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Discussion in 'Broadband' started by michael adams, Sep 18, 2014.

  1. michael adams

    Rodney Pont Guest

    Your brain does get used to that very quickly (a couple of days - if
    I'm remembering correctly) but you do still need two pairs of glasses
    since you have to tilt your head back and look down to read properly
    through the bottom of the varifocals and that does get very
    uncomfortable. At least you can read a label in a shop, for instance,
    with the varifocals.
     
    Rodney Pont, Sep 24, 2014
    #41
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  2. michael adams

    NY Guest

    Specsavers warned me when they made me a pair of varifocal glasses that it
    would take a while to get used to them, but after a week of feeling dizzy as
    soon as I put the glasses on, I decided I'd given them a fair trial. I never
    risked driving wearing them. I still had my old distance glasses at a
    slightly weaker strength so I used those. Specsavers were very good and said
    that not everyone takes to varifocal glasses, and made up two separate pairs
    (reading and distance) at no extra cost.
     
    NY, Sep 24, 2014
    #42
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  3. michael adams

    Dave Saville Guest

    There is a deal of difference between "budget" varifocals and a top of
    the range len. Having said that I dont have the readng problem.
    Usually "pointing one's nose" at what you need to be in focus is
    sufficient. I have on;y found two circumstatnces when they are a pain.
    In confined spaces, like under the car or tryimg to see down the back
    of a PC, or getting on down escalators. In both cases you are looking
    through the wromg part of the lens.
     
    Dave Saville, Sep 24, 2014
    #43
  4. Varifocals are a compromise and can't be ideal for everything, though
    it surprises me that you don't want to use them for driving, as I've
    found that to be the one situation where I can see everything is in
    focus - dashboard and forward view - without moving my head at all.

    Reading, particularly from a computer screen, is very much better with
    proper reading glasses that use the whole of the lens to put the whole
    screen, or page, in focus at the same time. It may not be obvious but
    it's not just a matter of focus, but contrast as well. With
    varifocals, only part of the lens is focusing the part of the screen
    you're looking at, while the rest of the lens is "fogging" the image
    with light which is not contributing to the focused image but only
    raising the black level and thereby reducing the contrast.

    It really is worth paying for decent thin lenses with all the fancy
    coatings, because they do make a difference. The last time I bought
    specs I was entitled to a free extra pair with bog-standard thick
    lenses and no coatings, and they're noticeably heavier and I can see
    reflections of windows and lights everywhere I look.

    Rod.
     
    Roderick Stewart, Sep 24, 2014
    #44
  5. Damn I hate thread drift... I missed this.

    My eyes are fine at a distance. Over about 2 metres right now, but I
    suspect it will be beyond infinity all too soon.

    But I tried some varifocals.

    Straight ahead, middle distance fine.

    Straight down, close up fine.

    So far so good...

    Off line - every point light is an oval. Significant astigmatism/
    cylindrical aberration. Enough to make them unusable - I don't want to
    turn my head every time I glance at the other screen on my PC.

    Is it possible to get some that _don't_ have this problem?

    Andy
     
    Vir Campestris, Sep 25, 2014
    #45
  6. Yes. Guess what though - they cost a bit more. You don't get quality
    for nothing.

    Poor quality varifocals will give a usable field that is roughly
    T-shaped, wide at the top for distance viewing, and narrower at the
    bottom for closeup, and even the best aren't perfect, but a lot
    better. You may recognise some of the brand names of the good ones as
    the same people who make top quality cameras. If you go to an
    experienced optician, particularly an older one who's actually wearing
    varifocals himself, a recommendation for a top brand is probably
    genuine.

    Note the other advice in my previous posting. If you spend a lot of
    time in front of monitor screens, it's worth getting a pair of fixed
    distance or "reading" glasses just for that. It's tiresome having to
    change glasses every time you get up from the desk, but it soon
    becomes a habit. I guess it's just an unavoidable part of getting old.

    Rod.
     
