This barlow arrived about 2 weeks ago but last night was my first opportunity to use it. I purchased it specifically to use with my 5mm Pentax XO, which then becomes a 4mm. But I also wanted to test it on a 10mm, which becomes an 8mm. It arrived in a nice little red box with two soft plastic caps.
It is nicely made and compact at 1" (26mm) long and has standard filter threads to screw into the barrel of an eyepiece. Vernonscope makes two models, a 1.5x and the 1.25x, and each of them is produced with either Brandon specific filter threads or standard filter threads... I chose standard threads for use on more of my eyepieces. Ironically, I cannot use it on my Chester Brandons which are very old and have no threads at all. The attached photo includes a UO HD 6mm for size comparison.
Using a TEC 140 and a Zeiss Prism Baader diagonal with the 5mm Pentax and Dakin 1.25x seemed quite satisfactory. Targets were Luna, Jupiter, the F-star in the Trapezium and double stars Zeta (2.5" sep), 32 (1.1"), and 52 (1.2") in Orion. Seeing was not the best and atmospheric moisture was obvious, but the image through the Pentax with the Dakin attached held up quite well and appeared to be at least equal to a UO 4mm Ortho. I'll have to wait for steadier seeing to give it a fair test though.
Attaching the Dakin to a 7mm RG ortho, UO 9mm ortho, and a UO 18mm ortho, provided satisfactory results. The field appeared very sharp on axis with little softening at the very edge.
Wide field eyepiece performance was good on axis, but dropped as the EOF approached. With a 20mm RG (Erfle), stars in focus on axis soften at about 70-75% from center, and the edge was obviously distorted. No seagulls... but bloated stars
I then attached it to a 10mm Ethos (making it an 8mm) and found that on axis was fine, sharp and clear, but softening started about 50% out from center and increased significantly to the edge. I don't think the Dakin was really made for a wide field eyepiece, since it is a barlow... light rays exiting it's lens are divergent. BUT on axis it was fine. So next time there is a clear, steady sky, I'll attach it to a 4.7 Ethos making it 3.7mm and look for a good target to put in the center of field.
I'll keep this little barlow for now, specifically for the Pentax XO, making the eyepiece serve double duty at 5mm and 4mm. I'd be interested to hear results from anyone else who has used one of these compact Dakin Barlows.