Monthly Archives: March 2016

Sensor Size and Depth of Field

It is commonly said that crop sensor cameras make images having both a narrower field of view and a greater depth of field. Well, that's partly right. (Bill Ferris)

It is commonly said that crop sensor cameras make images having both a narrower field of view and a greater depth of field. Well, that’s partly right. (Bill Ferris)

It is well-known that a lens of a given focal length will deliver different angles of view when used with cameras having different sized sensors. For example, the above image was made with a Nikon D90 and a Nikkor 200-500mm f/5.6E telephoto zoom lens at 500mm. The D90 is a DX format camera having a 1.5x crop factor. In other words, the DX sensor crops the outer portion of the image formed by the lens. As a result, photographs made with this camera will display an angle of view equivalent to that produced by a lens with 1.5x the actual focal length used. In the above image, the 200-500 is at 500mm but the angle of view matches that produced by a 750mm lens.

It is often said that a crop sensor camera will also produce an image having a greater depth of field. In other words, the same lens at the same focal length will produce, not just a wider angle of view when paired with a full frame camera, but also a shallower depth of field. The claim is that the DX sensor not only crops the angle of view but forces a significant increase in depth of field. That assertion is just plain wrong.

In the below test images, you’ll see side-by-side comparisons of photos made with Nikon FX (full frame) and DX (crop sensor) camera bodies. The cameras used were the full frame Nikon D610 and the DX format Nikon D90. These cameras were used with the following lenses:

  • Nikkor 200-500mm f/5.6E VR
  • Tamrom 70-200mm f/2.8 Di VC USD
  • Tamron 24-70mm f/2.8 Di VC USD

To isolate sensor size as the only variable, the comparison images were made with the lenses at the same focal length, focal ratio and at the same distance from a fixed position subject. The Nikkor 200-500mm f/5.6E and Tamron 70-200mm f/2.8 Di VC USD were mounted on a tripod in a fixed position. The Tamron 24-70mm f/2.8 Di VC USD has no tripod collar or foot. The cameras were mounted to the tripod with the tripod in the same position for each set of exposures.

To create a large enough set of images to suitably address the question, each lens was used at a multiple focal lengths:

  • Nikkor 200-500mm f/5.6E VR: 200mm, 300mm, 400mm and 500mm
  • Tamrom 70-200 f/2.8 Di VC USD: 70mm, 100mm, 135mm and 200mm
  • Tamron 24-70 f/2.8 Di VC USD: 50mm and 70mm

Each lens was used wide open at its smallest f-stop number. ISO and shutter speed were kept constant for exposures made at the same focal length with both cameras.

Why did I decide to test the notion that sensor size has a significant impact on depth of field? I performed this experiment to test my belief that that lens aperture and distance to subject are the two factors having the greatest impact on depth of field. In other words, if a lens is used at the same physical aperture and distance to make photographs of a fixed position subject with two cameras of different sensor size, the depth of field recorded in the two images should be identical or, at least, very nearly so.

If I’m correct in this belief, the images should confirm it. If I’m wrong and if crop factor needs to be applied to depth of field as well as to focal length, photos made under the above conditions should exhibit obviously different depths of field with the photo made using the full frame camera consistently displaying an obviously shallower depth of field than the photo made using the crop sensor body.

Keeping all this in mind, let’s go to the photos. Below, are ten composite images. The photo occupying the left half of each composite was made using the Nikon D610. The photo to the right of the divider was made using the Nikon D90. Since the same lens at the same focal length, f-stop and distance to subject was used to make each image in a composite, the image made with the crop sensor D90 (on the right) shows a narrower angle of view. In each composite, I’ve indicated similar sections of the two photos that, when compared, reveal both photos to have identical – or nearly so – depths of field. This conclusion is reached by comparing the relative size of the subject, a hula dancer toy, and the out of focus highlights and details in the background.

