Selecting Optics for Birding

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Mervyn Shelton
5 years ago
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and the terminology associated with the equipment.

1 Selecting Optics for Birding by Jim Jones, Fort Worth Audubon Society Please note this discussion is meant to introduce the novice birder to sport optics and the terminology associated with the equipment. If you wish to find more details and math behind the design of optics, you should visit the manufacturers websites.

Selecting Optics for Birding Most of us begin birding with our

But we soon discover that small birds are actually not all the same

They have different patterns and key markings that are not easily

2 Selecting Optics for Birding Most of us begin birding with our naked eye watching birds in our backyard. But we soon discover that small birds are actually not all the same species. They have different patterns and key markings that are not easily seen with our eyes alone. So we head off to the stores to buy binoculars, and we are quickly overwhelmed by sales staff and the multiple choices available.

3 There are two styles of binoculars Porro Prism binoculars where the objective or front lens is offset from the eyepiece. Porro prism binoculars provide greater depth perception and generally offer a wider field of view. PORRO PRISM ROOF PRISM Roof Prism binoculars where the prisms overlap closely, allowing the objective lenses to line up directly with the eyepiece. The result is a slim, stream lined shape in which the lenses and prisms are in a straight line.

4 Until the last 10 years or so, Porro Prism binoculars were more inexpensive. It was easier and less costly to assemble. However, with so many additional reflective surfaces in the porro design, manufacturers chose not to fully coat the glass lenses to keep costs down. Most manufacturers who make the Roof Prism design used fulland multi coated lenses which enhance the reflective surfaces to provide for more light to pass through the lenses to your eyes. Thanks to improvements in manufacturing techniques, you may now consider both styles with confidence that you are purchasing binoculars that will meet most requirements of the average birding enthusiasts.

5 Ocular Lens Assembly (Eyepiece & Adjustable Eyecup) Parts of the binocular to remember Focus Knob Diopter Adjustment Hinge Objective Lenses The Eyepiece provides the magnification power of the binoculars. The Adjustable Eyecups allow the user to correct for Eye Relief. (eye relief will be described later and what you can do to improve it.) The Diopter Adjustment is provided on one eyepiece (usually on the right eyepiece) for folks who have different vision strength between their eyes. The Focus Knob is used to make the image view sharper. The Hinge allows for adjustment of the width of the eyepieces to align with our eyes. And the Objective Lenses are sized to control the amount of light which enters the binoculars.

6 What the numbers mean Most binoculars are referred to by two numbers separated with an X. The first number is the power of magnification. With an 8X magnification the object will appear 8 times closer than when seen with the unaided eye. A 10X magnification will make the object appear 10 times closer. and so on. The second number is the diameter of the objective lens. The larger the objective lens, the more light enters the binoculars and the brighter the image appears to the viewer. Binocular Magnification best suited for Bird Watching The standard binocular for birding is an 8 x 42 binocular. To see more details on small birds at greater distances, you may opt for a 10x or a 12X magnification with a 42 or a 50 millimeter objective. Just remember that as the magnification increases, so does the weight and the need to hold the binocular steady to stop the shakes. I have used both 8X and my regular pair are 10X. For small warbler species that prefer tall trees, the 10X will reveal more details but require practice to focus on the object quickly.

7 Examples of Magnification Power at 30 feet 6X 1X Naked Eye 8X Note: my target objects are a 5.5 tall bird, a 5 tall bear, and a 10 paper ruler. 10X 12X

8 Examples of Magnification Power at 60 feet 6X 1X Naked Eye 8X Note: my target objects are a 5.5 tall bird, a 5 tall bear, and a 10 paper ruler. 10X 30X 12X

9 Examples of Magnification Power at 90 feet or More feet feet Note: my target objects are a 5.5 tall bird, a 5 tall bear, and a 10 paper ruler. feet feet

10 Other numbers and terminology shown on the box or in the owners manual: Minimum Focus Distance refers to how close you can stand to an object and still be able to see a sharp magnified image. Many 8X and 6X binoculars are able to focus down to 4 feet. 10X and higher will have a 6 feet minimum. Field of view is the side to side measurement of the circular viewing field or subject area. It is defined by the width in feet of visible view at 1,000 yards. Eye relief is the distance a binocular can be held away from the eye and still present the full field of view. Extended or long eye relief reduces eye strain. Binoculars come with twist up, pop up or soft rubber fold down eyecups for users depending if they wear eyeglasses or not. Eyeglass wearers should fold or twist down the eyecups to the minimum as our glass frames/lens already provide eye relief. Diopter Adjustment is available on most binoculars for users who have different vision in their eyes. This is usually a fine adjustment on one eyepiece after focusing in using the other eye.

