Just in case anyone's interested, here are some more thoughts about this
topic.
Summary: I found my glasses weren't good enough for birding, as the
off-axis vision was too blurry to give me time to id fast flying birds.
I tried contact lenses without success, but new glasses helped. The
contact lenses helped me notice something I was doing wrong with my
binoculars with glasses, and now I'm thinking of modifying the
binoculars to try to fix this.
******************************************************
My first trial contact lenses seemed a little strong (too hard to read a
book, etc), so my optometrist gave me some more to try. They were more
comfortable, but a touch weak for birding. He couldn't get anything in
between the two strengths in the same brand, so he tried a different
brand. These were so strong than nothing was in focus - near or far -
so he gave me weaker ones in that brand. I don't know what was wrong
with them, but they didn't work for me.
As people here had recommended giving myself time to get used to them, I
tried them for a couple of months, mainly the first ones.
They became comfortable to wear, but I still found my vision too
variable to be useful for birding, and occasionally it was shockingly
bad and no amount of blinking or rubbing or wetting would fix it. I
don't know why - maybe something unusual about the shape of my corneas.
My glasses gave me quite good vision right in the very middle, but the
good area was so small that I'd have to consciously move my head around
to get a bird right in that spot. It was almost like trying to aim
cheap binoculars.
After one arm of my glasses was bent in a recent car crash, I set about
checking that the frames themselves were straight, and discovered that
each side was angled back a little. I've since discovered that this is
normal, and is called "frame arching".
But I straightened them out, putting the lenses in line with each other.
I immediately found that the small area of good vision had enlarged to
the point where it was fairly useable. This makes me think that each
lens's "good spot" was not exactly in front of me, and that I was
looking through a tiny bit of overlap. After "straightening" them, this
overlap was greater.
There were already a few little chips in the lenses, and a new, deep,
scratch had appeared after the crash. I also wanted frames that came
with magnetic clip-on sunglasses, so I bought new frames and lenses.
The optometrist had always maintained that my prescription was still ok,
but I got him to increase the strength very slightly, not so much that
close reading is difficult. I was always under the impression that I
had aspheric lenses, and he recommended not to get these again because
of off-axis distortions, but it turned out I'd never had them in the
first place.
The end result is that, although I'm still annoyed by the poor off-axis
vision, the "good spot" is now so big that I don't have to search for
it, and the off-axis vision is slightly better than it was.
The new frames also have less of what is called "pantoscopic tilt" than
I had before. This means the lenses are more vertical when I hold my
head straight, and means I don't have to put my head back as far when
I'm looking in tree tops, etc.
So I'll be sticking with glasses. But using the contacts has revealed
another problem that I hadn't realised I had.
When you raise your binoculars to your eyes, you not only have to aim
them at the bird, you also have to get them exactly in front of your
eyes. Without glasses this is easy - you just jam them into your eye
sockets and they centre themselves. With glasses, they can end up a
little to the left or right, or up or down.
If this happens, you either find yourself looking at a partial image, or
the image blacks out completely. I think this depends on the amount of
relief, and maybe the exit pupil size.
To correct it, I guess you should move the binoculars slightly left,
right, up or down to line them up. I discovered that what I was
sometimes doing instead was to *tilt* them up/down or left right,
possibly because of my reluctance to drag them across my glasses lenses.
This gets you looking directly through them again, but now one eyepiece
may not be touching your glasses, or the binoculars may no longer be
perpendicular to the glasses. You may also end up looking through a
spot other than the centre of the glasses.
I've also noticed that sometimes this "tilting" results in one eye
seeing a lot of glare. Maybe lifting the eyepiece off the glasses lets
some light in the back.
The result of this will be an image that's worse than the binoculars are
capable of, and can have one fiddling with focus and the diopter setting
trying to fix it.
Practice should reduce this problem, but it might be useful to have
something to help locate them in the same place on the glasses each
time. Maybe custom eyecups with something to fit just over the edges of
the glasses. It would have a side benefit of blocking light from coming
in from the sides.
I'd be surprised if such a thing existed - has anyone tried making
something like that?
Hopefully all this is of some use to some other glasses wearers out
there.
Peter Shute
wrote on Wednesday, 10 October 2007
4:00 PM:
> Does anyone here use contact lenses for birding? I'm
> interested in your comments about them.
>
> I wear glasses for short-sightedness. My binoculars have
> enough relief to work with them, but it's still a pain for
> various reasons, including glare coming in the sides,
> eyepieces never being in exactly the same place in relation to my
> eyes, etc.
>
> I also find that my off axis vision (not peripheral) is
> blurred enough to make identification of birds flying from
> the side difficult until I can turn my head towards them -
> often too late. This is because I'm looking through the
> edges of my glasses, where such simple lenses have a slightly
> different strength.
>
> So I'm trialling contact lenses. My initial observations:
> - Without binoculars, they're far superior to glasses, but
> erratic. A blink can mean slightly blurry vision till the
> next blink. Off axis vision is as good as on axis vision,
> and I'm much better at identifying fast flying birds, and at
> spotting birds that aren't in front of me.
> - With binoculars, the glare and inconsistent eyepiece
> placement is eliminated, but I'm finding the image quality
> erratic. I can't put my finger on what's wrong. I think at
> times I can see more clearly, but at other times I'm
> searching for perfect focus and not finding it. I keep
> fiddling with diopter settings, then setting it back how it
> was again. Shutting one eye to set the diopter setting is
> pointless, as that upsets the lens in that eye for when I
> change eyes - I've taken to doing it by putting one hand over
> the objective instead. And do you think the birds wait around while
> I do this?
>
> Is this how it is for other contact lens wearers? If so, I'm
> not sure that I'll persist with them, despite the advantages.
>
> Perhaps I'm seeking a level of visual acuity that's not
> obtainable. My optometrist says I have better than 20/20
> vision with my glasses, and much better than what's legally required
> for driving.
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