6-9-07 First test fire-up using GP5
Guider: 50x350mm tube assembly, Tech2000 Cam # SIC4700/37 (NO IR FILTER)
Observing scope: NF 102x600mm refractor & 6x30 crosshair finder.
Loc: Monroeville Tech2000 shop, lots of light pollution in town, 9 mercury lights close.
Seeing: 4 rather poor at start but improved greatly later as described below.
Transparency: 9, a very clear day & evening. Excellent rating.
Temp: 56 Wind: Dead calm.
10pm - Lined up finder, main instrument, and guider all at one mercury lamp about 150 yards distant.
10:30 - followed Venus, fine focus, guider cam got a nearby star looking faint - seeing made it come and go.
11:00 - Mizar & Alcor just past zenith high overhead. Both easy by naked eye 2.3, 4.0 mag. Cam gets the 4.0 fine & GuideDog stays locked continuously while guiding on that. Snapped a single-frame pic shown above, the realtime frames look better.
12:00 - Seeing is much better, probably 7. There is a 7.6 mag star between Mizar & Alcor slightly offset (SAO 28748). Faintly visible in the 4" but only hinted at in screen viewing though its position is evident it could readily be mistaken for noise and so that mag could never be used as a guide star with this model. This just shows an upper-level limit faintly hinted at the 7.6 mark.
01:00 There is a 4.8 mag star directly east of mizar about 1/2 - to one degree or so (SAO 28843). Moved over to it & captured easily & GuideDog tracked 45 minutes never losing lock. Its pretty faint I gotta say looking in occular on the 4" but easily seen on screen, surely red & cleanly so in occular but whiter on screen, about 2 pixels not including color ghost (IR filter is removed). The steady air helps alot. Can not see it naked eye even when eyes are shrouded really well like Kenny in the SouthPark television series.
2:00 Packed & done. 3.5 hours run. Used alot about 40 hours now, the 9V battery is near dead on Nightfire drive, noticed when LED lamp showed a distinct visible flicker, then the tracking dial control setting needed large adjustment for faster/slower in a chasing fashion as the battery re-awoke when buttons were pushed. Pressed onward until the unit maxed-out around 40 hours use.
Summary: A typical mag 4 guidestar will be readily useable anytime and anywhere for this entry-level system since it has a cross point off-axis mounting to aim it anywhere irregardless of where the user is located or what the user can see or where the main telescope is ponted. Max is likely far more than above mag 5 since the 4.8 above was extremely easy on this good night with in-town conditions. The Mizar/Alcor pair have a separation of 12' (1/5 degree). Using a ruler and ratio measurement between them, compared to full image width, shows this unit yields very close to 1/2 degree FOV, ratiometrically less on the vertical of course. This closely matches the calculation I used from Joos Et.-Al. in "Theoretical Physics" (footnotes not included for brevity) as y' = f tan-a that yields a 3mm image field diameter prediction, which is quite close to the actual dimension of the photodiode array width that I have measured myself directly. Coalescence achieved! Notably this proto camera chip is offset from true center by around 30 arcminutes which does not influence test results but does influence illumination on guide stars since the .96" focuser barrel is long and partially vignettes the aperture. About 2 arcseconds guiding resolution should result with this 388 pixel-wide array and software like GuideDog typically will produce sub-pixel on the real-time analysis adjusting corrections thereby, then there is the dynamics of the mount which usually would make it even better due to inertial effects. As the lowest-cost 'entry level' complete guider system, it sure worked fine for me over many hours! I'll pick this one above the 100x600 NF refractor version anytime. Not just on the lower price but the fact that it performs very similarly and is much more compact. There are technical reasons for this otherwise puzzling discrepancy since you would naturally expect a 100mm aperture to beat a 50 soundly in magnitude instead of being almost the same. OK- now you got my attention!