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Binoculars for Birdwatchers:

First of a two part look at optical equipment for birdwatchers by Paul Laurie

Using binocularsThe main cause of headaches, eyestrain, neck & back pain and general tiredness is caused by the misuse of binoculars and the following article will help you to use, clean and prolong the life of your binoculars while lessening the difficulties that can occur. The cost of birdwatching increases as your interest grows. The huge market that surrounds the hobby will provide you with optics, fieldguides and magazines each one better than the last and normally more expensive. Though to start what you need is a pair of reasonable optics that is a pair that focus, don't weigh more than 800 grams and give a clear, bright sharp view. A pocket field guide with the familiar British birds and a notebook and pen/pencil. Unfortunately the notebook has become a rather seldom seen piece of equipment for any birders these days, though the electronic note pads are becoming popular.


These range from a pocket pair of 7x25 to a pair of 9x63 and almost anything in-between. When choosing binoculars the most important factor is the comfort you feel when using them, for example some binoculars are better for spectacle wears than others and a little experience with a few pairs will pay dividends.

Facts & Figures:


8x, 8.5x, 9x & 10x magnification are the most popular used by bird watchers and this is general governed by the habitats they bird watch in. For example if you are using them in the garden, local woodland and park then 8x magnification would be most suitable as these generally allow closer focussing and with a large objective diameter such as 42 - 50mm, will give a brighter image particularly at in poor light such as dusk. If your time is spent at the local reservoir or marsh then a more powerful pair of optics may benefit, as the birds are likely to be more distant the same is true if you enjoy sea watching.

Objective diameter

A clear, bright image is the most important consideration when using optics. The size of the objective lens is measured in millimetres and is the actual measurement of one of the object lenses. I.e. 42mm, this relates to the size of the picture you are viewing and when taken into account with the magnification demonstrates the field of view the optics gives. For example a pair of 12 x 50 binoculars would normally have a smaller field of view than a pair of 7 x 50, this becomes important when say searching for a warbler in a large tree as with the 12 x 50 a smaller percentage of the tree would be in view lessening your chances of finding the bird quickly and keeping track of it as it flitted through the leaf cover very little of the tree would be in view. This however is not always the case and a detailed look at the manufacturers specifications is always important.

The field of view is often expressed in terms of 131 metres at 1000m. This in simple terms means that if you were looking at the horizon a 1000 metres away you would see a 131 metres of the horizon at any one time.

The pupil of the eye is 2-3mm in daylight and 7mm in poor light, for example at dusk. The exit pupil for optics is calculated by dividing the object lens by the magnification. For example, a pair of 8 x 40 would have an exit pupil of 5mm making them bright for daylight use and reasonable for dawn & dusk birding. A pair of 9 x 63 optics would normally better for dusk birding than the 8 x 40, as they would have an exit pupil of 7mm.

Eye Relief

Eye relief is the distance between the lens of your eye and the lens of the optics. This distance is often different for each individual and is particularly an important consideration for spectacle wears. Most modern optics either has rubber eyepiece hoods that fold down or in and out eyepiece hoods that are pushed and pulled. The correct eye relief is important to ensure the full field of view is achieved. The in and out eyepiece hoods allow a greater flexibility as they can be adjusted for different eye relief needs.


The coatings on optics improve the light transmission and prevent the optics from giving a rather misty view. The coating is very thin, around 137 nanometre, and are mainly a magnesium fluoride substance. The coatings are evaporated onto the lens in a high vacuum. Normally the more coating the optics have the better the light permeability and hence brighter image.

Phase Coatings

This is the solution to the slightly polarised and out of phase light transmission that roof prisms have. The formula is a closely kept secret by the optic manufacturers.

Most objective lenses now have an anti UV infrared coating for protection of your eyes.


This is a lens that combines the colours red, blue & yellow in one focal point, and has no colour flaws.


Most manufactures of optics use the same abbreviations to express the different types of construction available.

  • B - The casing is a one-piece moulding
  • A - An American design noted for being modern and tough
  • Z - the objective lenses screw into the prism casing
    In the types B & Z the prisms are situated side by side
  • D - A roof prism model with the prisms in line, often making the optics slimmer
  • W - Wide angle
  • CF - Central focus
  • IF - Individual focus, where both eyepieces are focused separately.


Bushnell Tactical BinocularMany rubber finished optic look waterproof, this is not always the case and if you intend to spend many hours birding in the rain a pair of waterproof optics are a good investment. Spray proof will withstand a spell of rain but not heavy rain nor immersion in water and will often mist when entering a enclosed space such as a hide or vehicle. For sea watching and heavy weather a pair of nitrogen gas filled optics are the answer and often have a long term guarantee of 10 to 25 years duration.