    Roderick Stewart, Sep 25, 2014
    #46
  7. michael adams

    Graham J Guest

    I have what were described as "Office" glasses, from a local independent
    optician. Smooth gradation from about 1 metre focal length in the top
    half to 20cm in bottom half. Very small astigmatism correction for one
    eye throughout.

    So I can look straight at the computer screen, and down at a book or
    whatever. In fact they also change focal length from side to side, so
    the keyboard looks as if it's constructed on the side of a large barrel.
    It took me about a week to get used to that.

    Initally I daren't walk about with them, but I've got used to that over
    the past year. My accommodation has reduced in that time, so I now need
    the glasses to read subtitles on TV at about 2 or 3 metres.

    Curiously they do reflect on surface nearest the eye, so I can see the
    refelction of well lit objects behind me - previous glasses didn't do
    that. I suspect it has to do with the curvature of the near surface.
     
    Graham J, Sep 25, 2014
    #47
  8. michael adams

    NY Guest

    At a pinch I could have tolerated a T-shaped field of sharpness. I didn't
    notice much astigmatism - either the lenses that Specsavers uses don't
    suffer badly from it or else my eyes don't have much astigmatism to correct
    in the first place.

    But what rendered varifocals unusable was the geometric distortion that
    turned a rectangular object into a parallelogram that swayed one way and
    then the other as I panned across it. It was a bit like watching a video
    filmed on a camera with a rolling shutter where fast-moving objects slope
    backwards.

    The inconvenience of having to change between two pairs of glasses is minor
    compared with the "all at sea, perpetually dizzy" feeling that I got as soon
    as I put the varifocals on. The shop were very alarmed when I reported the
    symptom, which they'd never heard of before. They repeated my sight test and
    carefully remeasured the exact spacing of my eyes to make sure that the
    optical centres of the lenses exactly matched my pupils. The "rubber world"
    caused by the varifocals made me feel very dizzy.

    I'm lucky that my distance vision (anything over about 18") is good enough
    that I can manage without my distance glasses in normal life, and I just
    need the glasses when driving to make it a bit easier to read road signs
    from a slightly further distance than without them. It's only my close-up
    vision that is really screwed: reading a book is a real effort and reading
    small text on a mobile phone is impossible because it's too small at a
    distance where I can focus on it and if I move it close enough to compensate
    for the small size it goes out of focus. I used to have excellent vision
    until a few years ago, when reaching the magic 50 years and suffering a
    heart attack and cardiac arrest seem to have taken their toll on my near
    sight.
     
    NY, Sep 26, 2014
    #48
  9. T shape I could have lived with. This was I shaped. And that's one
    without serifs.

    As for swapping lenses... these ones came from a pound shop. I take them
    off, drop them, tread on them, then buy some more. There's a pair in the
    garden somewhere too...

    Andy
     
    Vir Campestris, Sep 27, 2014
    #49
  10. michael adams

    Jim Guest

    Thanks for that post. I have trouble too with
    mass-produced varifocals. I'll bear all that in mind
    next time I order new glasses.
     
    Jim, Sep 28, 2014
    #50
  11. michael adams

    Bill Ward Guest

    Bill Ward, Oct 29, 2015
    #51
  12. michael adams

    Bill Ward Guest

    I have always rejected varifocals due to cost. When once vaguely
    interested and told about £90 by the person testing my eyes it rose to
    over £300 when the dispenser started her sales talk about lens quality.
    Bill.
     
    Bill Ward, Oct 29, 2015
    #52
  13. One of the guys at work is a camera guru. He had a discussion with his
    optician, who knows he's a camera guru. He has bifocals - apparently
    varifocals have unavoidable cylindrical aberration to each side.

    Andy
     
    Vir Campestris, Oct 29, 2015
    #53
  14. That's me. I spent years enjoying the slow growth in size and resolution of
    desktop monitors and now that my eyesight is no longer so good I have zero
    desire to downgrade to a lesser display; nor am I so hooked on all things
    internet that I cannot do without it while out and about.

    Yes, I have a non-smart (and therefore minimally privacy-breaching) cellular
    phone that I keep for away-from-home emergencies only -- but it's normally
    switched off: I'm damned if I'm going to let people pester me when I'm out
    visiting, shopping, or whatever... in other words whenever it suits *them*,
    regardless of my preferences.

