Instructables
Earlier on this year we had a partial solar eclipse that was viewable from the UK. Luckily it was cloudy as I couldn't find any of those cardboard glasses or figure out how to safely photograph the eclipse. This did, however, start me on a journey to try and figure out a cheap and easy way to safely view solar events. I remember a long time back there was a transit of Venus, which was cool also.

Searching on the web revealed that you could buy a nifty folding viewer with a lens and a mirror that projected the image onto a white sheet for safe viewing. The cardboard version was £45 which I thought was ridiculous so I set out to make my own. I started researching and pretty soon realised that a pin-hole was the ideal lens for this job. It's simple to make and cuts out an awful lot of light!

This is a bit of a free-form instructable as I'm still experimenting and changing things around to get things better. But the bottom line is that I can totally safely and fairly comfortably observe the sun, so my main objective has been met. I think so far I've spent less than £5 on materials, and most of that was in the "I'm sure I've got one somewhere but can't find it right now" category!
 
Remove these adsRemove these ads by Signing Up
So if I have a longer box and a slightly larger pinhole, I can make a larger image? I am thinking a 2 meter box and 1.9 mm hole . We just received a 6-foot carton in the mail.

I am sorry if this seems obvious - it has been a dozen years since college physics.
Grahamwithimps (author)  CatTrampoline2 years ago
I've just run the maths and yes, 1.9 seems to work for a 2m focal length!

Good luck!

Graham
Thanks. Sadly, we had clouds at sunset so I did not get to see even the partial eclipse as the sun was setting.

There is supposed to be a partial view of a transit of Venus here in 3 weeks, so I can try for that as well as look for sunspots.
This is perfect! We are supposed to have a partial solar eclipse here this weekend and I need a viewer I can throw together last-minute within my skill set.

Now if I can just keep the cats out of the cardboard boxes long enough to finish...
Nebulosa3 years ago
The weird thing with the double image is likely because you didn't use a first surface mirror. You get a reflection from the surface of the glass and another reflection from the silvered back side of the glass.