Is 0mm or -30mm a better prism offset?
I think 0mm is probably the worst one to use. It results in the most dramatic movement of the nodal point if misaligned. Apparently 17mm or 40mm is the best, neither of which I have ever used. I believe Leica has done some extensive research and that is where they came up with 23.1 or whatever they use.
Is 0mm or -30mm a better prism offset?
Side shot, those 2 bright spots you see in the Leica 360 prism represent 2 different heights depending upon which side is facing the gun. When you need critical elevation for the point, you want one of the arrows pointing directly to the gun, or if you are behind the robot looking back at the gun you want a flat face looking at you which would put the arrow on the other side pointing the gun.
The difference is 0.03' between the two in elevation!! Try it and see.
Yes, we found out the hard way on this one.
John
Is 0mm or -30mm a better prism offset?
Side Shot: Is the offset between your camera flash(emitter) and lense(receiver) creating the double bright spot? I'm guessing the coincident emitter/receiver on the Leica wouldn't "see" the double reflection? I'm assuming the emitter/receiver are coincident on the Leica.
Is 0mm or -30mm a better prism offset?
Yes , those 2 bright spots were from the flash on the camera.
Surprised me that the prism reflected 2 spots.
Exactly what the gun would focus in on is anyone's guess.
Maybe the Leica knows better ?
Hit or miss I suppose, but kind of makes one not want to use
the 360 prism for anything beyond rough topo shots.
So using a 17.5mm nodal prism removes all doubts as to what
the gun is shooting.
Is 0mm or -30mm a better prism offset?
John
You are correct about pointing the arrows on an original Leica
360 prism toward the gun. Using the arrows I believe Leica claims
2mm of error and not using the arrows may result in 5mm of error.
This is with the older Leica GRZ4 360 prism. Leica's newer
GRZ121 360 prism claims 2mm error at any angle.
Leica's GRZ101 mini 360 prism claims 1.5mm error but $600+ for one
is hard to justify when I consider that I don't believe the robot
can track them very well and would only be useful for close in
stakeouts at which point I just use a 17.5mm nodal prism.
It gets even worse than 0.03' for the error from the 360 prism when
in closer than 100 ft and at steep vertical angles.
360 prisms are great for rough topo but anything critical best to
use round prisms and preferably nodal prisms whether 17.5mm or 40mm
Is 0mm or -30mm a better prism offset?
Good looking setup. What you mentioned about switching prisms is a best practice, but I would be reasonably comfortable using the 360 once I trained myself to orient via the yellow triangles on important shots.
Is 0mm or -30mm a better prism offset?
I've been using 0mm for a long time - no confusion on instrument or DC settings. Use the prism target for sighting, and point the prism correctly - no problems.
We've used -30mm in the past, and saw all kinds of different combinations of settings in the instrument and DC's, "fixed" by the crew chiefs.
