How To Choose Binoculars For Surveillance (Best UK Guide)

How To Choose Binoculars For Surveillance (Best UK Guide)

Whether you are a police officer, a private investigator or just want to keep an eye on a shady character that lives down the road from you, you’re going to find the job far easier if you’re using binoculars. The problems start to arise almost as soon as you decide you’re going to need some optical help with your surveillance. There are so many brands offering binoculars, and so many that, although sound good on paper, would be totally useless for covert surveillance.

So where do you start? Luckily for you, you already have started, and by reading this article, you are already putting yourself ahead of the game. Here at Binocular Base we spend our entire working life checking out the good and the bad in the world of binoculars so you don’t have to.

We’ll put you on the right path towards the best binoculars you’re going to need to get the best results. Our hard work will help your hard work pay off. For instance we are aware of the many pitfalls and mistakes the uninitiated make when it comes to buying the correct pair of binoculars for surveillance work. So let’s get straight into it.

What Are The Most Important Features For Surveillance Binoculars?

When choosing the perfect binoculars for surveillance there are a number of important features that need to be considered. Those features include:

Which Prism Type Is Best For Surveillance Binoculars?

This is the first consideration to make when looking for surveillance binoculars, and it’s a big one. There are two main types of binoculars for surveillance, they are :

Porro Prism Binoculars

The first difference between these two types of optical devices is the cost. Porro prisms have been around, at least the design hasn’t changed for more than 200 years. Because of this they have become far less expensive to produce than their roof prism counterparts. However, Porro prism binoculars are on the whole bulkier, heavier, larger, and easier to knock the prisms out of alignment (which can cause eye strain, headaches and migraines). Also due to their design, Porro prism binoculars are far less likely to be waterproofed or fog proofed either.

Roof Prism Binoculars

As implied by their name, the prism arrangement is situated in the roof of the lens tubes, which means the prisms are far less likely to get knocked out of alignment. This in turn, means far less eye strain, less headaches and no sight related migraines. Roof prism binoculars are also lighter, more compact, easier to carry, easier to conceal, easier to waterproof and easier to fog proof. Due to the precision instruments and intricate internal design, roof prisms are more expensive to construct and that cost is passed on to the customer.

So What’s Best For Surveillance Work Porro Or Roof Prism Binoculars?

Porro prisms tend to have larger objective lens diameter and higher magnification values than roof prisms which means they often have a wider field of view which is an essential quality for surveillance work. That said, roof prisms are far more compact making them easier to conceal, plus the ability to focus almost immediately at most distances is another advantage in favour of roof prisms. 

If you need to watch over large areas (like crowds) Porro prisms will remain focussed once they’ve been set up to your eyes. Using roof prisms under similar conditions could lead to eye strain even if you constantly refocus. This is because the eye tries to compensate for any blurred or distorted image. Surveilling fixed positions would be better using roof prisms, so it really is a decision only you can make.

Magnification, Objective Lens Diameter And Field Of View (FoV)

Most newbies to the world of binoculars assume that the highest magnification you can get, the better the bins will work for you. It’s easy to see why this is believed to be the case, but it’s totally wrong. That’s because all humans will begin to shake ever so slightly, when holding any object (no matter how light it weighs) out in front of us for any length of time.

This subtle shake is usually not a problem, but when the object that’s shaking is binoculars, the image seen through the lens is blurry at best and unrecognisable at worst. Think of a slight shake magnified by 12 times, that slight shake is now a major shake. This is why we never use binoculars with a higher magnification than 10x unless using a tripod.

I S Binoculars

Tripods are great for long distance surveillance ops but as most surveillance operations are relatively close distance, a tripod is not an option. So 10x is the maximum magnification for hand held binoculars unless you use IS binoculars. IS or image stabilized binoculars have incorporated the technology from camcorders and allow higher magnification without a blurry image.

We wouldn’t recommend I S binoculars for surveillance work, some do, but, firstly the added weight of the internal battery needed to power the I S tech can become a problem long term, and far more importantly in our opinion, I S can be quite noisy. Now we are supposing that your surveillance should be covert, and hearing a series of clicks as the I S cuts in would alert your subject to your presence fairly quickly.

Magnification And Objective Lens Diameter

It’s easy to tell the values for magnification and objective lens diameter, as it’s stamped onto the body of the binoculars. Look for a series of numbers separated by the letter X. Examples include 7×25, 8×32, 10×42.