Comparison #1: Nikkor 200-500mm f/5.6E (200mm, f/5.6)

The photo to the left of the divider was made with the Nikon D610 and Nikkor 200-500mm f/5.6E at 200mm, f/5.6, ISO 400, 1/200-second. The photo on the right was made with the same lens at the same distance from subject also at 200mm, f/5.6, ISO 400, 1/200-second. (Bill Ferris)

The photo to the left of the divider was made with the Nikon D610 and Nikkor 200-500mm f/5.6E at 200mm, f/5.6, ISO 400, 1/200-second. The photo on the right was made with the Nikon D90, the same lens at the same distance from subject also at 200mm, f/5.6, ISO 400, 1/200-second. (Bill Ferris)

Comparison #2: Nikkor 200-500mm f/5.6E (300mm, f/5.6)

The photo to the left of the divider was made with the Nikon D610 and Nikkor 200-500mm f/5.6E at 300mm, f/5.6, ISO 400, 1/200-second. The photo on the right was made with the same lens at the same distance from subject also at 300mm, f/5.6, ISO 400, 1/200-second. (Bill Ferris)

The photo to the left of the divider was made with the Nikon D610 and Nikkor 200-500mm f/5.6E at 300mm, f/5.6, ISO 400, 1/200-second. The photo on the right was made with the Nikon D90, the same lens at the same distance from subject also at 300mm, f/5.6, ISO 400, 1/200-second. (Bill Ferris)

Comparison #3: Nikkor 200-500mm f/5.6E (400mm, f/5.6)

The photo to the left of the divider was made with the Nikon D610 and Nikkor 200-500mm f/5.6E at 400mm, f/5.6, ISO 400, 1/250-second. The photo on the right was made with the same lens at the same distance from subject also at 400mm, f/5.6, ISO 400, 1/250-second. (Bill Ferris)

The photo to the left of the divider was made with the Nikon D610 and Nikkor 200-500mm f/5.6E at 400mm, f/5.6, ISO 400, 1/250-second. The photo on the right was made with the Nikon D90, the same lens at the same distance from subject also at 400mm, f/5.6, ISO 400, 1/250-second. (Bill Ferris)

Comparison #4: Nikkor 200-500mm f/5.6E (500mm, f/5.6)

The photo to the left of the divider was made with the Nikon D610 and Nikkor 200-500mm f/5.6E at 500mm, f/5.6, ISO 400, 1/250-second. The photo on the right was made with the same lens at the same distance from subject also at 500mm, f/5.6, ISO 400, 1/250-second. (Bill Ferris)

The photo to the left of the divider was made with the Nikon D610 and Nikkor 200-500mm f/5.6E at 500mm, f/5.6, ISO 400, 1/250-second. The photo on the right was made with the Nikon D90, the same lens at the same distance from subject also at 500mm, f/5.6, ISO 400, 1/250-second. (Bill Ferris)

Comparison #5: Tamron 70-200 f/2.8 VC (70mm, f/2.8)

The photo to the left of the divider was made with the Nikon D610 and Tamron 70-200mm f/2.8 VC at 70mm, f/2.8, ISO 400, 1/400-second. The photo on the right was made with the same lens at the same distance from subject also at 70mm, f/2.8, ISO 400, 1/400-second. (Bill Ferris)

The photo to the left of the divider was made with the Nikon D610 and Tamron 70-200mm f/2.8 VC at 70mm, f/2.8, ISO 400, 1/400-second. The photo on the right was made with the Nikon D90, the same lens at the same distance from subject also at 70mm, f/2.8, ISO 400, 1/400-second. (Bill Ferris)

Comparison #6: Tamron 70-200mm f/2.8 VC (100mm, f/2.8)

The photo to the left of the divider was made with the Nikon D610 and Tamron 70-200mm f/2.8 VC at 100mm, f/2.8, ISO 400, 1/400-second. The photo on the right was made with the same lens at the same distance from subject also at 100mm, f/2.8, ISO 400, 1/400-second. (Bill Ferris)

The photo to the left of the divider was made with the Nikon D610 and Tamron 70-200mm f/2.8 VC at 100mm, f/2.8, ISO 400, 1/400-second. The photo on the right was made with the Nikon D90, the same lens at the same distance from subject also at 100mm, f/2.8, ISO 400, 1/400-second. (Bill Ferris)

