Le samedi 30 Juillet 2005 15:59, Chuck Norcutt a écrit :
> Manuel Viet wrote:
> > circumstances that vibration "bug" would show ; maybe on landscape
> > pictures, tripod mounted, long exposures ? But then, why would so many
> > astrophotographers give an arm and a leg to get an OM today ? I'm
> > confused.
>
> I think most of what is known on the subject of OM vibration emanates
> from Gary Reese's extensive lens testing here:
> http://members.aol.com/olympusom/lenstests/default.htm
Nice site, thanks.
> Gary eventually realized that vibration with certain bodies and lenses
> was signfificantly impacting performance. In fact, many lenses, when
> retested using methods to reduce body induced vibration, showed much
> better performance than the initial testing. This probably happens with
> many other brands of camera bodies as well but you won't find it
> documented as you do here.
I read somewhere that lens tests were all flawed unless the test is shoot with
a body attached to a block of cement, on glass plate instead of film. Without
this setup, the quality of the lens is always degraded. The "nice" part of it
being that *all* lenses of any brand are affected as well.
> As to why astronomers want OM-1's and mirror lockup... conventional
> wisdom. Better they should remove the aperture arm from the camera
> which serves no useful purpose on a scope.
Aaargh.
> If you can, it's probably best to use the
> "hat trick" so there is no vibration at all. Place a "hat" or dark
> cover over the end of the scope, fire the camera shutter, wait several
> seconds for vibrations to settle, remove the cover from the end of the
> scope for the duration of the exposure, replace the cover, close the
> shutter.
I never did astrophoto myself, but I used that trick (well, sort of) to
"paint" pictures of nature stills in a dark room with a maglite. Fun results.
--
Manuel Viet
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