I was giving an eclipse presentation to one of the local Rotary Clubs in the area and one of the questions asked was, “Would it be safe to view the sun through binoculars if the viewer put solar viewing glasses on first?”
The quick answer to the question is that this scenario is extremely dangerous to the eyes of the viewer, because the viewer has essentially placed solar filters on the wrong end of the binoculars.
Since I’ve heard this question on several occasions in the past few months, I wonder how many people are considering this dangerous misuse of solar viewing tools in observing the sun/moon interaction in the upcoming eclipse.
To view the sun safely through binoculars or a telescope, the viewer must install acceptable solar filters on the front lenses of binoculars or the front end of a telescope. Filters do no good installed on the end of these instruments where the eye piece resides.
With the solar filter on the front of these devices, the intense solar light is filtered out before the light enters the viewing instrument. The light that remains after being filtered is then magnified by the instrument to bring the sun’s surface closer to the viewer.
This is the acceptable way to view the sun through these devices.
If the solar filter is placed on the eyepiece end of binoculars or a telescope, the instruments magnification will burn a hole through the filter and render it useless.
Consider the example of an inexpensive 2-inch diameter magnifying glass focusing sunlight to a 1 millimeter point on a piece of paper. Within seconds, the paper starts smoking and catches fire or else a hole is burned through the paper.
This happens because the sun’s energy, captured in that 2-inch diameter lens, is concentrated to a 1 millimeter point, which causes the heat to rise to a level well above the flash point of the paper.
If you replace the paper with the plastic film used in solar viewing glasses, it will melt the protective film and develop a hole within seconds.
Now imagine the inexpensive magnifying glass being replaced with the advanced optics of today’s binoculars or telescopes. The ultimate effect would be a devastating tragedy to the viewer’s eyes.
For the above reason, it is strongly recommended that viewers do not combine solar viewing glasses with binoculars or telescopes. The glasses are meant to be used by themselves.
Use them as directed and follow the common-sense guidelines published previously in The Missourian.
Ray Mueller is one of the amateur astronomers with the EMDSO astronomy group in Franklin County