Binoculars and Spotting Scopes

When it comes to optics and the purchase of either a pair of binoculars, or a spotting scope, I feel the more informed you are, the better. What I want to furnish to my readers is some basic information when it comes time for you to purchase whatever kind of optical device you need. I’m not going to endorse one product over another. What works for you is a personal thing, best left up to the buyer. And finally, only buy what you can afford to spend. If you look at the “My Gear”, section, you’ll notice that I don’t buy the most expensive when it comes to optics. Will having the most expensive pair of binoculars make you a better birder? Granted, a clear, crisp image is going to enable you to make a more precise Identification. But like I said, “If you can’t tell the difference between a Robin and a Wren, your pricey scopes are worthless”.

After examining various blogs, web sites, optical company sites, and  consumer reviews, I feel that I’ve come up with specific optical features that you need to take into consideration when it’s time for your next purchase of either binoculars, or spotting scopes.


Magnification: Binoculars are categorized by a series of numbers, such as, 10×50, 8×42, 7×35 and so forth. The first number is the magnification, or how many times closer the object will appear. So if you have a pair of  10x binoculars, viewing an object 100 feet away, will appear to be 10 feet away. So you may think that if I bought a pair with a higher magnification then I’ll be able to see the birds better. That may be so, but with higher magnification you lose your field of view. In other words, by narrowing your field of view, you’ll see less of the big picture than with higher magnification binoculars. I find having a larger field of view helpful when it comes to following birds when they jump around from branch to branch. With my 12×50’s I lose them when they move out of my field of view. I have to pull my binoculars away from my eyes to try and spot it again, and that’s time lost in trying to identify a bird. Some of the disadvantages of higher magnification are:

  • Smaller field of view
  • Heavier
  • More difficult to focus on close objects
  • Harder to hold steady
  • Takes more time to focus

Advantages are:

  • Easier to watch distant birds
  • Viewing in wide open spaces
  • Viewing birds that aren’t real active

If you know what kind of birding you’re going to  primarily do, then use this information to buy your binoculars. How about borrowing a pair and try them out. It wouldn’t hurt, and might sway you in picking the correct magnification. I had to learn the hard way, when I had to physically back up with my 10×50 to focus on some warblers that were too close. That’s why my 8×42 have a close focus of 8 feet. Sweet.

Objective Lens Diameter: The second number that’s going to concern you is the diameter of the objective lens. One of the points concerning objective lenses is that the larger the lens, the more light that’s going to be let in. And that’s still true. But with this larger lens comes the additional weight. That makes holding your binoculars steady a little more difficult. Then you have to haul them around with you in the field, unless your thinking about just birding from your front porch (and there’s nothing wrong with that). As a general rule pick a pair with the objective lens size between 30-50mm. If you go smaller than that, you gain in the compactness of them, but you give up the light that comes in. And when you bird in low light situations, you need all the light you can get. And try not to scrimp to much here on price, because paying more for a better pair of binoculars with 40mm lens will last longer than those cheaper 50mm ones. Remember to do your homework and try out plenty of different ones before you buy.

Exit Pupil: Talk about teaching a old dog new tricks, the same thing can be said about “exit pupil”. I really had no idea what it was till I read about it somewhere. What this is, it’s the diameter of light in millimeters visible through the eyepiece. Well smart ass how do you determine that? Some algebraic equation. No, just divide the objective lens diameter by the magnification. The answer will be your exit pupil size. The importance of this is that the pupil size of a  human eye is about 4mm to 7mm, considering your age and available light. So you want your exit pupil size to be as close to 7mm as possible. With a larger exit pupil, more light will be getting to your eyes when looking for that Barn Owl at night. Also remember that during bright light situations, your pupil will already be small, so if your using a compact pair of binoculars with a small exit pupil, your going to have to center your eyes exactly over the exit pupil to find the bird. Just remember, for general use pick a pair with at least 4mm exit pupil.

Prism Design: There are 2 different types of prism design, Porro and Roof.

Let’s do some side by side comparison of these 2 types of binoculars.

Roof Prism—————————— Porro Prism

Slim & stream-lined                                  Big & bulky

Lightweight                                                  Heavy

Internal Focus                                            External Focus

Small field of view                                      Larger field of view

Decreased depth perception                 Greater depth perception

Brighter                                                           With proper coating can be as bright

Weaker design                                              More durable

Typically cost less                                       Typically cost more

Close Focus: For me this was one of the big selling point when I recently purchased my 8×42 Roof Prism binoculars. The only pair of binoculars I had when I was up at Maggie Marsh during migration was my 10×50 Porro Prism model. And I suffered, because I had no close focus. Warblers dripping from every branch and I couldn’t focus on them unless I backed up. I was sad. So remember, as your magnification increases, the minimum close focus distance increases as well. A good close focus distance would be between 10-15 feet.

Binocular Eye Relief: This is very important if your an eyeglass wearer. The normal distance that non-eyeglass wearers need to be from the eyepiece and have full field of view, is  9-13 millimeters. If you wear glasses that distance is increased. So some binoculars have adjustable eye cups, while others have just rubber cups that fold down. This will help compensate the person who wears glasses. Because you don’t want to have to keep taking off, then putting back on your glasses when you bird.  This is where “Trying it on for size”, comes into play.

