Photographing a Blue Headed Vireo

Blue Headed Vireos appear more gray than blue during Fall migration. What makes them unmistakable are those lavish white spectacles on that gray hood. It starts with a heavy but incomplete eye ring that extends down to its thick hooked beak and into the neck and breast areas. The colorful olive green with black yellow and white patterns on his back don’t quite cover up the flecks of gray that trickle down from his head.

Flash. Figuring Out This Essential Tool

Flash enhancement has proven to be an essential tool when photographing in my darkly lit woods, assuming I get it right. As I set up the flash for this shoot, I planned to selectively brighten the vireo’s face and body, while leaving the background dark. My exposure parameters worked well partly because this smallish bird was only 15-16 feet away – an excellent distance for the fresnel enhanced flash.

The Distance Factor

The flash is designed to work with the camera to gauge the ambient light reflecting off of the subject and calculate how much flash is needed to maintain exposure parameters. The flash sends a weak pre flash to determine the amount of flash needed- but if the subject is distant, that pre flash would most certainly fall off and be unable to send critical info back to the camera. So experimentation using flash exposure compensation (FEC) becomes necessary, assuming the bird sticks around. (NOTE: I could always boost underexposed images after the shoot in post processing. I rarely do this because I simply can not replicate the quality of brightening in post processing that I can achieve in camera, at least not without repercussions to the final image.)

At times, ETTLII Flash with fresnel extender delivers too much  light…depending on how close the lens is to the subject. This is because the blast from fresnel flash extenders are always head-on… and concentrated. It is not suppose to scatter in multiple directions, but instead narrow its angle of coverage and gain distance. Perch location is critical. (NOTE: The flash bracket is essential to raise the flash off of the hot shoe and over the axis of the lens, hopefully casting the unwanted shadows to places where they won’t be bothersome…like below or behind the subject.)

Computational Powerhouses

My dSLR camera and flash are designed to work together in the way of sophisticated computers. Trying to understand precisely how the camera and flash use their computational power to meter reflected light is beyond me…. especially since it is so difficult to predict what a Canon camera will do when Evaluative mode is engaged. This multi-level internal light metering system evaluates whatever fills the frame using algorithms covering a complex arrangement of variables including the parameters preset in the camera and information taken in through the lens. (NOTE: Conditions affecting the light’s direction, tone, intensity, absorption and bouncability will impact how light travels through the lens and is evaluated by the camera and flash. To read about the physics of how light travels and reflects off an object, visit this link.)

So much to think about! Overall, I find that given all these variables and the speed at which calculations must be made, the rate of light metering success is very good, despite the distance of the subject. When the camera, the flash and the photographer get it right, it’s a good day.

Photographing a Yellow Throated Vireo

Lots of warblers coming through….. mostly drab coloring on the plumage. In most cases, I rarely get more than a glance. The camera’s lens is crucial to successfully examine colors and patterns.  Without it, I certainly couldn’t ID most migrators with any conviction.

Based on this bird’s shape, size and elusive prowling behavior, I was pretty sure I had some kind of a warbler. Then I took a close look at the digital image…examining the size of her beak and her lemon yellow chest, throat and eye rings. Not a long, thin, pointy bill like a warbler, but thick; more like a Shrike with that large hook at the end. And what about those large bluish gray feet? Definitely not a warbler.

Stray Light

The sky was dark and pouring rain when this little Yellow Throated Vireo plopped down on a nearby branch in front of the camera. Small, drenched service berry leaves in front of and around the bird prevented the lens from getting a clean shot.

Somehow, on 3 sequential images, the camera recorded foggy looking circular overlapping orbs on the foreground of the bird’s left foot and all across the bottom of the image. This despite low ambient light, E-TTLII flash, lens hood attached, and advanced optical design multi-coating technology on my 500mm Canon L lens.  OUCH!!

But Why?

• It was a dark day. There was no background source of ambient light equal or stronger than the existing light on the subject.
• The flash (with FEC set at -1/3) was doing most of the work.
• No pieces of dust, debris or water droplets were on the camera’s front or rear lens elements. (NOTE: Dust on the front of the lens hardly ever impacts image quality.)

It looks like overexposed lens flare, possibly combined with an out-of-focus elliptical Serviceberry leaf in the foreground. I can only surmise that those wet leaves in front of the bird bounced the light back toward the lens, causing not only lens flare, but also spotty reduction in saturation and contrast. (NOTE: Long lenses are more likely to produce pronounced lens flare.)

Unpredictable Lens Flare

Flare doesn’t require sun, just a light source. The light’s angle must have been just right to pass through multiple lens elements (and ultimately reach the sensor) and blast the images with little orbs. It all disappeared when the bird moved to a higher branch. I countered by moving the lens up, thus altering the angle of light. (See second photo.)

Flare and glare are unpredictable (for the most part) and can show up on digital images even when photographing on a dark day. In bird photography, I find these artifacts to be unattractive and distracting- an operator error which can be remedied if you notice it soon enough…. and the bird sticks around.

Exposure Tradeoffs

We all know the low light exposure conundrum. The more you open up the aperture, in any lens, but most especially in long telephoto lenses, the more shallow (to the point of being razor thin) your depth of field becomes. With bird photography, that means (depending on the pose) that much of the bird’s little body is simply NOT in focus.

When I’m out in the State Game Area in the early morning, there’s usually lots of glorious sunshine allowing me to tighten up the aperture to 8.0 or smaller. Here at home, light filters down on a sunny day to accommodate a comfortable aperture of f/5 (with low shutter speed –assuming there’s no wind– and relatively high ISOs). But when it’s cloudy and rainy, the aperture on my 500 mm f/4L II IS lens  is mostly wide open. I could swap out lenses and use my 300 mm lens (2.8 L wide open), but then I sacrifice amplification. I’d much rather have high noise in an image that does not need cropping/zooming in post processing.

What’s a “Fast” Lens?

Lenses on which the aperture opens wide and thus allows more light on the focal plane are referred to as “fast” lenses. The more that aperture can open to let in more light, the “faster” the lens. The more light transmitting through the lens, the more flexibility with exposure parameters the photographer has.

NOTE: In aperture speak, when you “stop down”, you are letting in less light…. making the aperture smaller (by moving to a larger number)– and consequently, getting a deeper depth of field. Remember: The f/ represents the size of the hole allowing light into the lens. The smaller the f number, the larger the aperture.

Shallow Depth of Field

When I was photographing this Blue Headed Vireo, I had the 500mm lens wide open to f/4. See photo above. The head and eyes of the vireo are sharp because those bird parts were within the in-focus DOF arena. Those bird parts that were too close or too far away from the sensor are blurred because at f/4 there are only a few millimeters on which to lock focus.

To get an idea of how thin your depth of field can be at wide open apertures, see this DOF calculator. And, of course, if you want this information readily available in the field, there are DOF calculator apps available for iPhones and Droids.

Entire Subject Parallel to the Sensor

In the photo below, shot at f/5, most of the bird’s body is parallel to the sensor, and consequently, overall sharpness is good.

A Good Telephoto Lens

High end prime (fixed) lenses are usually “faster” than zoom lenses. Faster lenses are usually larger, heavier (I usually prefer a tripod with fast 300mm+ lenses) and much more expensive because of the sophisticated optics and highly responsive autofocus and metering technology incorporated into these lenses. A good telephoto lens will always be distinguished by its largest aperture setting. On a cloudy day, that means a lot.

To read more about image sharpness, please press this link.