Olympus-OM
[Top] [All Lists]

Re: [OM] even more about the F280 (long)

Subject: Re: [OM] even more about the F280 (long)
From: frieder.faig@xxxxxxxxxxxxxxxxxxxxxxxxx
Date: Tue, 23 Apr 2002 13:56:25 +0200
On Mon, Apr 22, 2002 at 12:09:33PM -0400, Robert Swier wrote:
> While the F280 manual is generally useless, it does provide enough
> information to definitively answer the questions on flash dumps and flash
> duration.
> 
> The manual is online at
> http://olympus.dementia.org/eSIF/omsif/flashphotogroup/manuals/f280.pdf, and
> this information comes from page 51.
> 
> Let's first look at the number of flashes you can get from a single set of
> AA alkaline batteries. The expected number of flashes are:
> 
> Manual: 80 firings
> Normal: 80 -- 600 firings
> SuperFP: 80 -- 260 firings
> 
> Since manual mode results in a constant number of firings, we can conclude
> that all manual mode firings are the same. 
>
> -snip-
> 
> In SuperFP mode, we see that the number of expected firings is a range from
> 80 to 260. We already know that 80 is the number of flashes you get from a
> set of batteries when you dump the entire capacitor on every firing. So,
> SuperFP mode is capable of dumping the entire capacitor. But, it is possible
> to get up to 260 firings in SuperFP mode from a single set of batteries, so
> there must exist some SuperFP firings that do not dump the entire capacitor.
> In fact, if you dump this minimum amount in SuperFP mode each time you get
> about 260 firings.

To this point I´m really up with you. We know in normal auto mode the capacitor 
isn´t competely dumped to control the exposure. But is this also true for 
Super FP-mode? Or is the difference in dump only caused due to different
operating time of the shutter?
- For me this is the interesting question.
> 
> (It's interesting to note that the minimum dump in superFP mode (the amount
> that gives you 260 firings) is significantly more than the minimum dump in
> Normal mode (which gives you 600 firings), and that both are significantly
> less than a full dump (which gives only 80 firings.)

> Now look at the chart on expected flash duration (with the OM-4t (ti)):
> 
> Normal "OTF" Flash emission: 1/40,000 -- 1/1000 sec.
> Super FP Flash emission: 1/50 -- 1/25
> 
>-snip- 
> 
> However, the SuperFP flash duration could be as long as 1/25 sec. 1/25
> equals 60/1500. So given a curtain speed of 1/60 (or 25/1500 sec) we could
> have a SuperFP flash that is up to 60/1500 - 25/1500 = 30/1500 sec (or
> 3/150). Why would there be a SuperFP flash that lasts 3/150 sec longer than
> it needs to? The fact that such a long flash duration is possible with the
> F280 in SuperFP mode makes me think that the curtain speed might be slower
> than 1/60 second for some shutter speeds. Why this could be the case, I have
> no idea.

The time the curtain need`s to travel over the entire window is always the same.
I remember one of our repair-techs explained some time ago, that this is basic
requirement for proper exposure adjustment. 

There is a nice OM-1 timing diagram, for 1/60 sec, on the net at (scroll down):

http://www.mir.com.my/rb/photography/hardwares/classics/olympusom1n2/om1/index2.htm

For my considerations I assume 13.5ms travel time for each curtain. There might 
be
tolerances from body to body, but not from different exposure times.
I like to calculate in miliseconds only: 
        1/2000 sec = 0.5ms
        1/500 sec =2ms
        1/60 sec = 16.7ms
        1/30 sec = 33.3 ms
The FP flash needs to fire contnious from the start of the first curtain to the 
arrivial
of the second cutain:  -> "fire time" = curtain time + exposure time.
    For 1/2000 sec:  minimum fire time = 13.5ms + 0.5ms = 14 ms  (~ 1/70sec) 
    For 1/500  sec:  minimum fire time = 13.5ms + 2ms = 15.5 ms  (~ 1/65 sec)
    For 1/60   sec:  minimum fire time = 13.5ms + 16.7ms = 30.2 ms (~ 1/33 sec)
    For 1/30   sec:  minimum fire time = 13.5ms + 33.3ms = 46.5 ms (~ 1/22 sec)
I ignore the need for some security ms to compensate for timing overlaps to 
assure 
the whole image is covered with the flash. So a flash duration of 1/25 is 
necessay to
cover safely 1/60sec exposure time, and almost 1/30sec of exposure time.

Another interesting calculation:
  46.5 ms /14 ms = 3.32
  80 flashes  * 3.32 = 265 flashes
So I guess it is only the flash duration, which saves the energy of the 
capacitor, 
and that 1/50-1/25 sec is only a rough approximation. ... well I´m only 
guessing! 

 
   
Frieder Faig 

P.S: Still having a F280 for red eye control but no 4T/Ti.

< 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 >


<Prev in Thread] Current Thread [Next in Thread>
Sponsored by Tako
Impressum | Datenschutz