Spotting Scopes - Introduction    (For Binoculars please click here)

Next to binoculars and field guides, birders use scopes more than any other tool. The main reason is that scopes give much more magnification than binoculars. This allows birders to see detail on birds that are too distant to be safely identified through binoculars. They are designed to be mounted on tripods so they can be kept steady under normal conditions

Design

There are three basic scope designs: refractive, Newtonian, and catadioptric. Nearly all scopes sold for birding are refractive. A few are catadioptric, and the only Newtonian scope is difficult to find, both in stores and in the field.

The two main factors responsible for the low use of catadioptric scopes are the cost (3 to 5 times the cost of top end refractive scopes) and the body construction does not stand up to the rigors of birding. Even though catadioptric scopes produce cleaner images at higher magnification, few birders are willing to pay the higher costs. Therefore, in the rest of this discussion we will stick to refractive scopes.

There are two body designs used in refractor scopes: Angled and straight both have their proponents.

Angled Scopes Straight Scopes     Easier to share with a group Higher eye point means you can use a shorter tripod Better for birds soaring or in tall trees Less strain on your neck for level viewing Less chance of eyepiece collecting rain or dust Easier for viewing birds on the ground or water or below a cliff Easier to aim when inexperienced

To decide between angled and straight scopes, you will have to consider how you will be using yours.





Some Spotting Scope Specifications

Magnification / Power - Birders use scopes because there are many instances where binoculars are not powerful enough. Scope magnifications go from a low of 15x to a high of 75x. While higher magnification is theoretically possible, the resultant exit pupil would limit successful use to only the brightest lighting situations. When the exit pupil falls below 1.33mm, image quality begins to suffer. Also, very high magnification increases the likelihood of distortion from heat waves and scope movement, as these effects are magnified along with the image.

Objective Lens Size - Objective lens diameters fall into four size ranges. 50mm, 60-65mm, 77-85mm, and above 85mm. In the latter range, only the 100mm Pentax ED scope is currently available. Objective lens size is the main indicator of scope brightness, as that is dependent upon the area of the objective. There have been some new advances in scope quality in the 65-66mm objective range, but these scopes are still not up to the challenge of the 80mm+ scopes in the most adverse conditions. As with binoculars, larger objectives mean more weight, but they also allow for larger magnification. When deciding on the objective size for your scope, get the largest objective you're willing to carry. Unless you really need to save weight, you will be rewarded with a superior image, other parameters being equal.


Objective Lens Glass - The best scopes have objective lenses with special glass that corrects certain optical problems. Labeled Extra-low Dispersion (ED), Fluorite (FL), or High Density (HD), this glass makes it possible for all the wavelengths of light to focus at (APO = apochromatic) or very near (achromatic) the same point. This has an immense affect on sharpness, shows better detail on the bird, and reduces eye strain. Many scopes come in both ED/FL/HD and non ED/FL/HD versions, with the better glass adding 50% or more to the cost, but few active birders would say the price isn't worth the improvement in view.

Eyepieces - The part of the scope that determines the magnification is the eyepiece. For a given focal length objective, shorter focal length eyepieces give greater magnification. You don't have to worry about the math, however, as most eyepieces are labeled with the magnification they provide rather than their focal length.

Advances in zoom lens technology over the last decade have taken the zoom eyepiece from the lens to be avoided to the one most favored by birders. Zoom eyepieces allow birders to scan at low power, then crank up the magnification to get the most detail. There is nothing like a 60x image that is so sharp you worry about cutting your fingers on it. Other eyepieces have their place, however. 30x and 50x (give or take a few x) wide angle eyepieces are often favored by sea watchers and hawk watchers. A 27x eyepiece with long eye relief can be a boon to eyeglass wearers and digiscopers. If you're getting a scope that can handle its full range of zoom, go with the zoom eyepiece. If you plan to spend most of your scope time at Hawk Mountain or Pigeon Point, you might want a fixed wide angle, or you might want to consider getting both.

