But I think positive, this means I can compare them and the QC/reproducibility. Then I will duly return one,
Interestingly neither of the focuses started exactly at the low zero points, but both stopped precisely at the high zero. The focuser is 43mm long with a 10mm adjustment.
As shown one was 0.3mm past the low zero, and one was 0.45mm beyond. These numbers were to continue to have an effect; as when you reversed the direction of movement the ’play’ before movement was noticed was identical. In addition, the one with the most play also was noticeably stiffer when returned to a clockwise motion from counter-clockwise.
To be fair both were smooth in motion, and I’m sure the stiffness felt on one would relax with use. I then screwed down the offset screw to see if the rotation locked, it did, but the screw needs tightening hard to secure the barrel (otherwise the ’play’ was again evident).
As a practical test, I focused on the brickwork of the house next door (our weather was dire this weekend). I noted the reading, and then rotated the ring fully in one direction and then back (twice over). After this I focused the brickwork without reference to the scale. Both were spot on in the repeatability of the reading when focus was achieved. I found this a bit surprising; so I repeated the process reversing the direction of the rotation (high to low rather that low to high). I got the same result; it seems that the play is cancelled out whichever way you turn the ring. Good result.
Note on the adapters; both types capitively screw on at both ends, the effect of this is that the scale finishes up wherever the two threads tighten, it would be nice if there was a retainer with a free ring. To be fair this is a cost-saving I understand, given that the units are under £30. Be sure to tighten the adapter thread hard onto the focuser body, otherwise the rotation of the ring can undo the adapter.
The 0.05 precision quoted simply means that the ring is etched every half 0.1mm. This is specification fodder 0.1 etched marks would be fine, as most helical focusers have.
For the cost the focser works just fine, and is secure enough to hold a camera behind it. I'm pleased with them and for my use they are fine.
Again withthe plural; well it just so happens that the male
I would recommend the focuser, given the cost/performance ratio.