On 2013-01-02, Gunner wrote:
On Tue, 1 Jan 2013 13:32:27 -0700, "Steve B" wrote:
Let's say that I change my setting for either aperture, speed, or manual
priority.
I set the aperture for depth of focus, and the camera selects the speed.
I set the speed to freeze motion, and the camera selects the aperture.
I put it on manual, and can set both, even intentionally off if I want to.
Now, the question. I turn on the flash.
Does the camera use the settings I put in, or does it go into control of the
camera, and change any of the settings? I have taken many photos of the
same thing at many various settings, and I do know the photos come out
differently. I was just wondering about this part of the camera's actual
functioning.
I apologize for the basic question, but I want to learn this from the ABC's
up, and I have a few missing letters.
Steve
It depends on the type of camera..and the shutter mechanism.
If its a "focal plane shutter" the camera will set the shutter speed
to the X sinc speed..generally 1/ 60th of a second and then you or
the camera will adjust the iris...the F stop to capture the proper
amount of light.
Yes -- you can't control the exposure with shutter speed with
electronic flash -- the flash typically is shorter than 1/1000th of a
second total time. (Though a flash which is smart enough to quench the
flash before full discharge can control exposure there as well as via
the iris diaphragm. And (assuming digital, not film), the ISO
sensitivity of the sensor can also be adjusted.
If its an "iris" shutter..IE the lens opens and closes a shutter
mechanism like the apeture mechanism..
What I know as a BTW (Between The Lens) shutter.
..the camera will be setable for a
range of shutter speeds and apeture settings.
Except that the shutter won't have much effect on the exposure
with electronic flash. Even the fastest shutter speed on the Zeiss
Contax film camera (1/1250th of a second) is about the length of the
flash anyway.
The primary effect can be to use a quite slow shutter speed to
expose the background sufficiently to record, with the near objects
illuminated by the flash being a bit brighter.
Pretty much the same
for a simple "flipper" shutter, where the shutter simply swings to one
side and exposes the film/sensor.
Hardly a sophisticated camera, however. :-)
With some of the newer cameras..with spot and multipoint metering..the
same basic settings are used, however the cameras computer (or you)
will sometimes play with the shutter speed AND the F stop settings
assuming its not a focal plane shutter. Those are hard to "futz with"
*and* the sensor ISO, for a digital camera.
The problem with focal plane shutters..IE..a long thin "window" that
travels from one end of the film/sensor to the other..is that its
travels at a rate that may be longer or shorter than the duration of
the flash. If the shutter opens when the flash is at its
brightest..and closes before the flash duration goes dim..you are ok.
If it happens the other way around..you will have one side of the
photo nice and well exposed..and then start fading towards black on
the other side. With the old slow flashes..that flash was bright for
a long duration. The newer High speed flashes put out a ****load of
light..but for a shorter time frame. With a normal "iris" type
shutter..thats cool. For a focal plane shutter..it sucks badly.
1/60th of a second for the horizontally traveling shutter,
sometimes as fast as 1/120th of a second for vertically traveling
shutter. (The Zeiss Contax, and some of the Nikon cameras which came
out after the Nikon F -- the ones with the "Copal Square" shutter.
Few focal plane shutters expose the entire sensor/film at the same
time..ie..opens up wide so the entire sensitive surface gets the light
all at the same time.
Depending on shutter speed. Typically, the travel speed of the
curtains is fixed, and the second curtain (the one which closes) is
released a certain time after the first. This means that below a
certain shutter speed, the first curtain totally clears the frame before
the second starts. The fastest speed at which this happens is typically
marked with an 'X' -- or a different color fill in the shutter speed
dial -- typically red.
Note that back in the days of flashbulbs, there were two basic
types -- the standard ones for between-the-lens shutters, which burned
up to a peak and then started back down shortly after that, and the ones
for focal plane shutters "type F bulbs) which would rapidly build up to
a certain light level, and then keep it at about the same brightness
until the shutter had time to complete its cycle.
Note also that the two curtain approach was standard with 35mm
cameras, but other, larger, cameras like the Speed Graphic (4x5" film)
had a focal plane shutter (as well as a between-the-lens shutter
depending on the lens installed) which had one curtain with several
different width slots (four IIRC), and a separate spring which adjusted
how fast the slots moved. Those got faster speeds with both a narrow
slot and a high tension. There was one slot which opened fully, good
for electronic flash when that came around.
With the new cameras and much smaller sensors..this is changing.
Yes. The Nikon DSLRs have a pair of barn doors which open, and
then an electronic (liquid crystal, IIRC) shutter behind that, so the
exposure can go up to very fast with the full frame exposed.
Proably some of the other high-end DSLRs have that as well.
Enjoy,
DoN.
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