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Mini prism  

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Jim Frame
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I'm a big fan of the Leica GMP101.  Small, light, accurate and I routinely get over 1,000' robotically.  On the one I use the most I cut off the portion of the target that sticks out beyond the frame in order to allow me to get the prism closer to building corners and the like.

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lukenz
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I'm curious if you've had any tracking problems to the gmp101 in wet conditions?  The prism in use didn't have the rubber hood they supply them with but not sure that would have kept much rain off.

 

Demo'd a Zoom90 and while traversing a shower came through, enough for small drops on prism and I got some 0.04m tracking errors using atr on a couple of shots. Backsight was 250m, foresight 200m. Was doing the traverse in three separate jobs hence I could prove tracking error.  Not seen that sort of issue with the standard gph/got circular ones.

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party chef
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@jim-frame

I assume that you know the target plate is removable.

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Jim Frame
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@party-chef

I do, but removing the plate changes the offset, and I want all my minis to have the same 17.5mm offset.

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party chef
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@jim-frame

Check a little closer, the housing is offset to accommodate the plate, removing it will not change the offset.

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party chef
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I like to have the full size for running control, for distance, but mainly poor conditions, fog, dust etc.

Sure do hate being able to see the glass but not shoot until the fog burns off.

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Jim Frame
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Posted by: @party-chef

Check a little closer, the housing is offset to accommodate the plate, removing it will not change the offset.

I stand corrected.  I certainly removed the plate to saw it off, and I find it hard to believe that I was so inobservant as not to see the step in the housing, but the only thing I can figure now (about 9 years after the fact) is that I wanted the bottom part of the plate in place to make adjusting the prism angle with my thumb easier.

t

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dms330
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Posted by: @jim-frame

but the only thing I can figure now (about 9 years after the fact) is that I wanted the bottom part of the plate in place to make adjusting the prism angle with my thumb easier.

I'll buy that Wink  

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Norman Oklahoma
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Soooo...... Following up.

I took delivery of a Trimble S5 last week and bought a pair of Leica GMP101 mini-prisms, from Allen Precision, to use with it. They arrived last week and are extremely nice.  I also bought 5/8" thread to bayonet mount adaptors. Slick.  We used them for the first time on a site survey yesterday and something new, to me, came up. 

The prisms are clearly marked as having a +17.5mm offset. Turns out that is valid only if using them with a Leica instrument  (or, presumably, any of the several Leica derivatives). With any other brand you must subtract 34.4mm from whatever Leica has written. So this +17.5mm is actually a -16.9mm offset when used with my Trimble, or with my old Topcon. 

Conversely, when using non Leica branded prisms with a Leica instrument you must add 34.4mm to the rated offset.  

 

   

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