Comparison #7: Tamron 70-200mm f/2.8 VC (135mm, f/2.8)

The photo to the left of the divider was made with the Nikon D610 and Tamron 70-200mm f/2.8 VC at 135mm, f/2.8, ISO 400, 1/400-second. The photo on the right was made with the same lens at the same distance from subject also at 135mm, f/2.8, ISO 400, 1/400-second. (Bill Ferris)

The photo to the left of the divider was made with the Nikon D610 and Tamron 70-200mm f/2.8 VC at 135mm, f/2.8, ISO 400, 1/400-second. The photo on the right was made with the Nikon D90, the same lens at the same distance from subject also at 135mm, f/2.8, ISO 400, 1/400-second. (Bill Ferris)

Comparison #8: Tamron 70-200mm f/2.8 VC (200mm, f/2.8)

The photo to the left of the divider was made with the Nikon D610 and Tamron 70-200mm f/2.8 VC at 200mm, f/2.8, ISO 400, 1/400-second. The photo on the right was made with the same lens at the same distance from subject also at 200mm, f/2.8, ISO 400, 1/400-second. (Bill Ferris)

The photo to the left of the divider was made with the Nikon D610 and Tamron 70-200mm f/2.8 VC at 200mm, f/2.8, ISO 400, 1/400-second. The photo on the right was made with the Nikon D90, the same lens at the same distance from subject also at 200mm, f/2.8, ISO 400, 1/400-second. (Bill Ferris)

Comparison #9: Tamron 24-70mm f/2.8 VC (50mm, f/2.8)

The photo to the left of the divider was made with the Nikon D610 and Tamron 24-70mm f/2.8 VC at 50mm, f/2.8, ISO 400, 1/640-second. The photo on the right was made with the same lens at the same distance from subject also at 50mm, f/2.8, ISO 400, 1/640-second. (Bill Ferris)

The photo to the left of the divider was made with the Nikon D610 and Tamron 24-70mm f/2.8 VC at 50mm, f/2.8, ISO 400, 1/640-second. The photo on the right was made with the Nikon D90, the same lens at the same distance from subject also at 50mm, f/2.8, ISO 400, 1/640-second. (Bill Ferris)

Comparison #10: Tamron 24-70mm f/2.8 VC (70mm, f/2.8)

The photo to the left of the divider was made with the Nikon D610 and Tamron 24-70mm f/2.8 VC at 70mm, f/2.8, ISO 400, 1/640-second. The photo on the right was made with the same lens at the same distance from subject also at 70mm, f/2.8, ISO 400, 1/640-second. (Bill Ferris)

The photo to the left of the divider was made with the Nikon D610 and Tamron 24-70mm f/2.8 VC at 70mm, f/2.8, ISO 400, 1/640-second. The photo on the right was made with the Nikon D90, the same lens at the same distance from subject also at 70mm, f/2.8, ISO 400, 1/640-second. (Bill Ferris)

Comparing the above ten photo sets, it’s clear the photographs capture equivalent depths of field despite the fact that they’re made with full frame and crop sensor cameras. As expected, the crop sensor camera captures a more narrow angle of view. However, a comparison of the relative size of the hula dancer toy with the details of the out of focus background reveals that the DX format Nikon D90 captures the same depth of field as the FX format Nikon D610. This flies in the face of the common (but mistaken) belief that crop sensors significantly alter depth of field.

To understand the performance of each camera as illustrated in the above photos, one need only understand that photographic depth of field is largely determined by two factors: distance to subject and lens aperture. Each lens was kept at a constant position and distance from the subject for the photos made with the two camera bodies. By keeping focal length and f-stop constant in each photographic set, lens aperture was kept constant.

