amicus sidera
Carpal Tunnel
Reged: 10/14/11
Loc: East of the Sun, West of the M...
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Single-stalk teaching and outreach eyepiece
#5170806 - 04/13/12 05:16 PM Attachment (50 downloads)
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One very useful accessory for teaching and public outreach is the single-stalk finder eyepiece, and it seems that I have almost always had one in my field kit over the years. This is nothing more than an ordinary eyepiece of moderate focal length, into the focal plane of which is placed a single straight, thin stalk, extending from the barrel to almost the center of the field of view.
With this eyepiece, and a telescope equipped with a reliable clock drive, all one needs do is center the object of interest at the tip of the stalk... said object, which due to its small size, low contrast or the rich field of stars it is embedded in, might otherwise prove difficult for students or the general public to locate in the eyepiece field, is now easily spotted.
Below is a view through an Edmund RKE 21mm eyepiece that has been so modified:
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amicus sidera
Carpal Tunnel
Reged: 10/14/11
Loc: East of the Sun, West of the M...
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Re: Single-stalk teaching and outreach eyepiece
[Re: amicus sidera]
#5170808 - 04/13/12 05:17 PM Attachment (43 downloads)
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Here is a view showing the underside of the 21mm, with the bottom barrel removed... the thinness of the stalk is quite evident here:
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amicus sidera
Carpal Tunnel
Reged: 10/14/11
Loc: East of the Sun, West of the M...
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Re: Single-stalk teaching and outreach eyepiece
[Re: amicus sidera]
#5170809 - 04/13/12 05:18 PM Attachment (22 downloads)
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35-gauge copper wire was used for the stalk. I secured a little less than a foot of wire in a vise, and stretched it slightly with pliers, which both straightens and work-hardens it. A small section, slightly longer than the distance from the center of the eyepiece to the inside of the barrel, was cut from this piece, as shown below. (The rest of the straightened wire was set aside for possible further use, as one is never assured of success on the first attempt with an operation this delicate.)
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amicus sidera
Carpal Tunnel
Reged: 10/14/11
Loc: East of the Sun, West of the M...
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Re: Single-stalk teaching and outreach eyepiece
[Re: amicus sidera]
#5170810 - 04/13/12 05:18 PM Attachment (26 downloads)
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At this point the wire was bent at a right angle at the point where the length of the long portion would reach from the inside edge of the barrel to almost the center of the field... it was not desired that it should reach dead center, as that is where the objects of interest are to be positioned - the stalk merely acts as a pointer. It had to be the correct length at this stage, as any attempt to shorten it once it was attached to the eyepiece was almost certain to end in failure.
I found that the surest way to accomplish this bend was to lay a small (6") machinist's straight ruler on the long portion of the wire, and carefully lift up the short end with a razor knife until it was vertical and at 90 degrees, with the results as seen below:
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amicus sidera
Carpal Tunnel
Reged: 10/14/11
Loc: East of the Sun, West of the M...
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Re: Single-stalk teaching and outreach eyepiece
[Re: amicus sidera]
#5170812 - 04/13/12 05:19 PM Attachment (26 downloads)
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Now all that remained was for the stalk to be blackened, then attached to the eyepiece.
I used a permanent marker for the blackening, as any type of paint would have been much too thick for the fine wire.
After letting the marker ink dry thoroughly, I placed a drop of adhesive inside the eyepiece barrel, just above the field stop (I have had good results using an adhesive called Gem-Tac, available at craft stores). Then the short end of the stalk was carefully placed into the adhesive via tweezers, which operation, needless to say, requires considerable dexterity and good eyesight!
After positioning the stalk, the adhesive was allowed to partially dry. The stalk's placement was checked again, and then the assembly was allowed to dry thoroughly. At that point, the field stop was threaded back into the eyepiece, and with the field stop in focus, the stalk was moved ever so gently with a toothpick (at its base near the barrel, otherwise force applied to the stalk anywhere along its unsupported length would almost certainly deform it) until it was in perfect focus. The 1-1/4" barrel was threaded back on, and the job was finished.
Below is the stalk and barrel, ready for assembly:
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amicus sidera
Carpal Tunnel
Reged: 10/14/11
Loc: East of the Sun, West of the M...
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Re: Single-stalk teaching and outreach eyepiece
[Re: amicus sidera]
#5170814 - 04/13/12 05:19 PM
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Additionally, if one wishes to make this eyepiece perform double duty as an occulting-bar eyepiece, useful for blocking out the brighter of a pair of double stars, increasing the wire size is all that is needed for accomplishment... I would suggest using 24-gauge or heavier copper wire for this purpose, and applying flat-black paint, thinned if necessary, to reduce any possible glare from the primary.
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amicus sidera
Carpal Tunnel
Reged: 10/14/11
Loc: East of the Sun, West of the M...
