and procedures for using one instrument to help align another. I believe there is a way you can look from the instrument you want to align through the objective lens of another instrument to see the second instrument's cross hairs. Obviously you have to light the target instrument, etc.
But how far apart do you set the instruments? How much light is needed? etc etc
Thanks for your help.
One industrial metrology procedure is to focus the first instrument's optics at infinity, project its crosshairs towards a second instrument, also focused at infinity, and align the hairs. Note that this procedure only parallelizes the pointings of the two instruments; the optics and centerlines are not necessarily coincident.
To put them on the same line, you would need to interpose (at the midpoint) some kind of two-sided target and iteratively translate and re-sight one (or both, depending what you're doing) of your instruments.
The "jig transit" was commonly used in these procedures.
Kissam's Optical Tooling goes into this quite a bit.
That's my basically my understanding of what happens. My question more specifically is how to make it work. What I am trying to make happen is some very simple directions that I have that go something like:
- Focus a T3 at infinity
- Light it from the backside
- Point at the T4
- Look through the T4 to find the cross hairs in the T3.
Well, that sounds simple enough so I set up the instruments, did as directed, except that I couldn't find the T3 crosshairs when looking through the T4.
Not Sure It Is A Trick
Are you thinking of the use of an optical instrument as a collimating target as in the DIN18723 specs?
In that case you would need multiple instruments scattered about a circle.
By looking into the objective end of an instrument the observer's eye on the instrument being calibrated is tricked into thinking it is seeing a very distant target.
That test requires multiple pedestals for forced centering of all the equipment.
Paul in PA
> That's my basically my understanding of what happens. My question more specifically is how to make it work. What I am trying to make happen is some very simple directions that I have that go something like:
>
> - Focus a T3 at infinity
>
> - Light it from the backside
>
> - Point at the T4
>
> - Look through the T4 to find the cross hairs in the T3.
>
> Well, that sounds simple enough so I set up the instruments, did as directed, except that I couldn't find the T3 crosshairs when looking through the T4.
I've only personally done auto-collimation with Keuffel and Esser (K+E) jig transits. They have a special port between the eyepiece and the rest of the optics, about 1/4" diameter, that I could stick a small LED into. This projected the hairs outward, but still allowed me to simultaneously use the eyepiece, which is necessary for auto-collimating.
Also, I've only done this at a distance of about 10m at most, indoors, in a lab simulating the conditions of an industrial metrology context.
I'm not sure on the capabilities of the T3 and T4 to be operated this way... however, I'll outline a procedure that may or may not be useful to you:
Set up T3 and T4 about 10m apart.
Set up a tripod, tribrach and prism support/stem (but no prism), and place it roughly on line.
Set it to be more gooder on line. If you've got some kind of target that is visible from two sides and is a point (inverted prism pole, maybe).
(Need two people for this next bit)
Dial the T3 all the way out to infinity.
Aside: The optics for the K+E jig I used could actually focus PAST infinity (Buzz Lightyear, anyone?), meaning any light rays it projected would diverge, since optics focused at infinity = parallel light rays. What we had to do was dial out to the extent of the focusing knob, and then slowly bring it back to infinity. We knew we were at infinity because the blob of light resolved to a second set of cross hairs. Since we were auto-collimating, we were only worried about one set of optics and a mirror. You're working with two sets of optics that both need to be at infinity, I think.
I would propose an annoying process of one operator turning the focus 30min, waits while the other operator runs from one end of the focus knob to the other and back, and then turns another 30min or some such. I would suggest that, but boy does that sound, tiring.
Oh, here's a neat paper I just came across that might be useful to you:
http://turbolab.tamu.edu/proc/turboproc/T3/T3pg17-22.pdf
Wish I knew the date of publication for that baby.
Best of luck.
Thank you very much for this information. May be that I wasn't far enough apart. I was much closer based on seeing pictures of instrument adjustment set-ups where things were much closer.
I'll give it a try by spreading out.
We use auto levels on stands with a stand half-way between the two. A white night light bulb behind the reticle of the auto level illuminates the crosshairs. The objective lens is turned toward the instrument you are checking. An elevating stand is useful for getting the trunion axis height very near the same as the vertical center of the optics of the level.
I am describing what I have observed in our shop. I do not go near any piece of equipment with a screw driver. My main experience as a mechanic is on farm machinery.
I think the issue may also be that the minimum focus distance of the Wild T-4 is around 100 yards/ 300 feet.... the T-3 will need to be at least that far away from the T-4 to be used in a collimation-mode for alignment.
When calibrating the T-4 at Wild they used targets on other buildings around the Wild complex for calibration.
> and procedures for using one instrument to help align another. I believe there is a way you can look from the instrument you want to align through the objective lens of another instrument to see the second instrument's cross hairs. Obviously you have to light the target instrument, etc.
>
> But how far apart do you set the instruments? How much light is needed? etc etc
>
> Thanks for your help.
hello Dave,
if remember correctly the procedure is to first position something approximately half way between the instruments and set them both to focus at this halfway distance. then turn both instruments to look through the others objective lens. operator A moves out of the way while operator B aligns with the crosshairs of the vacated instrument. then operator B vacates while operator A aligns with B's crosshairs. this iterative procedure is repeated till neither instrument needs be aligned further.
you may need to provide some kind of light source through the eyepiece of the instrument being sighted if the ambient lighting requires it. i believe i may have used a bright torch behind a white piece of paper when i did it but this is almost 2 decades ago now (this detail may have been invented!)