The f-stop number describes the ratio of lens focal length to aperture. In other words, a 200mm, f/5.6 lens has an aperture of about 36mm. This is true regardless of the size of the sensor in the camera to which the lens is attached. Here’s a listing of the focal lengths and apertures for each set of photos:

Nikkor 200-500mm f/5.6E VR

  • 36mm aperture (200mm, f/5.6)
  • 54mm aperture (300mm, f/5.6)
  • 71mm aperture (400mm, f/5.6)
  • 89mm aperture (500mm, f/5.6)

Tamron 70-200mm f/2.8 VC

  • 25mm aperture (  70mm, f/2.8)
  • 36mm aperture (100mm, f/2.8)
  • 48mm aperture (135mm, f/2.8)
  • 71mm aperture (200mm, f/2.8)

Tamron 24-70mm f/2.8 VC

  • 18mm aperture (50mm, f/2.8)
  • 25mm aperture (70mm, f/2.8)

As you review the above list, notice the constant f-stop results in increasing lens aperture as focal length increases. By keeping subject distance constant and increasing the physical aperture of the lens, depth of field becomes more shallow. By definition, the reverse is also true. With subject distance kept constant, decreasing lens aperture would result in a deeper or increased depth of field. And as illustrated by the above comparisons, keeping both subject distance and lens aperture constant produces constant depth of field. This holds true regardless of sensor size.

How is it, then, that so many photographers have come to accept the false assertion that crop sensor cameras make images having increased depth of field? The key to understanding this is the concept of equivalence. In simplest terms, equivalence describes two images made with different cameras and lens settings but having identical qualities. There are many factors that go into describing truly equivalent images. For the purposes of this discussion, we’ll focus on angle of the view and depth of field.

This set of images compares performance between crop sensor and full frame DSLR bodies. The images in the left column were made with a Nikon D90. Images in the right three columns were made with a Nikon D610. Both cameras used the same Tamron 70-200mm f/2.8 Di VC USD zoom lens, which was set up on a tripod to ensure it would not change position during the test. Both cameras used ISO 200, center point average metering and were operated in Aperture Priority. The subject in these photos is a scale model of the Lunar Excursion Module (LEM) from the Apollo program.

This set of images compares performance between crop sensor and full frame DSLR bodies. The images in the left column were made with a Nikon D90. Images in the right three columns were made with a Nikon D610. Both cameras used the same Tamron 70-200mm f/2.8 Di VC USD zoom lens, which was set up on a tripod to ensure it would not change position during the test. (Bill Ferris)

Let’s consider the above image set made with the Tamron 70-200mm f/2.8 VC. Due to its smaller sensor, a photograph made with the D90 captures a more narrow angle of view in comparison with an image made with the D610 at the same focal length. To capture an equivalent angle of view at the same distance from the subject, the D610 needs to use a greater focal length. At that increased focal length, the FX format camera will capture an angle of view equivalent to that recorded by the D90.

If both lenses are used at the same f-stop of f/2.8, their respective apertures will be about 46mm for the 130mm, f/2.8 lens on the D90 and 71mm for the 200mm, f/2.8 lens on the D610. Bear in mind, both cameras are at the same distance from the subject. Due to the larger physical aperture of the 200mm focal length lens, it records a shallower depth of field. To match the depth of field of the D90, the D610 is closed down from f/2.8 to f/4. This closes the aperture from 71mm to 50mm, which roughly matches the depth of field recorded by the D90 and its 46mm aperture.

Also, compare the quality of the out of focus background detail in the photos made with the DX format D90 (left most column) with the same detail in the second set of photos made with the FX format D610 (middle of three columns). Pay particular attention to the grouping of four bokeh balls to the left of the lunar lander model. In the D90 photos and in the equivalent D610 photos (right most column), that grouping is well defined with clear separation. In the middle column of D610 photos, that grouping is more diffuse, less well defined and not as clearly separated from the background.

This is what we would expect, considering that all the photos in that collection were made with the cameras and lenses at the same distance from the subject. The first and third column sets of images made with the D610 were made with the same lens aperture as the D90. The third column set of D610 images were made at an equivalent focal length to the D90 images. Both the angle of view and depth of field are equivalent. The first set (left column) of D610 images, while showing a wider angle of view, have equivalent depth of field as the D90 images. Again, this is exactly what one would expect given that the D90, and first and third set of D610 images were made at the same aperture, while the second set (middle column) of D610 photos were made at a larger aperture.

