Generally speaking, if you only perform the hat trick for the few seconds
that's required for vibration to dampen out, the autoguider won't lose track
of the star if the mount is in any respectable shape.

Mike
http://www.concentric.net/~richmann/


> -----Original Message-----
> Sent: Friday, June 04, 1999 9:10 AM
> Subject: RE: [M]: OT:Astrophotography.
> Importance: High
>
>
> What happens to the autoguider thought if you are using it
> through an OAG?
> Would it not lose track of the star? I am using the camera on the 'B'
> setting.
>
> Cheers,
> Andy.
>
> > -----Original Message-----
> > Sent: 04 June 1999 13:40
> > Subject: Re: [M]: OT:Astrophotography.
> >
> > In a message dated 6/4/99 7:55:16 AM Eastern Daylight Time,
> >
> > << Can anyone tell me the best way to eliminate shutter
> vibrations of the
> > OTA
> > whilst doing astrophotography?
> > I have a 10" Lx200 and I'm using a Nikon FA 35mm camera >>
> >
> > I don't think the FA has mirror lockup, but if it does,
> that's a first
> > step.
> >
> > Shutter and mirror vibrations are only a problem in fairly
> short exposures
> >
> > because: for long exposures (over 1/2 second or so) you
> can use the "hat
> > trick" of holding a hat (or piece of cardboard) past the
> end of the tube,
> > tripping a Bulb or Time exposure, and using the hat as the
> real shutter.
> > For
> > fast exposures such as 1/250 or faster, it's also a
> non-problem due to the
> >
> > shutter speed. That middle ground of 1/125 to 1/4 is more
> problematic.
> > Mirror lockup and "hand holding" a rigidly mounted camera both help.
> > Squeeze
> > the camera with both hands, press your face against it, or
> do anything
> > else
> > you can to reduce vibration, just as when you hand-hold a
> telephoto lens
> > for
> > "normal" photography. You'd think that breathing and shaky
> hands would
> > hurt,
> > but it turns out they have fairly low frequencies, and you
> can apply a lot
> > of
> > damping for the higher-frequency vibrations of the mirror
> and shutter.
> >
> > Good Luck!
> >
> > John
>

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