Minor pundit, major pain, conservative community activist, author, Christian and Texan, I believe all we can take with us is our character.
Telescope eyepieces are responsible for focusing the enlarged image from the main tube of your telescope on the back of your eyeball. The the image made by an objective lens or telescope primary mirror is enlarged in the main tube and projects it to the eyepiece. And eyepiece can either increase or decrease the size of the image. Eyepieces can widen widen your field of view or improve detail of the object in the scope's field of view.
You can often find surplus lenses online or in military surplus stores or online websites. There some quite good lenses lying around loose online. I got lucky and got a whole box of labeled loose lenses. In choosing lenses for your eyepiece remember these two things:
- The greater the magnification, the dimmer the image becomes.
- Higher magnification also reduces the quality of the image due to air turbulence, flaws in the objective or movement of the telescope.
Here's what you need for this project:
- 1 – Telescope eyepiece lens kit from a surplus optics supplier or lens manufacturer
- 1 – two inch OD PVC pipe
- 1 – two inch PVC pipe endcap
- PVC glue and cleaner
- Fine tooth small hacksaw
- Epoxy Glue
- Thin cardboard strips
- Black electrical tape
Constructing the eyepiece tube
If you're going to build your lens, go with a 1-1/2" to 2" eyepiece. The larger lenses are much easier on the eyes. You might be able to find a smaller .965" focuser, but the larger ones are better on your eyes. Watch eBay and if you're patient, you'll probably find one. Just be patient. If you're going to build a telescope, build one with some power. It took me three years but I was able to pull together enough stuff for a 6" Dobson for not very much at one time. For this first time project stick with two lens designs. Then all you have to do is cut the tube and eyepiece end (PVC joint) to the correct focal length. You'll need a book on telescope-building or a website with information on how to calculate lens focal lengths. It's not hard but too much to explain here.
There are numerous telescope building websites out there. Check the spacing of the lenses for each eyepiece design. From the surplus lenses I found I had lens sets for a Super Plossl, a Huygens, a Kellner and a Newtonian. It even came with correct focal lengths. Check the requirements for your lens elements to help you determine the length your eyepiece tube needs to be. This information may come with the lens set or design you use or you can get the info from a variety of websites (see references below). The kit, if you use one, should also tell you which lens goes on top and which on the inside of the tube. Good eyepiece kits come with two or more lenses. Multiple lenses reduce color aberations and rainbowing. Fewer lenses, however, increase the brightness of the image. You should start with a simpler 2 lens kit.
Cut the tube to the proper length you have calculated for your two lenses. Blacken the inside of the tube. You can do that with spray paint or a large black marker to reduce stray light bouncing around inside the tube. Blacken the inside of the endcap too to absorb light.
If you are using a PVC tube, clean one end of the open tube with purple PVC cleaner. Spread a little glue around the end of the pipe with PVC glue. Let the glue set for 4 hours.
If you want to use a copper tube like I did with a couple of lenses you can end-cap it with the PVC cap. Allow to set for 2 hours. If you use copper tube, You can seal it with PVC cement and duct tape.
Mounting the Lenses
With your drill, bore a hole in the center of the endcap the same diameter as the outside lens of the set (the one closest to your eye. The hole needs to be a little bit bigger than the lens. That way you can easily slip the lens into place.Run the drill bit back and forth till the hole is large enough. You can glue or add tape to help the lens set in the hole. I used electrical tape wrapped around the outside of the lens. Once slipped into place you can put adhesive around the edges to set the lenses securely.
Another way to seat the lens is to cut a quarter inch wide strip of thin cardboard to sufficient length that matches the circumference of the inside of the hole you just drilled. You should be able to trial fit the cardboard inside the hole and set it so that the lens can be slipped inside the cardboard and sits centered in the hole, pressing lightly against the edge of the hole. Test fit the lens inside the cardboard strip to make sure that the lens fits snugly into the cardboard sleeve inside the hole in the endcap. You may have to enlarge the drilled hole a few times till the lens and its cardboard sleeve fits snugly into the hole in the endcap.
Superglue actually helped secure the cardboard sleeve strip in a couple of the lenses I made. It bonded to the pvc and to the cardboard sleeve inside of the endcap hole. I like to let the lens assemblies set for an hour. When it's set, hold the lens with a soft linen cloth to protect it from stray oils and adhesives. Very carefully, slip the lens into the cardboard sleeve. Once the lens is seated, apply 3 small drops of superglue evenly spaced around the edge of the lens. Be very careful. I applied the superglue with a drop on the end of toothpick. Just don't get superglue on the surface of the lens.
Here's the tape method for the lens on the inside of the tube. Lay a long strip of black electrical tape out on a flat surface flat up on a table. Turn the lens vertical and starting at one end, carefully roll the edge of the inside lens along the strip of tape. You probably want to wear soft gloves or finger cots when handling the lens at this point. As you roll the lens, let the tape wrap around the outside edge of the lens. Do not touch the lens with the sticky side of the tape except at the edges. Roll up enough tape around the lens to make a tube of tape with the lens in the middle. The tube should fit snugly inside the PVC eyepiece tube at the open end opposite the endcap. Push the tape and lens assembly up inside the tube so that the inside lens is where it should be in relation to the outside one according to the focal length you calculated. The black tape should be entirely inside the eyepiece tube.
Now you get to test your handiwork. Slide the eyepiece into the focuser and try it out. If you found some good surplus lenses, you will have made a stunningly good objective for your scope. .
If you've got a 1.25 inch focuser, You can also use it for an objective. Just drill holes in both ends and mount the lenses. If you can only obtain a smaller .965 focuser and buy an adapter that allows you to use a 1.25" objective. This allows you to use your nice big lens with so you can use your larger lenses with a smaller scope.
For more frequent lens work, you should buy a pair of soft linen gloves for handling the lenses. You want to keep the oils on your hands off of your lenses. Buy a pair of soft linen gloves to use when handling lenses during assembly.
On-line optical surplus companies often carry surplus assortments of lenses. That will be a deal worth hunting for. Many surplus optics places package low cost lens kits for 10 to 30 dollars. The one I found came with complete instructions and specs for the optics. I could have spent dozens of hours and hundreds of dollars collecting these lens sets but some kindly surplus company put together lenses for 4 very fine objectives. All I had to do was mount them in the appropriate size tubes.
A small amount of glue is all that's necessary to seat the lens. Use a toothpick end to carry the tiny drop to it's place.
Do not drip superglue on the lenses or you'll ruin them.eyepieces.html
- Homemade eyepieces, finder scope, and other misc accessories -
- Scope Making Net http://www.scopemaking.net/
- The Frugal Telescope Maker - http://homepage.mac.com/astronomyteacher/documents/buildatelescope.pdf
- Larry Brown: Homemade Astronomy - http://homemadeastronomy.com/
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