Another approach to producing equivalent depths of field, would have been to increase the lens aperture on the D90. The D90 would need a 130mm f/1.8 lens, which would have a 72mm aperture. That’s very nearly identical to the 71mm aperture of the 200mm, f/2.8 lens on the D610.

If equivalence is your objective, applying the crop factor to the f-stop allows you to calculate the aperture needed to make a photograph having an equivalent depth of field at a focal length delivering an equivalent angle of view. This adjustment can go either way. We can use a larger f-stop (multiply by the crop factor) to close down the aperture of the lens on the larger sensor camera or we can use a smaller f-stop (divide by the crop factor) to open the aperture of the lens on the smaller sensor camera. Either approach will produce equivalent apertures on the two cameras, which allows them to capture matching depths of field.

This is what has led so many photographers to mistakenly conclude that crop sensors significantly alter depth of field. What folks overlook is that the crop factor is applied to allow the lenses on the cameras to operate at the same physical aperture. Again, the key to understanding depth of field is recognizing that distance to subject and lens aperture are the critical factors. If you keep subject distance constant, keeping lens aperture constant will deliver equivalent depth of field. This holds true even if the lenses are used at focal length delivering non-equivalent angles of view.

Wildlife photographers often choose to shoot with crop sensor cameras to effectively bring the animals closer. They want the narrower angle of view delivered by the crop sensor. Shooting at 500mm f/4 with a DX camera will not only produce a larger image of the subject (in comparison with a photograph made using the same lens at the same distance on an FX camera), the DX camera will also record the same shallow depth of field and beautiful, buttery bokeh. That’s a huge advantage and a big reason why crop sensor cameras are so popular with sports and wildlife photographers. Of course, the smaller sensor also captures less total light with each exposure and this has implications for image noise. But that’s another blog entry.

In the meantime, armed with this new information and understanding of the role lens aperture plays in depth of field, let’s get out and shoot.

Bill Ferris | March 2016

Nikon TC-14E III

The Nikon TC-14E III teleconverter increases a lens' effective focal length by 40 percent. (Bill Ferris)

The Nikon TC-14E III teleconverter increases a lens’ effective focal length by 40 percent. (Bill Ferris)

Teleconverters have a long and complex history in photography. In 1833 – six years before Louis Daguerre invented the daguerreotype process that launched a worldwide fascination with a new artistic medium, photography – Peter Barlow invented a negative lens that, when fitted to a telescopic eyepiece, extended the effective focal length of the telescope in which Mr. Barlow’s lens was used. In so doing, the magnification of the lens and the image scale of the subject were also increased. Known simply as the Barlow lens, this optical accessory is widely used by amateur astronomers. Commonly available in 2x and 3x versions, the modern Barlow is especially popular with lunar and planetary observers.

Nearly sixty years later in 1891, Thomas Dallmeyer and Adophe Miethe simultaneously developed nearly identical optical designs for photographic telephoto lenses. Both designs featured a front achromat doublet lens system and a rear achromat triplet grouping. The rear lens grouping acted much as Barlow’s negative lens, increasing the effective focal length of the front imaging elements. Dallmeyer and Miethe had independently invented the first photographic teleconverters.

Today’s modern teleconverters are also quite popular though not without their critics. No optical lens system is perfect and the teleconverter is certainly no exception. In addition to magnifying the subject of a photograph, a teleconverter also magnifies optical aberrations, making them more readily apparent. Commonly found in 1.4x, 1.7x and 2.0x versions, teleconverters typically magnify by as little as 40% (1.4x) and as much as 200% (2x). The biggest cost of this increased magnification is a loss of image brightness. By increasing the effective focal length of the lens while keeping the lens’ physical aperture constant, the maximum focal ratio of the lens increases by an amount proportional to the increase in effective focal length. For example, a 1.4x teleconverter increases focal length and focal ratio by 40%. A 200mm f/4 lens becomes a 280mm, f/5.6 lens. The teleconverter results in a loss of one stop of light.

