Eyeglasses and Added Magnification (1 Viewer)

[elkcub]

As mentioned in a recent post concerning the 8.5x44 Swift 828 HHS, the design tradeoff between field of view (336 ft.) and eye relief (19mm) for the first time makes it possible for me to see the entire field comfortably with my glasses on. http://www.birdforum.net/showthread.php?p=527119#post527119
Although I can drive legally without glasses, there is a minor astignatism correction that much improves the view using the upper distance portion of my tri-focals. I'm sure many folks know what I mean.

Playing around with the mid- and near-distance portions of the tri-focals, however, it has also become apparent that they each afford additional magnification to the binoculars, with a corresponding reduction in the field of view. In fact, I'm not sure if I prefer using the upper portion of the tri-focals, providing an 8.5x view, or switching to my computer glasses that add something like a 1.5x boost. Image size with the latter seems to be about the same as the 10x42 SLC (with no glasses), so can it be inferred that the magnifications of the glasses and binoculars are additive?

I'm sure this is not a new observation to many eyeglass users, but I just haven't seen the topic discussed anywhere (assuming it's worth discussing). I don't think my brain is making this up, and it might even be a poor man's way to use a single instrument for multiple purposes.

Is there an optician or optometrist out there to explain or verify how this works, and comment on whether there might be problems with its use, like eyestrain and the like?

Ed

 

[Swissboy]

As mentioned in a recent post concerning the 8.5x44 Swift 828 HHS, the design tradeoff between field of view (336 ft.) and eye relief (19mm) for the first time makes it possible for me to see the entire field comfortably with my glasses on. http://www.birdforum.net/showthread.php?p=527119#post527119
Although I can drive legally without glasses, there is a minor astignatism correction that much improves the view using the upper distance portion of my tri-focals. I'm sure many folks know what I mean.

Playing around with the mid- and near-distance portions of the tri-focals, however, it has also become apparent that they each afford additional magnification to the binoculars, with a corresponding reduction in the field of view. In fact, I'm not sure if I prefer using the upper portion of the tri-focals, providing an 8.5x view, or switching to my computer glasses that add something like a 1.5x boost. Image size with the latter seems to be about the same as the 10x42 SLC (with no glasses), so can it be inferred that the magnifications of the glasses and binoculars are additive?

I'm sure this is not a new observation to many eyeglass users, but I just haven't seen the topic discussed anywhere (assuming it's worth discussing). I don't think my brain is making this up, and it might even be a poor man's way to use a single instrument for multiple purposes.

Is there an optician or optometrist out there to explain or verify how this works, and comment on whether there might be problems with its use, like eyestrain and the like?

Ed

I have trifocals too, also with astigmatism. I'll try to use the lower portion(s) next time I'm out, though they are a bit narrow. So far, my experience has been that I need to look through those when someone wants to show me some bird with his angled scope set a bit high for me. And I never have it in focus then, and always with what seems to be a rather narrow FOV. So this would explain why.

That the magnifications are additive is clear to me because I have a two-piece handlens made by Eschenbach, Germany, and it says on it 3+6=9. So one lens magnifies 3x, the other one 6x, and if I use them together I get the 9x mag.

 

[elkcub]

Robert,

Yes, it's literally a pain in the neck trying to use the lower portions of tri-focals. Fortunately, I also have a pair of computer glasses with only the center portions. I also intuit that power is additive, but, curiously, nobody seems to mention this. Extra power on demand.

Ed

 

[Swissboy]

Robert,

Yes, it's literally a pain in the neck trying to use the lower portions of tri-focals. Fortunately, I also have a pair of computer glasses with only the center portions. I also intuit that power is additive, but, curiously, nobody seems to mention this. Extra power on demand.

Ed

Ed, I use the middle part of my trifocals for computer work. How do your computer glasses work, do you have a center area for the computer and the surrounding area set for distance viewing?

 

[elkcub]

Ed, I use the middle part of my trifocals for computer work. How do your computer glasses work, do you have a center area for the computer and the surrounding area set for distance viewing?

Oh, I have a separate pair of glasses with only the center correction. This is good for looking at a computer screen, but not always a good idea since the near reading focus is not available for data entry, like for taxes.

Now I may have another use for them
Ed

 

[trashbird]

I ntoice that when I take off my glasses and look through binoculars, the image appears bigger. Not sure whether this is really a change in the power of the bin. Also, with the glasses off I am able to focus closer.

I have my distance glasses, and my computer glasses. The computer glasses are basically what the lower part of the bi-focal would be for me. I don't wear bifocals.

I birdwatch with my distance glasses and binocs. I can't see very well with my computer glasses past about 6 ft., so they really aren't an option for birding.

To look at a field guide I take off my glasses, or pull them down on my nose and look over them. Like most nearsighted people, I can see perfectly at a distance of about 10 inches.

 

[elkcub]

I ntoice that when I take off my glasses and look through binoculars, the image appears bigger. Not sure whether this is really a change in the power of the bin. Also, with the glasses off I am able to focus closer.

I have my distance glasses, and my computer glasses. The computer glasses are basically what the lower part of the bi-focal would be for me. I don't wear bifocals.

I birdwatch with my distance glasses and binocs. I can't see very well with my computer glasses past about 6 ft., so they really aren't an option for birding.

To look at a field guide I take off my glasses, or pull them down on my nose and look over them. Like most nearsighted people, I can see perfectly at a distance of about 10 inches.

Right. It would appear that we are opposites. I'm far sighted and you're nearsighted. So, different results are obtained by way of magnification/minification. Sorry about that, but thanks for pointing it out. Where is that optometrist anyway? |:S|

Ed

 

[trashbird]

Right. It would appear that we are opposites. I'm far sighted and you're nearsighted. So, different results are obtained by way of magnification/minification. Sorry about that, but thanks for pointing it out. Where is that optometrist anyway? |:S|

Ed

The optometrist is busy counting his money from people like you and me. ||