    So get off my lawn, all you wretched, gormless, dumbed-down kids.
     
    Peter Boulding, Oct 29, 2015
    #54
  15. They do, but you get used to it. The distortions are less with better
    quality lenses, but as you'd expect, they're more expensive.

    Rod.
     
    Roderick Stewart, Oct 29, 2015
    #55
  16. michael adams

    Tim+ Guest

    I'd agree that they are overpriced *but* better quality lenses do make a
    difference. The cheapest varifocal lenses are quite horrid but improve
    greatly as you move up the price range. It's almost as if they deliberately
    make the cheap ones horrid....

    Tim
     
    Tim+, Oct 30, 2015
    #56
  17. michael adams

    Graham J Guest


    A couple of years back I got some "Office" lenses from a high street
    optician. They are varifocal. The focus in the centre and upper half
    is set for my eyes at a computer-screen viewing distance. The
    magnification increases towards the bottom for book-reading at about a
    foot disance.

    Obviously distance viewing is blurred and initially this was
    disorientating, but I simply close my eyes as I get up from a chair or
    move about; or take off the glasses.

    Over time my accommodation has deteriorated, and I found that I could no
    longer focus on the screen; also that I needed the glasses to see the TV
    properly at the other side of the room.

    So in the last month I have bought a new pair with a revised prescription.

    At the same time the optician suggested I ought to wear glasses for
    driving. So he made some conventional varifocals: the distance vision
    is corrected for my eyes and does make a marginal improvement to the
    sharpness of objects at infinity. The transition to closer focus starts
    too high up the lens (but some ajustment of the nose-pieces has lowered
    that), and the close focus allows book-reading as well as viewing the
    display on the dashboard.

    It ought to be ideal, but these lenses have what is described as
    "orientation zones" to the left and right extremes of vision, with some
    intermediate magnification. This is in fact really DIS-orientating, and
    renders their use for driving quite unsafe.

    I think this is the "cylindrical aberration" mentioned above; and it
    certainly isn't present in the "Office" glasses - it is very much a
    deliberate design feature and it ought to be possible to have your
    glasses made without it.
     
    Graham J, Oct 30, 2015
    #57
  18. michael adams

    Martin Brown Guest

    I suspect it is quite a challenge to make a really good graded varifocal
    lens even with todays CNC design tools. The aberrations you see will
    also alter with iris size due to ambient light levels.

    I don't like the way magnification varies from top to bottom. YMMV

    Bifocals are worse in that respect I have seen plenty of people with
    them "put" something small on a shelf and miss by about an inch.
     
    Martin Brown, Oct 30, 2015
    #58
  19. michael adams

    Bob Henson Guest

    My story is similar. I have had "computer" varifocals as well as
    "normal" varifocals for some time. I initially had ordinary varifocals
    that claimed to cover all distances. They did, but with a problem -
    whilst distance vision for driving and TV watching was perfect and
    reading was fine, the intermediate distances from key board to screen
    had a very limited field of view - only the centre 10cm square of the
    computer screen was in focus at any one time without head movement. That
    was OK for a book, but useless for a computer. The solution was a second
    pair of "Interview" lens specs (as they call the computer varifocals)
    which hang permanently round my neck on a string when at home.

    It is a nuisance having to use two pairs, but "normal" varifocals just
    cannot cope with all circumstances - even the very expensive lenses fall
    down on those intermediate distances with regard to field of view. On
    the other hand, my expensive Varilux lens are fine with regard to
    peripheral vision when driving unless you try to look sideways through
    the extreme edge of the lenses, so you get what you pay for.
     
    Bob Henson, Oct 30, 2015
    #59
  20. michael adams

    tim..... Guest

    Well if my experience is anything to go by, all that does is vow the
    consumer to avoid the damned things like the plague, not trade up to the
    "rip-off" version.

    If an optician wants me to buy varifocals again it will be on six month FREE
    trial or the answer is NO!

    tim
     
    tim....., Oct 30, 2015
    #60
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