DA7 has a focal length of 6 with a 2.75X magnification.
Binocular Magnifier
OptiVisor® Professional Magnifier – SEP Tools
Magnifier Headband Lens 1.5x Magnification DA2 Donegan Optivisor - HH505
Lensplate #7 Magnifies 2.75X at 6 - Optivisor LX Binocular Magnifier - Donegan Optical
Visor Magnifier
Donegan DA-10 OptiVisor Headband Magnifier, 3.5x Magnification, 4 Focal Length : Buy Online at Best Price in KSA - Souq is now : Health
Donegan OptiVISOR® with Four Acrylic Lens Plates - RioGrande
Magnifier Headband Lens 1.5x Magnification DA2 Donegan Optivisor - HH505
Binocular Lens
Donegan OptiVISOR® with Four Acrylic Lens Plates - RioGrande
Genuine #7 OptiVISOR 2.75x Optical Glass Magnifier Binocular Adjustable Headband