About two weeks ago, I ordered one of the super-cheap "30X" triplet loupes on ebay for less than $2 shipped (see photo on right). 30X should be 8.3mm (FL = 250mm / magnification, for magnifiers). It came a couple of days ago. To my disappointment, it has turned out to be about 8X (looking on amazon reviews of similar products, this isn't uncommon), i.e., about 31mm. Handheld in my F/4 8" (not the ideal test-bed for this eyepiece!) and pointed at Jupiter it showed significant CA on axis (but it was hard to keep on axis, so I can't swear that the CA was on-axis). I did see one cloud belt, which is about all I can see with that scope. I also tried it on the Double Cluster, and it looked OK, but the AFOV was low.
Today, I used the lens it in a Spenser microscope (just placed it right on top of the eyepiece tube). There it came into its own. I compared it to the Leitz 10X eyepiece (I don't know of what variety) that the microscope came with. The magnification of the triplet was slightly lower. AFOV was about the same, maybe around 30 degrees. Eye-relief was huge (which isn't a plus for me--I like short eye-relief eyepieces). But what was really impressive was the vibrant color and on-axis detail, both significantly better than the Leitz 10X. Despite the magnification being slightly smaller, I could see detail better. The sharpness dropped off significantly in the last 30% of the field. (Visually, the image was much sharper than in this photo, and the usable area bigger.)
Reading Amazon reviews of similar products led me to the following hypothesis. There are two very-similar loupes being sold out of Asia, both marketed as 30X triplets with 21mm diameter lenses. One variety has "TRIPLET 30X21mm" stamped on it, and it actually is a 30X. The other variety has "30X21mm" stamped on it, and it is close to 10X. It is, nonetheless, a nice piece of glass, but only 10X. (The seller is refunding me my $2.)
Friday night, for $6 shipped, I ordered one of the ones stamped "Triplet" from a US seller whose ebay ads warn against being duped by competitors. The seller avers that his are genuine 30X triplets, and based on an email exchanges with him, I am inclined to trust him (after all, if it's not 30X, he'll have to refund the money, and if he doesn't I'll put in a paypal claim). I should be getting mine in a couple of days, and will report. I am not posting a link until I've actually tried out the lens.
If that fails, I know a third loupe vendor, out of Canada, who has actually had his optometrist test his 30X Hastings triplets, and found that they are not only 30X, but have AR coatings on one of the surfaces. He sells them for $22.
When it comes, my plan is to bore out a 1.25" dowel and stick the 30X lens in. If it works out, I might even sell a few super-homemade (and not filter-threaded) hardwood triplet eyepieces for some very low price. Or at least give them away to friends. :-)