There is a trade off.

The higher the magnification, the lower the light throughput.

The ‘Exit Pupil’ of the binoculars is calculated by dividing the objective lens size by the magnification.  So in a pair of 8 x 42 Nikon Monarch ATB binoculars the exit pupil is 42/8 = 5.25.  Is that good or bad?

A key component of the functioning of a pair of binoculars is the human eyeball, and particularly the iris.  In daylight the aperture in your eye tightens down to a mere 3mm.  So a beam of light 5.25mm across is plenty. 21/7 = 3, and that shows why a compact pair of binoculars is absolutely fine for daytime use.  But as dusk approaches, the human iris widens out, to around 7mm.  So, for peak light performance in the evening, to get a 7mm beam of light for an 8x magnification binocular you need 7 x 8 =56mm.

But – binoculars with 56mm plus lenses are heavier and bulkier.  And night time bird spotting offers limited rewards.  So the 5.25 throughput of the 8 X 42 Nikon Monarch offers a reasonable compromise.  By comparison, the 10 x 42 is only letting through a 4.2 mm shaft of light.  Again this would be perfect for daylight conditions, but not so good as dusk approaches.  So that is why many birdwatchers are prepared to forego the extra magnification that is available, and I would agree with that general opinion.

So when it comes to specifications of binoculars, there is no such thing as ‘the best magnification’ but in the view of ReviewBinoculars 8 x on a 40 or 42 mm lens is pretty good for birdwatching and other outdoor activities.

Magnification: τ

Real field of view: 2ω

τ x tan ω=tan ω’

Apparent field of view: 2ω’

Dull if you don’t want to know it, but saves you hunting around if you want this nugget as part of your understanding of binoculars specifications.  And if you are on this site about binocular reviews and click on a dreary title like apparent and real depth of field related then it seems reasonable to assume you are interested in information, though probably not this bit!

The following artwork and text is taken from Nikon, and I hereby acknowledge their copyright.  They are a little mean in their use of language so I have given an extended explanation. My interspersed rambling are in italics.

Real Field of View
Real field of view is the angle of the visible field, seen without moving the binoculars, measured from the central point of the objective lens. The larger the value is, the wider the viewfield available. For example, binoculars with a wider field of view are advantageous for locating fast-moving wild birds within the viewfield. This also applies for finding small nebulas or a cluster of stars in astronomical observations.

The illustration above on the left shows a pair of binoculars with a small objective lens ie 25mm, which has a restricted field of view of only 5.6 degrees.  Or in simple language, you cannot see much of the tree.  The illustration above on the right shows a pair of binoculars with a more average (though slightly uncommon) specification of 42mm.   This happens to be the specification or objective lens size of the Nikon Monarch ATB 8 x 42.  The illustration show a real field of view of 7 degrees.  You can see most of the tree.  This wider field of view is not primarily of benefit for tree spotters.  What it means for a birdwatcher is that you can see more of the sky at one time, and it is therefore easier to pick up a bird. particularly if it is fast moving (though you may like to look at my post on using binoculars).

As a rough guide, real field of view varies between about 5 and 9 degrees.  Feel free to find examples that prove me wrong, but as a quick gauge those numbers will get you started.

If that is now crystal, I shall proceed to muddy the waters.

There is a European standard on the issue (three cheers do I hear you say?)  namely ISO 14132-1:2002.  It is available for purchase if you are that sort of a masochist.

This uses a different definition of field of view, namely Apparent Field of View.

The gentleman in the red sweater below is standing 1,000m away from a tree looking through a pair of 8 x magnification binoculars with a Real Field of View of 7 degrees.  However, the effect of the 8 x magnification is to move the tree closer to him, which is the same relatively speaking as moving him closer to the tree.  The tree now appears to be only 125 meters away (which is 1000 divided by 8).  And the apparent field of view is 52.1 degrees.

Thank you to Nikon for the above illustrations.

The maths of field of view is posted elsewhere on this site.

If you are reading  manufacturers specifications or retailers short details, they may not always be clear with their wording distinguishing between real and apparent depth of view, but the numbers speak for themselves.  A pair of binoculars with a 50 degree field of view is NOT a massive improvement on a pair of binoculars with a 7 degree field of view.  The above illustration shows 8 x binoculars with a 52.1 degree field of view.  Binoculars with a 60 degree plus field of view (is should be apparent by now that this is the apparent field of view) are called wide field of view.

Then for the ultimate ability to zoom in on a distant bird perched high on a cliff, a telescope and tripod is the finest optical setup you can achieve.  But four birders piling out of a car to ‘get’ a bird with scopes and tripods is a messy and harrowing spectacle, and is less than nimble for opportunistic spotting and identifying of avian friends.

So a good pair of birding binoculars, which may well also be the best binoculars for wildlife, will to some extent be a compromise between the compact 7X20mm pocket bins, and the ultimate solution of a telescope.

Without a doubt binoculars are critical bird watching equipment, and the general compromise is to go for an 8X40, that is to say, an 8 times magnification with a 40 mm objective lens.  My post on field of view goes a little more into the discussion of the compromise created by the fact that a higher magnification implies a reduced field of view.  A larger objective lens gathers more light, but adds size and weight, and these contrary factors make it impossible to definitively proclaim any binoculars greatest for birdwatching.

However,  if pushed  to answer the question posed by  the title of this post, then  with the caution that everything involves setting one factor against another, at the moment Review Binoculars would say that the Nikon Monarch 8 X 42 ATB could be considered to be the best binoculars for birdwatching.

And if you would like to buy a pair you can buy them now on Amazon at a saving of 34% off list price

The RSPB has been running a second hand binocular scheme since 1985.

Your old optics could join over 8,000 items collected by the RSPB and sent overseas for use in educational projects.

Recently there have been donations in Kenya, Brazil, Angola, Zimbabwe, Ecuador, Lebanon and Morocco.

People in more than 90 countries have been beneficiaries of this scheme with Angola receiving equipment for a first bird hide, Tanzanian youngsters getting the chance of close up views of wildlife and park rangers in Brazilian rain forests receiving equipment to help deter illegal wildlife poachers.

Project co-ordinator Ann Favell said; “As people upgrade their equipment they put old binoculars and telescopes in the back of cupboards. This is a really good way of putting them to further use.”

Old equipment in good working order can be sent to; RSPB second hand binocular scheme, c/o St Martins Business Centre, Unit 17, Cambridge Road, Bedford, Bedfordshire, MK 42 OLH.

You can also contact Ann Favell on 01767 680551 or email binoenquiries@rspb.org.uk to discuss your second hand binoculars and tell her review binoculars sent you please.

Nikon 7294 Monarch ATB 8x42

The Nikon Monarch ATB bins are a fine pair of binoculars.   Canon optics are excellent and top of the range in the camera business.  To read a review of this fine optical intrument and find out more please click here