A teleconverter attaches to both the lens and the camera as an intermediary lens within a photographic optical system. The TC-14E III is an f-mount design that is compatible with all Nikon film cameras and DSLR cameras. Nikon teleconverters are generally compatible with longer focal length telephoto and telephoto zoom lenses. (Bill Ferris)

A teleconverter attaches to both the lens and the camera as an intermediary lens within a photographic optical system. The TC-14E III is an f-mount design that is compatible with all Nikon film cameras and DSLR cameras. Nikon teleconverters are generally compatible with longer focal length telephoto and telephoto zoom lenses. (Bill Ferris)

This increase in focal ratio has a couple of potentially significant drawbacks. Compared to an f/4 lens, an f/5.6 lens will require an exposure twice as long to render a properly exposed image. Another option would be to increase the ISO (in-camera exposure brightening) or increase the brightness of the exposure during post-processing. Either approach will introduce some additional noise into the final image.

Another potential issue that results from an increase in focal ratio, is that of compromised autofocus performance. The brighter the image falling on the sensor, the faster and more accurate the camera’s autofocus system tends to be. As the f-stop used to make an image increases and image brightness on the sensor decreases, the camera eventually will not have enough light for reliable autofocus performance.

Because the function of a teleconverter (TC) is to extend the reach of a lens, to bring a photographer nearer the subject without having to physically move closer to the subject, it is a popular accessory for wildlife and bird photographers. With my growing interest in this type of photography and the recent purchase of a Nikkor 200-500mm f/5.6E VR telephoto zoom lens, I decided to give the Nikon TC-14E III 1.4x teleconverter a try. Attached to the new lens, the TC-14E III would have the effect of extending its zoom range to 280-700mm. The TC-14E III also facilitates communicates between the lens and camera, including effective focal length, f/-stop, shutter speed, AF mode, burst mode…the full suite of functionality one would expect of a Nikkor lens mounted to a Nikon camera body,

The main price to be paid for the extended reach achieved with a TC is an increase of the lens’s maximum f-stop. In the case of the 200-500mm f/5.6E, the focal ratio increases from f/5.6 to f/8. At f/8, the zoom would be operating at the very threshold of my Nikon D610’s ability to autofocus. This raised two issues of concern: would the lens be sharp at 700mm and would the f/8 maximum focal ratio allow for adequate autofocus performance?

A juvenile bald eagle soars over Lake Mary on a mid-winter northern Arizona day. (Nikon D610 w/ Nikkor 200-500mm f/5.6E and TC-14E III at 700mm, f/11, ISO 2500, 1/2000-second)

A juvenile bald eagle soars over Lake Mary on a mid-winter northern Arizona day. (Nikon D610 w/ Nikkor 200-500mm f/5.6E and TC-14E III at 700mm, f/11, ISO 2500, 1/2000-second)

One of the biggest technical challenges of bird and wildlife photography is capturing birds in flight. It is this aspect that makes bird photography so appealing to me, the challenge of mastering my equipment and expanding my knowledge of the animals to make good photographs. Bird photography also gives me an excuse to get out in nature and to be near these magnificent creatures. When the TC-14E III arrived, I couldn’t wait to run it through its paces by photographing the eagles, hawks and other birds found during winter in northern Arizona.

The above photograph of a juvenile bald eagle in flight illustrates the challenges I’ve been working to overcome. As you can see, the photo was made on a bright, sunny day. I used a shutter speed of 1/2000-second to freeze the action. The 200-500mm is at full zoom, which produces an effective focal length of 700mm with the 1.4x teleconverter attached. The maximum f-stop is f/8 but I chose to work at f/11 to produce an image with greater sharpness. In the photo’s caption, you’ll notice an ISO of 2500 for this exposure. That’s very high for a bright, sunny day. Now, if the above were a full 6,000 by 4,000 pixel image, the level of noise at that ISO would be quite acceptable. However, even at 700mm focal length, the raptor only covers about 1/5 the surface area of the D610’s sensor. The above image represents roughly a 2500 by 1700 pixel crop, which makes the noise more noticeable. In fact, I would judge the level of noise to be at the very threshold of what I consider, acceptable.

