No, its not too late
I like it. [msg=207201]The innocent but deadly art of Two Lath[/msg]!
Kent,
What brand and model of prism pole tripod do you use? I like the idea of being able to rotate the prism pole within the tripod assembly to check the adjustment of the bubble.
Al
> What brand and model of prism pole tripod do you use? I like the idea of being able to rotate the prism pole within the tripod assembly to check the adjustment of the bubble.
Al, I have always used SECO prism pole tripods. My favorite SECO tripod is one of their earlier models that is no longer made, but the newer ones are serviceable. The one bit of advice I have is based on discovering the last time I bought some replacement tripods from SECO that they were selling them with only two quick-release legs and one with a thumbscrew lock. I bought three tripods and traded out the quick-release legs on one for the thumbscrew lock legs on the other.
In my opinion, having all quick-release legs is just easier and worth the small extra money. Some of my SECO prism pole tripods are now 25 years old and working great.
Thanks, Kent.
So, to check the bubble as you describe, you first set up the tripod so the bubble is centered. And then, you have to slightly loosen the clamp that holds the tripod to the pole?
Al
> So, to check the bubble as you describe, you first set up the tripod so the bubble is centered. And then, you have to slightly loosen the clamp that holds the tripod to the pole?
The old Seco tripods have a split ring made of some kind of hard but somewhat flexible plastic that encircles the pole. The thumbscrew bears upon the outside of this ring, decreasing the diameter of its inner circumference and thus securing the pole. Slightly loosening the thumbscrew allows the pole to rotate within the ring pretty smoothly. I'm not sure how well this works with the new models in which the thumbscrew pushes the pole directly against a V-shaped bracket.
> I'm not sure how well this works with the new models in which the thumbscrew pushes the pole directly against a V-shaped bracket.
It works best on the new-style tripod if the head of the tripod is fairly level. That is accomplished by a somewhat different setup procedure than the older SECO prism pole tripod with the split Delprin bushing in a swivel joint (a better design as long as you're using only one diameter of pole). Using the new-style tripod, you clamp the head to the tripod and plumb the pole with the vial as you release the legs. This is why having three quick-release legs is an improvement, in my opinion.
How does that work?
I roughly plumb the pole, push the two buttons so two legs drop, plant them while pushing the buttons, release the third leg but leave the thumb screw loose, fine plumb the pole then tighten the third leg thumb screw.
Thanks for all the responses, Jim, Kent and Dave.
I think I understand more about how this would work in practice. Aside from traditional instrument tripods, I have only limited experience with tripods designed to incorporate a center pole. I have a 2 meter constant height GPS pole/tripod made by Hixon that involves some of the same setup procedures. Though, I have to say, it has been my experience that once three legs are down, it becomes tricky to complete the setup, leaving all three legs firmly embedded in the soil, and the bubbles centered.
> I roughly plumb the pole, push the two buttons so two legs drop, plant them while pushing the buttons, release the third leg but leave the thumb screw loose, fine plumb the pole then tighten the third leg thumb screw.
Well, as long as the tripod head is approximately level, it shouldn't be a problem. If the head is too far off level, the pole tends to get pulled to perpendicular with the head when the clamp screw is tightened and that will pull the pole point off the ground mark if you're not careful. As far as the set up, I follow the same procedure you do, i.e. watching level on the pole while stamping in the feet of a leg, one at a time, and then doing any touch-ups on the setup after all three are stamped in and the pole is rotated to check the bubble, clamping the pole in the tripod as a last step (and verifying that the damn point didn't get pulled off the ground mark).
The earlier SECO prism pole tripod with the Delprin bushing in the tripod head making a swivel joint was easier and more forgiving of out-of-level tripod head, and so was easier to set up in my experience. On the other hand, if the pole was dirty, the Delprin bushing was a problem and the new design both accommodates different pole diameters and doesn't care about mud and muck on the pole tip.
> I have a 2 meter constant height GPS pole/tripod made by Hixon that involves some of the same setup procedures. Though, I have to say, it has been my experience that once three legs are down, it becomes tricky to complete the setup, leaving all three legs firmly embedded in the soil, and the bubbles centered.
These require a somewhat different setup approach because the center pole is fixed to the tripod head. My technique is to set the point on the mark, release one of the legs (on the Seco models I own, the leg with the thumbscrew) and place it approximately where you want it. Then place the two quick-release lets in position, holding the release down while pressing in the foot of each. Press the thumbscrew foot in while the thumbscrew remains loose. Using the two quick-release legs, plumb the pole, then finally tighten the thumbscrew.
The trick with all of these "tripods" -- they're actually quadripods once set up -- is to minimize the stress between the legs produced by having 4 fixed points of contact rather than 3. If there's too much tension between legs, the point is liable to lift off the mark and settle in a position that results in the least interleg tension.
Excellent description. Thanks, Jim.