Sky-Watcher Skymax-102 OTA on Dobsonian and AZ Base

The Skymax-102 on Dobsonian and AZ Mounts - Introduction | Skymax-102 OTA on Heritage 100P Base | Skymax-102 OTA on Star Discovery AZ GoTo Mount | Preliminary Conclusions | Links

On this page, I describe my attempts to use my Sky-Watcher Skymax-102 OTA Maksutov-Cassegrain tube on two mounts that I own:

The Omegon Dobsonian table-top mount is too shakey for the relatively heavy Skymax -102 OTA; therefore, I use it only for the lighter Heritage 100P tube.

*) In the meantime, I came to the conclusion that the 100P base trembles too much for this tube that magniefies more than a Dobsonian telescope. That's why I'm going to use it for this tube only when traveling. At home, I will use the a little too large base of the P130 Dobsonian telescope, which is more stable and trembles less. For this basis, the same applies as for the 100P base.

Note: On a further page , I describe the Skymax-102 OTA.

 

The Skymax-102 OTA on Dobsonian and AZ Mounts - Introduction

When I ordered the Skymax-102 OTA after getting good advice from the dealer, I did not realize that the tube is meant for an equatorial mount and that the prism rail should be mounted horizontally. In the Star Discovery AZ Mount, in the Virtuoso as well as in the Heritage 100P and other simple Dobsonian table-top mounts, the rail is, however, rotated by 90 degrees and thus, mounted perpendicular. This has implications for the location of the controls and, as I learned, affects different aspects, depending on the base. In addition, the prism rail of the Skymax-102 as well as that of the Heritage 100P has only on one side (on the left side in viewing direction/seen from the back) three holes for the screw of the locking knob (the Heritage P130 does not have any holes in the prism rail...). Although these holes may limit the adjustment range, they offer the advantage that the tube cannot slip out from the mount accidentally (and thereby might possibly be damaged).

I then looked at the manuals for the Heritage 100P and P130 once again to find out how the locking knob should be oriented. For the 100P it is shown pointing downwards, for the P130 pointing upwards (where this can be seen...). This might mean, that if there are holes in the prism rail, the locking knob should point downwards. In addition, the arm of the table-top mount always appears to the right of the telescope (in viewing direction). For the Star Discovery AZ GoTo mount, the arm is also on the right of the telescope (in viewing direction), but the locking knob is shown in the manual as pointing upwards for an unknown telescope tube. In the end, it seems that it does matter for this mount, in which direction the locking knob points.

Since you can arrange the locking knob in two ways (pointing upwards or downwards), and the arm of the mount either right or left (in viewing direction) of the telescope tube, this results for each considered mount in four different ways of mounting the tube. The following table for the Skymax-102 OTA is meant to illustrate this point and also lists the advantages and disadvantages of the different options (it is only in part valid for Dobsonian tubes!):

 
100P Base (P130 Base ditto)
   
Star Discovery AZ GoTo Mount
Tube Sits in Mount in Viewing Direction on the ... of the Arm
Prism Rail Holes Pointing to the Screw of the Locking Knob?
Yes
No
 
Yes
No
Left ("Correct" Viewing Direction) Position 1 Position 2   Position 1 Position 2
  • The locking knob points downwards
  • The locking knob points upwards
 
  • The locking knob points downwards
  • The locking knob points upwards
  • The "arm" of the table-top mount is located to the right of the telescope tube (in viewing direction)
  • The focuser sits on top*, i.e. above the diagonal mirror; this is acceptable
  • The red dot finder sits at the bottom left and is more or less unusable in this position (at the 100P, it sits at the top left)
 
  • The "arm" of the mount is located to the right of the telescope tube (in viewing direction)
  • The focuser sits on top*, i.e. above the diagonal mirror; this is acceptable
  • The red dot finder sits at the bottom left and is more or less unusable in this position (at the 100P, it sits at the top left)

Right (Opposite Viewing Direction)

Not Suitable for certain Dobsonian Tubes***

Not Suitable for the Star Discovery AZ GoTo Mount

Position 3 Position 4   Position 3 Position 4
  • The locking knob points upwards
  • The locking knob points downwards
 
  • The locking knob points upwards
  • The locking knob points downwards
  • The "arm" of the table-top mount is located to the left of the telescope tube (in viewing direction)
  • The focuser sits at the bottom*, i.e. below the diagonal mirror; this is acceptable
  • The red dot finder sits at the top right, which is "acceptable"
 
  • The "arm" of the mount is located to the left of the telescope tube (in viewing direction)
  • The focuser sits at the bottom*, i.e. below the diagonal mirror; this is acceptable
  • The red dot finder sits at the top right, which is "acceptable"

*) If you would mount the Heritage 100P* (and P130) "against" the viewing direction, the eyepiece would point downwards - the telescope cannot be used this way. For the Skymax-102, however, the eyepiece opening points backwards; you can rotate the diagonal mirror so that the eyepiece opening comes up.
*) Normally, the focuser of the MAK90 and 102 sits to the right of the diagonal mirror.
**) The asymmetry of the "arm" of the Dobsonian mounts is purely cosmetic and does not interfere with its use.
Gray typeface: Not suited to this mount
Yellow Background: My preferred way of mounting the Skymax-102 on the Heritage 100P table-top mount.
Blue Background: My "preferred" way of mounting the Skymax-102 on the Star Discovery AZ GoTo mount. But in this case I would have to look for a solution for the red dot finder....

*) Note: The Heritage 100P eyepiece is located on top of the tube and the viewfinder to the left of it.

 

Skymax-102 OTA on Heritage 100P Base

In the following, I present photos that demonstrate the four positions.

