An occasional solar, but even long before GPS almost everything would be tied to state plane.
We do a lot of night work for urban topo, but our instruments are set up to do that.
OK. Here's the Mark III GLOWSURV Back Sight
Could you simplify things but just having say a red 3mm led viewed directly. That way you'd also have a height reference as you're sighting a 3mm red dot.
LED direct illumination
> Could you simplify things but just having say a red 3mm led viewed directly. That way you'd also have a height reference as you're sighting a 3mm red dot.
"Been there; done that" as the saying goes. I've tried LED's, both micro grain round ones, and vertically aligned rectangular.The one I tried is about 2mm wide and 5mm high. See here:
I've found there are two "problems" with this approach. Of course a tiny terrestrial light is often recommended for azimuth backlights when doing astro..."a distant radio tower" etc. but finding a tiny LED locally at your backlight location is not as easy as finding some larger target, within which is the target center (the "V" or tip of a cone, as in previous examples).
The other "problem" is that, unless you have reticle illumination, this just about won't work at all. You need to place the cross hair, which is black, in front of a lighter target. A tiny LED is so small that you can rarely see it until you're upon it. Granted, illuminated reticles help with this, but it's certainly easier to find a billboard, in the middle of which is what you're looking for, so to speak.
In addition, I've found that a lamp of any description (LED, incandescent), creates bloom because to be bright enough to see from a distance, it needs a pin point source of very bright light, which creates bloom. My first examples photographed earlier in the thread, show bloom because of the photograph. In the dark, they're actually quite bloomless.
And finally (since we're kicking this horse around far more than I thought we ever would 🙂 , one of my design parameters is compact and robust...something that can be pulled out of a bag, turned on, slipped into the tribrach (or screwed on), and that's it. It doesn't want to be prone to scratching when thrown in a field bag.
I'm envisioning an extremely compact, solid tube that has a high resolution, bloomless "V" target within, as well as illumination built in.. Stay tuned.
We have a problem, Houston!
So I ventured out again this evening...a crystal clear (yet arctic) night. I used the Mark IIIb, which had a Mag "Solitare" flashlight, embedded in it, illuminating the cone at the top.
The brightness was great (at first), then as dusk fell, it kept getting dimmer. Hmmm. Maybe I could call this a feature rather than a bug! It was actually fine until my third round, which was well before Nautical Twilight, when....Nada; Zip. Lights out.
One AAA alkaline battery at 10 degrees F for an hour will not do it.
Back to the drawing board.
Also, note to self: Talk to the professor who wrote the lesson plan to do astro shots when it's single digits out.:pissed:
We have a problem, Houston!
That's actually not a problem in Houston. You'll figure it out, you, or we (however this is working out) have all winter.
We have a problem, Houston!
The low tech alternative? I'm reminded of the 'goose' type paraffin lanterns we used on grass airstrips at night, no cables or batteries to go wrong.
We have a problem, Houston!
The voltage needed to light a LED varies quite a bit with the design and color. I haven't played with a recent crop of them, but I'm sort of surprised you got it to light on one cell of about 1.2 or 1.3 volts. The LED is operating well below its nominal current. Current is a very sensitive function of voltage if you don't have a series resistor. A two-cell battery without a resistor might blow it out.
So if it was drawing a fraction of its current and barely lighting with 1.2 volts at room temperature, a very slight decrease in voltage when cold will be expected to have a serious impact on the current and brightness.
You might have better luck with an old-fashioned carbon-zinc AAA cell(if you can find one these days, recognizable by lack of mentioning any other chemistry), since its room-temperature voltage is more like 1.5 V. You will need a series resistor to set the current at a safe and desirable level. Or go back to multiple alkaline cells with the appropriate resistor.
A possibly useful link:
http://dangerousprototypes.com/docs/Basic_Light_Emitting_Diode_guide
Oops...My bad
> The voltage needed to light a LED varies quite a bit with the design and color.
Thanks for all the LED info. I neglected to mention that this Mag light Solitare flashlight does not use an LED...it's an old fashioned tiny bulb...not sure what kind (Xenon)?
At any rate, your comments are excellent. The final design will almost certainly be LED, with a larger battery, for use in cold weather.
Oops...My bad
In case you have a small prism, you may want to also experiment with using a retro-relector as the target, illuminated by a light source at the instrument. Those work great over long distances. Sweeping the horizon with a flashlight will get a return flash from the prism, even at ranges well over a mile. A small prism lighted with the reflected light from small penlight source might work at much shorter ranges. The obvious advantage is that the intensity of the light can be adjusted if it is at hand rather than at the target.
