>What is amazing is the time scales here. 1/10,000's of a >second look like minutes to the electronics. So they light the scene, take a >meter reading, evaluate it, and then set the appropriate power output. All >in the twinkle of an eye.
Hi Bob. Yah. It's serious stuff, isn't it! Aside from P-TTL, the other feature that I'm trying to get my head around is high speed flash sync, whereby the use of any shutter speed (focal plane shutter) can be used with flash. My understanding is that the actual second flash duration is lengthened considerably to accomodate a shutter exposure of anything between (in my case) 200th sec and 4000th. So: the button is pressed, the mirror pops up, the pre-flash fires, the exposure is read and calculated, any adjustments are made to the flash, (then, crucially) the second flash fires and continues to fire while the shutter opens, the exposure is made, the shutter closes, and finally the second flash finishes. This is the only way that I can see how flash can be used with a speed, say, of 1/1000th sec. So, I assume that for any given exposure with the flash switched to high speed sync, the flash power must be reduced to compensate for the necessary longer duration. If the normal flash duration is 1/15,000 sec (say) at X power, then in high speed sync mode the flash duration must be increased to about 1/200th sec (my normal flash sync speed) at Y power (which would be less powerful I presume). This would then be able to cope with any exposure faster than normal flash sync speed of the camera up to the fastest shutter speed of the camera. I also presume this method will be that employed by any camera/flash manufacturer. Anybody know if I'm still on track here, or have I hit a patch of oil and heading for the scene of th accident? Regards, Cotty ____________________________________ Oh, swipe me! He paints with light! http://www.macads.co.uk/snaps/ ____________________________________ Free UK Macintosh Classified Ads at http://www.macads.co.uk/ ____________________________________
