On Tuesday, April 23, 2002 at 9:43, William Sommerwerck
<olympus@xxxxxxxxxxxxxxx>
wrote re "[OM] a final answer on F280 flash d" saying:
> "On auto exposure, the duration is always ~1/25. This is close to the full
> time
> from 1st curtain open to 2nd curtain close at 1/60. The curtains take 1/80
> (12.5ms) to go across the frame, so for 1/60th (16.666ms) exposure the shutter
> travel is 16.666 + 12.5 = 28.66 ms or 1/29 second. For 1/2000, .5 + 12.5 =
> 1/77. Of course, on auto, you don't know the final shutter speed when you
> start
> the exposure and you don't want to run out of light before you finish."
>
> I hadn't thought of that. Right! It takes 1/60 s for the first shutter to
> open,
> then another 1/60 s for it to close (at an effective shutter speed of 1/60),
> so
> the flash would have to fire for at least 1/30 second.
Don't forget, for a focal plane shutter, as soon as there's film showing,
the flash has to be on. For 1/60, the full frame is open only for 4 ms or
less - most of the exposure time (actually about 29ms) is while the lead
curtain is opening or the trailing curtain is closing. Every photo, even at
1/1000, actually takes about 1/30th for the whole frame to be exposed, tho
any part just gets the dialed in amount.
> If the shutter speed is higher, then the closing of the second
> shutter curtain can terminate the flash. This (finally!) explains
> the variation in Super FP flash time.
>
>
> In any case, I'm going to call Olympus tomorrow and try to get a full
> explanation of all the details of how the F280 works, along with the design
> theory and goals.
Check http://www.rit.edu/~andpph/text-streak.html
--------------- http://groups.yahoo.com/group/Olympus-Documentation
tOM Trottier, ICQ:57647974 http://abacurial.com
758 Albert St, Ottawa ON Canada K1R 7V8
+1 613 860-6633 fax:231-6115 N45.412 W75.714
"The moment one gives close attention to anything,
even a blade of grass, it becomes a mysterious,
awesome, indescribably magnificent world in itself --
Henry Miller, 1891-1980
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|