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Introduction
Even if you own a very inexpensive reflecting telescope, it probably has instructions for "collimation" - aligning the primary and secondary mirrors for best image quality. What the manufacturer probably did not include was any sort of "sight tube" or "collimation eyepiece". A sight tube assists you in keeping your eye centered while looking in the focuser so that you can easily collimate the mirrors. And yes….YOUR scope DOES need to be collimated. I check mine every single time I use it.
This web page will not address how to collimate your scope. There will be some links to collimation info at the end - and we plan to create a collimation instruction page in the near future. Rather, this page will show you how to make your own collimation eyepiece for almost zero cost. This tool can get you by until you can afford commercially made collimation tools - or forever if you have an inexpensive long F-ratio scope (F8-10).
No, this little plastic gem is not intended to replace a full set of fine commercial collimation tools - but it may be just the thing for owners of inexpensive scopes - and for seasoned veterans who find themselves miles from the nearest set of Tectron's.
Parts:
- 1 - 35mm Plastic Film Canister
Get a black or brown one….not a clear one. Kodak seems to put thier film in black canisters.
If you don't buy film often - try the local 1 hour photo store. They probably have billions
of canisters they are trying to get rid of.
Tools:
- X-acto Knife
- Drill
- 1/16" Drill Bit
- 1/8" Drill Bit
Construction
USE EYE PROTECTION! JUST DO IT!
Making this thing is super easy. I have made several in the field with a Swiss Army knife. Just follow the steps below, using the pictures above as a reference.
- Drill the Hole
Take the cap off of the film canister and discard it. Stand the canister upright so you are looking at the closed end. There is usually a small nib in the exact center left over from the plastic molding equipment. Carefully remove the nib with your knife (or a finger nail!) Use the 1/16" bit and drill a hole in the exact center of the canister. Be careful to hold the drill square to get a straight hole. You may be tempted to just turn the bit in your fingers because the plastic is so soft - but use the drill - you will get a much cleaner hole. If there are any burrs left after drilling, very carefully trim them away with your knife.
- Remove the Rim
Use an X-acto knife to cut off the rim where the cap snapped on. Make this edge as straight as possible - but don't spend the rest of your life on it.
- Test It
Put the canister in your focuser with the bottom end with the hole you just drilled facing out and tighten the set screw. Be careful to keep the canister from sliding all the way in to the tube. Point your scope at an even light source - like a brightly lit wall or the daylight sky. (MAKE SURE IT'S NOT POINTED AT THE SUN!) Look through the hole in the canister. You should be able to see the entire surface and outside edge of the secondary mirror. If you cannot see the entire secondary, re-drill the hole with the larger 1/8" bit. This is most likely necessary if you have a very tall focuser. Don't make the hole bigger than 1/8", as this would defeat the purpose of using a sight tube.
- USE IT!
See these links for collimation info:
Tips
- You can wind a few wraps of black electrical tape around the canister to prevent it from slipping too far into the focuser.
- An alternate design is to drill a hole in the cap and cut off the bottom end. This makes a cleaner looking sight tube and has the added advantage of not falling down the focuser. Just be careful to cut the bottom off straight, as you will not have the rim as a guide. Also, cut the entire bottom off - don't just drill a hole - or you will severely limit the field of view and the amount of light you have to work with.
- The hole needs to be in the exact center and needs to be round. If you drill off center or end up with an oval hole, throw it away and start over. Film canisters are cheap!
- You are not out of luck if you have a .965" focuser like those found on "department store" telescopes. I have had good luck using just the cap from a film canister. Drill a hole in the exact center of the cap and tape it on top of the focuser by wrapping it with masking tape - being careful to center the cap on top of the focuser.
- A very professional looking sight tube can be made for both 1.25" focusers and .965" focusers by removing the lenses from the shortest focal length eyepiece you got with your telescope. No - don't destroy a good eyepiece - but most department store scopes come with a useless 4mm eyepiece made with very tiny lenses. These eyepieces are usually of poor manufacture and design - and they give way too much magnification to be useful. Unscrew bottom of the eyepiece and drop out the lenses. Reassemble the eyepiece without any glass - and you have a great looking sight tube designed fit your scope!
Questions, Comments, Accolades, & Death Threats
May be sent to cosmicone@lymax.com.
Disclaimer
This information is provided free of charge and is probably worth precisely what you paid for it. If you build one of these devices, it is likely that it will fly apart and kill everyone within 5 blocks. Construct and use at your own risk.
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