Some manufacturers use the same eyepiece mount for both their 60-66mm scopes and their 77-85mm scopes. Because of variations in body design, some scope brands will have the same magnification for a given eyepiece with both scopes while others will have different magnifications. In the latter case, you may see a designation that says:

Zoom eyepiece 15x-45x/20x-60x for 65mm/80mm scope. This will mean that with the 65mm scope this eyepiece has a zoom range from 15x to 45x, but with the 80mm scope the range is 20x to 60x.



Exit Pupil

This is the size of the image at the focusing point of the binocular. It is computed by dividing the objective size by the magnification (power). You can find exit pupils ranging from 7mm (7x50, 8x56) to 2mm (10x21). A larger exit pupil means a brighter image. It also means that it is easier for your eyes to stay on the image when it is bright out and your pupils are contracted.



Eye Relief

Eye relief is very important to eyeglass wearers. It is the distance behind the ocular lenses at which the image is in focus. Since eyeglass wearers can't get their eyes as close to the lenses, longer eye relief will project the image beyond their glasses. With sufficient eye relief, usually at least 15mm, eyeglass wearers can see a full image. Long eye relief will usually reduce field of view. If you are nearsighted or farsighted, you can use your binoculars without wearing glasses and the binocular's focus will compensate. However, if you have astigmatism, you will need to use your glasses.



Twilight factor - Exit pupils should not be your sole judge of a spotting scope, however. A 60mm scope at 20x and a 90mm at 30x both have 3mm exit pupils ?but the 90mm scope is brighter due to its better light gathering. The twilight factor is a better way to judge how well a scope performs in low light than the exit pupil, as it balances light-gathering and magnification (both of which affect how much detail you can see.) You find the twilight factor by multiplying the scope's magnification by the diameter of its lens, then finding the square root of that product. The larger the twilight factor, the more suitable a scope is for early morning and twilight use. A 60mm scope at 20x, for example, has a twilight factor of 34.6, while a 90mm at 30x has a twilight factor of 52, which explains the better low light performance of the latter despite their identical exit pupils. If low-light birding is important to you, and you can't decide between two different scopes, find the twilight factor of each at a similar magnification. The scope with the higher twilight factor will show you the most detail in low light.

Focusing - There are three focusing mechanisms used in refractor scopes: single knob, double knob, and helical. Single knob is the most common. It tends to be a bit slow, but very precise. Double knob, available on Leica, consists of two knobs with different drive ratios for the same internal focusing gear. The fast knob allows for quick focusing travel while the slow knob gives precision once you're close to the proper focus. Helical focus, available on Swarovski and some Nikon scopes, consists of a collar around the scope body to drive the focusing gear. They are good for rapid focus changes. Now that variable speed focus is available on Brunton binoculars, expect to see this type of focusing on future scopes.


Near Focus - How close you can get to your target and still see a sharp image in the scope is called the "near" or "close" focus. Because a spotting scope's field of view is narrow, most scopes are not designed to focus as close as binoculars, with 25' to 35' being the norm.



Eye relief - The minimum distance between a scope's eyepiece and your eye that allows you to see the entire field of view is the eye relief. While long eye relief is important for observing comfort, it is especially important if you must wear eyeglasses to observe, as your glasses can keep you from getting close enough to the eyepiece to see all of the already-narrow field. If you are near or farsighted, or have only mild astigmatism, you can usually leave your eyeglasses off when using a spotting scope, as the focuser has enough range to accommodate these conditions. If severe astigmatism forces you to wear glasses at all times, however, eye relief should be 12-15mm or longer to allow you to see most of the scope's field of view.


Mountings - All spotting scopes are equipped with a built-in 1/4"-20 thread adapter that allows them to be mounted directly onto a standard camera tripod. The majority are light enough to be usable with virtually any camera tripod at low powers. Although skimping on the stability of the tripod to save a few dollars can lead to frustratingly unsharp images at high powers due to a trembling tripod.





How to Pick the Right Spotting Scope

Picking the right spotting scope is easier than picking the right binocular. There are fewer decisions to make and fewer models to choose from. It's almost a matter of letting your budget decide which spotting scope is best for you.

