Helpful Suggestions for Studying and Photographing Birds
by Bob Augustine

Range Finding with a Digital Camera

There is a simple way to determine the distance or altitude of a bird you have photographed with a DSLR or mirrorless camera.
The formula is: D=OF/I where:
D is the distance in feet
O is the object size in feet
F is the focal length of the lens in mm
I is the size of the image on the sensor
To get I you need to measure the image on the LCD then divide by three.
Example: A Golden Eagle has a length of 32" or 2.67'. Using a 400mm lens produces an image on the LCD of 9 mm. The image on the sensor (I) then is 3 mm.
D=2.67 x 400/3=1068/3=356'
(Note that all the units cancel out.)
Another way to remember this is to start with:
A 400mm lens at 400 feet produces 1 mm of image for each foot of object
Then multiply or divide for other object sizes, focal lengths, or distances (e.g. A 400mm at 200 feet produces 2mm for each foot of object.)
The bird's size should be taken from a reliable source like Robbins' Birds of North America that measured each in natural postures, not stretched-out museum skins.

If you don't convert O from inches to feet, the distance you get will be in inches. Divide by 12 to convert it to feet.
The 10X enlargement feature on most DSLRs helps get more accurate measures of the image size.
This technique was developed originally for film cameras where image size could be measured directly from the negative or slide. Digital cameras require translating the LCD image back to its size on the sensor. The translation factor varies with sensor size, but most are about 3X.)

Using Saccadic Eye Movements to Better See Flying Birds

Can you stare at something? Yes. It is an act of will, involving a system that is mostly automatic. If you stare at a black spot on a wall, it will soon disappear. This is called habituation. The eye gets tired of repeating the same old message.

Fortunately, we have evolved a system that largely prevents this from happening. Tiny, quick, short movements of the eye prevent an image from lingering too long on one spot. The "blind spot" we all have where the optic nerve enters the retina is avoided as well. These fast, jerky movements are called saccades.

Here's the thing: You can learn to control these movements and put them to use. Run a saccade across the flight path of a bird and you get in effect a freeze frame image in which you can see details that would otherwise be just a blur. Saccades are very fast, like a many-frames-per-second movie camera. They are fast enough to stop the motion of a flying bird at close range.

To gain control of saccades you mostly just have to will it. It's biofeedback. It's like blinking. It happens all the time automatically, but you can also make it happen. Now that you know that this is possible, order your brain to make it happen on demand.

Experiment. Try not only perpendicular movements but also following movements. There's a lot of speed there to work with, and practice makes perfect. You'll need it to get the timing right.

Shakeless Scope Photos

1/30 second at 60X? There is a method for taking photos through a scope that produces shakeless images. This is an upgrade on the method I presented in my Feb. 1991 article (Birding, vol.23 no.1). Basically it is just to move the camera lens away from the eyepiece so there is no touching after you've used it to focus the scope. Most people can hold a camera pretty still in three dimensions for the few seconds you need. Absolute stillness is not necessary. You'll improve with practice too.

1. To begin, set the camera's normal lens at about f2 or f2.8 (i.e.wide open). Remove any filters.
2. Select any ISO you want.
3. Put the camera in Aperture Priority Mode so it selects shutter speeds. Any speed of 1/8 or faster is OK.
4. Focus (only) the scope while pressing the camera lens against the eyepiece--your scope or any you can borrow for a few seconds. You must use the camera to focus or the focus will be off.
5. After focusing, pull the camera back just off the eyepiece with your finger on the shutter button.
You will note that even as the camera moves around a little, the image in it remains still as long as the scope isn't bumped or shaken by the wind. Even a flimsy tripod will hold the scope still if you don't touch it.
6. Take a picture.

This is what I call OESEP, for Off Eyepiece Scope Eyepiece Photography. Its miraculous secret is what I call NOISE, for Natural Optical Image Stabilization Effect. The curvature of the camera lens redirects any off-axis errant rays back to the same focal point. The result is that the image doesn't move.

