Cone error adjustment

[brisguy]

Hello,

I tried using ConeSharp last night for the first time and had trouble finding stars in the desired locations, due to my limited sky view. However, I got through the procedure twice. Once it said I had an error of 1.0 minute and the next time, it said over 5 minutes of error. I have two questions.

1. The results said the scope was pointing 'away from the mount'. Does this mean the front of the scope needs to be lowered relative to the rear?
2. When I tried to adjust the bolts on the dovetail, the scope was in the last position used, so AZ about 180 and ALT about 35 (due to my latitude). As I loosened the main bolt, the scope immediately slid down, basically ruining whatever alignment I had gotten to that point. Is there a dovetail that would prevent this?

Thanks!

[admin]

Hi,

if there are any errors/inaccuracies in the GOTO movement of your mount then those end up in the calculation, and can throw the results off. Backlash is a typical cause of this sort of problem. Sometimes it can be helped by running the GOTO twice - the first time when it moves a long way can be inaccurate, the second will sometimes re-center on the target with more accuracy (depends on the mount).

As to the adjustment, if it says that the front of the scope is pointing away from the mount, that means that you want to increase the dovetail spacing at the back (or reduce it at the front) to try to pull the front of the scope back in.

I have usually made adjustment using this sort of dovetail

PXL_20230420_132128010.MP (Medium).jpg (222.81 KiB) Viewed 879 times

The center bolt holds the dovetail to the scope and the two side bolts can be adjusted to add spacing. I seem to recall the trick was to put a little extra tightening on the side bolts first, then a bit off the center bolt, then repeat. This keeps the tension on and should stop everything from flopping around. The opposite if you want to reduce the distance between the dovetail and the mount.

I must admit that I personally don't worry about this much any more - reliable plate solving means that a missed GOTO is fixed within 20s or so, so why worry...

cheers,

Robin

[brisguy]

Thanks for the reply. I’ll try putting tension in the offset screws. The cone error affects my ability to get a good PA since it throws off the center axis Calc. It also can affect guiding since the PA accuracy changes with mount position and changes the DEC tracking. Plus, I also use my setup for visual and would like better GoTos.

I’ll also try a GoTo near the desired start point and correction before I start the cone error measurement.