Field Of View: The field of view is measured as the width of area visible at 1,000 yards from the observer. A wider field of view will enable your to find and track birds easier. Higher magnification will reduce your field of view. So there’s a trade off. To determine field of view on your binoculars look for the “Field Degree” number near the eyepiece. Let’s use my Leopolds as an example shall we. My angular field of view in degrees is 7.5. Now we multiple that by 52.5 (which is the number of feet in 1 degree at 1,000 yards) to come up with a field of view of 393.73′ at 1,000 yards.

Lens Coating: Lens coatings are important in increasing light transmission and improving image brightness. Lens coatings will lower reflective losses that will result in a brighter and sharper image. Here are some coating terms and their definitions.

  • Coated: A single layer on at least one lens surface.
  • Fully Coated: A single layer on all air-to-glass surfaces.
  • Multi-Coated: Multiple layers on at least one lens surface
  • Fully Multi-Coated: Multiple layers on all air-to-glass surfaces.

Now with more coatings, the price goes up. But you’ll get a pair of birding binoculars with a better image.

Binocular Weight: For me the weight of my binoculars isn’t a big deal. I’ve carried my 12×50’s around all day without complaining about the weight. So if your a frail little thing, then buying a light weight pair might be an option. For all day birding a pair weigh less than 30 oz. is where you might need to head. I think that having a balanced pair of binoculars is more important than the weight. An off balanced pair will wear you out faster than a pair that’s on the heavy side.One piece of equipment that I’ve heard really helps is a harness instead of the neck strap that comes with most binoculars.

Waterproofing: With this option it’s not only water we want to keep out, it’s also dust, dirt, or baby drool. As for me the real scare is internal moisture. Considering where I live, (it gets very humid in southwestern Ohio) the fluctuation in temperature and humidity will fog up those cheapies you just bought. And since I bird year round, nothing will frustrate a birder more than to take your nice, warm binoculars out of your warm vehicle into the cold winter air. FOG! And if your a clutz, remember the last time you fell into the stream. Enough said.

Rubber Armoring: Read my lips here when I say, RUBBER ARMOUR DOES NOT MEAN THEY ARE WATERPROOF. But they feel real good in your hands though. And it is a good thing to think about if your suffering from incurable butter fingers. It will add to the overall price.

Spotting Scopes

Magnification: A general rule of thumb is a good range of magnification for bird watching will be between 15x & 60x. If they fall below 15x, then you might as well just carry binoculars. And anything above 60x the field of view narrows so much you won’t be able to make anything out in low light. The key point to remember is the higher the magnification, the larger the objective lens needs to be.

Objective Lens: As discussed earlier, the larger objective lens will result in clearer, crisper, brighter, images. Bird watching objective lenses range in size from 50mm to 80mm. And some go as large as 100mm. Consider the size your will to pay for as well as carry. Larger objective lens means more weight. Also remember that during low light situations, the larger objective lens will result in a clearer image when your zoomed in all the way.

Exit Pupil: When it comes to determining exit pupil for a spotting scope, the same mathematical equation applies. Divide the objective lens size by the magnification. With a spotting scope we really don’t want the exit pupil size to fall below 1.33. With my spotting scope, which is a 20-60 x 80mm the exit pupil size will be 4 for 20x, and 1.33 for 60x. With anything lower, then you’ll lose a lot in low light conditions.

Eyepieces: One thing to remember here is that all spotting scopes don’t come with eyepieces. What’s that you say! That’s right, you may have to buy a separate eyepiece. It’s kind of not giving you the tires when you buy the car. Your eyepiece is what determines your magnification, field of view, exit pupil size, and eye relief. So if your new scope give you an option of different eyepieces, determine what kind of birding  you’re going to do. They can get pricey, so knowing ahead what you’ll need is critical. That’s unless your rich, then you’ll take one of each. I’m not going to bore you with all the different types of eyepieces for all the different scopes on the market, but I will suggest that you have the proper size objective lens to match whichever magnification eyepiece you buy.

Body Design: Straight or Angled: Since nearly all birding scopes are refractor scopes, then the next thing for you decide is whether you want an angled or straight body design. Well for me this is a personal thing. For the advocates of using the straight style, they like the straight line of sight for ease of aiming. If you bird from your car, a straight scope will be easier to use with the proper window mount. And lastly, they can follow birds that are moving easier. I’ve not had any of those problems with my angled style scope. One thing I like is not having to put my tripod all the up to look through it. I’m not terrible tall, but my inexpensive tripod only goes so high. Just try both out and see which one fits you better.

Focus Mechanism: There are 3 different types of focusing mechanisms on the marker and they are:

Single: Most common, slow, but precise, not as accurate with fine focus.

Double Knob: One knob gives fast, coarse focus, other gives precision fine   focus.

Helical: Slower on coarse focus, better fine focus control, works well for observing objects that are quickly changing distances, near to far.

Glass Coatings: The same holds true with binoculars as they do with spotting scopes when it comes to lens coatings. The price will go with the better coatings. But so does the clarity, detail, sharpness and eyestrain from trying to determine what kind of bird that is through this non-coated scope.

Water & Weather Proofing: This shouldn’t be an option. Your scope needs to be protected from whatever Mother Nature throws at you. Maybe some rubber armoring would be nice. Protection from blowing stuff, like sand and dirt. And if you look at the “My Gear” section of this blog you’ll notice I go that one step further and got mine fitted with a cover. Yet another option for you to consider. Is your head about ready to blow up with all this info?

I certainly hope that what I’ve presented will be of value to you in the purchase of either your next pair of binoculars or a spotting scope. Remember, stay within your budget.


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