Using your binoculars

There are three steps to focusing you optics for your personal use.

First by adjusting the distance between the eyepieces to the same distance as between your eyes. This will give you a complete, single picture. Pivoting the two halves closer together or further apart does this.

Next use the central focus control to focus both lenses on an object. As often one eye differs in focusing from the other it is now necessary have additional correction.

Finally cover the right objective lens with your left hand without touching the glass, focus with the central focus control on an object some 80 - 100 metres distant until the image is sharp. Then using your right hand cover the left objective lens and turn the individual eyepiece adjustment on the right eyepiece, either in the direction on the + or - scale, until the image is sharp. If the eyepiece adjustment does not lock in to this setting then note exactly where the scale is for your use and if the adjuster is a little free moving you can use a little tape to secure it. This prevents constant checking that it is in the right place.

Some optics have the individual focusing coupled with the central focusing control and it is often found by pulling the central focus control towards you and the pushing it back in place one set correctly for your use.

If after you have completed the above the image is not clearly in focus then start again.

Note: Always read the manufacturers instructions to achieve the best results from your optics.

The best way to choose a pair of binoculars or telescope is to field test them when birding. I often find that friends and clients are willing to let me try their optics and you can quite quickly tell if they feel right and are comfortable. Many of the optic suppliers hold field days around the country at nature reserves and are an ideal opportunity to try many different makes, designs and specifications.

Birding with binoculars

Don't let your binoculars hang around your lower stomach or groin, not only is it dangerous! But improper wear can also result in headaches, neck ache and back ache. Your binoculars should be high on the chest just allowing enough room to put the strap around your neck when wearing a thick winter coat. Having them in this position not only makes them far more comfortable to wear but they are less likely to be damaged when squeezing into the seat in the hide or into the car. I have seen and heard many a thump as a birder whacks their optics against the resting shelf and it's not pretty! The higher the binoculars are on the chest the less torque on the neck and the less pendulum like swing and therefore the less strain on the neck. The other advantage is that the distance the binoculars have to travel from starting point to your eyes is less giving you a better chance of seeing any fast moving birds. I would advise using a wide, soft & smooth strap that be very comfortable and will also stabilise your binoculars when not in use and lessen the weight on the neck.

An essential piece of optical equipment for binoculars is a good fitting rain guard. This will help keep water, dust and pollen of the eyepieces and will help the performance of the binoculars in adverse conditions. Rain gaurds come in many different forms from hard plastic to soft rubber and many binocular are purchase new will have a ran guard that should be attached to the strap of your binoculars on one side only. If you attach both sides to the strap this will cause difficulties in lifting your binoculars and you may cause minor damage to your chin, lips and nose. It is also tiresome when trying to locate a flying bird quickly if the rain guard is impeding you.

Cleaning your optics

An airbrush is very good for removing particles of pollen, grit, dust and sand as well as breadcrumbs, cake & biscuits. All of which can damage the glass and the coatings if rubbed into the glass. The best tool I have found for cleaning optic lenses is a Lens pen which has a carbon fibre pad that removes watermarks and finger prints very effectively without leaving any residue on the glass or causing any damage if used correctly. The Lens pen has a brush at one end for cleaning the small particles off the glass and then the carbon fibre pad is gently rotated on the glass removing all marks.

Clean your optics after a birding trip and they will be ready to use the next time, avoid cleaning with anything but lens cleaning cloths or a carbon fibre tool.

It is very important for the long life of your binoculars that you brush the lenses before rubbing them with any cloth to ensure that no hard particles scratch the lenses.

Nitrogen gas filled optics that have done a days sea watching, and therefore often covered in salt spray can be put under a running tap to be washed very effectively without concern for water penetration. Non-waterproof optics should be cleaned thoroughly if subjected to salt water though care must be taken to not allow any water penetration of the body.


Your binoculars will have been purchased with a case, normally these days a soft case with a sachet of nitrogen crystals that will help prevent misting on the inside of the lenses. Optics are best stored in the this manner in a cool dry place. If you have any moisture penetration then the optics should be left in a warm, airy position but not on or by a hot radiator as this may make the problem worse in the long term. It is not good practice to leave optics in a vehicle as they tend to create their own atmosphere during damp cool periods and can cause optics to mist when first used during the day.

Most binoculars will stand a little wear & tear, though leaving them on the car roof as you drive off is often too much for them to bear as the lenses are precision fitted and once one lens is out of place they become unusable and difficult to repair. The better you care for your optics the longer they will last and the better they will perform.

Paul Laurie runs birdwatching tours in Norfolk through his Bird ID Company. Paul is also currently writing a book on birdwatching and this article is taken from part of a chapter on optical equipment - we will bring you full details of the book when it is published.