Trimble S6 - autolock collimation

As I understand the procedure: it's automatic. You just start it and it does it's thing. The cross hairs won't center on the target, it's the way it works. If it is way off it could be there is something behind the prism which is either confusing it or grabbing it away, something reflective.

There is a procedure where you manually aim, I do 10 in Face1 and 10 in Face 2 at 100 meters or more plus the trunnion at something like 60' to a steeper sight, a bolt on the arm of a power pole works for that.

exbert, post: 329847, member: 6143 wrote: Anybody have any advice for collimating the autolock via the data collector? I tried to do it today, but got stuck while trying to aim the crosshairs at the target. The instrument won't let me turn the vertical angle up to the center of the prism. It keeps locking down below. I tried turning autolock off before doing the process and it automatically turned it back on. I tried taking the battery out of the MT1000. I tried standard mode and tracking mode. It will not let me move the crosshairs to where I want them to be. I know this all sounds whacky. Anybody else been through this and discovered a trick? Thanks in advance. (I do know that the instrument looks a little off the center of the prism in active tracking, but this S6 is looking way too low)

Yes just let it lock in Autolock, it won't let you move the crosshair. It can then turn face 2 and calculate it's autolock offset to apply internally. This is the difference you see between the cross-hair and the target it is locking on to.

I would always do this calibration with a full size circular prism and make sure there are no other reflective objects (eg prisms) anywhere near.

I do not have an EDM with autolock...
But I have heard about the sighting of cross-hairs problem...
why would the cross-hairs not be centered on the prism....?
does it effect the location / position of what is being sighted?
Please ...
no manufactures technical jargon...

My understanding of the situation is this -

When a non electronic theodolite is made I imagine the cross-hairs need to be physically aligned to the right place by sighting face left face right and adjusting by mechanical means. This will form part of the calibration procedure very year I also imagine.

On an electronic theodolite / total station this can be done without mechanical adjustment, the software simply adjusts the displayed angle by the offset given by the calibration procedure.

With a Trimble autolock instrument (not sure how Leica and others handle this) there will be another separate autolock offset. The autolock does not use the cross-hairs but rather some kind of sensor, a CCD I think. This will not be perfectly aligned to the corss-haris or anything else, not to the required accuracy.
As before - rather than mechanically aligning it, the software can calculate the offset by face left/face right measurements and apply it to the displayed angle. The offset for the autolock sensor will not necessarily be the same as the one for the cross-hair so this gives rise to the cross-hair not being co-incident to the centre of the prism when in autolock mode.

The instrument is not using the cross-hair.

All of the above can be checked and verified by sighting a prism in autolock mode then manually. (after calibration !)

The autolock calibration does not put the crosshairs in the middle of the prism, as others have stated. If you then do a manual sighting with the crosshairs, the angles will be consistent, in other words the difference between autolock sighting and manual sighting (i.e. turn autolock off, manually point) is very small, not discernible.