EBBCO sextant - filters have UV removing properties?

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Sailingsaves

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We all know that good sunglasses remove UV (not sure if it is UVA, UVB and/or UVC) - can't remember which are the bad (or worst ones) and that toy sunglasses are worse than useless because they simply open the pupil and allow the bad UV in.

So does anyone know if the old EBBCO sextants have the correct safe filters?

Otherwise I guess I'll be cutting up the lens from sunglasses and cobbling something together, or buying aluminized mylar film (internet stated that filtered UV although a quick google seems to indicate it is opaque?)

But calibrating and playing with the sextant was good fun - until I started to wonder about the filters...
 
No, plastic.

It is probably the second cheapest sextant one could buy (£20 ebay), but it calibrated well and I had good fun with it.

I imagine simply placing the lens from a pair of sunglasses over the end of the telescope should filter out the UV - will look naff but cheap.
 
I don't know, but given the "fit for purpose" aspect of UK consumer law, I don't see how a sextant that didn't have UV filters on the shades could possibly be marketed. It would, by definition, be unfit for purpose, and Ebbco would have been taken to the cleaners by the first person who was blinded by exposure to UV through an instrument that is designed to look at the sun. And if it is marketed in the States, they'd have been sued for even more!
 
AntarcticPilot said:
I don't know, but given the "fit for purpose" aspect of UK consumer law, I don't see how a sextant that didn't have UV filters on the shades could possibly be marketed. It would, by definition, be unfit for purpose, and Ebbco would have been taken to the cleaners by the first person who was blinded by exposure to UV through an instrument that is designed to look at the sun. And if it is marketed in the States, they'd have been sued for even more!
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Yes, but aren't these EBBCO sextants obsolete and really old and therefore pre-nanny state?

In which case they (EBBCO if that is the name of the company) may not have even known about UV in all honesty?

Or they may have not cared because the litigation paranoia of nowadays didn't exist then?

Company may not even exist now.

With no access to a lab an longer I can't perform a decent test for UV, so unless anyone knows for sure I will be cutting up a pair of sunglassess because my little ol' eyes are still useful to me and I want to play with the sextant a lot more.

I'd love to do a Jester Challenge one day and who knows, even a Shrimpy, and being able to use an infallible piece of equipment (upgrade to davis MK25 by then) with no electrickery would be useful.
 
I never used to go anywhere without my Ebbco sextant. I don't think that it was ever designed to be a primary sextant for astro but was useful as a spare and for other purposes. Distance-off was the usual usage. I don't think I ever achieved a fix by horizontal angles.
 
Sailingsaves said:
Yes, but aren't these EBBCO sextants obsolete and really old and therefore pre-nanny state?

In which case they (EBBCO if that is the name of the company) may not have even known about UV in all honesty?

Or they may have not cared because the litigation paranoia of nowadays didn't exist then?

Company may not even exist now.

With no access to a lab an longer I can't perform a decent test for UV, so unless anyone knows for sure I will be cutting up a pair of sunglassess because my little ol' eyes are still useful to me and I want to play with the sextant a lot more.

I'd love to do a Jester Challenge one day and who knows, even a Shrimpy, and being able to use an infallible piece of equipment (upgrade to davis MK25 by then) with no electrickery would be useful.
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They aren't THAT old! The effects of UV in sunlight have been well known for a long time (I'd guess 1930s or 40s), and the Sale of Goods act is from 1979. The need for good quality shades in sextants has been known for at least 2 centuries!
 
I tried to buy an ebbco on eBay. All of them had patchy degraded filters. The first one I bought had unusable filters so I returned it. Thereafter I sent a question to all sellers and everyone replied that the filters had degraded, become patchy or totally opaque. You can buy a new version but the second hand ones are all duds in my experience.
 
Will try to use sunglasses (next time sun is out) but not always easy to wear sunglasses with this simple sextant as telescope aperture is tiny (need to get eyeball up really close).

Yes, the filters on this one are delaminating, but still useable enough for me for learning use of sextant.

Didn't know they made new ones, so that is good.

I now have an itch to make my own super tough, super accurate and larger sextant, but I am forcing myself NOT to go that route as it will be a hard slog and I really should be concentrating upon other things. But us boaters, it pulls you away from everyday things doesn't it?
 
Sailingsaves said:
this simple sextant as telescope aperture is tiny (need to get eyeball up really close).
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By coincidence, I was reading Moitessier last night and he was advocating using a sextant without a telescope - he said the resulting sights were more accurate in rough seas.

