Thanks everyone for the replies. Next clear sky I will do not only longer but also staggered images for blinking. I would have done a guided image to go deeper but a 60-sec image is normally deep enough for mag 15 (and I had a minor hardware hiccup stopping me from guiding for that occasion).

Query solved :-)

Lawrence

--- In guide-user@yahoogroups.com, Bill Gray <pluto@...> wrote:
>
> On 02/16/2013 06:52 PM, jimborm@... wrote:
> > I too agree with your coordinates, but I wonder if the comet is bright
> > enough to show in a 60" image. GUIDE shows me that its magnitude should be
> > about 15.2 (although I don't remember where I got my mag data from).
>
> Comet mags are bound to be somewhat iffy. They're usually based on an
> effort to fit the entire observed arc, which may mean it'll fit well
> in one place but not another, especially if outbursts are involved.
> (If the comet suddenly brightens by six magnitudes, for example, you
> can't really tweak one set of magnitude parameters to show both "before"
> and "after" magnitudes correctly.)
>
> I went to the MPC Database Search at
>
> http://www.minorplanetcenter.net/db_search
>
> and in the first edit box, for "Data about an object", I entered ISON
> and clicked on "Show". That got me several orbits, and further down,
> it said there were 2078 observations available and that they were available
> for download.
>
> Doing so and scrolling down to the bottom, I saw several dozen observations
> made on 11 February, with magnitudes of 16.0 to 17.2. (With a few outliers
> brighter or fainter than this.) So it would appear to be fainter than
> predicted, at least right now.
>
> -- Bill
>