Overview of the Positions - Selected Views

Position 1 Position 2 Position 3 Position 4

Front view; the finder is at the bottom left (viewing direction), the locking knob points downwards

Ditto; the finder is at the bottom left (viewing direction), the locking knob points upwards

Ditto; the finder is at the top right (viewing direction), the locking knob points upwards

Ditto; the finder is at the top right (viewing direction), the locking knob points downwards

Rear view; the finder is at the bottom left (viewing direction), the locking knob points downwards

Ditto; the finder is at the bottom left (viewing direction), the locking knob points upwards

Ditto; the finder is at the top right (viewing direction), the locking knob points upwards

Ditto; the finder is at the top right (viewing direction), the locking knob points downwards

View from the side; the focuser is at the top, the locking knob points downwards

Ditto; the focuser is at the top, the locking knob points upwards

Ditto; the focuser is at the bottom, the locking knob points upwards

Ditto; the focuser is at the bottom, the locking knob points downwards

View from the other side; the focuser is at the top, the locking knob points downwards

Ditto; the focuser is at the top, the locking knob points upwards

Ditto; the focuser is at the bottom, the locking knob points upwards

Ditto; the focuser is at the bottom, the locking knob points downwards

Example: Position 3

The following photos illustrate how the Skymax-102 OTA looks on the Heritage 100P table-top mount for the yellow-marked case in the table above (position 3: against the direction of view, the locking knob points to the holes in the prism rail). The red dot finder is located at the top right (seen in viewing direction), the focuser below the diagonal mirror.

Skymax-102 on Heritage 100P base; the locking knob points upwards

Ditto, front view; the red dot finder sits right to the eyepiece (viewing direction)

Ditto, front view, closer

Skymax-102 on Heritage 100P base, other side; the red dot finder sits on the top right

Skymax-102 on Heritage 100P base, seen more from the back

Ditto, details (the focuser sits below the diagonal mirror)

More Photos of the Different Positions

In the following, I present a larger number of photos of the four positions.

Position 1

Skymax-102 on Heritage 100P base seen from the side; the focuser is on top

Rear view; here the position of the finder is easy to see

Ditto, but more from the side; the focuser is on top

Ditto, but more from the other side

View from the other side; the focuser is on top

Front view; here you can easily see the positions of the locking knob and the finder

Ditto; here you can easily see the position of the finder, the locking knob points downwards (see the same view in position 2 for comparison)

 

Not visible: The screw of the locking knob points to the holes in the prism rail

Position 2

Skymax-102 on Heritage 100P base; the locking knob points upwards, the focuser is at the top

Rear view; the locking knob points upwards, the finders is at the bottom left (viewing direction)

View from the other side; the locking knob points upwards, the focuser is at the top

Front view; the viewfinder is at the bottm left, the locking knob points upwards (see the same view in position 1)

Detail: The screw of the locking knob points to the side of the prism rail without holes

 

Position 3

Skymax-102 on Heritage 100P base; the locking knob points upwards, the focuser is at the bottom

Rear view; the locking knob points upwards, the finder is at the top right (viewing direction)

Ditto, more from the side; the locking knob points upwards, the finder is at the top right (viewing direction)

View from the other side; the locking knob points upwards, the focuser is at the bottom

Front view; the finder is at the top right (viwing direction), the locking knob points upwards (see the same view in position 4)

Detail: The screw of the locking knob points to the side of the prims rail with holes

Position 4

Skymax-102 on Heritage 100P base; the focuser is at the bottom

Rear view, more from the side; the focuser is at the bottom, the finder at the top right (viewing direction)

Ditto, more from the other side

View from the other side; the focuser is at the bottom

Front view; the finder is at the top right (viewing direction), the locking knob points downwards (see the same view in position 3)

Not visible: The screw of the locking knob points to the side of the prism rail that has no holes

 

Skymax-102 OTA on Star Discovery AZ GoTo Mount

The Skymax-102 OTA can be positioned on the Star Discovery AZ GoTo mount only in viewing direction - otherewise tracking and GoTo functionality would not work. This leaves only positions 1 and 2. In position 1, the red dot finder is located at the lower left (is also true for position 2), which is very inconvenient. The following photos serve to illustrate the latter point:

Skymax-102 tube on mount (overall view)

Ditto (Detail)

Front view - you can easily see the unusable position of the red dot finder

Skymax-102 tube on mount, turned around (overall view)

Ditto (detail) - you can easily see the unusable position of the red dot finder

Rear view

 

Ditto (detail) - you can easily see the unusable position of the red dot finder

 

 

Preliminary Conclusions

Heritage 100P Base

For the simple table-top mount of the Heritage 100P, it does not matter if the Skymax-102 OTA is mounted against the "prescribed" line of sight (position 3, table cells highlighted in yellow). Then the focuser sits at the bottom, and the red dot finder sits at the top right. Both positions are not optimal, but acceptable. This is my preferred position for mounting the Skymax-102 OTA on the Heritage 100P base. This also applies top the simple Omegon Dobson base that I might use alternatively for this tube.

In the meantime, I came to the conclusion that the 100P base trembles too much for this tube that magniefies more than a Dobsonian telescope. That's why I'm going to use it for this tube only when traveling. At home, I will use the a little too large base of the P130 Dobsonian telescope, which is more stable and trembles less. For this basis, the same applies as for the 100P base.

Star Discovery AZ GoTo Mount

For this mount, only position 1 (table cells highlighted in cyan) and 2 can be used. Position 1 allows to utilize the holes in the prism rail, but moves the red dot finder in an awkward position, as does position 2 that cannot utilize the holes. I will go with position 1, but I will have to look for a better solution for the red dot finder (maybe, a Rigel finder?) with respect to its positioning...

Luckily, you need the red dot finder with a GoTo mount (more or less...) only for the setup of the telescope...

 

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25.10.2016