If serious photography is planned, keep in mind that catadioptric scopes (and the few high-end prismatic exceptions noted in our catalog, particularly those with ED glass or fluorite optics) generally make better telephoto lenses than a small prismatic scope.

If low light performance is important, look for the highest twilight factor.

If you spend a lot of time in the field, look for a reasonably light weight.

If you expect rough treatment or regular soakings, consider a rubber-armored and/or waterproof scope.

If getting the sharpest, highest contrast image possible is more important than convenience or price, consider single power eyepieces rather than a zoom. Also consider ED glass or fluorite lens systems for ultimate sharpness.

From $200 to $2000, each time you double the retail price of a spotting scope you can expect about a 10-15% improvement in optical performance. Don't be afraid to buy a spotting scope at the lower end of the price spectrum, however, as they are all quite good. We're weeded out the poor performers for you, choosing to carry only those which meet our standards, which tend to be high.

But don't think you have to strain your budget to buy the most expensive scope simply because it has the best optics. It may not fit your birding style or your requirements for durability, field of view, low light capability, etc. Pick the spotting scope with the features and performance you and your budget will be comfortable with - but don't underbuy, either. Buy the best optics you can afford. As we're said before, good optics are a lifetime investment - and investing in quality always pays visible dividends

Photography using scopes

There are two ways to take photos through a scope. You can get a camera adapter that allows you to attach a 35mm SLR to the scope. This system will have a fixed focal length and you will need to use the camera's viewfinder as your eyepiece, and there will be no way to change the aperture. Or, you can put a digital camera up to the back of your scope. In either case, you will get the best results by using a scope with the largest possible objective lens, as it will gather the most light.

Choosing Tripods

Tripods are critical to the operation of your scope. If the tripod is not sturdy enough to keep the scope steady, all the money spent on the scope will go to waste.

Especially when using a straight scope, it is essential to know how to choose a tripod of the proper height. The most important measurement for stability is the height of the tripod with the center column retracted. As you raise the center column, the scope becomes more susceptable to vibration.

To calculate the tripod height you need, work downward from the top of your head. Your eyes are about 4 to 5 inches from the top of your head. The scope eyepiece is about 4 inches above the bottom of the scope's mount plate, and the tripod head is about 4 to 4.5 inches high. Adding these up, we get 12 to 14 inches, which is the amount less than your height that the tripod need to be without a head. If you're very tall, you may not find a tripod that gives you that much height without raising the center column, so get one that requires as little column rise as possible.

Each tripod also has two critical weight specifications. The obvious one is the weight of the tripod. Remember here that you'll have to include the weights of the head and the scope to get the total package. The other critical weight is the maximum load capacity. This is an indication of the strength of the tripod, and should always be larger than the weight of the head plus the weight of the scope.

For 50mm and lightweight 60mm scopes, you should be okay with any of the better single unit tripods. Be sure to get one with a video style head, not one designed for still photography. If possible, get one with fluid damping in the head.

For the better (heavier) scopes from 60mm on up, you will want a tripod that has separate legs and head - not for flexibility, but because these tripods are sturdier.

Carbon fiber tripods are much lighter at the same strength and sturdiness compared to aluminum. Carbon fiber can save up to 30% in the weight of the legs over the same size of aluminum tripod. It can also put a huge dent in your checkbook. Costs can be more than doubled.

Again, heads should be video style and fluid damped. They should also be rated for the weight of the scope. Some heads designed for small video cameras will not be able to support an 80mm scope.

By the way, it is usually okay to get your legs and head from different manufacturers. All tripods have standardized mounting screws for the head. This is usually a ¼-20 bolt affixed to the center column, but may occasionally be a 3/8" bolt. In either case, your head should be able to accept the screw by installing or removing a ¼-20 to 3/8 adapter.

No matter what size tripod you get, you will want one that accepts a quick release plate. This is a plate that screws onto the mounting plate of the scope and pops in and out of a socket on the top of the center column, allowing for quick attachment and removal of the scope to and from the tripod. You certainly don't want to spend lots of time attaching your scope to your tripod every time you go birding.