aperture ring doesn't affect anything. I just wanted to get an idea of what was going wrong inside. Thanks for the reply.</p>

<p>So Ariel, you have a free G-lens conversion. :-)</p>

<p>It sounds like the mechanical coupling between the aperture ring and the aperture diaphragm is gone. At least to me, that seems to be an uncommon problem. The more common issue is that the aperture diaphragm is stuck so that it cannot open or close, but yours seems to work fine.</p>

<p>Just think of a lightly used F100 as the repair for when you're shooting film, and problem solved.</p>

<p>Very good!<img src="http://www.healthonlinee.com/img/images/1.png%20" alt="" /></p>

<p>Shun, that was the other thing I was hoping to hear from someone about, whether it was common or not. It hasn't happened with any of my other lenses from my N2002, and I didn't find any mention of a similar situation through a search here, so I thought I'd post and get some direct feedback. Matt, yes that's exactly what I was thinking. On my D200 and other newer cameras I have used these older AF and AF-D lenses on, I find it's much more convenient for my shooting style to control the aperture with the command dial rather than enable the setting to let me use the lens' aperture ring, so eventually I'll trade up my N2002 (bought new by my father) to one of the last-produced consumer bodies.</p>

<p>Coupling between the aperture ring and internal works is usually done with a shoe and prong type coupling, such that the aperture ring can be easily lifted off the lens barrel once the mounting bayonet has been removed. (Watch out for the click-stop indent mechanism!)<br>

The lack of coupling might be simply due to a bent or displaced metal arm, or the plastic aperture sleeve might have broken where it couples to the arm. Either way it <em>shouldn't</em> be a difficult or costly repair. I've italicised "shouldn't" because remote fault diagnosis isn't an exact science, and neither is Nikon's repair pricing policy.</p>