Hi All,
The 127mm Triplet APO from North Group in Nanjing, China has an excellent price/performance ratio, with good resolution, flat optical field and fair colour correction. I think it’s an ‘excellent’ visual instrument and a ‘good’ imaging scope. However the focuser, as supplied, has some issues.
Issues:
Some issues with the focuser are:
1)The 2” eyepiece holder has trouble gripping some tubes evenly and securely.
2)The focuser has trouble lifting any more than about 600 grams. A camera or a heavy wide-field eyepiece can cause it to slip.
3)The focuser lock has poor grip and causes image shift.
The best ‘performance’ option is to replace the focuser with a 2 ½” Moonlite unit, however the cost is somewhat daunting and more than half the original scope price. That said you’ll have a very nice scope for much less cost than the nearest competition.
Another option is to make a few simple changes that will reduce the issues with the original focuser. I investigated the issues one at a time and came up with some modifications.
Modifications:
Adjust compression ring tension
Adjust tube inside diameter
Adjust mechanical: preload and bearings
Summary:
The 127mm APO is a great telescope, and probably the best value in a large refractor at this time.
The focuser issues should be deemed an annoyance rather than a major fault; the focuser is as good as or better than the focusers on many other ED and semi-APO telescopes. Many users will be satisfied with the focuser as delivered.
The quality and size of the optics on the 127mm APO allow the use of high-end eyepieces and cameras which in turn place great demand on the focuser. Simple modifications and careful mechanical adjustment will help the user realize the full potential of the 127mm APO.
Please find a technical article with images at my webspace, the filesize is 640k
http://homepages.ihug.com.au/~robk/astronomy/127APO/127mmAPOFocuser.pdf
As always, amateur astronomy projects are a work in progress so I welcome advice and corrections from other owners as well as those who know more about focusers than I do...
Cheers,
Rob
