In my continuing (and almost Arthurian) quest to find a 3x Barlow that meets my particular requirements I may have found the grail, or at least struck gold. Well, black and gold. The ‘BST StarGuider 4-Element 3x Deluxe Apochromatic Barlow’ often retails around £70. Although I got mine twenty quid cheaper, which is slightly ironic. A few years ago I bought the 2x (3-element) version for over £80 from Astroshop. It has ‘Omegon’ written on it, but although I didn’t know it at the time, it was made or distributed by BST. These can now be purchased as a ‘BST StarGuider’ in the UK for nearly half of what I paid. I believe the 2x, 3x and 5x versions of these Barlows are sold under a variety of brand names.
The 2x version is surprisingly good and was perfect for use in a diagonal. In fact I’ve always rated it very highly. I make the 3x version an acceptable 149 grams in weight and 99mm tall.
Which is a whole 19mm taller than the 2x. However the 3x barrel is a few millimetres shorter at about 30mm. By my reckoning there is 22mm of clear
The unit itself has a quadruplet optical structure as opposed to the triplet 2x BST Barlow. Unlike the 2x there is a barrel undercut.
I was initially concerned about four elements as I would have preferred less, although producing a short 3x Barlow with three elements or less seems to be problematic to original equipment manufacturers. I’m guessing that you just can’t change the laws of physics! I assume the StarGuider is more of a conventional Barlow than a four element amplifier. The unit is aesthetically attractive, mostly painted black with a gold stripe.
I experienced no snagging with the undercut when it was placed into an adapter with a compression ring. It held the Celestron zoom easily and securely. On the night I first tested it there were no clouds but the overall seeing wasn’t very good. With my modified ST80 I started off viewing as many double stars as I could between 50x and 150x.
As far as I could tell the 3x StarGuider revealed little or no chromatic aberration and ε Boo B was easily perceived this time. The binary companion to ε Boo A (Izar) is a hydrogen-fusing dwarf about twice the size of the Sun and separated from Izar by under three arc seconds. I had difficulty splitting these with the
The BST 3x StarGuider may not quite be the Holy Grail of Barlows, but it has a little magic all of its own.