The high-speed flashes actually give a series of flash pulses that cover the shutter travel time. All the best! Raimo Personal photography homepage at http://www.uusikaupunki.fi/~raikorho
-----Alkuperäinen viesti----- Lähettäjä: Cotty <[EMAIL PROTECTED]> Vastaanottaja: Pentax List <[EMAIL PROTECTED]> Päivä: 30. joulukuuta 2002 16:47 Aihe: Re: Current Cameras with TTL Flash Metering? >>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 > >
