Celestron 8SE - Altitude GoTo Approach

[craigb1970]

I have set up my scope but I'm not clear whether the Altitude GoTo Approach should be set to positive or negative and would welcome any advice.  My Lat/Long is 54,33,57,98   /   00,59,52,52, I'm not sure is this would make a difference.   At the moment I have set both my Altitude GoTo Approach and Azimuth  GoTo Approach to positive.

[jonathan]

I have the 8SE but I don't recall a GoTo Approach setting, must be new (or I just missed it).  Does it have anything to do with being in the Northern Hemisphere?

[Peter Drew]

I think that setting is correct specially if your subsequent movements are in the same direction. This recommendation is outlined in the Michael Swanson book covering the Celestron GOTO instruments. I believe that setting up this way takes up any "slack" in the drive system thereby improving the GOTO accuracy. 

[craigb1970]

Thanks for the responses.  The Celestron knowledge share indicates that it is to do with accuracy of Goto and should be set in the opposite direction of load.  Therefore as I have me scope set slightly front heavy, then Alt Approach set at 'positive' would seem to be correct, however if I were to change the balance by adding in say a barlow or camera this would alter the load and, if significant, it maybe necessary to amend Goto approach.

I think I'll stick with the positive setting and only change if it becomes obvious that I need to.

[jonathan]

I'm a little confused when the Az would require a different Approach setting if this is just the base turning, as surely there should be no balance problems, and it must spin in both directions.

My other iPad is an iMac.

[craigb1970]

As I'm a novice I'm relying on advice from forum members and Celestron knowledge share but my understanding is that the Goto Approach setting reduces the effect of backlash when tracking and slewing.  I have copied below an extract from Celestron Knowledge share that might provide some clarification, I used this and a set up procedure I found  which has certainly improved things:-

"

How can I use GoTo Approach to minimize backlash with my NexStar SE mount?

Press Menu > Scope Setup > GoTo Approach. This will enable you to choose the direction the scope will use when approaching an object during the final slewing. The directions can be either positive or negative and are defined as seen from the back of the scope. For altitude, positive moves the front of the tube up, negative down. For azimuth, positive moves the front of the scope to the right, negative to the left.

Always set the direction of approach in the opposite direction from the load pulling on the scope. This minimizes effects of backlash in the gear train. The load in altitude is usually because of gravity acting on the scope’s imbalance from accessories (eyepieces, cameras, etc). The load in azimuth is due to tracking and is opposite (in reaction) to the tracking direction, so the approach direction will be the same direction as tracking.

Whether to set positive or negative in altitude or azimuth depends on your scope, the type of mount, its orientation, Southern or Northern Hemisphere location and the load from attached accessories.

In a typical situation with Schmidt-Cassegrain (SCT) telescopes, the tube will be back heavy, because accessories are attached. The load acts to pull the front of the tube up (positive), so the opposite direction (negative) should be chosen for the GoTo Approach. For azimuth, the scope's tracking determines the load. When the telescope tracks to the west (positive), the GoTo Approach should be set to close in from the same direction, moving west (positive).

Many users stay with the default, which is altitude negative, azimuth positive. For the SCT with a StarDiagonal, GoTo slews will be seen as moving to the up and right with these settings.

In the Southern Hemisphere (as seen from behind the scope), the west is to the left, reversing the GoTo Approach settings for azimuth.

Note: When aligning the mount, use the same approach directions to center your alignment stars as you are using for the GoTo Approach for the best GoTo performance."