NavList:

"One question: can I hurt my eyes doing this?

Patrick"

I think we have been here before, in the context of the Observator Mark 4 telescope, which has shades of photographic film inside the telescope.

Two shades (giving three combinations) were thought to be enough for several of the WWII bubble sextants, including the A10, A12 and SOLD. The Freiberger yachting sextant also had only two horizon shades. A sextant made during WWII for the US Maritime Commission by Leupold and Stevens had two horizon and three index shades. See it here:

http://sextantbook.com/2010/12/14/a-us-maritime-commission-sextant/

In full sun at about 35 deg south, it is possible to view the sun with either horizon shade though it is uncomfortably bright through the less dense red shade, and it is very comfortable with the two shades together.

It is definitely not a good idea to look at the sun through an unshaded telescope, but the occasional accidental flash of light over the top of the horizon mirror is unlikely to give Patrick retinal burns or cause other damage.

Bill Morris
Pukenui
New Zealand
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