Tim Engel wrote: >I've been trying to rationalize that train of thought, and I keep >disconnecting. I'm not a camera-tech or an authority on SLR design by any >means, so feel free to point out the error of my ways. But here's what >I'm thinking... > >With regard to limiting fast shutter speeds: >A heavy aperture diaphragm (lots of blades) should have no impact on fast >shutter speeds. The sequence of events in an SLR is: >1) Mirror opens / Aperture stops down. >2) Shutter fires. >3) Mirror closes / Aperture opens. > >Each step executes to completion on it's own, and upon completion triggers >the next step. Step 2 alone controls the exposure time. Steps 1 & 3 can >be timed with a calendar, and the shutter can still produce as fast an >exposure as it's technology will allow. The only impact if steps 1 & 3 >are slow is the amount of dark time your eye sees in the viewfinder. The >film will see the exposure time allowed by the shutter in step 2.
The aperture diaphragm is closed by the lens's internal spring at the same time the mirror is flipped up. It is conceivable that with a heavy, slow diaphragm with lots of blades that it might not be finished closing by the time the mirror reaches the end of its travel and the shutter fires. In fact, this is exactly what happens when oil gets on diaphragm blades and they become sluggish. -- Mark Roberts www.robertstech.com - 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 .
