There are some which are supplied to those with partial sight, these seem to
be a bit like opera glasses but thinner and hinged on the bridge. The idea
is to flick them down when a bus is coming and twiddle the knob to get an
enlarged but smaller field of view to help read the number. I have never
tried them but some people seem to find them useful. The idea of having
sufficient adjustment in one pair of glasses sounds a little suspect to me,
one assumes plastic lenses or they would be heavy like the ones I mentioned
above.
As for filters, that sounds like one of the filters used in a clean air
room I used to visit. It also had high voltage ionisers and all sorts of
other filtration systems in it.
Brian

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The Sofa of Brian Gaff...

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"alan_m" wrote in message
...
On 19/01/2021 22:59, Roger Mills wrote:

One is for adjustable spectacles, where you twiddle a knob each side to
adjust the diopter rating of the lenses. Each lens is in two sections,
which move relative to each other. I can't work out whether they slide
from side to side or simply move apart axially. The prices in the Twitter
adverts are ridiculous - special half price offer for *only* £59 -
whereas Amazon and Ebay have very similar offerings for a fraction of
that price.




And have you read the amazon reviews?


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