Instructables

Making Solar Filters for Telescopes

Picture of Making  Solar Filters  for Telescopes
Table of contents:

Introduction. Inspired by a storm warning.
step 1 Materials.
step 2 Score pieces of scrap glass.
step 3 Separate the pieces.
step 4 When you get good, switch to the mirror.
step 5 Conclusion.
Comments



There is no license. The reader can use this information as they wish.

Introduction;

Early in 2010, some NASA scientists predicted a solar storm to occur in 2012 or 2013. I decided to make a solar filter for my telescope and monitor solar activity. And, I thought, why not make notes and pictures to post on the web so everyone else can do the same.

I wanted a circular filter, a filter that I could mount to a screw-in front lens cap that came with my telescope.. so I started by studying an old October 1965 Popular Mechanics article on glass cutting called “All You Need To Know About Cutting Glass” by Walter E. Burton. Then, I set about working out a method and practicing with what I had on hand.

I didn’t want to use eyepiece projection because all that light and resulting heat is concentrated in the eyepiece. I had read that eyepieces can be damaged by the heat, with cemented lenses burning. I also didn’t want to use any eyepiece solar filters because there is said to be a danger of them cracking from the heat.

Here is a picture of the completed filter mounted on the telescope.

 
Remove these adsRemove these ads by Signing Up

Step 1: Materials:

Picture of Materials:
Photo A shows some of the tools you will need.

1. Piece of wood, plastic, or metal to use as a beam.
2. A “C” clamp to hold the glass cutter in place.
3. A suction cup to anchor the beam to the glass.
4. A nail or wire to connect the beam to the suction cup.
5. A set of milk crates or other platform to work on.
6. A piece of suitable “leaky” mirror.

Other than a great treatise on how to cut glass circles, this is just the worst way to go about getting a solar filter on your telescope.

1] Mirrors of any kind, especially "leaky" ones, do not make good solar filters. In fact, they can be extremely dangerous as they can allow damaging amounts of IR and/or UV that will cause permanent damage not immediately detectable.

2] The lip of the mount is insufficient to securely hold this design. You have no time to react when (not if) it falls off. Permanent blindness will result immediately if you are looking in the eyepiece. when it happens.

You only have two eyes. Is destroying one of them worth less than the $20 - $100 you save by using scrap material? Do a bit of research regarding home built filters before even thinking about building one along these lines.

If you need a solar filter, buy one from a reputable source (Thousand Oaks, Baader, Astronomics Celestron, Meade).

Search the web for "Solar viewing safety". Here's a few to start:
http://eclipse.gsfc.nasa.gov/SEhelp/safety2.html
http://tinyurl.com/solar-filter-safety
http://astronomyonline.org/solarsystem/solarsafety.asp

I know of what I speak and I associate with those who taught me:
http://tinyurl.com/gmartin-asem
http://www.slasonline.org
http://www.asemonline.org
ShutterBugger (author)  gmartin20001 year ago
The filters on the Astronomy Online link are leaky mirrors. The filters I have seen for sale are either leaky mirrors or screw on ND filters for the eyepiece.
~Bob~
The filters at that link are not "leaky mirrors". They are not even mirrors. They are specially designed and manufactured filters solely for solar viewing with a telescope.

You can get anything online. Wether or not it is any good is for an expert to determine.

A warning to anyone wanting to observe the sun with a telescope: Consult your local astronomy club before buying or building a solar filter. Do not use eyepiece filters under any conditions and be very suspicious of anything not sold by a legitimate outlet catering specifically to the field of astronomical observing.

The last word: You only have two eyes. Do you really want to risk one of them on something you found here or on ebay that has not been approved by an expert? Follow my links previously posted.
ShutterBugger (author)  gmartin20001 year ago
A leaky mirror is a semi-transparent mirror, consisting of a sub strait like glass, with a metal evaporated onto the surface. The metallic coating reflects most of the light, while admitting only a small amount. For telescopes, chromium is often used because it gives a yellow image of the sun.

The Astronomy Online site has a photo of leaky mirrors, one of which is on binoculars. These photos are toward the bottom of the page. The Baader Planetariums AstroSolarTM safety film referenced is a leaky mirror.

The main problem with making your own is that most of the mirrors I have found do not block nearly enough light and makers may not test the transmission to make sure the mirror is safe.

I recommend these filters for, say, long exposure pictures of busy streets to get that abandoned look.
~Bob~
Nirgal382 years ago
Have you tested this for UV transmission? It may only transmit as much visible light as your commercial solar filter but UV can be really damaging contributing to cataracts and retinal damage.

When it comes to your eyesight, it's always a good idea to err on the side of caution.
ShutterBugger (author)  Nirgal382 years ago
This did worry me because the image of the sun is very blue. I added a dark red glass filter at the egepiece to block UV. I have not tested the combination for UV transmission.
~Bob~
vishalapr2 years ago
Rated 5*!!Awsome ible and amazing photo quality!
Have a look at my latest ibles!
Pro

Get More Out of Instructables

Already have an Account?

close

PDF Downloads
As a Pro member, you will gain access to download any Instructable in the PDF format. You also have the ability to customize your PDF download.

Upgrade to Pro today!