Atmosphere of Venus: Problems in perception

The Quick Study regarding Mikhail Lomonosov’s viewing of the 1761 transit of Venus is disturbing for a number of reasons. The authors claim that an achromat objective “focus[es] all colors to the same point,” which is well known to be false. Achromats, whether their two lenses are cemented together or separated by air, bring two wavelengths—typically blue and red light—to a common focus while leaving other wavelengths significantly uncorrected for axial chromatic aberration. But more serious is the authors’ use of smoked glass as the solar filter. Viewing the Sun through smoked glass can damage an eye in several ways. The 1/1700 attenuation cited by the authors for their actual solar filter is dangerously weak. Moreover, placing their smoked glass at the eyepiece rather than at the objective lens makes it even more apt to produce eye damage because of the higher concentration of solar energy at the eyepiece—which therefore needs additional attenuation—coupled with the increased risk that the concentrated heat will cause the filter to crack.

The author’s own statement in the article makes the case: “Solar viewing was barely tolerable” with their smoked glass. Naive readers attempting to replicate solar viewing in this fashion risk damaging their eyes. Those readers would probably have no method of verifying the attenuation level of a piece of smoked glass across the UV-visible-IR spectrum, so the experiment would be for them a trial-and-error process. Error in this case could cost one his or her eyesight.