Binos - What do the figures mean?
The first figure refers to the magnification - usually 8x, 8.5x or 10x.
The second figure - usually between 20 & 50 refers to the diameter, in millimetres, of the larger lens, the one you don't put your eyes to!
Binos - What to consider when buying?
Price you want to spend - can range from about £50 to £2,000
Size & weight ie comfort of using
Type of use - amount of magnification you'll need
Binos - Different types
Miniature perhaps 8x20's - useful for just putting in your pocket/rucksack or wearing "just in case" on a dog walk etc.
Porro Prism old type with stepped barrels + therefore tend to be slightly larger than Roof Prisms.
Roof Prism newer type with straight barrels - tend to be smaller + most popular these days.
Binos - In general
Lower the magnification = lower size/weight/price, larger depth of field/field of view (more in focus + to see) + closer focus for insects etc.
Higher the magnification = more detail ie useful in hides or for studying distant subjects. Need to be held steady to avoid potential shake etc.
Higher the price = better glass, build, longer guarantee, better waterproofing and usually gas filled to avoid steaming up etc.
Binos - How to set up
Just as important (if not more) than getting the right set of binos is to set them up correctly for yourself.
Firstly - Eyecups. Most binos are now designed to be used with or without spectacles and have "eye relief" of at least 14mm. This means that those who don't wear glasses should fold out the eye cups or screw them out to get their eyes approx 14mm etc away from the lenses.
Glasses wearers should have the eye cups folded down or screwed in as, on average, their eyes are approx 10-12mm from their glass's lenses which are approx 2mm wide - thus totalling the approx 14mm to get as good/wide a view as those not wearing glasses.
Secondly - Correct Calibration
Most binos have a focussing wheel in the center of them which focusses both barrels together and also an adjustment ring called a diopter that adjusts the focus on one barrel independently of the other to compensate for any differences you may have between your left and right eyes.
This Diopter adjuster is usually located on the right barrel of your binos near the eyepiece and usually marked with.... " - 0 + "
How to Calibrate your Binoculars - Only needs doing once unless your eyesight changes or you let someone else (with different eyesight) borrow your binos. Then it's just a matter of focusing on the subject using the main central focussing wheel:
If the diopter adjustment ring is on the right barrel, shut your right eye (or put a cap over the right objective lens or cover it with your hand), look through the binos with just your left eye and use the main focus wheel to focus on an object about 20 yds away.
Then do it the other way round by looking through the binos with just your right eye (with the left one shut) and adjust the diopter wheel on the right barrel until the same subject as before is at its sharpest.
Finally - look through the binoculars with both eyes open, and you should have the best view those binos/your eyes will give you of that subject.
Some people take a note of the right eye diopter reading (+3, -1 etc) so they can easily set that adjustment into other binos they use and some even put a blob of tippex etc on the reading to easily see if their diopter is set right after lending out to others etc.
Glasses wearers should find, in general, that a right eye diopter of "0" is OK as their glasses prescription should ensure both eyes are equal.
Binos - How to buy
Personally, I wouldn't buy without trying a few pairs out in the price range I'm comfortable with.
Locally, places like RSPB Fairburn, RSPB Old Moor & RSPB St Aidan's hold "Optics Days" at their reserves with a good range of RSPB, Viking, Nikon, Swarovski, Leica & Zeiss etc models to try out with experienced Optics Volunteers to assist you. The "Optics Days" are usually the first full weekend in the month - check sites for latest events.
In addition, shops like "Bass & Bligh" in Harrogate and "In Focus" in Denby Dale will also have a good stock of different models including a few 2nd hand ones which could also be of interest. You'll also find plenty of adverts in Birding Mags and shops like Currys & Argos etc sell them.
Binos - What do I use?
I don't think there's a "one bino fits all needs" so I might use a pair of Leica 8x20 for dog walks, Swarovski 8x32 for most birding and Canon 12x36 image stabilised for serious long stuff! I can recommend each one for their performance in those circumstances.
Binos - What do others use?
I recently did a survey of 44 "Yorkshire Bird & Birders Facebook Forum" members and the main results of their useage showed:-
Favourite Model 8x42 (37%), 8x32 & 10x42 (each 16%)
Favourite Make Swarovski (31%), Hawke (15%), Leica & Zeiss (both 13%)
Favourite Magnification 8x (57%) 10x (27%)
Favourite Objective Lens 42mm (61%), 32mm (18%)