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Re: (meteorobs) trifocals
However if one has very bad astigmatism, plastic lenses may be the only
option. I was told the opticians would just laugh if they were asked to
make glass lenses to my prescription. (At best focus without my glasses
a star in a telescope eye piece is a streak 7 times as long as it is
wide.) I also wear trifocals and have an extra pair of glasses with
just my distance correction for meteor observing. This is one reason I
do my meteor logging by writing in the dark because I can't see what I'm
writing anyway.
Paul Martsching
Robert J. Gardner wrote:
> Tom;
> I am an old man and have been wearing trifocals for many years now. I
> went to trifocals because of the need to read things at intermediate
> distance when you are shopping for example. I have the large lens
> 6mmX5.5mm. I have no problem driving and need the trifocals to read my
> dashboard. Over 20 years ago I got a PC(yes, before the internet became
> common). To read the screen with the middle lens I had to tilt my head
> back and that caused me neck problems. So I had special spectacles made
> of the intermediate focal length just for use at the computer. My
> computer screen has always been further away than the normal reading
> distance. However that fixed the neck problem. I also had a pair of
> glasses made with the long focal length for observing meteors and
> stars. I had them coated for low reflection but later tests showed that
> to be of no advantage. The last time I changed spectacles my optician
> said that all the astronomers at Cal Tech had glass lenses in their
> spectacles, so I went that route. They are of course heavier than the
> plastic lenses but I do think they are better. It may be that the
> dispersion of the glass is less than the plastic lens or I may have just
> got a better fit this time. The difference between coated and uncoated,
> plastic and glass is so slight that it is hard to be certain about it.
> However my next star spectacles will indeed be glass. Experience in
> night hiking indicate to me that the reflection of night light on your
> face by your spectacles reduces the contrast of the image you see. One
> experiment that I would like to try is to blacken the area around my
> eyes with the black grease that athletes use.
>
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