The first group of numbers including the X tells us the magnification value, 7x means objects viewed through the binocular lens will be seen 7 times larger than with the naked eye at that same position. The last number indicates the diameter of the objective lens in millimeters, so 7×25 gives us a 7 times magnification, and an objective lens diameter of 25 mm.

Field Of View (FoV)

The field of view is the total width of the image seen through the lens, from right to left while looking straight ahead. In the bino specs it will be stated in one of two ways, angular FoV, or linear FoV. the angular value is expressed in degrees and an acceptable angular field of view is between 6° to 8° which in linear terms is anywhere between 315 feet per 1,000 yards to 420 feet per 1,000 yards, or  105 metres per 1,000 metres to 140 metres per 1,000 metres (which are all the same, expressed three different ways).

If you have two or three pairs shortlisted and the FoVs are expressed differently, it’s easy enough to convert them all to the same numerical system.  1° is equal to 52.5 feet or 17.5 metres. So if you have two pairs expressed in feet per 1,000 yards (or metres per 1,000 metres just multiply the degrees by 17.5 to find the value in metres or 52.5 to find the value in feet.

What FoV Is Best For Surveillance Work?

For surveillance work, the wider the field of view the easier it is to keep track of the subject under surveillance. You can follow them easier if you don’t have to keep removing the binoculars from your eyes, allowing your eyes to refocus, find the subject, place the binoculars back to your eyes, allow them to readjust and so on. 

The best FoV for surveillance will be as close to or above 8° (420 feet per 1,000 yards, or 140 metres per 1,000 metres) as possible. This means you’ll be looking for a relatively low magnification.

How Does Magnification Affect FoV?

It’s a simple fact of science that as the magnification increases, the FoV decreases. There are countless formulaic ways to prove this but the easiest way is to use a simple demonstration. 

Hold a business card in front of your face so that the whole card is visible. Now slowly move the card closer to your face, as you focus on one or two words, the rest of the card becomes obscure, until it eventually becomes unreadable. 

So as you moved the card closer, you increased magnification, the words on the card eventually disappeared, as the FoV decreased. 

Objective Lens Diameter

The objective lens diameter size is important for a number of reasons. All of which have some bearing on the overall effectiveness of the binoculars.

  1. The objective lens diameter indicates the relative weight of the binoculars.
    As the size of the objective lens increases, so does the overall weight of the binoculars.
  2. The size of the objective lens diameter affects how bright the image appears through the binocular lens.
    The larger the size of the diameter of the objective lens, the more light is allowed into the binoculars which makes the object viewed through the binoculars brighter (and clearer).
  3. Binocular sizes are determined by the diameter of the objective lens
    Full size binoculars have an objective lens greater than 40mm
    Mid size binoculars have an objective lens of between 30 to 40mm
    Compact binoculars have an objective lens lower than 30mm
  4. Having the numbers for both the objective lens and the magnification makes calculating the binoculars exit pupil easy
    The exit pupil is the size of the shaft of light that leaves the binoculars eyepiece and hits your eye. This is not a big deal for daytime surveillance, but at night or during periods of low-light it can be the difference of seeing your subject or missing them completely. To determine the exit pupil just divide the objective lens size with the magnification. 8×25 binoculars have an exit pupil of 3.13 which is OK in daylight hours as our own pupils are roughly 2 to 4mm during the day.

    It’s at night that the exit pupil comes into its own though, because the human eye has a pupil diameter of 7 to 8mm at night so the best binoculars for use at night would have an exit pupil of somewhere between 7 to 8mm. A 7×50 binocular has an exit pupil of 7.14 which is well within the 7 to 8mm parameter.

What About Zoom Lens Binoculars?

Zoom lens binoculars can focus in at a relatively low magnification and then zoom in at a far higher magnification, the numbers on the binocular body will look something like 8-20×50 This represents 8 times magnification, rising to 20 times magnification and an objective lens diameter of 50mm. They sound ideal for surveillance work as you can start off in a low mag and once you identify your target, you can zoom in for a far closer view.

The problem with these zoom lenses tends to be, as you increase the zoom the image becomes blurry especially around the edges. This is due to the way the lenses operate which without getting too technical causes one or the other of the lenses to drag which is what causes the blurred image. The image almost appears to be like looking through a tunnel. The bottom line is, you get a poor image when it’s zoomed and you lose so much FoV as to make zoom lens binoculars pretty useless especially for surveillance work.

