Naked-eye sunspots

In message , OG
writes

Can I just warn others that using binoculars for solar observation is never
recommended, even if the sun is dimmed through smoke, dust etc.

Although though the visible components of the solar radiation may be reduced
due to dust scattering, the infra-red radiation is much more effective at
passing 'straight through'.

Due to the longer focal length of refracting systems for infra-red light,
the heating effect of the rays, (after collection and concentration in the
binoculars) actually takes place deep in the retina, where permanent damage
can occur within a very short timescale. I have seen it written that there
are no heat detecting nerve cells in the back of the eye, so damage can take
place without any immediate discomfort.

The safest way of observing using binoculars is to use them for projection
onto a white card.

From the point of view of the health of the binocular the best method is
to make a filter from Baader film or other approved material, and test
it for pinholes before you look at the sun.
The sun's heat can do very nasty things to binocular eyepieces.
--
Rabbit arithmetic - 1 plus 1 equals 10
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