Question about vision magnifiers

[David Dalzell]

This question is in reference to magnifying my vision when sharpening saws. I use a pair of magnifying eyeglasses to sharpen saws. I don't know the magnifying power, but the focal length (distance from my eyes to the saw teeth is from 7" to 12". Within that range the teeth are sharp and well defined. Closer, or farther than that and the saw teeth get blurry.

I would like to buy one of the "Donegan OptiVisor Headband Magnifier". Donegan has a wide range of magnifications available. Each of the magnification levels specifies an associate focal length. Anywhere from 4" to 20" depending on the magnification.

My question is this: If I buy a Donegan 2x magnification head band with 10" focal length, and use this while wearing my magnifying glasses, with 7" to 12" focal clarity, will the overall focal length still be 10". Or do focal lengths of glasses plus lenses have some other factor to be considered?

Obviously my eyesight is not what it used to be. But anyway getting old has its benefits, I just don't remember what they are.

[Winton Applegate]

I can not answer your question but those are good magnifiers ; I have a head band for each of three lenses at home and one for at work.
be sure to get at least one of the lights made for it (http://www.loupe-magnifier.com/quasar_ls_lighting_system.htm). The batteries last for ever and very handy even for when you just want to look directly down in a recess but don't need mag and have your hands free. Better than a forhead light or side lamp or flash light.

They could improve the pivot tension knobs on the visors they tend to loosen but for the price they are fine. Personally I would pay more for a more pro oriented assembly maybe with some metal and a coil spring in it for tension but people in Hell want ice water.

[Tom M King]

I don't know why anyone wants to wear glasses, but those magnifying hoods give me headaches. I first bought a fixed magnification one recommended on a well known tool manufacturer's site, and then ordered the one with interchangeable different magnifying lenses that you swap out. Both gave me the same kind of headaches. Finally, I ordered some 2X Dental Loupes with LED light off ebay, and those things are Da Bomb for small saw teeth. If anyone wants the regular hoods, send my your address.

[David Ragan]

Also available on ebay are the customized surgical loupes-a cheap $30 version of what vascular/neurosurgeons wear. Eyeglasses w a small magnifier in each; i just went there ebay- also have lots of jewelers loupes

I would post a link for yhe math of focal length/magnification- but its way too com

[David Ragan]

Complicated for me
maybe not for you......

[John Dana]

Your focal length will be shorter if you combine your magnifying glasses with the Optivisor. I wear 1.0 magnifier reading glasses to see small print and I had purchased a 2x Optivisor for some inlay work. The 2x was way too short a working distance for me. I will be getting the 1.5x (which I think is the minimum) which should put me at 20" give or take. The 10" field was nice for really examining the work but super, super uncomfortable to actually physically do the work. Something to keep in mind when picking out an Optivisor. I didn't measure how much the field shortened when I had my reading glasses on behind the optivisor but it was noticeably closer.

[Tom M King]

The Dental Loupes come in a range choices for focal length for each of the different magnifications. I can't remember which my 2X loupes are, but it's more than 10 inches. I measured with a metric tape measure before I ordered. I think the most common focal length is what' comfortable for dentists to use working in someone's mouth. The only thing that changes is field for view for a given focal length for the different magnifications, and probably a little depth of field difference too.

[Brian Ashton]

My question is this: If I buy a Donegan 2x magnification head band with 10" focal length, and use this while wearing my magnifying glasses, with 7" to 12" focal clarity, will the overall focal length still be 10". Or do focal lengths of glasses plus lenses have some other factor to be considered?


Easiest way to to put them both on and see where focus is achieved.

Regarding wearing multiple lens setups at the same time, you're introducing error with each set you add to the path of vision from the work piece to the eye. Each setup has it's own refractive capabilities, ideal alignment and distance to the eye and the work piece... Which will most likely not play well together without a precise setup. KISS, keep it simple... and you'll probably find the quality of the picture will be better. If you're eyes are not able to focus crisply to start with then you'll have to add corrective lenses but to try and line up to lenses simply to increase magnification and or change focal length isn't necessary considering the number of lens options available.

[Mark Salomon]

To answer your question: if you buy the 2X Optivisor headband and wear it with your normal reading glasses the focal length will probably decrease too much for them to be useful. I found myself using an old pair of lower magnification reading glasses with my 2X headband--it results in a focal length that is just right for dovetailing. I found the focal length with my normal reading glasses and the Optivisor resulted in a too short working distance for comfort. I guess you'll just have to experiment to get it to work for you. BTW, I bought a pair of cheap dental optical magnifiers/loupes off the bay and tossed them--IMHO the Optivisors are much better for woodworking.

[Tom M King]

Here are the ones I ended up using for sharpening tiny saw teeth. They have all sorts of adjustment for eye width, parallax, and focusing. I'm not sure if they have enough focus control for someone who normally wears glasses, but I would think they do. I should have gotten the same ones without the light. I have a bright light over my saw sharpening area anyway. Focal length of 420mm is about 16-1/2" which works out comfortably for me sharpening a small backsaw. The field of view is pretty small, but it doesn't take long to get used to it.
http://www.ebay.com/itm/Sale-Dental-Surgical-Medical-Binocular-Loupes-2-5x420-LED-Head-light-lamp-RED-/191474356647?pt=LH_DefaultDomain_0&hash=item2c94c2d1a7

[Brian Ashton]

To answer your question: if you buy the 2X Optivisor headband and wear it with your normal reading glasses the focal length will probably decrease too much for them to be useful. I found myself using an old pair of lower magnification reading glasses with my 2X headband--it results in a focal length that is just right for dovetailing. I found the focal length with my normal reading glasses and the Optivisor resulted in a too short working distance for comfort. I guess you'll just have to experiment to get it to work for you. BTW, I bought a pair of cheap dental optical magnifiers/loupes off the bay and tossed them--IMHO the Optivisors are much better for woodworking.

I have the one from Lee Valley with the x1.75 lens. I also wear certified coke bottle +7 corrective lenses, so the loupe maximum focal distance is about 10 1/2" as opposed to the stated 14". I also have the x2.75 lens also and the focal distance is reduced to about 4 1/2" as opposed to the stated 6".