This thread is meant to compliment the discussions already presented in this thread concerning the Orion ST120 Achromat:
This purpose of this thread is to document some aspects of the mechanical build quality and optical performance not covered in Ed Ting's evaluation video. This scope is NOT the sample used by Ed during his video. Rather, it is a brand new sample obtained by me.
The scope arrived today, was well packed and undamaged. It appears to be a new, original sample, and not a repackaged return sample. No nicks, dents, scrapes, scuffs or other cosmetic defects were noted. Glass and coatings are very clean.
The focuser is really very good, tight, no play, but easy to use and could handle my Denk bino-viewers well without slipping...at least at the basement temperatures. It has about 2.5" of total draw tube travel. The draw tube has two internal light baffles. (more on that later). The visual back is OK, with two set screws, 90 degrees apart and secure 2" accessories well. The 1.25" adapter is fine with a single set screw.
The focuser collimation is excellent with the laser beam coming within a mm or so of the mask's center. The beam stayed put when racking the focuser through its entire range of travel. Excellent.
As judged by the reflections off of the back surfaces of the two elements, as seen in my Cheshire "eyepiece", the lens "collimation" was is quite literally "spot on". As you see in the picture, the element reflections fall right on top of each other. Impressive!
I have to say, this is outstanding mechanical build, especially for the money.
One thing I have noticed is that this sample seems to have basically a "zero" sized fully illuminated FOV, meaning the light baffles internal to the focuser and main tube allows only a fully illuminated "point" at focus, not a fully illuminated circle, at least with a two inch diagonal. Now the aperture is only slowly masked as you move off of the center axis, but I find that a little disappointing, considering my main reason for getting this scope is for wide field, low power viewing and one of the advantages of a refractor is the ability to make it so that you can have a pretty hefty fully illuminated FOV. .Fortunately, as I'm going to keep this scope, I will either remove and/or reposition the internal baffling to open up the fully illuminated FOV (but I suspect the inner diameter of the focuser draw tube will be the ultimate "choke point" for the size of the field illumination. Repositioning the baffles will also let me see the full aperture during DPAC, and yes, I've already had a peak at that.....which is why I'm keeping the scope....but more on that later too.