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What is eye relief? And other interesting facts | Optics and Lab Equipment

What is eye relief? And other interesting facts

Last Updated: 22.11.19


The magical world of optical gadgets allows you to peek into the daily lives of birds, wild animals, and even microorganisms and learn everything you want about them. Whether we talk about a high-performance and portable optical microscope or a pair of binoculars, the final scope is to get a clear image of the object or life form in front of us in order to better understand how it works and how it can affect us.

Unfortunately, finding the right piece of equipment for your needs could prove a difficult thing, especially since most technical aspects of these devices are hard to understand by regular people. In the following lines, we will try to describe and define some of the most important technical features of eye devices and provide as many interesting facts about them as possible.

What is an eye relief?

When it comes to the inside workings of magnification instruments, including binoculars or microscopes, you need to know exactly how well the device will work for various purposes and if it the right tool for you.

One of the mystery technical details you are most likely to find on the box of your brand new birding binoculars is the so-called eye relief. This characteristic of magnifying optical instruments represents the distance from the last surface of an eyepiece within which your eyes are able to capture a full viewing angle.

Although the calculation of the eye relief is complicated and complex, as a general rule, the higher the magnification rate, the shorter your eye relief will be. For each pair of binoculars or each telescope, there is an ideal distance that should be put between you and the eyepiece, so you get a full image of the object you see and not just a part of it.


Should we all be concerned?

Although all users will benefit from an ideal eye relief, the ones who should really be concerned about this specification are people who wear glasses or contact lenses.

Wearing glasses will make things a bit more complicated because you won’t get your eyes close enough to the eyepiece in order to obtain a clear field of view. The minimum eye relief required for people who wear glasses to see a clear image is 15mm, although an ideal one would most likely get close to 20mm. The eye relief is influenced by your diopters as well.

Therefore, if you wear glasses, we strongly suggest you pick products that will allow getting a full and clear image of your studied objects so you won’t force your eyes even more.

However, it would be even better if you would get to try the device on your own before purchasing it. Go to a professional store and try as many products as you want until you find the right one for your glasses. In your case, ordering your wildlife viewing binoculars online is not recommended.

Looking on the bright side, each device comes with its own ideal eye relief distance that is clearly stated by the manufacturer on the package or the label of the product. Most of these measurements are given in millimeters (mm), so you’ll have to convert them in inches.

How to read eye relief

Having a tool with a long eye relief is the ideal situation because you are able to see a full field of view while keeping your eyes further away from the device. In the long term, this won’t add too much pressure on your eye muscles, meaning it won’t cause vision problems or headaches from having to focus on an image too closely.

As the eye relief number decreases, you will have to place your eyes closer to the eyepiece. This is especially true for devices with an eye relief of less than 15mm. Ultimately, it all gets down to how clearly you want to see the picture and how much time it will get you until you adjust the eyepiece according to your needs.

If the ideal eye relief number is not stated in the description of the product, you can find it by positioning your eyes at a particular distance from the eyepiece and noticing whether or not you have a clear view. Move closer or farther away from the device until you get a full field of view.


What does it mean for birdwatchers?

If one of your hobbies is observing the life and habits of wild birds, you know that you only get one chance to spot something spectacular like a mating ritual or a fight between males. Therefore, you should focus on finding the right pair of binoculars that not only fit you well and are comfortable, but also allow you to see the bigger picture.

Sometimes, the most amazing reactions won’t last more than a second, so having to constantly look for the ideal eye relief can make you miss all the action. Our advice is to work around your binoculars and exercise with them until you establish the perfect eye relief for your needs. It may take you some time, and you’ll even have to get to your observing spot before the crack of dawn, so you’ll have everything settled before the birds start their activity.

Other things you should take into account

If you plan on watching an object outdoors, getting a clear and full view depends on numerous factors. The time of the day, as well as the weather conditions, can influence your vision and even mess up with your optical device. Fog or raindrops can easily get between the eyepiece and your eyes, blurring your vision.

Strong sunlight can also affect your vision, adding extra pressure on your eyes and making them tired sooner.



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