Various tests have found that small differences in camera vibration can make big differences in resolution at moderately slow shutter speeds. People on the Olympus list have tested their cameras with or without diaphragm pre-fire, and it turns out that even the vibrations from the diaphragm closing down makes a substantial difference to resolution.
This is apparently not something you can solve by locking the camera down, no matter how rigid the tripod. It seems to occur not because the camera moves, but because its body vibrates. I suspect that it has to something to do with the fact that the metal in cameras is mainly brass (the same metal used in musical instruments because it vibrates so well). When Keppler did a test (POP, June 99) of cameras with and without the mirror locked up, the biggest difference was around 1/15th of a second, where locking up the mirror could increase the resolution from a 135 mm lens by 80%. If you use a long exposure, like a few seconds, it won't make that much difference, since the vibrations will occur only for a small percentage of the time the exposure is underway. With a 5 second exposure, Keppler found that there was no difference in resolution with or without the mirror locked up. This might be why Mark Roberts likes his K2 "with small apertures, long shutter speeds." When Popular Photography tested the K2 (December 1976) they reported the shutter vibration was about 0.7 volts, double the average of cameras tested up to that time. (For the cloth focal plane shutter MX, by contrast, the vibration level was about 0.2 volts). An easy subjective test you can do at home goes as follows: Set a small shot glass with about half an inch of water in it on top of the flash shoe, fire the shutter and watch for the ripples. You will find that you get much bigger ripples from a K2 (mirror locked up) than an MX or ME (mirror not locked up). As somebody suggested, it is possible that the K2's vibrations are mainly when the second curtain of the shutter hits the far end, in which case it won't cause much of a problem. Anybody who has a K2 can test for this quite easily. Lock up the mirror, set the shutter speed to B, and release the shutter with a cable release, holding it open. Watch for ripples in the water. If the camera is good, the ripples should be minimal. Then let the shutter close, and see if most of the ripple action is concentrated at that end of the cycle. I hope somebody tries this, and reports back to the group, to clarify this issue. I will be happy to revise my opinion of what is in many ways a fine camera. (I just did this test with my MX, at 1 second exposure, with the mirror locked up. Vibrations when the shutter opened were almost non-existent. BTW, on my MX the quasi-MLU does not seem to work at B.) _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
