What are some reasonable (ie: safe, portable, reusable) ways to start a fire with a magnifying glass without damaging my eyes from staring at the focused sunlight?
I recently started practicing some different fire starting techniques than I usually use, including starting a fire with a magnifying glass. When starting a fire with a magnifying glass, you focus the sun's light into a small but super-bright spot on a material to heat it up.
Image Source: ScienceABC
My biggest problem when trying to light my kindling with a magnifying glass is keeping track of the blindingly bright spot that is necessarily part of this process. It is difficult for me to keep track of what I am doing since I try not to stare at the bright spot too much. Looking straight at the spot for an extended time is dangerous to your eyesight.
The last two times I tried this I have burned spots into my vision. One of the times I gave myself temporary color blindness for a while.
Per comment by fgysin, I will try to find something more than my anecdotal evidence for the danger of this.
Now I'm worried about this and want to make sure I stay safe. Fire safety factors aside for this question; I am asking strictly about eye safety, and strictly about over-exposure to sunlight when concentrating said sunlight with a magnifying glass.
Some criteria to make a good answer:
- Must allow user to look at the focused spot without damaging eyes
- Must allow user to look at the focused spot long enough to start a fire with it (One minute is probably more than enough once I get better; less is needed in optimal conditions)
- Must be reusable a lot of times. If the method requires something to be continually replaced, like batteries, then I might as well just bring matches and keep replacing them
- Should be portable for recreational use such as while camping or hiking; the more portable the better since I would like to take it in a long-duration hiking pack.
Please keep other reasonable factors in mind, even if I have neglected to mention them.
Some ideas I had which I don't think will work
These ideas can form a baseline by demonstrating what I think is almost reasonable but not quite good enough. If you think I am wrong about any of the following, then please do make an answer refuting my worry.
- Welding mask
- Phone camera (or other digital camera) for indirect viewing
The sunglasses I assume are not strong enough, and after my previous two attempts I'm too scared to try it.
A welding mask would technically work but it is big and bulky and would serve no other purpose.
My welding mask does allow me to remove the small viewing "window" from it, essentially allowing me to hold up a small (approximately 2-or-3 inch by 3-or-4 inch) light-blocking lens. This is almost an answer, but my welding mask requires batteries to operate.
Likewise, other bulky eclipse-viewing devices should be considered out of scope if they are not easily portable.
A mirror just redirects the problem, I think, but maybe there is a clever way to use a small hand mirror to safely redirect the image that I'm not aware of.
I have read that some cameras can be damaged by imaging the sun if I use it a lot combined with the magnifying glass, I'm afraid it will be ruined and therefore not be a good solution.
So, does anyone have any ideas for how to do this without going blind after a few camping trips?
Experience from people who do start their camp fires with magnifying glasses is obviously great but not necessary, so please don't hesitate to pitch in with ideas you think could work. If they sound safe, I'll try to attempt them.