At 03:36 PM 12/5/01 EST, Mafud wrote:
>In a message dated 12/5/01 12:03:46 PM Eastern Standard Time,
>[EMAIL PROTECTED] writes:
>
>> "The replies to my original query seem to agree with what I was told - that a
>> variable aperture zoom lens will vary the amount of light admitted as you
>> zoom in and out, no matter what I set the aperture ring to."
>>
>Not true. The variable aperture function happens only with PK/A lens in the
>"A" position. Your question specifically stated: "when ~I~ set the aperture".
>**Otherwise, you could not choose your apertures for lighting or depth of
>field.
>
That's precisely the point - that because the zoom lens is variable
aperture, I cannot be guaranteed that the amount of light admitted through
the lens will be constant over the zoom range of the lens.
I *thought* this phenomena applied to variable aperture zooms only when set
wide open. I'm trying to determine if this applies to *all* aperture
settings of the lens.
Depth of field is *usually* desired in relative amounts ("more depth of
field" or "less depth of field" than it is in absolute amounts ("I want 3.5m
of acceptable focus") so having an effective aperture change of about 1 stop
probably won't screw up your desired depth of field. But it will mess up
your exposures.
>Remember: other than setting depth of field, the aperture has little to do
>with flash photography (assuming you lights/strobes are capable of producing
>f/22 [f/32 for medium, f/45 for large format] lighting).
>
Aperture has everything to do with flash photography. I cannot adjust the
shutterspeed more than 1 stop. Too slow and I get camera shake, too fast and
it won't sync with the flashes. 1/60th, or 1/100th are my choices (on a ZX-7).
Adjusting studio strobes can be tricky - sometimes your strobes only adjust
1 stop up or down, sometimes you can adjust in .1 stop increments. Sometimes
you cannot physically move the lights to adjust their intensity.
Film speed is also fixed - 100 or 160.
That leaves adjusting the aperture to match your lighting.
Except that a variable zoom lens can give a perfect exposure at 50mm,
overexposed at 35mm and underexposed at 80mm, even though the aperture ring
is set to f8 the entire time.
>Though you didn't say so, on PENTAX camera bodies with the "AE" function,
>~if~ your shutter is set on manual, and your lens is on "A," you're in
>shutter priority mode. But it seems you're describing manual studio
>operation, both shutter and aperture being ~set by you~. If so, and since you
>didn't mention using a light meter, the presumption is you're using the
>camera meter. In such a studio situation, what you describe is full manual
>operation.
>That is: you've manually set the camera to "X" speed (or slower), then set
>the aperture for depth of field. In that situation, zooming only frames your
>subject (again, depending on the power of your lighting).
This is metered with a handheld meter, full manual mode on the camera.
Now, it *MIGHT* be possible, for the camera to adjust for this effect. If I
set the aperture on the BODY, and I use a FA lens, the camera could detect
the focal length of the zoom, and compensate automatically when closing down
the aperture.
That is, if the lens does truly let less light in at the tele end than it
does at the wide end, then the camera could close down the aperture a little
bit less, to maintain consistent exposure.
Anybody know of any systems that do this?
--Mike
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