The one problem you may run into, easily dealt with using a little cardboard or even paper, is extraneous light. You want the only light entering the camera lens to be the beam exiting the scope eyepiece (called the exit pupil). This is best met with a black cardboard or paper disk cut to fit in the camera lens filter threads with a hole in its center about 1/2 inch across (which I call a centering disk). Alternatively, you could make a 3 or 4 inch disk that fits around the eyepiece.


When you see how well this works, you may be tempted to try it with digiscoping. With a DSLR or mirrorless camera it will work fine, but digital point&shoots, the kind usually used for digiscoping, have very small sensors with very small lenses and so are very difficult to line up with the scope. That's why an adapter is required for this. It centers the camera on the scope and keeps it there. The margin for error in alignment is too small to be of value handheld. OESEP with such cameras can only be done by resorting to a second tripod for the camera (see Sidebar 1).

Other limitations

Obviously, this technique is not suitable for flying birds--or running, swimming, or jumping birds. If you can lock a scope on it, you can get a photo of it.

No wind or other vibrations shaking the scope.

This is for so-called Normal lenses (equivalent to about 50mm on a 35mm film camera). Most zooms and kit lenses won't work well, but an old 35-70mm might. Non-manufacturer's lenses can be used with a T-mount for your camera as infinity focus is not needed. (In fact the camera lens needn't be focused at all).

Scopes with LER (Long Eye Relief) eyepieces are best.

This is for DSLRs or mirrorless cameras, not point & shoots or any other cameras with very small sensors.

This may not become your main method for photographing birds, but it's a useful option for situations when your usual equipment is not at hand. Being able to use slow shutter speeds is a big advantage. It means you don't have to avoid low light, high power, or stop down disks (see Sidebar 2).

Sidebar 1: OESEP With Two Tripods

If you get to a shutter speed slower than 1/8, you can only continue if you make the quite difficult effort to set up a second tripod for the camera. This is needed for small-sensor cameras too.

Center and lock the scope on target. Then position the second tripod so the camera lens is close to the scope eyepiece.

1. First check from the side that the lens is parallel to the eyepiece, not tilted up or down.

2. Then move the camera (and tripod) sideways to line up the camera lens and scope eyepiece.

3. Lastly, use the tripod's elevator crank to raise or lower the camera as needed to match height with the eyepiece. You may need to move it a little closer.

You can release the shutter with your finger--even at 200X and 1/30 second. The scope doesn't move, and the motion of the camera is compensated for optically.

Sidebar 2: Stopdown disks

With OESEP the quality of your photos will be limited only by the quality of your scope. It will not be affected by any kind of shake or vibrations from a mirror or focal-plane shutter. The quality of many inexpensive scopes can be improved by simply covering the outer portion of the objective lens. Make a disk out of cardboard or even paper (black is best) to fit in the scope objective's filter threads. Put a hole in the center about half the disk's diameter. This will reduce the amount of light by about 2 stops, but the resulting slower shutter speed will no longer be a problem with OESEP. You'll find heat haze penetration and images through glass windows are also improved.

Sidebar 3: Visual Use

When I was a child I found that I could combine optical instruments like binoculars and telescopes. But in trying it, I found the power too high and the images too dark and jumpy.
The trick is to use lower powers. Set a scope at 20X and combine it with 8X binoculars and you get 160X, which is more than twice what most scopes provide. Without a big lens in front though, it will be dimmer but possibly useful. Try it on Jupiter or Saturn (at night you won't have to worry about blocking external light.
But the really amazing thing is when you break the contact and hold the binoculars still--not absolutely, just fairly still--behind the scope eyepiece without touching it, the image doesn't move--at all. Cameras aren't the only things that can benefit from NOISE.

I have used this technique to read the neck collar number on a Snow Goose too far to get with the scope alone. A still image can build up on your retina and so won't look so dark. As with the camera lens, the curvature of the binocular lens redirects errant image rays right back to the focal point where they are all supposed to go. It does so in exact proportion to the degree of deviance, resulting in an unmoving image.