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View from a Scope | July 25, 2021

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How to Make a Solar Filter

How to Make a Solar Filter

The summer time is not a great time for stargazing, the nights are very short and the it does not get dark until very late.

However I decided to use this as an opportunity to do some solar gazing.

It is a VERY VERY VERY BAD IDEA to look directly at the sun especially through a telescope. It is for this reason we need to use a solar filter.

Below I will outline the steps to create a solar filter that is safe to use.

Things you will need

Filter film – This is the filter I would recommend (Baader AstroSolar Safety Film ND 5.0)

Sheets of stiff cardboard

Double sided tape

Sticky Tape.

Step 1.

The firs thing we will make is the filter tube, this is the section that slides over the telescope. For this you will need some stiff cardboard.

I got a pack of A4 cardboard from the local newsagents the same stuff that you would use in a printer.

This on its own is to light so I folded it in half and stuck both sides together with double sided tape.


I made 3 of these which was enough to go around my 6″ telescope, you would need to adjust for your own setup.

You could also double up again on these by folding over first and then stacking two folded sides on top of each other, this would give a sturdier tube.

Step 2.

Now the next step is attach these folded sections to your telescope to make the filter tube the correct size to fit over the telescope.

WP_000202Place the first section on the telescope tube as shown and tape this down.

Also be sure to place a strip of double sided tape on each short end of the folded sections. This is to allow the next section to easily stick to the previous.

Once you have the first section on and taped down as shown, place the next section slightly overlapping the previous and make your way around the scope. taping each section down before moving onto the next.WP_000203

This will create a nice ring of cardboard that fits snugly around your telescope.

Once the ring is complete remove the tape sticking it the scope carefully. We need to do one more thing to complete this filter tube.



Step 3.

Now that you have a tube of cardboard that fits snugly over your telescope we should just reinforce it a bit. For this I just used masking tape.


Just work you way around the edges taping them down more with the masking tape. Also it is a good idea to tape the edges of each section down as well.

A word of warning though don’t tape both ends (see in the picture above only the top side is taped) this is to allow some give in the tube to squeeze over the telescope.

Step 4.

Now that we have the tube built, it is time to put together the actual filter. For this we need two flat sheets of stiff cardboard.

You need to cut out an area similar size to the aperture of your telescope on both pieces of cardboard.












Ideally these should be ring shaped but I found it difficult to get that right. But squares should be fine as well.

Step 5

Now we need to sandwich the solar filter between the two pieces of stiff cardboard.

To do this you need to cut the solar filter to the right size. The easiest way to do this is place the filter paper between 2 sheets of normal paper and cut it with a scissors. Something a little larger than the hole you cut in the cardboard would be fine.

Now to create the filter sandwich. Tape a piece of tissue to the table and place the filter paper flat on it.


Put some of the double sided tape on one of the cardboard pieces.WP_000215

Hold that about 10mm over the filter tape and drop it. Be sure to press firmly down.


Now flip this over and place more double sided tape on the other side. The get your other piece of cut cardboard and attach the two together trapping the filter paper between them.


Now we have the two pieces required to make the filter. We just need to join them together.

Step 6.

To join the two pieces together, place the tube over the flat cardboard piece, Run the masking tape around the edges to attach the two together. Use as much as you can you want these two pieces to firmly stuck together.


Step 7.

Once you are sure that both pieces are firmly stuck together it is time to step back and admire your handywork.


Before you use:

Make sure to bring out the filter and look at the sun through it (minus the telescope) You are looking for pinholes in the filter paper or any gaps in the cardboard.

Once you are happy that no sunlight is getting through you are ready to use your filter. Enjoy.

The Easy Way.

The above filter gives you a full aperture view of the sun, however an easier quicker way to create a filter, albeit a far smaller aperture one is to use your dust cap cover.


Tape a small piece of filter paper of the dust cap cover. Then simply put on the dust cover and unscrew the small filter point to get a solar filter view.


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