Buying Binoculars

Binocular Crib Sheet

• Price – can be anything from £100 to £2500
• Pay for what you get
• Don’t discount 2^nd hand
• Try BEFORE you buy – Cley Spy is a good starting place
• Magnification 8x or 10x most popular – 8x has wider field of view and is generally brighter
• As one gets older 8x are easier to handle and hold steady
• 8x42 binoculars – first number magnification, 2^nd is diameter of objective lens in mm
• Greater objective lens diameter, greater light gathering capacity
• Exit pupil is diameter/magnification – this is diameter of exit beam of light into your eye. Anything above 8mm is wasted as this is normal maximum pupil size
• Poro Prism -v- Roof prism – roof prisms are lighter and more expensive - Poro’s usually give a wider field of view and a more 3D effect
• Gas Filled binoculars are water proof and dust proof
• Balancing binoculars – cover objective lens with dioptre fitted & focus on subject. Cover other objective lens and focus with dioptre adjustment on same subject – do not close either eye as closing one eye effects muscles in the other
• Twilight Factor – Square root of Objective lens size x magnification – ie 10x40’s = 400 = 20, 8x42’s =336 =18.3 The higher the twilight factor the greater the resolution
• Consider minimum focusing distance
• Eye Cups – with glasses put down without glasses pull up – but this is very much a personal preference
• The general feel must be good – very much a personal choice
• Straps must be wide – consider using a harness if uncomfortable
• Choose a good rain guard that falls out of the way when you raise your binoculars
• Clean lenses with a blower then a brush then a cloth with an alcohol cleaner
• Protect the coatings they do the heavy lifting regarding light transmission to your eye