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Re: Single-stalk teaching and outreach eyepiece
[Re: amicus sidera]
#5170830 - 04/13/12 05:28 PM Attachment (30 downloads)
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As completed, this is the view one should expect:
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skyward_eyes
Reged: 12/12/06
Loc: California
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Re: Single-stalk teaching and outreach eyepiece
[Re: amicus sidera]
#5171291 - 04/13/12 11:15 PM
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Wow, thats pretty neat actually. I might have to give this a try sometime. Thanks for sharing that!
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davidpitre
Post Laureate
Reged: 05/10/05
Loc: Central Texas
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Re: Single-stalk teaching and outreach eyepiece
[Re: skyward_eyes]
#5171600 - 04/14/12 08:42 AM
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What a wonderful idea. Thanks.
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StarStuff1
Carpal Tunnel
Reged: 04/01/07
Loc: South of the Mason-Dixon Line
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Re: Single-stalk teaching and outreach eyepiece
[Re: davidpitre]
#5171745 - 04/14/12 10:34 AM
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Years ago I bought a used scope. The previous owner had put a home made finder on it made from binocular optics. He had put a needle at the focal plane pretty much as the OP describes. The point of the needle was at the center of the finder FOV. Worked pretty good!
Cool idea to use it for an outreach eyepiece in the main instrument!
Edited by StarStuff1 (04/14/12 10:47 AM)
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Brian Reed
Reged: 10/29/04
Loc: North East Illinois
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Re: Single-stalk teaching and outreach eyepiece
[Re: StarStuff1]
#5172061 - 04/14/12 01:28 PM
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Great Idea! Just added this to my favorite thread list.
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amicus sidera
Carpal Tunnel
Reged: 10/14/11
Loc: East of the Sun, West of the M...
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Re: Single-stalk teaching and outreach eyepiece
[Re: StarStuff1]
#5172577 - 04/14/12 07:18 PM
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Quote:
Starstuff1 wrote:
Years ago I bought a used scope. The previous owner had put a home made finder on it made from binocular optics. He had put a needle at the focal plane pretty much as the OP describes. The point of the needle was at the center of the finder FOV. Worked pretty good!
Cool idea to use it for an outreach eyepiece in the main instrument!
That is a wonderful suggestion! A small, thin sewing needle or pin is an excellent substitute for the thin copper wire used in the example above, which can be difficult to procure in small quantities.
The only caveat that I might offer would be to snip off the point of the needle or pin, so as to leave a flat end that would be more readily seen to stop against the sky background, instead of slowly fading into it and possibly obscuring the object of interest..
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pedrete
member
Reged: 01/05/11
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Re: Single-stalk teaching and outreach eyepiece
[Re: amicus sidera]
#5173569 - 04/15/12 11:56 AM
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It's a wonderful DIY! Thank you for sharing that. 
If it's intended for a showing purpose, I wonder if it would help just to touch the end of the wire with a little bit of fluorescent paint
Best from
Pedro
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Nils Olof Carlin
Pooh-Bah
Reged: 07/26/04
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Re: Single-stalk teaching and outreach eyepiece
[Re: amicus sidera]
#5173965 - 04/15/12 04:03 PM
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One variant of this is to use a sewing needle, with one half of the eye ground away. This way. you have a "fork" to center the star without obstructing it.
(You can even make the cut slanted and illuminate with a LED, and have 2 small, faint illuminated spots, if you would like. You may not bother).
Nils Olof
(the idea is from Sven Rehnlund)
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amicus sidera
Carpal Tunnel
Reged: 10/14/11
Loc: East of the Sun, West of the M...
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Re: Single-stalk teaching and outreach eyepiece
[Re: pedrete]
#5174118 - 04/15/12 06:01 PM
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Quote:
It's a wonderful DIY! Thank you for sharing that.
If it's intended for a showing purpose, I wonder if it would help just to touch the end of the wire with a little bit of fluorescent paint
Best from
Pedro
Pedro, that is an excellent idea!
In a suburban area with some light pollution the stalk will usually show up clearly against the lighter sky background, but from a darker site the slightly-glowing phosphorescent painted tip would be of great help in delineating the end of the stalk.
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amicus sidera
Carpal Tunnel
Reged: 10/14/11
Loc: East of the Sun, West of the M...
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Re: Single-stalk teaching and outreach eyepiece
[Re: Nils Olof Carlin]
#5174127 - 04/15/12 06:07 PM
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Quote:
One variant of this is to use a sewing needle, with one half of the eye ground away. This way. you have a "fork" to center the star without obstructing it.
(You can even make the cut slanted and illuminate with a LED, and have 2 small, faint illuminated spots, if you would like. You may not bother).
Nils Olof
(the idea is from Sven Rehnlund)
Nils, that would work very well, especially with a higher-power eyepiece, I would think... one could even spread the two points apart a little to create a "vee" of sorts. If an LED can be fitted, so much the better!
Wow, so many great ideas by all! I'm very pleased that the information and concept was found useful.
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