Joined: 01 Aug 2006
Location: Richland, Washington State, USA
|Posted: Sun Aug 13, 2017 11:17 pm Post subject:
|Normally I agree with Enrico's assessments.
But in this case, I think the review at http://savazzi.net/photography/wormscrew_stage.html closes on a note that is far too negative.
What that page says, at this moment, is:
|All this, however, is made useless by a single poorly designed part (the half-nut that engages the wormscrew) that causes a backlash of about 1 mm, far too much for the intended use in macrophotography. |
I just now tested my units (two, purchased as a pair), and in contrast to Enrico's assessment I find them to be completely adequate for low mag focus stacking, much more in line with the reports by other users at http://www.photomacrography.net/forum/viewtopic.php?p=203280#203280.
My test was to set up vertical, with a Canon T1i and MP-E 65 hanging off it, and shoot a focus stack at 2X, f/5.6, focus step 0.1 mm. The results can be seen at http://www.photomacrography.net/forum/viewtopic.php?t=35024 .
Wanting to be quick and lazy about the actual stepping, I first attached a larger knob, made by drilling and filing a piece of plywood to make a loose press fit, then wrapping the rail's knob in tape and epoxying the plywood to the tape. I also made a paper guide with dots corresponding to 0.05 mm movement.
As for backlash and stick-and-slip, I did experience both of those on reversal of rail movement. I did not observe stick-and-slip during one-way movement. For focus stacking I make movements in one direction only, so the backlash is not a problem for me. As an experiment, I tried focusing precisely, wide open at 5X, and found that I had no trouble doing that by approaching carefully from one direction. This has also been required for all other worm drives that I've used, so no surprises there. The backlash on my unit was much less than 1 mm, more like 0.2 mm (4 dots on my dial) in the area that I was testing. The device is certainly not as comfortable as a micrometer driven slide or a microscope focus block, but on the other hand it's a cheap and easy off-the-shelf solution.
This is not high tech, and I don't expect it to be. My "intended use" is to model what somebody might try to do with a $60 rail that they can buy from Amazon, use as is out of the box, and maybe make some simple DIY improvement to.
Based on my own experience, I will have no trouble recommending this rail to other people in that market class.