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(meteorobs) trifocals
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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