Dave Wilden

Hi, Last night, with my Az-GTI in equatorial mode, despite achieving "excellent" polar alignment ( less tha 10 arc sec overall error, according to Sharpcap's Polar Alignment Tool) the longest sub exposure I could get away with before I saw elongated stars (with 420mm scope) was just 8 secs. This is frustrating, as I really want to be using 30 to 60s subs, othewise the deadtime transferring data from the camera to Sharpcap becomes excessive. So I'm trying to understand what affects the tracking accuracy of my AZ GTI in equatorial mode: is it just the accuracy of polar alignment, or does the "2 star" alignment accuracy also impact on tracking? My process has been: 1. Level tripod using spirit level built into the Star Adventurer wedge. 2. Roughly align mount with north pole (with mount turned off at this point) 3. Perform Polar alignment using Sharpcap polar alignment tool (manually rotating the scope through 90 degrees when requested) 4. Put mount back into approximate equatorial home position (pointing to N pole with counterweight down) 5. Power on the mount, connect to Synscan and perform 2 star alignment. Last night I got the polar alignment to 10 arc sec accuracy (as measured by the Sharpcap tool) at step 3 yet when I later selected to slew to named objects, the scope was often 5 degrees of more out (as determined by plate solving). Am I right in thinking that the "slew to object error" is due to the fact that the mount was only roughly in the correct "home position" at step 4? If so why didn't the 2 star alignment process correct for this? This is not a major problem as I can use Sharpcap 's "Plate Solve and realign" to correct the error. A much bigger problem for me is that despite getting "excellent" polar alignment (accoing to Sharpcap) the longest sub exposure I could get away with before I saw elongated stars (with 420mm scope) was just 8 secs. In equatorial mode, I thought that all the mount does is rotate the RA axis at the siderial rate, so as the RA axis was accurately aligned to the North Celestrial pole, why am I still getting elongated stars for such short exposures? Or is there more to it than that - does the "2 star" alignment error some how impact on tracking accuracy as well? Or is this just an inherent error in the mechanical gearing that does the sidereal rate rotation? Any suggestion gratefully received Dave

I have a second hand Az GTI mount which I'm really pleased with apart from one intermittant problem. Very occasionally while it is slewing to a new position, it seems to lose power to the control unit, which causes it to stop transmitting a wifi signal, and hence the mount loses control from the SynScan app. When this happens the red light which normally blinks when its transmitting wifi goes out and the mount freezes at whatever position its in at that point - i.e the slewing stops. If I move the scope manually in azimuth away from the position it froze in, the red light comes on again, and I can make it go out again just by moving it back slighly again. The problem is that although I can reposition the tripod to avoid the problem position, I then have to go through the alignment process again. I've had this problem occur 5 or 6 times over 6 months of use, but most of the time it seems to be fine and I can slew the scope repeatedly through 360 in azimuth in either direction without it freezing. But on the odd occasion it does happen, it seems to have a repeatable fault at a specific position as explained above. I'm not sure if its always the same azimuth and elevation its happening at each time it occurs, as when I try to investigate it, I cant make it happen!! BTW When the fault occurs, it doesnt matter whether its running on external DC power or internal batteries, so its not a case of the DC power jack failing to make consistent contact. So I suspect its an internal problem - I am wondering if there any slip rings inside the unit which transmit the power to one or other of the stepper motors? And if so could these have a bad spot where the power is not being transmitted through the slip ring? I'd be interested to know if others have seen this problem, and if there's any solution, fix or or work-round. Dave