About central (diaphragm) shutters at high speeds/large apertures

Re: About central (diaphragm) shutters at high speeds/large apertures

On 16 Aug, 17:32, pehache-tolai <pehach...@gmail,com > wrote:
> Hello,
>
> I have a old 6x6 TLR (Zeiss Ikon Ikoflex), it has a mechanical central
> shutter (Compur Rapid).
>
> I remember that there is an issue with the exposure at high speeds and
> large apertures with this kind of shutter, because of the time needed
> for the shutter to fully open (and to fully close).
>
> This raises two questions:
>
> -- when we select a speed of 1/125 (for instance), how does the
> shutter is supposed to behave ? If it starts opening à t=0, does it
> starts closing at t=1/125s ? Or does it actually start closing
> *before* that, so that it is fully closed at t=1/125 ?
>
> -- typically, how fast were these shutters to go from full closure to
> full aperture ?
>
> And finally: are there some tables around that give the exposure
> corrections for that ?
>
> Thanks,
>
> --
> pehache

There is a common misconception about this. The shutter speed is
really a measure of the amount of light it allows to fall on the film.
The true time it takes will be longer as the shutter has to speed up
to open and speed up to close.

Re: About central (diaphragm) shutters at high speeds/large apertures

On 18 août, 11:53, RolandRB <rolandbe...@hotmail,com > wrote:
>
> There is a common misconception about this. The shutter speed is
> really a measure of the amount of light it allows to fall on the film.

Yes... but at which aperture ?

It appears from the tables posted by other contributors that the
shutter speed is usually calibrated for the full aperture and that
corrections are needed for small apertures.

--
pehache