| review: Newtonian Reflector Dobson Starsplitter Tube 10 inch ( € 1900,- ) |
The Dobsons from Starsplitter claim to give best performance available with this design.
In fact the 10 inch f/6 tube looks very well designed.
Here is the specification:
- 10 inch f/6 mirror (254mm with focal length of 1524mm)
- mirror mount is 9 point cast aluminum
- 2 inch crayford focuser with adaptor to 1 1/4 inch (optional)
- eyepiece height is 60 inch (1500mm)
- turnable tube for comfortable eyepiece location
The assembled scope looks really impressive with it's height of 2m (78 inches).
I can just reach the eyepiece when it is pointed to Zenith withou a ladder:
My first test was a bit disapponting: none of my eyepieces reached focus!
By the means of extension tubes I found that the primary mirror was not close enough to the secondary by 1 inch (25mm) or so.
The optional crayford is not of extreme height but may be to high.
The mirror might have been placed for use with an ultra-low-profile focuser.
I unscrewed the mirror, drilled three new holes to the sonotube and reassambled the whole thing.
Not a big deal but neither a very good start with a new scope.
The mirror cell looks really solid and is promising good performance.
The open structure can cool down the mirror very fast.
This is very important for a Dobson with sonotube.
Because a sonotube is somehow sensitive to moisture I will store the scope indoors.
Therefore it is important that the mirror can reach environment temperature soon.
Actually this is reached within 30 minutes to max. of 1 hour in the wintertime.
If you are more unpatient you can get the optional cooling fan from Starplitter.
After shifting the mirror the scope was not balanced anymore.
Inside the rockerbox and not visible from outside there is a long slit in where the bearings are screwed to the box.
Here you can shift the bearing relative to the box and thus balancing the whole scope.
This is a very good solution but not even mentioned in the manual.
The moving of the alt-bearing is smooth but sticky enough to be able to balance for all my eyepieces.
Its made from Teflon and FRB.
Only for almost horicontal positions (I never can use anyway because of my location) there is not enough friction and the scope tends to slip downwards.
With good assistance by the two big lifting handles I braught the scope to outside.
And waited for the scope to cool down...
The scope now was ready for first light.
I had a night of very good seeing.
So I first used my Pentax SMC XL 14mm together with a 3x barlow lens.
This gives 320x and is big enough to make a star test.
I watched a bright star inside and outside of focus.
The star's diffraction pattern looked *very* similar and this is the proof for *very* good optics!
So I changed to the 40mm eyepiece and enjoyed the view.
The Pentax gives a wide field of view which is a hard test for off axis coma or vignetting.
But the f/6 mirror did not show any problems!
There is a slight coma visible at the corners of the field of view.
But this is normal with a Newton's parabolic mirror especailly when it is as fast as f/6.
Moving the scope is smooth and easy in both directions.
I changed back to 320x. With this magnification a star is moving quite fast in the field of view.
But it was easy to track it with the Starsplitter.
A great plus of the Starsplitter's design is the rotatable tube.
You can see the little white wheel running on the rockerbox.
This is the mechanism to turn the tube in a smooth way.
If you use a chair for comfortable watching you do not need to adjust the height when changing to higher declinations because you can turn the focuser (with the tube) up and down.
It may sound unimportant but this little feature is what I *really* miss on other Dobsons since I used it with the Starsplitter.
Summary
After the annoying part of setup, drilling and mirror shifting the telescope turned out to be very good.
It is a pleasure to use and the mirror is fine.
This will stay my visual telescope for a long time.
At least if I can cool down my aperture fever.
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