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Birdwatching 101: All About the Bins

by Maia Tanedo

Binoculars are the most basic equipment a birdwatcher must have to be able to fully enjoy watching birds. Bins or binocs enable us to get close-up views of our subjects and has converted many of us from people ignorant of the birds around to fully fledged birdwatchers the moment we see birds up close and in more detail.

Since becoming a birder and acquiring my first pair of binoculars in 2010, I have upgraded once to a much better pair (in my opinion) and have been enjoying it up to now. I’ve been meeting a lot of people who are interested in getting their own pair of bins so here is a short article about binoculars and what you should know about them.

That’s me with my Minox bins.
Photo by Andrew Sebastian


Binoculars are optical instruments used to magnify the view of distant objects. They are actually two telescopes mounted on a single frame. Binocs have a myriad of uses from the opera to the military, hunting and birdwatching, astronomy and sightseeing. Whatever the purpose, binoculars allow us to get great views of the subjects we are viewing.

For birders, a good pair of binoculars is a long-term investment that will enrich the hobby (or should I say passion… obsession?) that is birdwatching.

WBCP members and their bins in Ulsan, Korean during the 8th Asian Bird Fair


There are basically two kinds of binoculars which can easily be told apart because of the structure: Porro prism and roof prism.

The first kind is the older design which is the Porro prism binoculars, named after its inventor Italian optician Ignazio Porro who patented his design way back in 1854. This design features a Z-shaped configuration that bounces images in a zig-zag pattern.

My old Porro prism Bushnell bins beside my newer roof prism Minox pair.

Roof prism binoculars were introduced much later on and featured a straight and more compact design, but are actually more complex inside which accounts for its heavier price tag.

Here’s a diagram from the B&H website where you can read all about the nitty gritty of roof vs. Porro prism designs AND order bins too (*wink-wink)

Photo from

My Personal Experience: I started out with Bushnell Porro prism binoculars and am now using Minox roof prism bins. I prefer my roof prism bins and chose to “upgrade” to them primarily because of the more compact design and considerable lightness compared to the Porro prism bins.


Binoculars come with a 2-number specification such as 7×20 or 10×42. Let’s dissect those two numbers to know what they actually mean.

Magnification – The first number in the specs pertain to the magnification. Magnification is the number of times the object is magnified through the lens. So, for “7×20” bins, the image is magnified 7 times and for “10×42” bins, the image is magnified 10 times. Depending on the purpose, the recommended magnification varies but since we are talking birding here, the recommended magnification is between 7x to 10x magnification. If you are feeling needy and demand higher than 10x magnification, the recommendation is to go for a scope, since the higher the magnification, the more noticeable the hand shake.

Here’s a graphic to show the difference between a 7x and 10x magnification.

Objective Lens Size – The second number in the specifications refer to the size or diameter of the objective lens of the binoculars in millimeters (mm.) The objective lens is the lens closest to what you are looking at and is responsible for the amount of light entering the bins. The bigger the number means a bigger objective lens which means more light which gives the viewer a brighter image. So, 10×42 (or 42mm) bins will have a much brighter image than a 8×30 (30mm) pair.  This number also reflects the actual size of the lens and correspondingly the binoculars: 30mm is smaller than 42mm. The recommended objective lens for birding is somewhere between 30mm to 42mm. Anything lower is considered compact binoculars while anything higher, such as 50mm bins, are usually too heavy and bulky for birding.

Weight – Usually, the bigger the objective lens size, the heavier the binoculars. This is because of the larger glass involved. You may get a brighter image with a larger objective lens but will have to lug around a heavy pair of bins, and weight is another big consideration when choosing a pair of bins since you may have to trek or remain standing for long periods of time. So find a pair that suits your optics requirements and at the same time will be comfortable enough for you to carry for prolonged periods of time.

My Personal Experience: I use an 8×42 pair and I am happy with the magnification. I sometimes try Djop’s 10×42 bins and find it a bit more sensitive to handshake (pasmado kasi ako…) but they do give a larger image compared to mine. The size and weight of my 8×42 is perfect for the field although I’ve met some birders who have a more compact pair in their bag at all times for those spur of the moment birding opportunities. You know who you are <3


Weatherproof-ness – As birders, we usually find ourselves in micro-climatic conditions and it is important that we and the gear we are using are weather proof. It is recommended that the binoculars we use are waterproof and even fog proof (usually stated as nitrogen filled.)

Eye Relief – I’ve only just encountered this term while doing research on this article and, given my proneness to vertigo and dizziness, found it quite important to understand. Eye relief is the distance between the viewer’s eye and the optics being used. When using binoculars, this is the distance between your eyes and the eyecups. This is the concept behind twisting the eyecups down for people who use eyeglasses and twisting them up for those who don’t. It is actually an adjustment of the eye relief and this determines whether you get a full view through your bins or get an obstructed view with those pesky black shadows covering part of your view. Knowing this concept will enable you to properly adjust the eye cups and also how you hold your binocs against your eyes.

Birding in wet, windy, and humid conditions makes having weatherproof equipment a must!

Price – Of course, one of the major considerations when buying a pair of binoculars is the price. I have my own pair of “dream binoculars” which has a hefty price tag of USD2,000! Since I do not have the luxury (yet!) of purchasing those dream bins, I opted to go for my current pair of Minox 8x42s which I am very happy with and cost me approximately USD300. Just work within your budget with the specs you are looking for, but remember that binoculars ARE a long-term investment for any birder and you might as well shell out some hard-earned money for your optics.

Other Features – I’ve enumerated the basic features that I personally find important to know regarding binoculars. But there are more features you can consider such as housing styles and housing material, field of view, focusing distance, lens coatings, and more. Here are some links to articles you can refer to for more information:


  1. Pingback:Through the Lens of a Birder on a Budget: A Photo Essay on Digibins – Wild Bird Club of the Philippines

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