Hi Jim,

I've posted a single 5 minute exposure of M42 in my folder taken with
a Canon 400D and Takahashi FS-78 at 630 mm. This was polar aligned
with the AstroTrac polar scope without using the second and third star
gaps in the reticle. I simply rotated the polar scope until the Ursa
Major and Cassopiea markings lined up with the constellations in the
sky and positioned Polaris in the gap marked same. I haven't found it
necessary to try drift alignment yet.

It is a little difficult to compare the AstroTrac's tracking error
with a mount which uses a worm gear, such as the Sky Memo, as the full
error in a worm is seen every turn of the worm, which is typically
between 5 & 10 minutes. With the AstroTrac, the drive screw is
analogous to the worm, except it has a period of 2 hours. We calibrate
each AstroTrac to make sure the tracking rate is as accurate as we can
get it. A typical unit will have around 5 arcsecond peak-to-peak
tracking error over a five minute period. The error depends on the
where the drive arm is on the screw. A single unit can have regions
where tracking error is as low as 1-2 arcseconds over five minutes and
as high as 10-15 arcseconds over five minutes.

As a rule of thumb, the AstroTrac is good for focal lengths of at
least 500 mm over 5 minutes.

We have conservatively rated the AstroTrac payload at 10 kg (22 lb).
We know it can take a lot more weight than this, due to the preloaded
bearings, but more weight requires a more rigid mounting for the
AstroTrac. With rigidity comes weight, and this tends to defeat the
ease of use aspect of the AstroTrac.

I hope this helps.

Best wishes,
Richard

--- In astrotrac@yahoogroups.com, "paulo_eamp" <paulo_eamp@...> wrote:
>
> Hello Jim.
>
> I`m interested too in the Astrotrac and the kenko mount. I´m deciding
> which to buy. The prices are similar. I think the kenko maybe can have
> better tracking. I have heard that the astrotrack above 200mm needs a
> drift alignment to do the work. I have seen images with the kenko
> mount up to 300 or 400 and the folks don´t mention if a drift
> alignment was neccesary. I think the astrotrac is more easy to use and
> support more payload....The kenko has a very good presentation and it
> has been on the hobbie for some years. I don´t know if this kenko
> mount is made of Japan. It looks well done to me.
>
> Regards
> Paul
>
> In astrotrac@yahoogroups.com, "Jim" <jwaters125@> wrote:
> >
> > Hello
> >
> > I plan to purchase one of these products. Does anybody have any
> > experiance with the Skymemo and what's you recommendation on the
> > AstroTrac vs. the Skymemo. I plan to use a Canon XTi camera with
> > lenses up to 300mm.
> >
> > Jim Waters
> >
>