On Wednesday, April 24, 2002 at 6:22, ClassicVW@xxxxxxx
<olympus@xxxxxxxxxxxxxxx>
wrote re "Re: [OM] F280 ModPhoto" saying:
> Tom,
> I think this is exactly what some of us have been saying- the OM-4Ti will
> balance both the ambient and flash light to achieve the proper exposure. So,
> if you change the aperture, which forces the camera to change the shutter
> speed (in Auto) you, in effect, by changing that aperture and shutter speed
> are changing the range of the Super FP flash, and, changing its impact on the
> overall 'correct' exposure. At least I *think* that makes sense from a
> practical standpoint...
>
> George S.
I don't think the 3T or 4T will "balance" the flash by any of its
operations. I think it will only prevent overexposure in auto mode by
choosing the shutter speed. So *within* (not just at) the GN
distance, you will be properly exposed.
The flash vs ambient ratio is governed by the distance from flash to
subject only. The GN distance would depend only on the ambient light,
since when you change film speed or aperture, both shutter speed and
GN change. So if you are within the GN distance, the flash will
predominate. At the GN distance, it would be balanced. Beyond, the
ambient would dominate. The fill-in flash contribution can be
calculated in the usual inverse square way:
At GN distance - 1:1 ratio flash:ambient
at 1.4x GN distance - 1:2
at 2x GN distance - 1:4
at 2.8x GN distance - 1:8
etc.
This makes sense when you think of it. The flash contributes a
constant amount of light, and it can only match brighter scenes at
closer distances.
Note that at the "balanced" distance, the subject (if not the
background) would be getting both ambient & flash light, so the
shutter speed chosen by auto would be about twice as fast as
indicated.
Here is a calculated chart of F280 GN distance in metres vs scene
brightness. Stay this far away for a balanced exposure, twice as far
for a 1:4 ratio fill. Shutter speed must be in the range 1/60 to
1/2000.
FC=FootCandles, EV=Exposure Value for 100 ASA film, M=metres.
FC Lux EV M Scene description
15,200164,000 16 0.33 Subjects in bright daylight on sand or snow.
7,60082,000 15 0.46 Subjects in bright or hazy sun (Sunny f/16
rule).
3,80041,000 14 0.65 Full moon (long lens). Subjects in weak, hazy
sun.
1,90020,500 13 0.92 Gibbous moon (long lens). Subjects in cloudy-
bright light (no shadows).
95010,250 12 1.3 Half moon (long lens). Subject in heavy
overcast.
4755,125 11 1.8 Sunsets. Subjects in open shade lit by bright
sky.
2382,563 10 2.6 Landscapes and skylines immediately after
sunset.
Crescent moon (long lens).
1191,281 9 3.7 Landscapes, city skylines 10 minutes after
sunset.
Neon lights, spotlighted subjects.
59641 8 5.2 Las Vegas or Times Square at night. Store windows.
Campfires, bonfires, burning buildings. Ice shows, football, baseball
etc. at night. Interiors with bright fluorescent lights.
30320 7 7.4 Bottom of rainforest canopy. Brightly lighted
night-time
streets. Indoor sports. Stage shows, circuses.
15160 6 10.4 Brightly lit home interiors at night. Fairs, amusement
parks.
7.480 5 14.7 Night home interiors, average light. School or church
auditoriums. Subjects lit by campfires or bonfires.
3.740 4 21 Candle lit close-ups. Christmas lights, floodlit
buildings, fountains, and monuments. Subjects under bright street
lamps.
1.920 3 29 Fireworks (with time exposure).
0.92810 2 42 Night Lightning (with time exposure). Total eclipse of
moon.
0.4645 1 59 Distant view of lighted skyline.
0.2322.5 0 83 Subjects lit by dim ambient artificial light.
0.1161.3 -1 118 Subjects lit by dim ambient artificial light.
0.0580.626 -2 166 Night, away from city lights, snowscape under
full
moon.
0.0290.313 -3 235 Night, away from city lights, subject under
full
moon.
0.0140.156 -4 333 Night, away from city lights, subject under
half
moon. Meteors (during showers, with time exposure).
0.0070.078 -5 471 Night, away from city lights, subject under
crescent moon.
0.0040.039 -6 666 Night, away from city lights, subject under
starlight only.
(Scene descriptions, FC, Lux0 from THE ULTIMATE EXPOSURE COMPUTER
http://www.fredparker.com/ultexp1.htm )
(Note, EV=Exposure Value. EVs are numbers which refer to certain
combinations of lens aperture and shutter speed. Combine it with a
film speed and you have a proxy for scene brightness.
EV 15 is 1/125 at f/16 - the sunny-16 exposure for 100 speed film
EV 14 is 1/60 at f/16 or 1/125 at f/11. The lower the EV, the more
light gets let in. See
http://www.chem.helsinki.fi/~toomas/photo/ev.html )
As you can see, the F280 is useful only with fast films and lenses in
indoor or very close up situations.
This is purely theoretical on my part, so any expert F280 users,
please enlighten me if I have it wrong.
tOM
> Tom@xxxxxxxxxxxxx writes:
>
> Has anyone tried this? From the slit article and other posts, I suspect
> this is wrong and that the only way to control the fill ratio is the
> distance of the flash to the subject. Shrinking the aperture affects both
> flash and ambient light.
...
------- Quidquid latine dictum sit, altum viditur -----------------
,__@ Tom A. Trottier +1 613 860-6633 fax:231-6115
_-\_<, 758 Albert St.,Ottawa ON Canada K1R 7V8
(*)/'(*) ICQ:57647974 N45.412 W75.714
---------------------------------------------------------------------
Laws are the spider's webs which,
if anything small falls into them they ensnare it,
but large things break through and escape.
--Solon, statesman (c.638-c558 BCE)
< 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 >
|