11 Other numbers and terminology shown on the box or in the owners manual: Exit Pupil is a number for image brightness. Binoculars with a large exit pupil rating will provide brighter images under very low light conditions. Calculate Exit Pupil by dividing the objective lens by the magnification: for example on a 7 x 35 binocular, divide 35 by 7 gives you an exit pupil diameter of 5mm. For normal daylight viewing, an exit pupil between 2.5 and 3.0 is fine. There are some optics that boast high exit pupil numbers (higher than 7!) But this much light is wasted as the human eye cannot open wide enough to accept more light than 7. As we get older, our eyes begin to deteriorate and will not accept light above a rated 3 to 4 exit pupil. Along with exit pupil, two other terms bandied about are Relative Brightness and Twilight Factor. All three numbers are calculated using the eyepiece type, its magnification and objective lens size. They do not take into account any lens coatings... so they are numbers that should not be taken too literally.

12 Other numbers and terminology: The last adjustment number listed will be the inter pupillary distance. This is the distance between your eyes. You want to insure the binoculars will bend at the hinge to fit your eyes comfortably. Fog proof and waterproof housing. Look to see if the binoculars were filled with an inert gas such as nitrogen which prevents moisture build up on the interior lenses and surfaces. O rings are used in the assembly of the binoculars to seal the unit. Note: they are usually only rated waterproof against rain and maybe a quick drop in a puddle. Weight of the binocular. The Porro design has a larger housing so they tend to weigh more. But even a roof prism design will start to feel very heavy on your neck after a long birding session. So consider the weight. Or better yet, purchase a shoulder harness which moves the weight to your shoulders (and stops the binoculars from swinging about.)

13 What factors affect the cost of binoculars? The most important and expensive elements in a binocular is the optical coating of the lens. As light hits a lens some is lost in the optic and does not transmit further. To achieve greater light transmission, optics are coated with special chemicals. There are four types of coatings: coated, fully coated, multi coated, and fully multi coated. Fully multi coated lenses have multiple layers of coatings on ALL air to glass surfaces. It is possible to achieve almost 95% light transmission. (Zeiss recently introduced their new HD series binoculars with a 95% light transmission!) When you are at the store and see the range of prices, you will quickly understand why some binoculars cost more than $2,000 and why some will cost under $100. The housing construction is important, but the coatings used inside the housing are what drives the price.

14 What I did for my latest purchase and what I suggest: A few years back I wanted a medium size pair of binoculars. I went to Bass Pro in Grapevine to their binoculars display. (Go on a weekday when they are less crowded.) The sales clerks are usually willing to pull out a few pairs of binoculars from the display case allow you to focus on different nearby objects I looked at the wild animal displays for distance and close up views, and then down towards the dark areas between shelves. I judged how quick it was to adjust focus; how bright the object appeared; how close I could focus; the weight and feel; etc. Cabela s and other sporting goods stores will also allow you to handle their merchandise. I believe Cabela s and Bass Pro will have the widest selection of brands. From my own experience, I suggest you save up to purchase at least a mid price range pair of binoculars (from $250 to $600.) I began with a $100 pair and was disappointed with the image view after seeing the brighter detail in better models carried by other birders. Some older birders will say to save for Leica, Swarovski and Zeiss. These are great, but expensive ($1,500 to $2,800.) With recent manufacturing improvements you can do very well with Nikon, Leupold, Eagle Optics and Vortex brands as well.

15 Seeing beyond.. SPOTTING SCOPES

Many wildlife refuges and sanctuaries do not permit travel off established trails for the sake of habitat preservation and

16 Spotting scopes become a necessity when watching waterfowl out on alake, or watching a pair of Bald Eagles feeding their chick from 250 yards away. Many wildlife refuges and sanctuaries do not permit travel off established trails for the sake of habitat preservation and the welfare of wildlife, and rightly so. However, these restrictions can sometimes put even songbirds beyond the range of binoculars. A spotting scope can be very useful in these areas, and for any type or species of bird.

17 Eyepiece Parts of a Spotting Scope Base Flange Focus Knob Objective Lens The eyepiece is the most important part of your scope equipment. Manufacturers of mid to hi end scopes will offer multiple eyepieces. I carry both a fixed 30X eyepiece which is designed to transmit more light, and a 30X to 60X zoom. The zoom is more helpful for bird identification. If doing digiscoping (connecting a camera) or using the scope for early morning and twilight birding, the fixed is better as it will allow more light to reach your eye.

