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Re: [OM] XA2 aperture - fixed or variable

Subject: Re: [OM] XA2 aperture - fixed or variable
From: HI100@xxxxxxx
Date: Sun, 16 Apr 2000 23:27:52 EDT
 jlind@xxxxxxxxxxx writes:

<< The practical limit on a leaf shutter is about 1/500th.  Shutter
 speeds faster than 1/500th can have problems with producing an even
 exposure across the film plane. >>

John,
        I don't know what is used in the XA but..   If it is a leaf shutter 
it has a circular opening so at high speeds it just has a variable F-stop as 
the blade travel time becomes a significant part of the exposure time. Thus 
the exposure remains even across the film plane even if it is slow. In some 
small auto only cameras the diaphragm is the shutter and it only opens part 
way so the travel time is less significant at small f-stops. (Thus program 
mode is a good fit :small f-stop+high speed) Similarly if the shutter and 
diaphragm are placed close together. The distance that the blades have to 
travel in an XA is also probably much shorter than say a large format leaf 
shutter that struggles to get to 1/500sec. As an aside, some cheap auto 
cameras have terrible bokeh as the combined shutter/diaphragm has only two 
leaves with aa approximately rectangular shaped opening.

Regards,
 
  >>>Tim Hughes<<<

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