I've been thinking about this option for awhile now as I'm chasing that millimeter accuracy in setting up the instrument over a control point. I was wondering if a pefectly calibrated Leica tribrach (professional 5000 series) with an optical plummet would give me the rigidity and centering repeatability I am looking for. I find the laser plummet too bright in lower lighting conditions even at the lowest power setting and the reflections around the center of mag-nail are really confusing as to where exactly that laser dot is located. I started marking the center of the nail with?ÿ a black?ÿ marker and painting the rest of the nail with orange spray paint to reduce those unwanted reflections, but the result was just slightly better than the unpainted nail.?ÿ
Has anyone here tried this setup - optical plummet on a laser plummet instrument??ÿ
Thank you for your input.?ÿ
I haven't tried it, but I would expect the fit between alidade and tribrach would be good given the provenance of GeoMax guns.?ÿ You'd lose the ability to check plumb by rotating the alidade, but other than that I expect it'd work.
I'm not a big fan of the laser plummet either.?ÿ I carry a white card in my vest pocket that I use to check centering.?ÿ Swiping the card across the point multiple times (it's easier to do than to describe) lets me see its position better than just eyeballing it while standing up.?ÿ This means that I usually have to crouch down a couple of times per setup as I shift the gun around, which I wouldn't have to do with an optical plummet.
On the other hand, setting up over a monument in a deep hole is one place that a laser plummet really shines (pun intended).
I have been using a combination of optical and laser plummets for years.?ÿ I find the laser plummet useful in many situations.?ÿ I use the GDF321 which comes sans plummet combined with either the instrument's laser plummet, a GZR103 carrier with optical plummet or a SNLL121 precision carrier with laser plummet.?ÿ That way I can choose the best plummet for the situation.?ÿ All have the same plummet accuracy of 0.5 mm while the SNLL121 has a prism centering accuracy of 0.3 mm vs the standard carrier accuracy of 1.0 mm.?ÿ The SNLL121 is great but they come with a hefty price tag and in my experience have a pretty significant failure rate.?ÿ I have four or five dead ones ($6K) sitting on the self.?ÿ Either the lasers or the switch dies and you have to replace both which costs almost the same as buying new.?ÿ As for the reflection, I have found that if you move the laser plummet around until the reflections come together that corresponds to the optical plummet.?ÿ Also, if needed I spray the whole mag nail head with paint it works better.?ÿ What you are really trying to do is dull the reflection on the center dimple of the nail.?ÿ
The latest robot I own (Leica 1205+) came with an optical tribrach even though the laser was alive and well. I've used plenty of optical plummet instruments over the years, but never any tribrachs so equipped. I find it harder to sight through than an instrument body mounted OP. It's lower down (not much) and fixed, so rotating is more problematic. And the latter, to me, seems to be the biggest problem. I used to remind myself every week or so to check the OP after setting up and leveling by rotating thru 360 while trying to keep my eye attached to it. With a laser, I can do that much easier with practically every set up.
I know what you're saying about the Mag nail reflection, but again, I spin the gun around a few times to check the laser wobble outside the dimple and that usually solves the centering issue. The only down side with the laser is setting over an open pin/pipe and trying to center it. I've been carrying a plastic cap from an OJ/milk carton in my pouch for these occasions and they fit 1/2" pipe quite well. Even have a dimple centered on the top.
@beartow
Nice hack with the OJ cap.?ÿ If I'm going to use a pipe as a control point or double tie it I usually slam a ginney in it.
@john-putnam Tks, these also seem to work on stuff around 3/4". Don't know what to call them, snap caps? They have a nub on the underside which I shove an ice pick thru to make something akin to a re-rod cap.
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I have my Zoom 90 with an optical plummet and absolutely love it. Best thing about it is that I can just pop the gun off and leave the tribrach, replumb over the point and replace it with a stem and prism after I??m done with the setup. I suggest carrying a flashlight on you though as it can be difficult to sight the center of a point in dark areas. I usually just use my flashlight on my phone and prop it on my tape measure when it??s too dark. Other than that, I won??t go back to a laser plummet until my eyes are shot.
I have had the idea that a nice way to run things would be tribrachs with no plummet, simple adapters with no plummet, one of these plummets for setting out prisms and I suppose the instrument if you do not like or are unsatisfied with the laser.
Tribrachs with fixed optical plummets are a pain in the behind in my opinion. Using a jig to check or the old pencil on the tripod head show is tired.
