Last year I detailed my struggles with intermittent flashing from my SB800 mounted on a D200 hotshoe. The solution appeared to be to work on the flanges of the hotshoe to narrow the gap that that the flash fits into to eliminate short circuiting that triggered the random firing and activation of the focussing assistance.
Did I speak too soon? Sort of. The adjustment of the hotshoe did work for a while but now the problem is back. Another look at posts on the web suggests that the glitch is also affecting D700s - not a good sign as I was considering moving up to one of those. Some people have had replacement parts fitted. I wonder if they have worked long-term? Maybe it only affects models with pop-up flash as there is less room for a more substantial hotshoe pressing.
It seems to me that there could be a flaw in the design of the SB800 and the hotshoe as a combination. Examining my camera I see that there is more play, when the flash is mounted (particularly when unlocked), on the right side of the hotshoe and the pressing on the right is fractionally angled up compared to the one on the left. When I am working with camera mounted flash I often carry the D200 sideways in my right hand with the flash pointing forward. The SB800 is a heavy lump and my theory is that the when tilted from the vertical the gravity takes over and pulls down on the gun and gradually, over multiple instances of this action, levers the pressing open.
The lock may also contribute to this. If you look at the flash unit off camera and move the locking lever you will see a small lug move up within the channel on either side of the contact plate. These presumably should grip the flange of the hotshoe and make the assembly rigid. Without another new gun for comparison I can't say whether the extent of that travel in my unit is enough or standard but it isn't much. Not much of the lug appears. I wonder if the cam in the locking lever can wear? More seriously though, this is where I see what could be the design flaw...
The locking lugs do not extend out to the full width of the flash contact plate. When they push up to exert pressure on the hotshoe they are pushing up on the edge of the pressing and not into the corner of the formed channel. The dimension of the pressing is fixed at the inner corners - you can't stretch the metal at that point. The edge of the flange can move though. I can bend it in by pushing down (with a cramp - or a hammer...!) and conversely upward pressure from underneath can push it away from the camera body. If the lugs extended to the edge of the flash plate they would not be able to affect the angle of the flange. Just a thought.
Adding shims? Some others have found this short term fix has not succeeded in the longer term. The ability of the flash lock mechanism and the weight of the flash pushing at the pressing will push up the flange while there is any play between the gun and the hotshoe. Eliminating that play with shims may work but it could make insertion of the flash quite difficult. It also won't stop the locking lugs from pushing up and distorting the angle of the flange. My feeling is that the shim would need to be fitted to the underside of the flange so that there was no risk of the electrical pin contact being compromised. Getting something to attach that wouldn't just wear off or get dislodged upon flash insertion may be difficult.
What to do? Short term fix is to apply my previous solution of downward pressure to reduce the gap. Might try a fraction of a millimeter further this time and see what happens. Whatever happens it is pretty annoying and particularly worrying that Nikon haven't sorted the problem in later models. In the real world photographers will carry their cameras in ways that mean pressure is exerted on the interface between flash and camera. Nikon need to make sure that this cannot distort or affect performance over the lifetime of the units especially in semi-pro and pro models.
So I have gone ahead and reapplied the clamp to the right hand flange and pushed it down a bit more. I tried one application and fitted the gun. Now it was tighter but bizarrely the intermittent flashing seemed worse. It would fire if I nudged the camera as it sat on the bench and the red focussing light flickered on and off. I got some electrical contact cleaner and wiped it over the terminals and other parts of the flash and hotshoe to remove dirt and grease. It seemed a bit better after this but still would fire now and then if I pushed gently on the gun.
More use of the clamp and the flange bent down a little more. Barely perceptible but it does make a difference. Now there is no movement of the gun in the hotshoe when the locking lever is in the open position and the flash is a secure fit. I also remembered that the spring clip can be removed so I levered it out with a blade. The underside was a little dirty. Could there be some crud that was having an influence on the earthing or shorting it out? I cleaned it all up with contact cleaner and refitted the clip. Now when the gun is locked in I cannot get it to give out the random flashes no matter how much I manipulate it or shake it. Problem solved again - at least for the moment.
One thing - and I did double/triple/quadruple check that this wasn't the problem all along - I have the Func button set to FV Lock (so if you press it you get an exposure pre-flash). It is quite possible to trigger this accidentally, and no doubt I have on occasion. It isn't the source of the annoying mini flashes though. Definitely.
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