Y'all may remember the other day I was looking for information on the tricks to using one instrument to align (collimate) another. Well, here's an update.
After some of the suggestions I received, I decided to try it again - that is try to see the cross hairs of the T3 looking through the T4. Set the instruments up about 15' apart. Backlit the T3 with a small flashlight and diffused the light with a paper filter. Aligned them up with each other, looked through the T4, and lo-and-behold, there are the T3 cross hairs. Even did my first check of rotating the T4 eyepiece 90 degrees to make sure the reticles are centered. As close to perfect as I could hope for.
The real trick is to get the T3 focused right at infinity.
Now to let everything settle down, level the instruments carefully, refine the alignment, and start checking things out.
Probably also play around with the intensity of the light behind the T3.
Surveyors let very strange things excite them - Kent's rock piles, Jerry's buried section corners, etc., but this has got my juices flowing!
good stuff, dave. i was afraid it would not work, as the t4 has such a long minimum focus.
i am looking forward to some observations in the next week. i could use my t1a, but the trunnion axis is worn. this creates a horizontal error only if i use the vertical circle lock. fortunately, there is enough friction in the instrument's axis that i do not have to use the lock normally. the other option is the t2, which is in fantastic working condition. it has slimmer crosshairs than most t2's and an inverted image, so it is MUCH harder to do night work with it.
what do you think i should use?
Congrats, that's pretty outstanding!
I'd use the T2. Do some practice with it and we'll go back to Corbin next year and do a better job. I'll take my T3, but I'll also take the T4.
I'm going to get you some info soon (I hope) on the auto-collimation eyepiece on your T2.
Also, once you get used to the inverted image it's not a big deal.
> I'd use the T2. Do some practice with it and we'll go back to Corbin next year and do a better job. I'll take my T3, but I'll also take the T4.
>
> I'm going to get you some info soon (I hope) on the auto-collimation eyepiece on your T2.
>
> Also, once you get used to the inverted image it's not a big deal.
thanks dave. tricky thing for me is the combination of the very thin crosshairs with the inverted image at night. sometimes the star crosses my crosshair line, and i do not notice. end up wasting a minute before i realize i need to turn in front of it and wait for another observation opportunity. maybe i just need a bit of practice
Eddie,
Mike H here, Are you using a lighting attachment that gets those crosshairs visible?
Dave... good work. Now I have to try something similar with a pair of T-3s that I have in the basement. Thanks for sticking with it and working it out. Dumb question maybe but now that you can do it...Is this the best way to get them collimated?
Is this the best way - that I'm not sure. But the advantage is that I'm doing this indoors under controlled conditions. I did my T3 indoors just by sighting on fine targets because you can focus the T3 right on down to a few feet. I did it at 20'. I've got the T3 so that I can repeatedly turn horz or vert angles to less than 2" and most of the time sub-second. And at 20' that's pretty fine shooting.
The T4 presents problems because you can't focus close. It's designed to be used at infinity, although you can focus down to a couple hundred yards. What that means is that without a collimating target, you have to do it outdoors and deal with all the associated elements.
By using the T3 as a collimating device, you trick the T4 into thinking it is looking at infinity so you can see the cross hairs of the T3 clearly.
I do know that instrument shops have set-ups so that they can do things indoors. There's a set-up on eBay now that I'll post a link to in a minute so you can see what one looks like.
Here's the eBay link:
http://www.ebay.com/itm/3-TUBE-COLLIMATOR-/230900939458?pt=LH_DefaultDomain_0&hash=item35c2c4bac2
And here's a pic of the device:
mike and dave...
> Eddie,
>
> Mike H here, Are you using a lighting attachment that gets those crosshairs visible?
> Dave... good work. Now I have to try something similar with a pair of T-3s that I have in the basement. Thanks for sticking with it and working it out. Dumb question maybe but now that you can do it...Is this the best way to get them collimated?
hi mike,
no light kits for now. i simply use some small led type keychain lights