Comparison scale test of a DIY Barlow lens made from the elements of a cheap Praktica 2x teleconverter (compared to a Prime focus image).
The central lens cell was simply unscrewed from the teleconverter barrel mount and slid into a 35mm film canister (with the end cut off). The film canister fits an empty 1.25" barrel/extension tube, or empty Barlow lens.
This DIY project is a lot cheaper than buying an expensive 3-4 element Barlow lens, and produce better images than standard 2 element lenses.
Telescope Buying Guide: Barlow Eyepiece
Barlow eyepieces for telescopes are sold in different magnification factors. Find out about a Barlow eyepiece for a telescope in this free video on home astronomy from a telescope salesperson.
3x Compact Barlow Lens This 'achromatic' Barlow lens supposedly fits onto the end of an eyepiece (with 30x1mm thread eyepiece barrels) to increase the image magnification by 3x.An unstated fact is that it uses just one (small) simple lens rather than a conventional double lens achromat - with 'multiple broadband green coatings' limiting the effects of chromatic aberration. The reality is that the image still suffers badly from chromatic aberration.
Price: £9.99The price seems tempting, but it is not worth paying anything for this Barlow lens - the best place for it is the Laurentian Abyssal Plain.The bottom line is that we must give this Barlow a wide berth.Web Link
SkyWatcher 2x De-Luxe Achromatic Barlow Lens£29.99A Barlow lens in 1.25" for doubling the magnification of your existing eyepieces.Includes a T thread allowing T rings to attach directly to this Barlow for imaging with DSLR cameras."The barlow did a good job on our test subjects, which also included the Moon and Venus as well as our deep-sky objects... This barlow lens certainly performs well at its main job of doubling the magnification of an eyepiece, and what's more it is also the cheapest in the test" - BBC Sky at Night Magazine
Ed ~ A little tip is to blacken the lenses edge with a permanent black marker to increase image contrast. Unscrew the black front lens holder from the silver barrel and with a fingernail unscrew the internal locking ring. Disassemble with care, and note which way the cemented two lens are positioned. Apply the ink marker carefully, and in stages, to make sure it does not bleed between the lenses. Reassemble.
The 2X Barlow black front lens holder can also be screwed directly to your eyepiece to increase the magnification by 1.5X
Meade 2x Apochromatic Barlow Lens: The most advanced Barlow lens yet developed for commercial telescopes, the Meade #140 2x Apochromatic Barlow includes a 3-element, air-spaced telenegative lens unmatched in image resolution, contrast, and colour correction.
The Barlow lens, named for its creator, the English engineer Peter Barlow, is a diverging lens which, used in series with other optics in an optical system, increases the effective focal ratio of an optical system as perceived by all components after it in the system. The practical result is that inserting a Barlow lens magnifies the image.