Canada geese cruise the northern Arizona sky near Mormon Lake on a mid-winter's day. (Nikon D610 w/ Nikkor 200-500mm f/5.6E and TC-14E III at 700mm, f/9, ISO 720, 1/2000-second)

Canada geese cruise the northern Arizona sky near Mormon Lake on a mid-winter’s day. (Nikon D610 w/ Nikkor 200-500mm f/5.6E and TC-14E III at 700mm, f/9, ISO 720, 1/2000-second)

The above photo of Canada geese flying through northern Arizona’s winter sky is a roughly 1500 by 1500 square aspect crop. Notice the shutter speed is the same 1/2000-second exposure as used to make the previous image of a bird in flight. Also, please note the f-stop and ISO. The f-stop is f/9 or 2/3-stop brighter than the first image. As a result, the ISO is much lower. This was another bright, sunny day in northern Arizona so, lower the f-stop (increasing the aperture) allowed me to make an image with much less post-exposure brightening. At ISO 720, I was able to do an even more significant crop but without the noise penalty of the first image.

ISO, is the central issue when using a teleconverter with a moderately fast lens. Pro telephoto lenses offer maximum f-stops in the f/2.8 to f/4 range. The large apertures of these long lenses collect and deliver a lot of light to the sensor. As a result, even with a 1.4x TC in the mix, they still operate at f/4 or f/5.6, delivering enough light to the sensor to allow a camera’s AF system to be snappy and accurate. Using the TC-14E III with a lens such as the 200-500mm f/5.6E, a modestly slow zoom, immediately puts you right at the brink of acceptable performance.

The 200-500’s maximum f-stop (with the TC) is f/8. At f/8, the optical system captures images with noticeable softness and chromatic aberration. Closing down the aperture just by 1/3-stop to f/9 largely compensates for these aberrations and allows the lens to deliver crisp, true color images to the sensor. At f/9, the lens is operating outside Nikon’s official boundary for full AF performance. At f/9, you’ll no longer be able to work in AF-C, 3D mode. That option isn’t even available in the D610’s menu at f/9. However, I’ve been able to get good AF performance in AF-C, 9-point mode, my preferred autofocus setting for dynamic bird and wildlife situations.

A western bluebird sits perched atop a common mullein near the windswept waters of lower Lake Mary in northern Arizona. (Nikon D610 w/ Nikkor200-500mm f/5.6E at 700mm, f/8, ISO 1600, 1/2000-second)

A western bluebird sits perched atop a common mullein near the windswept waters of lower Lake Mary in northern Arizona. (Nikon D610 w/ Nikkor200-500mm f/5.6E and TC-14E III at 700mm, f/8, ISO 1600, 1/2000-second)

The above photo illustrates the price one pays when losing focus even for a moment while doing photography with an f/5.6 (or slower) telephoto and a teleconverter. Again, this photo was made on a bright and sunny afternoon. I shot with the 200-500 and 1.4x TC combo wide open at f/8. Why? It was late in the afternoon. The sun was about an hour from setting, low on the western horizon and not quite as bright as during a midday exposure. Notice the shutter speed of 1/2000-second. That’s for a photo of a perched bird. OK, the bluebirds were flitting from plant-to-plant and not spending more than a few seconds on any one perch. However, when they’re perched, the birds aren’t moving…at least, not nearly as much as when in flight. By shooting at 1/2000-second in late day light, the ISO was jacked up to 1600. I probably could have used a shutter speed of 1/800-to-1/1000-second, which would have cut the ISO to 800 or less.