He never used a telescope when taking star sights - too easy to loose the star as you bring it down (which is the trouble I have).

He never got lost.
 
Having used sextants professionaly, mainly for taking around 100 horizontal angles a day as a surveyor pre GPS, I would recommend a second hand metal framed instrument if you can find one within your price range. Much easier to use and probably more accurate. Definately to be prefered if intending to use the instrument at sea.

I have tried using plastic sextants but found the mirrors small and fiddly and was never able to correct them satisfactorily. I usually found that the frame was bending slightly as I turned the adjusting screws for the mirrors.

While teaching navigation to deck officers we had a couple of micrometer drum sextants for students to practice with. These had been donated by mariners who had retired many years before I joined the staff yet shades and mirrors were in very good condition and they were much easier to use than an Ebbco. In fact we were also given an Ebbco, but I never showed it to students as it was too dificult to use effectively.
 
There's a misunderstanding here. The filters aren't for UV protection, they are there to attenuate the visible and infrared spectrum so that you don't burn your retina looking straight at the sun through a telescope. UV effects of solar radiation on the eye arise from long-term exposure, not a few minutes looking through a sextant.
 
andygc said:
There's a misunderstanding here. The filters aren't for UV protection, they are there to attenuate the visible and infrared spectrum so that you don't burn your retina looking straight at the sun through a telescope. UV effects of solar radiation on the eye arise from long-term exposure, not a few minutes looking through a sextant.
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I was wondering why this was a non-issue, and you've explained it nicely.
 
andygc said:
There's a misunderstanding here. The filters aren't for UV protection, they are there to attenuate the visible and infrared spectrum so that you don't burn your retina looking straight at the sun through a telescope. UV effects of solar radiation on the eye arise from long-term exposure, not a few minutes looking through a sextant.
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Everyone knows that is the primary purpose of the filters. I want to know if the manufacturer took protecting the user from UV into consideration.

Quote:
"UV effects of solar radiation on the eye arise from long-term exposure, not a few minutes looking through a sextant."
Can you supply scientific evidence for this please?

I plan to be using the sextant quite a lot in order to learn how to use it. So would that not count as long term exposure?

The filter will enlarge the pupil, just as toy sunglasses do. Thus allowing more UV radiation into the eye.

To say most sunglasses do not filter UV is WRONG.

Any sunglasses that do not filter UV are positively dangerous and that is for general use, not staring AT the sun as sextant users will be doing.

I bought cheap polarising sunglasses from Ebay (£5 China type) so I could see through the water better and took them to an optician and asked him to test them for UV protection and he stated they did filter the UV out. So even the cheapest knew to include UV protection.

The optician did not see it as non-issue. Or is that simply journalist speak? "Explained it nicely?" Really? I like evidence. But I know some journalists aren't too bothered about that.

There are different types of UV and it formed part of my degree studies so long ago that I have forgotten almost all of it, but I know too much is not good especially for anyone that is supposed to be avoiding it and certainly not good for the retina via an enlarged pupil.

I know what precautions I will be taking at negligible cost and time and effort.

If anyone else thinks otherwise, so be it, the issue has been aired at least and people can react as they see fit.
 
Sailingsaves, feel free to believe what you like. Using a filter on a sextant does not cause the pupil to dilate. It reduces the amount of light entering the eye to acceptable levels. It certainly doesn't increase UV exposure. The lenses in a sextant are glass. Glass completely blocks UVB, and attenuates UVA: see http://www.ncbi.nlm.nih.gov/pubmed/19614895. I doubt very much that you will be spending hours looking through a sextant, and if you are out and about on a sunny day you can wear your sunglasses when you aren't looking through your sextant. As for the effects of UV on the human lens, see http://www.medscape.com/viewarticle/761737.

Any UVB reaching the cornea goes no further. Of the UVA reaching the lens, only about 1% reaches the retina. See http://www.who.int/uv/faq/uvhealtfac/en/

In plain English, exposure to normal sunlight creates no significant risk of ocular damage from UV radiation. People exposed to a high solar load probably have an increased incidence of cataract: that is, people working out of doors in areas between the tropics where there is usually little cloud cover. Not 50-something degrees North with partial cloud cover for most of the year. Using a sextant creates no additional risk of ocular damage from UV exposure.

Sun beds and UV lasers are, of course, a completely different matter.
 
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