Use the no-battery approach
Although the lux emissions drop with ambient temperature, they last longer in cold weather. Warming them above 40 degrees F before activation helps.
Instrument that emits out a 'Lumi Guide'
My Nikon 821 has a Lumi Guide.
I have used that brilliantly in the night time.
I did a GIS pickup for vegetation types a few years back and the pole was about 1200 meters away and it shone like cats eyes when the instrument was turned to it.
They really are very good and I have found them accurate for the type of work I'd do at night.
Once the telescope is pointed at the prism the prism is actually good to sight to.
Not sure how many instruments have such a feature?
I like the idea of a light stick and can see its advantages.
I'm curious how much that sort of a light would 'bleed' into the surrounds. I think others indicated similar.
When you get old and your vision is not as focused as it could be and other eye related issues come into play those lights can get a flare that others with younger and less issues with eyes don't see.
Oops...My bad
> In case you have a small prism, you may want to also experiment with using a retro-relector as the target, illuminated by a light source at the instrument. Those work great over long distances. Sweeping the horizon with a flashlight will get a return flash from the prism, even at ranges well over a mile. A small prism lighted with the reflected light from small penlight source might work at much shorter ranges. The obvious advantage is that the intensity of the light can be adjusted if it is at hand rather than at the target.
I've tried illuminating the prism from about 150'. Here's the problem: Unless the light is coaxial to the instrument (collimated), as is the edm beam, the reflected light is "off target" by the center to center distance between the light and the telescope.
While it can illuminate the apex of the prism even so offset, it's still not that easy to ignore the center of the light and shoot the apex.
Finally, my prisms are not nodal, so depending on the care of the set up, it may introduce a small pointing error; I may be striving for unreachable precision, but, given the choice, I'd prefer to not introduce ANY source of error that can be avoided with other approaches.
Finally, unless I rig a mount for the light on the instrument, this would be a pain in the butt to hold while shooting a precise back sight. Just sayin'.
Use the no-battery approach
> cyalume night sticks
>
> Although the lux emissions drop with ambient temperature, they last longer in cold weather. Warming them above 40 degrees F before activation helps.
I'm liking this. They're cheap enough and easy to deploy. It's got me thinking back to using them as just a light source for my standard target...could tape it on very close to the "V", and you're done. They also might work as the target themselves, but that's more messing with masking the V target on them. The ones you link to though are only .250" diameter, so it might not take much to get a shot to the center. Loom might still be an issue, but we'll see. I have some coming; stay tuned.
You just shine a regular flashlight on your backsight - no big deal.
> Yes, indeed, folks. It's here: The Mark II Glowsurv Back Sight. Ready 24/7/365. For those Astro sights, or just for your second and third shifts to keep the income rolling at night.
>
> Tribrach ready; runs on (3) triple A's for 10 hours+ of operations. No more field parties coming back to the office at 1700 hrs claiming "waning light"!
>
I usually use darkness as an excuse to go home, but fog is a real problem. I would be interested in seeing how this works with fog. The light would have to be much brighter than when simply working in the dark.
They make stroboscopic back sights
> I would be interested in seeing how this works with fog. The light would have to be much brighter than when simply working in the dark.
My final version (The Mark VI)
Well, after much additional testing at single digit temps, I've decided on this:
http://www.lifegear.com/glow-sticks-1/glow-stick 
These things are cheap ($5). I replace the whistle top with the free polyethylene caulking tips that come with an adhesive we use around here. Finally, I've made a tiny inverted "V" target at top, but this really isn't needed at distances greater than 250' because you can easily center the reticle on the 3mm+/- tip of the unit.
The unit uses three cheap LR44 "watch" batteries, and lasts a long long time in 10 degree weather (I left it on for two hours and it's still way bright enough). It also flashes, lol, with a push of a button, lol. Oh, and if you lift it out of the Tribrach, there's a flashlight on the other end! Handy for setting the bubbles on the tribrach in total darkness LOL.
I'll still explore direct lighting of a proper Prism target with the Cyalume sticks when they come Wednesday, but I'm calling this a wrap.
Besides, I've got to go to work on my EL (ElectroLuminescent) Wire Suspended Plumb Bob.:-D
For all you "old timers"
I know, I said I was done with this thread, but I couldn't resist this one more....
"Hey Dude! Where'd the Back Sight Go?....OH!....Wooooooowwwwww! That's pretty!"
