Glasses / spectacles and medicals (merged)

Thank you very much, dirkj. FWIW, the lenses are like in post 18.

I actually have these done now. Well, nearly. The guy said “nobody can do +0.5” so he suggested changing the +0.75 to +1.00 and forgetting the +0.50 reading insert (obviously, he went for the mid-point). Well, I could see the rationale and it “looked ok” on a quick test, but it really does not work in the real world. Having +0.75 is vastly better – even without the reading insert, and having the +0.50 insert makes it perfect, with both eyes focusing at the same distance on the kneeboard. I checked it with the test kit this morning. The guy here is going to re-do the left lens but I am not yet sure if he can do the +0.50; I told him about Seiko but got no reply.

If I can get the specs made exactly as per my numbers, with my existing frame, for say 150 quid (and only the left lens needs doing) I would go for that He just phoned saying he can do the left lens, from Seiko, and charge me just £50. So let me run with that for now

I hope others here find this useful even if nobody sez nuffink :smike: I know from off-forum feedback that lots of people take a keen interest in “medical threads” but obviously almost nobody wants to post about it.

I vaguely remember reading somewhere that Selectspecs and their competitors are not using ready-made lenses but rather make them individually for every order on programmable machines.

That would make a lot of sense. I think the “lens catalogue” system became popular because the lenses can be made very cheaply in China and this opened up the way to various online shops selling glasses for 10-20 euros (not bifocals) albeit in fairly crappy frames. OTOH, how did opticians do it in decades past? Were they all custom made by some factory?

Yes; Ultranomad posted that in the post above. You can just bet the battery will go flat just as you want to read something important, like an approach plate

To dig out this old thread… I have been wondering about the general question of whether it is possible for any spectacles to improve visibility.

It is a physical impossibility to increase contrast, using a passive system e.g. passing the light through some material. This is because materials are linear in their attenuation.

The only thing which can be done this way is to selectively filter a multi colour scene. For example, somebody told me years ago that green lenses make white buildings surrounded by forest more visible. This has obvious applications for flying, for finding airports, without using a GPS. But green lenses bugger up the vision of lots of other colours…

There are amazing claims made in the ski scene – example. There is a real problem when out under a very even cloudy sky, when the snow texture is hard to see. The ground is just one uniform shade of grey. But I am convinced the two side by side images there are fake… photoshopped with a big tweak on the contrast slider

And the ski scene is full of snake oil – like a lot of these sporting areas.

Aircraft have however crashed into snow slopes, due to there being no visible texture. Same with calm water.

The other thing which is obviously possible is to improve vision of a too-bright scene, simply by attenuating everything. That’s what sunglasses do… And you can do the same with hearing. The principle there is simply attenuation to avoid saturation.

Yes please; that would be very interesting to read.

That is impressive – thank you!

I will try to google translate it. No luck so far; google takes 1MB max