Optimum Optical Numbers For Surveillance Work

It’s choice time, you will find you need different magnification and objective lens diameter values for different surveillance operations.

  • Long-Distance Surveillance Work
    If the subject of your surveillance is dangerous, or it’s important they don’t realise they are being surveilled, you will need to rely on binoculars with a large objective lens diameter, and a relatively high magnification.
  • Short-Distance Surveillance Work
    For short-distance or close up surveillance, you won’t need such high magnification, but you’ll still need a large objective lens diameter. To keep the subject in view at all times.

Binocular Lenses For Surveillance Work

To reduce the glare on the lens of the binoculars a good lens coating is important. As with most things when it comes to binoculars, the descriptions used for lens coatings can be confusing. The best from a surveillance point of view is fully multi-coated lens. This means that all lenses have been coated with multiple layers both inside and out. This will not only reduce the glare but will also improve light transmission, brightness and contrast.

Prismatic Glass

The glass used to create the prisms is important, because it can make a huge difference in the clarity of the image seen through the lens. There are two main optical glasses used in the production of prisms for good quality, high end binoculars. They are;

  • BAK-4
    Within the binocular industry, BAK-4 glass is considered the absolute top quality especially for prisms. Both are optical glass which is designed to produce clearer brighter images (which is important for surveillance equipment).  
  • BK-7
    BK-7 optical glass is still very high quality but has more impurities that have a slight impact on the image clarity. To be fair that impact is not easily noticeable and so either is more than good enough for surveillance work.

ED Glass

Extra-low Dispersion glass is another feature you might notice in the binocular specs concerning the prisms. If you’ve ever seen a diagram of a prism, it shows white light entering, with rainbow colours emitting. The lower the dispersion the brighter the colours remain, also if there is high dispersion, there is a likelihood of noticing a halo effect around the image seen through the lens.

Is Waterproofing A Good Idea For Surveillance Binoculars?

We live on a planet which is made up of around 71% water, and in a country where the only way to detect Summertime is usually by the warmer rain. At some point you and your binoculars will get wet. Once the internal workings of the binoculars get water on them, they’ll never work as well again.

There is a coding system in place in the UK to take any confusion away from mistaken (or fraudulent) claims concerning levels of waterproofing. Unfortunately that coding system is quite confusing so to make it simple, you’ll need binoculars with an IPX6 coding (or above) to keep the rain out.

What About Fog Proofing?

Spending long hours in cold and often wet conditions could lead to the lenses of your binoculars fogging up. To prevent this from happening, binocular manufacturers remove the air from the lens tubes and replace it with an inert gas (usually argon or nitrogen) that contains no moisture and so cannot react with rapid fluctuations in temperature, and don’t fog up. As these gasses are sealed inside the lens tubes, no microbial particles can enter which prevents dust or mould spores from becoming a problem.

Rubberised Protective Coatings – Are They Worth Having?

Definitely not from a waterproofing perspective, but to protect the binoculars casing from accidental damage, having a rubberised coating is well worth having. It also makes the binoculars easier to grip and cuts down on reflective glare which could be very handy during covert surveillance operations.

Night Vision Binoculars

More surveillance work is conducted at night than during the day so night vision binoculars seem like a good idea. But they’re not without their problems. For instance, after using night vision binoculars you will be “night blind” for some time. This is because at night our eyes get used to the lack of light and adjust to accommodate the low-light conditions. 

Using night vision entails the image you see to be artificially brightened, so you can see it. Once you remove the optics from your eyes, you’ll not be able to see anything for a period of time (until your eyes reacclimatise to the low-light conditions). In our opinion, you’d be better off using a night vision monocular.

As you will then have vision in both camps as it were, able to see what’s happening in the dark with one eye, while maintaining a dark optimised eye with the other.

Frequently Asked Questions

Why do detectives use binoculars?

Detectives, whether they’re private investigators or law enforcement officers, use binoculars for surveillance purposes. Allowing them to keep their suspect in view from a safe distance.

Which is better roof or Porro prism binoculars?

For surveillance purposes, both Porro and roof prism binoculars have their good and bad points. You would need to decide on which circumstances called for which type and act accordingly.