Standards for LVAs

[edKENdance]

I have a client who needs to use magnifiers of varying strengths to help her throughout her day. She picked up a 3x magnifier that she was happy with when she was in the US. I ordered her a 3x magnifier from a different supplier and the strength of magnification is discernibly different, about 2 dioptres different when I threw it in the lensometer. I understand the actual magnification changes due to the focal length but are there any standards in place to measure this or is it up to the manufacturer or country of origin?

[Barry Santini]

Magnification= FLcm/25cm
magnification = Lens power in diopters/4; OR /4 + 1 (marketing!)

b

[uncut]

I have a client who needs to use magnifiers of varying strengths to help her throughout her day. She picked up a 3x magnifier that she was happy with when she was in the US. I ordered her a 3x magnifier from a different supplier and the strength of magnification is discernibly different, about 2 dioptres different when I threw it in the lensometer. I understand the actual magnification changes due to the focal length but are there any standards in place to measure this or is it up to the manufacturer or country of origin?

I am not sure of all the international standards, but thickness, raw material used, asphericity, would all be calculated into the better ones, like from coil, or eschenbach....resulting in different powers, and rating would probably be based on the result at the focal length of the lens?

Magnification is a comparison, therefore the reference distance might also come into play in the ratings, often shared with microscopes.

[edKENdance]

I am not sure of all the international standards, but thickness, raw material used, asphericity, would all be calculated into the better ones, like from coil, or eschenbach....resulting in different powers, and rating would probably be based on the result at the focal length of the lens?

Magnification is a comparison, therefore the reference distance might also come into play in the ratings, often shared with microscopes.

One of them was from B&L and the other was from Hilco. The ones I have from Schweizer are measured in Diops so I don't have a 3rd I can compare to.