Binocular use with bifocal spectacles (1 Viewer)

[I've just asked this question on the Zeiss sub-forum (where I got some very helpful and encouraging responses - thanks folks), but I've just realised that there's also a more general binocular forum - Doh!]

Unfortunately I need to consider changing to bifocal (or varifocal) spectacles - so that I can read maps, use an iPod, consult field guides, tell the time, see my feet, etc as well as looking at distant objects, eg birds!

I use Zeiss Victory 8x32 T* FL binoculars for birding - which work really well with my current (conventional) specs.

I'd be very grateful if others could share their experiences of using bins (and 'scope) with bifocal or varifocal specs.

Richard

Richard Klim said:

[I've just asked this question on the Zeiss sub-forum (where I got some very helpful and encouraging responses - thanks folks), but I've just realised that there's also a more general binocular forum - Doh!]

Unfortunately I need to consider changing to bifocal (or varifocal) spectacles - so that I can read maps, use an iPod, consult field guides, tell the time, see my feet, etc as well as looking at distant objects, eg birds!

I use Zeiss Victory 8x32 T* FL binoculars for birding - which work really well with my current (conventional) specs.

I'd be very grateful if others could share their experiences of using bins (and 'scope) with bifocal or varifocal specs.

Richard

Click to expand...

I have even trifocals, and I get along very well with my Zeiss 8x42 FL binoculars. The only problem I encounter is when some taller person lets me look through their angled scope. I then get into the near focus portion which would mean changing the focus of the scope. At the very least, it's not feasible for just a quick glance.

I have progressive bifocals (the ones that show no edge). I have not noticed any difference or had to modify my viewing habits through binoculars or scopes in any way compared to when I did not have bifocals.

Jim

The worst problem with bifocals is the "line" catching the light and messing with the view. If it's not catching the light and isn't in the center of the field then your visual system "dissolves" it away. The problem comes when if you scan your eyes around the field then you notice it.

You could avoid this by having "special" birding glasses made with the bifocal line much lower than normal (so it doesn't appear the bins ocular). For most bins (say maximum 24mm diameter occular) that would put the line at 12mm (or slightly more) below the center of your pupil. Usually the "line" is placed level with the lower eyelid. In my case, eye center to lower lid is about 6 to 7mm. Of course this means that you need glasses with "larger" frame: something like 12 to 15mm above the center of the pupil + 12mm down to the line + height of the reading segment (a minimum of 10mm). That's a absolute minimum of 35mm but usually you'll need more (as the bridge may not allow you to set the glasses quite were you want them ... I have a set of 35mm glasses like this that don't quite work perfectly). So say 40mm to 45mm especially if you want a larger reading segment.

Or you could just have single vision distance glasses made. This of course is cheaper but a pain when you need to write notes or (shudder) looking stuff up in a field guide. But don't myopes forget you can mitigate the latter effect by carrying a magnifying glasses or if you are a myope like me flip up the glasses and read the field guide very close up with one eye (about 8" for me -- where us can actually focus even as we get older!). It's fiddley and not too convenient but works for some.

Another possibility if you consult the guide infrequently is something like "golfers glasses" that are mostly single vision with a small offset round reading segment.

http://www.optiboard.com/forums/archive/index.php/t-10640.html

Or you can go for varifocals/progressive lenses but be aware that by their very nature they distribute astigmatism across the field (it increases in magnitude as you go away from the center line of the lens) so they can smoothly vary their power from the distance segment to the reading segment. But if you don't scan around the field much you won't see the effect and getting rid of the line and having bins you can read with could be a win. I've seen recommendations to drop the "fitting cross" (the mark on the lens that is aligned with the center of your pupil) 2mm for birding PALs but PALs are usually very critical in their fitting for best results so I'm not sure that's a win.

Another consideration if you are getting "birding glasses" is to go for round lenses that are as small in diameter as needed (so they are well ventilated and fog less often) in frame that can be fit closely and snugly to your face (to minimize eye relief) and can easily take the pressure of holding bins firmly against them (I find older, not trendy stainless steel frames work well for this but finding anything with round lenses is a challenge these days).

For a simple review/intro to Ophthalmic Optics see this good and rather short paper:

http://www.ucm.es/info/euoptica/org/pagper/jalda/docs/libr/ophthaloptics_eoe_o3.pdf

Many thanks for the helpful replies. Kevin, your comprehensive account of the factors involved will be extremely useful when discussing the options with the optician.

Richard