dioptre

[Dave Plowman (News)]

If specs improve your distance vision when driving, you'd be wise to use them at all times. Even more so in poor visibility when the depth of field decreases.

[Dave Plowman (News)]

It's simply a fact of life. Everyone's accommodation gets worse with age, although not necessarily at the same speed.

An optician pal said man's natural lifespan is about 35. So you could still see to make arrows in poor light. ;-)

[dennis]

Can you try that in English?

[dennis]

Nowhere near that big.

[Harry Bloomfield]

Dave Plowman (News) explained on 20/01/2017 :

I do have them checked, but the correction needed for driving is so marginal, that the wearing of lenses itself offers only a marginal advantage versus naked eyeball.

I don't like the idea of wearing contacts.

My accommodation is still pretty good most of the time, I can just about read without glasses, with a bit of effort.

No actual strain, just much easier wearing the correct glasses. I'm lucky, both of my eyes are identical.

[Harry Bloomfield]

The first time I began to need multiple pairs, I ordered varifocals. I just couldn't get on with them at all. I tended to walk about with my reading glasses on and still do. I found that the varifocals so distorted the position of things whilst walking I was constantly tripping up.

[Dave Plowman (News)]

Generally, if a decent optician says you need correction for distance, you should use that all the time when driving.

I only mentioned that because it means my eyes are corrected for distance. So allows me to use non prescription reading specs. It's not so convenient to wear one pair of specs on top of another. ;-)

If you are slightly short sighted, that makes sense.

[Bob Eager]

I had some 'driving specs' made. Just right for driving, but bifocal so I can see the instruments properly without having to squint and take my eyes off the road for more than a glance.

The bofical 'line' coincides with the top of the dashboard.

[Dave Plowman (News)]

That's interesting. I've got no problems reading the instruments on either of my cars. Perhaps they are further away from me than on some?

Or rather, the only thing I can't read easily is the old rotary odometer on the Rover. And no chance at night. But all the important ones are OK.

[Harry Bloomfield]

Bob Eager brought next idea :

I still have the bifocals, the only bifocals I ever ordered, around somewhere. I keep intending to see how they might perform for driving. I don't have a problem reading the dash and the satnav wearing my usual driving glasses, but I suspect it might be even clearer with bifocals.

[DJC]

More relevant is the diffusion of light as it passes through the atmosphere.

[Vir Campestris]

I found they were great straight ahead. I could look at a computer screen at arms length, and a book under my nose, and have perfect focus on both.

Trouble is I have two screens at work, and to look at the other one I had to turn my head - horrible distortion if I tried to use the side of the glasses.

I really ought to get some bifocals, but poundshop readers work for me. My distance vision is still OK (albeit not perfect) and quite good enough to drive with.

Andy

[Harry Bloomfield]

Harry Bloomfield expressed precisely :

Now done, but just as a follow up....

Using a light source a worked, but not by trying to measure and use the reciprocal with a light source a room distance away. Measuring produced too great an error to be useful.

I ended up using those glasses (spectacles) which were marked with their dioptre, along with a light source as far away as I could get it, to make dioptre marks along some masking tape along a bench.

Some of the glasses (not many) didn't focus on the marks, but rather they focused in between calibration marks - so glasses bought as 2.25 might well be 2.35. The process enabled me to put them all into marked containers, so I can readily pick out what I need for any purpose.