What saved this exposure was the fact that I’d noticed the western bluebirds flitting about from stalk to stalk and had pre-focused on this stalk, ahead of time. It’s still a cropped final image but at approximately 3350 by 2240 pixels, there’s enough real estate on the camera sensor to mitigate the noise. If this was shot with a 500mm f/4 telephoto and the Nikon 1.4x TC, I could have shot at f/5.6 and kept every other setting the same with the camera selecting and ISO of 800 or lower. Being a professional quality optic, the 500mm f/4 would probably be very sharp even wide open with a TC. With a consumer, telephoto zoom such as the 200-500, the margin for error is much more narrow. You’ve got to pay attention to the details and look for every opportunity to balance that f-stop/shutter speed/ISO triangle in your favor.

A red-tailed hawk launches from atop a Ponderosa Pine along Lake Mary Rd near Flagstaff, Arizona. (Nikon D610 w/ Nikkor 200-500mm f/5.6E at 700mm, f/9, ISO 720, 1/1600-second)

A red-tailed hawk launches from atop a Ponderosa Pine along Lake Mary Rd near Flagstaff, Arizona. (Nikon D610 w/ Nikkor 200-500mm f/5.6E and TC-14E III at 700mm, f/9, ISO 720, 1/1600-second)

Here’s an image that’s a product of a collection of lessons learned during my first few weeks of ownership of the TC-14E III 1.4x teleconverter. It’s a photo that was made in good light on a  clear day. The red-tailed hawk was perched atop a Ponderosa pine scanning the nearby shallow water lake. Anticipating the bird would launch within a few minutes (at most) of my arrival, I had selected a shutter speed of 1/1600-second…fast enough to mostly freeze the action of wings flapping but slow enough to catch a bit of motion and convey a hint of the dynamic action. I chose an f-stop of f/9 to noticeably sharpen the resulting image while still putting a bright image on sensor. The combination of these choices resulted in an exposure where the D610 chose an ISO of 720. In my experience, keeping ISO at or below 1000 is essential to producing noise-free images in exposures that will likely be significantly cropped.

After shooting with the TC-14E III on the Nikkor 200-500mm f/5.6E VR zoom lens for several weeks, I’ve learned the following:

  • The TC-14E III is sharp. Comparing exposures made with the bare 200-500 and exposures made with the combo of the 200-500 and TC at equivalent focal lengths, any differences in image quality are subtle, at most, and only discernible at the pixel level.
  • When shooting at 700mm, I prefer to stop down the combo to f/9. Even the 1/3-stop closure is enough to noticeably improve image quality. Beyond that, IQ does improve up to about f/11. However, the gain is so marginal as to be not worth (in my opinion) the associated loss of quality that comes from using a higher ISO or (for BIF) a slower shutter speed.
  • For best image quality when photographing BIF (a scenario where significant cropping of the resulting image is likely), I target a shutter speed of 1/2000-second but will slow the shutter shutter speed to 1/1000 in low light and will slow the shutter speed to 1/500 for perched birds.
  • I need to continue experimenting with shutter speed. At 1/1000-to-1/1600, the wing motion blur helps convey the dynamic action of flight. It’s not unlike prop blur in photographs of piston engine planes in flight. The prop blur conveys the power of the plane. Wing blur with a sharply focused face communicates the dynamic nature of the bird.
A juvenile bald eagle gazes intently in search of a distant opportunity for a meal or an approaching threat. (Nikon D610 w/ Nikkor 200-500mm f/5.6E and TC-14E III at 700mm, f/11, ISO 450, 1/800-second)

A juvenile bald eagle gazes intently in search of a distant opportunity for a meal or an approaching threat. (Nikon D610 w/ Nikkor 200-500mm f/5.6E and TC-14E III at 700mm, f/11, ISO 450, 1/800-second)

I’ll leave you with one last sample image. The 200-500/teleconverter combo is great for perched birds. In good light, I can close the aperture to ensure tack sharp detail, make exposures at relatively slow shutter speeds (under 1/1000-second), and still keep ISO under 1000. These settings deliver excellent detail in a properly focused image.

With all that potential awaiting you, there’s no excuse. Get out and shoot.

Bill Ferris | March 2016