BetterPhoto Q&A
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missing 1/2 picture

ps. Even on some pictures that are a full image, it is darker at the bottom of the picture.

Thanks in advance,
Ray

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March 07, 2003

You may know some of this already. In focal plane shutters, the shutter curtains always travel at the same speed, regardless of shutter speed. The delay between releasing the opening curtain and the closing one is what determines shutter speed. As shutter speed is increased, the delay becomes shorter. At X-Sync speeds and slower the opening curtain fully travels before the closing one is released. At speeds faster than X-Sync the closing curtain is released before the opening one fully travels. At the highest speeds of 1/1000th, 1/2000th, etc., a narrow slit is traveling across the film plane. It is critical for proper exposure of the entire film plan that both curtains travel at the same speed across it. Again, if the opening one is slower, the closing one will narrow the gap, and at a shutter speed high enough it will completely close it.

The "poor man's" test for this:
This works **only** at speeds faster than X-Sync and works best with a fast, standard 50mm lens. Open the lens up to its widest aperture. Don't worry about focusing it. Open up the camera back, turn it vertical (because of the direction your curtains travel), and aim the camera straight at your computer monitor from about a foot away. Works best if the computer monitor has a very plain, light colored screen showing. Be careful in handling the camera with the back open!! You don't want to "fat finger" the shutter curtains or anything else delicate inside the camera. Fire the shutter about a half dozen times at each shutter speed faster than the X-Sync.

You should see a diagonal band from the computer monitor across the film plane as the curtains travel in at least some of them. The faster the shutter speed, the narrower the band, and it should look about half the width of the one for the next slower shutter speed (if you're doing this in full stops; e.g. 1/500th vs. 1/1000th). Don't try to get to exacting about this, it's not that accurate. If the band changes width, one curtain is traveling faster than the other.

Principle of operation:
You are making use of the scan rate of your computer monitor and the fact that a "slit" is traveling across the film plane. Exactly where you see the diagonal band across the film plane, and at times whether you even see one, depends on what portion of the monitor screen is being scanned and your timing of the shutter release. There is no way to sync the shutter release to what portion of the monitor is being scanned. This is why you need to trip the shutter a about a half dozen times to see a decent diagonal band a couple of times. Don't want to do this in front of your computer? It also works with a television which uses a raster scan method of puting an image on the screen.

Doing this with nobody else around is recommended lest they think you've lost your mind. Also avoids trying to explain what you're doing and the techno-babble of how it works!

-- John

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March 08, 2003

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March 08, 2003

Since this is a Nikon FM, do a search for the Nikon Historical Society web site. I believe they have a list of reputable resources for getting older Nikon cameras repaired (small shops that specialize in working on them). A complete overhaul should not run much more than about $125 - $200. If this seems steep and you think you might simply replace it with a used one, remember you don't know the history of a used camera body. A properly overhauled one done by a reputable shop can be a better deal. In the end, it's a tradeoff decision you must make.

Even though I have a different camera system from about the same era, I admire the FM and its successor, the FM2. They fall into a "semi-pro" class just below the heavier F2 and F3, and a lot of pros are still using them because of their lighter weight. They are well designed and well made. There's really nothing that can be done with one of the current "wonder bricks" that cannot be done with your FM . . . and IMHO, they're better made and a properly overhauled one will last longer than current consumer camera bodies. I suspect it's suffering from age . . . something that catches up with every camera.

-- John

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March 08, 2003