MnAstro Forums

Hi all,

I have the 10" Dob MAS loaner scope. I can't quite figure out how to use the telrad. Can anyone provide some advice on this?

Thanks!

....well... basically, the outer circle is 4 deg full width on sky, mid circle 2 deg, and inner circle is half deg equal to 30 arc minutes on the sky when viewed from a foot or two directly behind the open end of the 45 deg angle plexiglass heads-up display. Check the batteries inside are ok. Remember to turn the switch down so you can see the stars and off at the end to avoid new batteries every time. The circles can be made to scale on mylar etc for a set of star charts so you can see how the visible stars should lie on the Telrad red circles for a particular charted object. Does this help and make sense? More questions? ...if so, ok ask....

Greetings,

In addition you need to make sure the Telrad is lined up with what you are actually looking at.

1. Pick something really easy for you to identify - such as a bright star, really bright nebulae, the tip of a neighbors rooftop (the farther away the better, to avoid inaccurate alignment due to parallax), a far off water tower or radio tower (easier in the day).

2. Find the object in the eyepiece of the telescope.

3. Using the three knobs on the back of the Telrad that are in a pyramid configuration, adjust the bullseye to match what's in the eyepiece.

Hope this helps.

-matt

When I turn the Telrad on, I can see the circles, but can't see anything in the background. Do you have to do anything beside put it on the scope and turn it on, e.g. open the end of it, etc...? I don't see how one is able to see the stars in the background.

Thanks!

Just hold it up to the sky for now. Make sure the end with the three little adjustment knobs is facing you, and look through the 45 degree slanted window from behind the Telrad. Your sightline will be parallel to the length of the Telrad. You should see the three circles superimposed on the background. This works best at night because the three circles get washed out in the bright lights of the daytime.

Try it against a distant bright star or small light source. The little window does darken the distant object somewhat. If you have one of those flip-up dewshield covers make sure it is flipped up so it doesn't cover the window. You have to be able to see through the 45 degree slanted window. You can keep both eyes open, with one eye looking through the window and the other eye looking past the Telrad directly at the distant object if it helps you.

You may need to turn down the intensity of the red circles as they can get to be much brighter than the stars and wash them out so it is hard to see them. Also, with some practice you can keep both eyes open and let your brain do the superimposing.

After you get the hang of it, mount the Telrad on your scope and you can use the three little knobs to adjust it to align the target circles of the Telrad with the view of your scope. Center your scope on a distant, easily recognizable star or light, and then adjust the three little knobs to put that object in the middle of the smallest circle in the Telrad.

Good luck. The Telrad is the best invention since canned beer.

Bill Kocken

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I hear ya. I'm not a Telrad-guy myself for I think maybe the same reason. In practice out in the field in the dark the 45 degree sloped plastic you're looking at the stars through definitely weakens the stars, and that doesn't count for its tendency to attract dew/frost.

My theory is that the theoretical way to use it is with BOTH eyes with no convergence of the eyes on the close focus on the circles. Hard to explain. Both eyes looking at infinity stars with one eye looking through the circles and the other eye looking alongside the Telrad hood, both eyes wide open.

Perception then should be fuzzy out of focus circles on sharp stars in sky. But this takes practice, and I use telrads only when I need to (looking through them and dealing with stars disappearing by reaching up and turning the circle intensity off to see the stars and on weak to check position, off to move scope position, on to check star position).

I find it quickest to start by having circles full-bright so I can find the right eye position behind the telrad which is sometimes difficult. Then turn down intensity, and then on-and-off circles and wide field eypiece in scope unitl target is located successfully. But better skill than mine with telrads is sure possible and after using a telrad for a while you very well might love them.

So, mount the telrad with the 45degree piece high open end toward the mirror end of scope. Collimate the Newt scope, then align the telrad (unsing the 3 little screws with the eyepiece view of the scope so they're pointing at the same thing, and you're good to go, I guess.... Is this making more sense now?

---Tom
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I will go out and try it.