I have the Optivisor (#DA-4 ) 2x magnification @ 10" focal length) which works for me. If 10" distance is too close for you, then the #DA-3 as armorer951 uses might be better for you but you do get slightly less magnification. They do sell optional lenses that can be swapped in and out but I've never had to bother as the DA-4 seems to work just fine.

I'd really suggest getting the US made Optivisor brand which sells for around $35 - $38 bucks on ebay and other sites. Their optics are way better than the Chinese brands I have tried in the past and will not scratch nearly as easily. Also, when I wear mine for extended lengths of time the Optivisor head band is pretty comfortable as it is lined with a piece of leather. It is also very easily adjustable with a few knobs. REALLY a great product!


http://www.doneganoptical.com/products/optivisor