18 Other characteristics of a Spotting Scope As with binoculars, the Objective Lens size determines how much light is transmitted into the scope. There are two common size groups of objective lenses: 60mm & 65mm, and 82mm & 85mm. (There are a few aditonal size offerings such as a 100mm by Pentax. I ve never known anyone who bought one, so I can t say what that extra amount of light does for the viewing.) If you plan to primarily use the scope for birding, go with the smaller size group they are very adequate, lighter to carry, and not as costly. I use a Zeiss 85mm because I do a lot of digiscoping. After a long hike, my arms feel as if they have been stretched. You also need a heavier tripod to sturdily support a larger scope and camera mount. I believe my setup weighs over 15 lbs! A lot of weight to carry into the field. How fast it focuses. I never considered this until I recently read a Birder s Digest article that the number of turns of the focus knob it takes to focus is acritical decision. I never counted the turns and it has never prevented me from getting focused in on an object quickly.

19 Other characteristics of a Spotting Scope to look for: As with binoculars, look for fully coated lenses, and nitrogen purged for fog proofing, waterproof housing, and a carrying case. You will also need to decide on an Angled Body or Straight Body. I use the angled body because of my 6 height. It is more comfortable looking down into the eyepiece rather than straight ahead for long periods of time. An advantage of straight scope bodies is you can more easily use them from inside a car with a window mount. When pricing a scope, make sure the price includes both body and eyepiece. The high end scopes are usually sold in a combination package with both body and eyepiece. But an on line site may try to make their merchandise look more inexpensive by listing the items separately. Warranty: The high end scopes come with a lifetime warranty! Make sure the seller is an authorized dealer.

A few words about camera lens magnification. Camera lenses are labeled by their focal length size in millimeters, not by their magnification power.

There are hours of articles detailing how to calculate your lens magnification. For this discussion I will attempt to keep it simple.

20 A few words about camera lens magnification. Camera lenses are labeled by their focal length size in millimeters, not by their magnification power. Their magnification power depends on two factors: the focal length of the lens, and the type of camera body & sensor the lens is used on. There are hours of articles detailing how to calculate your lens magnification. For this discussion I will attempt to keep it simple. The two main types of camera bodies include: SLR (single lens reflex) Cameras which have detachable lenses, and point & shoot cameras with a fixed mounted lens. The newer digital SLR cameras are split into two types as well: FX (full frame) and DX (cropped frame). Check your owner s manual for your camera model type.

21 The FX (full frame) camera sensor is comparable in size to the older 35mm film cameras. When selecting a telephoto lens to use with 35mm film, we divided the lens focal length size by 47.5' to get a rough approximation of the equivalent magnification power of binoculars and scopes. (Most photographers rounded this number up to 50'.) On afx camera sensor, a 50mm lens is roughly equivalent to 1X. A 400mm lens is equivalent to 8X power, a 500mm lens is equivalent to 10X power, and so on. A DX camera sensor is cropped about 1.5 times smaller than the FX sensor. This makes the cropped picture image appear to be 1.5 times larger on your print. So photographers using a DX camera body will use 33' as the equivalent to 1X. This impacts calculating the power of the lens considerably. On a DX camera, a 280mm lens is equivalent to 8X power, and a 350mm lens is equivalent to 10X. Choosing a DX format SLR can also help your wallet. A good quality telephoto lens usually costs about $15 per mm. If you are in the market for a SLR camera for bird and wildlife photos, the DX format is very adequate. The FX format is better if you also plan to take landscape photos, large herds of animals, or groups of people.

22 The point and shoot cameras are even more confusing thanks to the individual manufacturers who want to wow and woo, you with big numbers. These cameras will be advertised using zoom and megapixel numbers. Some zoom sizes are advertised as high as 30X! This is not magnification power. The zoom number on a point and shoot camera is the ratio between the longest and shortest focal length of it s fixed zoom lens. To determine what the actual magnification power is for your camera, you must first find its 35mm equivalent on the Specifications Page in your camera s manual. For example, a Nikon Coolpix camera is sold with a 5X optical zoom. Its lens has a focal length that zooms from 6.3mm to 31.5mm. The owner s manual lists the 35mm equivalent as 36mm to 180mm. Using the accepted 1X equivalent of 50', this camera s magnification zoom is 0.72X to 3.6X.

gladly share (unless at that precise moment a Snowy Owl lands nearby.

23 Another way to check out binoculars and scopes is to join one of our field trips. Ask one of the other participants if you could look through their optics I am sure most will gladly share (unless at that precise moment a Snowy Owl lands nearby. Then you re out of luck.) If you have further questions, come to one of Our General Meetings and speak to one of our members.

Congratulations on selecting your new Carson binoculars!

INSTRUCTIONS Congratulations on selecting your new Carson binoculars! With reasonable care, your binoculars will provide you with years of enjoyment. In order to achieve optimum performance, please read