How To Buy A Spotting Scope (here’s what you need to look for)

If you’re looking to invest in a spotting scope, but don’t actually know what you’re looking for, read on. We’ve put together the ultimate guide with everything you need to know before you spend any money. There are a lot of technical terms and it can seem quite confusing but as with everything, once you understand these terms it all becomes clear.

What Is A Spotting Scope?

A spotting scope is a small portable telescope which is mainly used for land observation as opposed to astronomical observation. Spotting scopes are similar in design to monoculars, telescopes and have sometimes been described as one side of a pair of binoculars. Where spotting scopes beat binoculars and telescopes, is because in certain situations a spotting scope is almost like a cross between a telescope and a pair of binoculars.

Spotting scopes provide a clearer image, higher magnification, but are heavier and more cumbersome than binoculars. Scopes are also more robust than a telescope, gather more light, and are more suited to daylight observations too.

Angled Or Straight Bodied Spotting Scope?

The difference between a straight scope and an angled scope is 45 degrees. What this means in practical terms is you have the choice of either looking straight through the eyepiece at the object you’re viewing or, looking down to see the same image straight ahead. Angled scopes are more practical for many situations including;

• Sharing Images With Others
  As the scope will be set focussed on the image, all others need do is look down at the lens without touching the scope at all.
• Far More Stable Than Straight Scopes
  This is due to being able to use a smaller tripod that doesn’t need to be extended too far.
• Bird Watching (in treetops etc)
  There is a condition known as Warbler’s neck, which is caused by constantly looking up at tree tops and high bushes, this condition is eliminated by using an angled scope. As you are not looking up constantly.
• Stargazing
  Just like looking up at tree tops, stargazing using an angled scope prevents neck pain.
• Digi-Scoping
  Many camera adaptors will only fit onto an angled scope.

Whereas straight scopes are better for hunting or if you prefer laying flat when bird watching etc.

Spotting Scope Range Of Magnification

Unlike binoculars that usually have specifications consisting of two numbers, spotting scopes have three. The first two indicate the range of magnification and the third is the diameter of the objective lens in millimeters. For instance 20-60×80 would indicate a magnification starting at 20x and zooming to 60x with an objective lens diameter of 80mm. This means that at the lowest magnification level on this particular scope you will see objects 20 times larger than with the naked eye. Rising to 60 times larger than with the naked eye when fully zoomed.

There are a few problems associated with zoom lenses including;

• As you increase the magnification you narrow the field of view
• As you increase the magnification you lose the depth of view
• High powered magnification increases the effects of heat distortion and haze
• Higher magnification means light loss
• Any magnification above 10x will require a tripod 

Why Is The Objective Lens Diameter Important?

The only way the object you see through the lens is illuminated is via the objective lens. So the larger the diameter of the objective lens, the more light can enter the scope and the brighter the image will appear. As the objective lens is made from optical glass, the bigger it is, the heavier it makes the overall weight of the scope. The objective lens size along with the magnification value determine the exit pupil of the spotting scope.

What Is The Exit Pupil?

The exit pupil is the beam of light that enters the spotting scope through the objective lens. The exit pupil is important because it should match the size of our own pupil as closely as possible. The human pupil has a diameter in bright daylight of between 2 to 4mm and dilates to around 6mm as the light fades.

The exit pupil isn’t always specified in the scopes specs but it’s an easy calculation to make. Just divide the objective lens diameter by the magnification value, the result will be the exit pupil in millimeters. With zoom scopes you will get two different exit pupil values, one for each level of magnification. The scope in our earlier example 20-60×80 has an exit pupil of 1.33mm and 4mm respectively because 80÷60=1.33 and 80÷20=4.

Fixed Eyepiece Or Zoom Lens?

Lots of scopes come with a fixed eyepiece, this means your magnification level is permanently set and cannot be changed, unless you actually replace the eyepiece. A zoom lens allows you to change magnification level without having to replace anything. Generally a 20-60 zoom is a great place to start.

Fixed eyepieces are generally used for surveillance and stargazing, and zoom lenses are better for hunting and bird watching.

Eye Relief

The eye relief is the perfect distance between the eyepiece and your eye to get a full, clear image with no black rings or other distorted image. Most scopes have an eye relief that will be comfortable for your eyes unless you wear glasses full-time. In which case you will need to opt for a scope with long eye relief which allows more space to accommodate for your glasses whilst still maintaining the correct distance for perfect viewing.

Close Focus

This is the term used to describe the closest object you can see through the lens of the scope. It is often overlooked when it comes to spotting scopes, but if you’re planning on digi-scoping it can be an important factor.

Digi-Scoping

Digi-scoping is a way of combining your spotting scope with a digital camera. Most scopes have the ability to attach an adaptor to the scope to attach a digital camera and take amazing images. A decent spotting scope can provide a level of magnification that would equal 1,250 to 3,000mm if using a DSLR camera.

Tripod Support

As spotting scopes are capable of high magnification levels, they will need to be supported to prevent a shaky image. All hand held optical equipment with a greater magnification than 10x will exaggerate the slight shake we all have when holding anything for prolonged periods of time. Most decent scopes are supplied with a tripod but check before you buy.

Light Transmission

As we said earlier, the only way we can see any images through a spotting scope is because of the light that enters the scope. To improve on light transmission, spotting scope lenses are made using extra-low dispersion (ED) or high density (HD) glass. The prisms are constructed using either BAK-4 or BK-7 glass. Both of these are high quality precision optical glass with low amounts of imperfections which helps improve light transmission. BK-7 has slightly more imperfections than BAK-4 but both are high quality.

Lens Coatings

To improve the light transmission further, look for FMC or fully multi-coated lenses. These have every surface of the lens coated in multiple layers of light transmission improving, glare reducing coatings.

Prism Types

The magnification of a spotting scope is created by the use of glass prisms. There are two types of prism systems used in spotting scopes (and binoculars) ; they are roof prisms or Porro prisms.

Porro Prisms

This type of prism arrangement uses two offset prisms to magnify and set the image back up the correct way. They make the scope bigger, heavier and bulkier and can easily get knocked out of alignment which can cause eye strain and headaches. Porro prism spotting scopes are cheaper to produce and that saving is passed on to us, the buying public.

Roof Prisms

Roof prism scopes have the prism set into the roof of the lens tube. This allows them to be smaller, lighter and more compact. However due to a phase corrective coating that is necessary in roof prisms to produce a clear image, they are considerably more expensive. 

Spotting Scope Focus Systems

There are two main types of systems when it comes to spotting scopes. One has a collar that twists the whole barrel. The other has a small knob which is normally fitted on the top of the scope, close to the eyepiece. The second type takes longer to adjust but it does allow far more accurate and precision focussing. Your choice is between precise focussing and ease of use.

How Much Does A Spotting Scope Cost?

As with all precision optical equipment, prices vary greatly. We would never recommend buying a very cheap scope as the quality is not good. Whether you choose an angled or straight scope, the prices are roughly the same. The difference in price comes down to performance and quality. Spotting scopes cost from around £100.00 to £5,000.00 but for around £250.00 you can buy a 20-60×80 spotting scope with a lifetime guarantee.

Warranty

Most decent spotting scope manufacturers offer a lifetime warranty that will repair or replace your scope if it develops a fault. Even some of the cheaper models offer 12 to 24 month warranties.

Frequently Asked Questions