• Can TPoint fix my tracking in addition to the pointing?
• Do I really need a good polar alignment?
• How to Polar Align using TPoint includes use of additional terms

• Paramount out-of-the-box (first time users)

• What kind of pointing can I expect?

When using ANY German Equatorial "goto" mount it is perfectly normal to completely miss the first star (but usually no more than 2 to 3 stars) after the meridian flip before TPoint can kick-in. That is when no stars have been mapped on the opposite side yet of the meridian REGARDLESS of many stars have been already mapped on the other side!! Repeat, mapping more and more stars on the opposite side does not fix the flipping offset error. However, if you have a very large field of view say 20 arcminutes or more and a reasonably accurate polar alignment AND a reasonably orthogonally mounted OTA all stars should fall on the detector regardless of which side you are pointing. If your polar alignment is off by say a degree or more and same for the OTA mounting on the versa plate this simply will not be the case. After collecting enough TPoint data you will precisely how much error there is for both and also in what direction the error lies. TPoint accept no substitute!

TPoint for Windows has been specifically modified to support the German Equatorial mount design. And with the Paramount ME there is no need for using two separate models - one for each side of the meridian which of course would further complicate things.

Of course a fork mounted scope does not have the meridian flip issue (but they are far less versatile in regard to mounting a wider range of telescope sizes) and more often than not the common commercial SCT's using fork arm mounts have mirror slop to contend with. Random mirror slop can be many arcminutes of random error and also requires a delay after slews giving the mirror time to come to rest. For these reasons Software Bisque created the SCT locking collars years ago. More often than not the problem with pointing and repeatability (or lack there of) in the end it turns out to be related to the OTA or other equipment not the Paramount.

NOTE: The meridian flip introducing additional pointing inaccuracies is true for ALL German Equatorial mounts, regardless of how well they are built. Don't be fooled by reports from those employing very short focal length scopes with huge fields of view that don't appear to have this inherent pointing issue because the star has fallen somewhere in the very larger field. These days 30 arcminutes to a full degree is actually common. However, I argue the smaller live video field of view for initial polar alignment is currently (currently) the BEST way to go.

When crossing the meridian the optical system (OTA) is now flipped 180 degrees and all of the cumulative system errors related to pointing manifest themselves in poor pointing after the meridian flip, that is until TPoint has enough data on the opposite side after the meridian flip. Generally mapping about 12 to 15 stars on both sides of the meridian will yield very good all sky pointing - on the order of 2 to 5 arcminutes RMS is common. To achieve 15 to 30 arcsecond RMS pointing requires a very repeatable system and a much larger set of mapping data on the order of a one hundred well mapped points or even more. When employing "ProTrack" to make tracking corrections you should shoot for more like 300 well mapped points.

The pointing problem after the meridian flip is not just related to the mount but rather the entire system, the optical alignment and/or collimation of the optics in the OTA, the mounting of the OTA on the mount, the perpendicularity of the RA and DEC axis, and so on. But this is EXACTLY why TPoint is recommended in the first place. TPoint for Windows will fix all of these pointing related issues (including meridian flipping with the Paramount ME) and more.

TPoint can be used as a tool to quantify the magnitude of these errors and more importantly, assuming they are repeatable, TPoint can fix the error as opposed to the user having to shim the OTA and/or mount at the hardware level. This is a very tedious task requiring many iterations to get just right and for the most part not necessary. In order for TPoint to fix the pointing errors on both sides of the meridian it simply needs enough data mapped on each side. And again this is why when starting out concentrate on one side of the meridian, as opposed to flipping back and forth across the meridian. After mapping sufficient stars (at least 12 to 15) on the first side flip over the meridian and start mapping the opposite side starting in a small area first then expanding.

In my case using a C-14 at f/7 with a small live video detector yielding a field of view ~6 by 4 arcminutes. I always find that the very first star is completely missed in the very small field after a meridian flip  Again, this is completely normal and nothing to be concerned with. Now in my case after only one star has been accurately mapped after the meridian flip (with a fixed mirror) all other stars within say 1 degree of the newly mapped star now fall in the field the smaller chip. Then mapping an additional 3 stars after the flip 1 to 2 arc minute RMS pointing is achieved.

Before trying to slew several degrees away to the next target(s) after a flip stay very close to the first mapped star (say within a single constellation). This makes searching out the next few stars less of an issue. Then after mapping say 5 to 8 stars after the flip start expanding the mapping and TPoint will dramatically improve the all sky pointing on both sides of the meridian. When enough data has been gathered on both sides of the meridian AND the proper use of additional terms is used you will see very good all sky pointing- 15 to 30 arcseconds RMS is quite common with the Paramount ME when using a fixed mirror OTA or refractor.

Do I really need a good polar alignment?

Although TPoint can compensate for the polar alignment error in regard to pointing (and even in regard to tracking when properly employing "ProTrack") it is still useful to get a reasonably accurate polar alignment ~1 arcminute or better in each axis. Using TPoint as a tool this can be done very accurately and reasonably quickly with practice (less than 1 hour) and once mastered it is always worth the extra time when imaging. The biggest advantage to being very near the pole is the pointing will be improved when TPoint is not making the necessary pointing corrections and it minimizes field rotation in very long exposures. By starting with a good polar alignment it makes initial mapping points easier since the stars will be very near or in the the field of view before TPoint can kick in and remove polar miss-alignment.

How to use TPoint to accurately Polar Align the scope

Can TPoint fix my tracking errors in addition to pointing errors?

Yes - provided you are using a Paramount ME/GT-1100S  or other mount employing the Software Bisque Telescope Control System with an extensive TPoint model and an OTA, focuser, optics, CCD camera, rigidly mounted and not subject to any random errors like mirror or foucser slop.

In these cases the lower level tracking kernel known as "ProTrack" can be used to improve the tracking in addition to the pointing by making the necessary corrections to compensate for non-perfect polar alignment, out-of-roundness of the gears, tube flexure, atmospheric refraction, and so on. Paramount ME customers have submitted un-guided exposures as long as 10 to 20 minutes in length with perfectly tracked stars without guiding (1 arcsecond level) by properly employing TPoint/ProTrack

What kind of RMS all sky pointing should I expect?

This is a VERY loaded question and the answer depends on a number of variables! With a well built "goto" mount and a bit of experience (and no random errors like mirror slop) one can expect 1 to 2 arcminute RMS pointing with minimal effort. In order to achieve better RMS pointing the proper use of additional terms is ALWAYS required. You simply cannot expect 15 to 30 arcsecond RMS pointing without using more than just the 6 basic EQ terms OR without physically making hardware corrections to the mount ONLY after properly using TPoint as a tool including the use of the additional terms, catch-22.

Please refer to the web page TPoint Evaluating Polar Alignment for details including RAW data showing why this is simply not the case and yes it may (does) contradict other modeling software claims. In my own personal experience I have never seen sub-arcminute RMS pointing with any off-the-shelf "goto" mount WITHOUT using additional terms (more than the 6 basic EQ terms) or without making hardware changes to improve the mount itself in an attempt to fix the pointing problems. Keep in mind that evaluating the errors cannot be done without employing the additional terms either! And for accurate polar alignment information here too you need the additional terms.