These top selling precision folding magnifiers have glass lenses that ensure a complete, distortion free view (see note below about lenses).  They are made with a fiberglass body and a dust proof enclosure.  Also have a loop to attache a carrying cord or neck chain (No. 9870A):

No. 9870-B - 7/8" diameter coated achromatic glass lens with Dual (3X + 6X = 9X) magnification. Completely distortion free.  Dealer recommended.

No. 9870-N - 7/8" diameter coated aplanatic glass lens with 10X magnification.  Recommended for Diamonds.

The magnifiers below have a chrome plated, brass body with a loop for carrying cord (neck chain No.9870A), metal lens frame painted black and a precision glass optic, truly a top product:

No. 9870-C - 5/8" diameter achromatic glass lens with 10X magnification in a chrome plated brass body.  (also Recommended for Diamonds)
No. 9870SP - 9/16" diameter achromatic glass lens with 20X magnification in a chrome plated brass body.

No. 9870-A - 1-1/16" diameter biconvex glass lens with Dual (4X + 6X=10X) magnification in a chrome plated brass body.

No. 9870-F - 1-1/16" diameter biconvex glass lens with 5X magnification in a chrome plated body.

No. 9870-L - 13/16" diameter, 6X aplanatic glass lens in a chrome plated body
No. 9870-M - 13/16" diameter, 8X aplanatic glass lens in a chrome plated body
No. 9870-G - 13/16" diameter, 10X aplanatic glass lens in a chrome plated body

No. 9870-E - 5/8" diameter, 12X aplanatic glass lens in a chrome plated body
No. 9870-K - 9/16" diameter, 10X aplanatic glass lens in a chrome plated body
No. 9870-H - 7/16" diameter, 15X aplanatic glass lens in a chrome plated body
No. 9870-I - 5/16" diameter, 20X aplanatic glass lens in a chrome plated body

No. 9870A Neck Chain for all loupes of the No. 9870 series as shown above. Chrome plated, 3 feet long.

No. 9538 Precision Metal Folding Loupe - 15X - 5/8" diameter aplanatic lens. Supplied with case
Double lens system. Chrome plated brass body with black metal lens frame. (not by Eschenbach)

No. 9849-A, with 13/16" diameter, 10X aplanatic light-weight lens, in a rugged plastic case, distortion free

No. 9858-D, Watchmaker's Loupe (fits into eye socket for hands free usage) with 13/16" diameter, 10X biconvex lightweight lens
No. 9858-I, Watchmaker's Loupe, with 13/16" diameter, 7X plano convex lens lightweight lens
 

Note about lenses:

Biconvex lens: Distinguised by two spherical (convex) surfaces. Used in large field, low power reading magnifiers. Magnification usually up to 4X.
Aspheric Lens: Aspheric curves allow higher magnification with less distortion. Used by holding the more convex side (side with imprint) towards the eye. Magnification up to 12X.
Aplanatic Lens: Consists of two equally strong plano-convex lenses. The convex sides are arranged face-to-face. Full image is clearly defined and free of distortion. Magnification up to 20X. (Magnification up to 4X useful for persons with macular degeneration.)
Achromatic Lens: Top quality lens. A color-corrected lens system that guarantees a clear, sharp image. Completely distortion free. Magnification up to 25X.