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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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