Homemade Solar Finder Scopes

I've made a couple of homemade solar finder scopes in the past and have written about them here in this blog.  I made two additional solar finder scopes over the past few days out of unused parts for two reasons...  first, I could always use an extra solar finder scope for a second or third telescope, and second, we have an upcoming solar eclipse and I plan to have a few telescopes set up for viewing that day.  

The upcoming solar eclipse has prompted me to jump on this little project just in case the weather is good enough for us to view the eclipse (which still does not look promising).  I plan to have a few telescopes in the backyard so that a few people can view at the same time and there really should be a finder scope on each telescope to make pointing the telescope at the sun much easier.  You'd think it would be easy pointing a telescope at the bright sun but the sun is so blindly bright that this usually becomes an exercise in frustration. 

I've had two small 30mm nighttime finder scopes sitting in a drawer, never used, for many years.  These 30mm finder scopes are so small that they are virtually useless for any adult...  well, useless for any average-sized adult.  These tiny finder scopes are better suited for children.  Besides, these are the type of finder scope that you view 'straight-through' which means you need to contort your neck and body in painful ways to get a glimpse upward toward the sky and through these tiny scopes.  Then, because they are so small, it is almost impossible for an adult-sized eye to see through the scope.  As nighttime finder scopes, these two scopes were useless to me so it was time to redesign them and repurpose them.

I decided to remove all the lenses in each finder scope and convert them to rather basic solar finder scopes.  For this type of finder scope, there is no need to place your eye on the solar finder scope so the size of these scopes is not a problem.  There is no need for lenses in this type of finder scope either.  This is a very passive design that you simply utilize from a distance.  

My plan was to remove the front objective lens from each of these finder scopes and replace the lens with a metal disk with a small hole drilled in the center.  The sunlight would stream through this tiny hole and then be projected on the rear end of the scope as an illuminated dot.  I cut these two disks out of some sheet metal...

I now had to figure out how to get this metal disk to fit where a lens that was about twenty times its thickness fit perfectly.  In the end, I used some flexible styrene sheet cut into an eighth inch strip to use as a spacer.  This worked just fine and it was easy to make. This styrene spacer was wrapped along the outside of the inside of the tube.  It was then held in place by tightening down a threaded ring.

I also created a 30mm diameter bullseye on my computer and printed it on yellow paper.  The paper was thin enough that the light from the sun would be projected onto this bullseye at the rear end of each of the finder scopes and still be visible on the backside of the paper...  

I sanded each metal disk and then spray painted them with a flat black paint to cut down on reflections.  In the photo below, you can see one of the styrene spacers at the right.  This flat spacer is flexible so it was easy to bend into position berween the flange holding the metal disk inside the front element tube and the threaded ring that previously held the lens in place...

Below is the painted metal disk installed inside the front end of the solar finder scope...

This next photo is a photo looking through the open rear end of the scope toward the metal disk at the front of the scope.  The sunlight will stream through that sharp small hole projecting a dot of light on the rear bullseye...

Here is a shot of both scopes in their mounts.  These mounts fit in the standard Synta finder shoe found on virtually every telescope...

Adapting the rear end of these finder scopes was a bit more time consuming and difficult.  Each scope had a series of lenses inside the rear end as a permanent eyepiece.  This eyepiece part that threaded onto the tube here was a far smaller diameter than the main tube.  This rear eyepiece part was probably less than 20mm in diameter and I had no use for something that small.  

I didn't want the rear end of the scope to be smaller than the front end so I cut this smaller part off saving the threaded end and then sanded the exposed lip smooth where I had made the cut.   I needed this threaded part because it would hold the rear projection screen in place.  

I used yellow paper for the projection screen and sandwiched it between stiff clear plastic.  I needed to make some sort of stop for in front of these rear projection screens to keep this bullseye sandwich of parts from falling into the tube which required some fabrication.  That was definitely the most time consuming part of this project.  These finder scopes were not identical so I needed a different plan for each but I designed a solution for each and successfully assembled each solar finder scope...

It was snowing all day today and is still snowing outside but, the moment I finished assembling these finder scopes, the clouds opened a bit so I was able to test them.  Here is a photo of the sun illuminating the rear projection screen right in the center of the bullseye...

The great thing about these solar finder scopes is they were made from parts I had lying around.  These little 30mm finder scopes seem to come with most telescopes so, every time I purchase a new telescope, I end up with one of these useless finder scopes.  I have now turned these useless finder scopes into useful solar finder scopes!

I only worked on these for about an hour each day.  I'm still recovering from COVID and long-COVID will continue to linger for a few more months, at least, so I don't have much energy.  I putter around for about an hour and then I need to lie down.  I usually will pass out for about three or four hours afterward.  Fortunately, this was a small project that didn't require a whole lot of energy.  It was more about time than energy and I seem to have plenty of time...  well...  most of my time is spent sleeping but I have a little bit of spare time after sleep!

My right leg is still quite weak but it hasn't buckled out from under me over the past day or two so that is good.  I still have pain in this nerve down my leg but I'm doing a bit of light physical therapy every day to get back to walking again.  This physical therapy is definitely helping to alleviate the pain and build up strength in my leg again.  My leg is so weak that I cannot drive.  I can't handle being in a car longer than about ten minutes anyway due to all of the bumpy potholes that seem to trigger my mast cell disease as well as cause pain throughout my spine.  

So, I'm still home looking for some small projects to accomplish each day.  This was a great little project and I'm pretty satisfied with the results!