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Autofocus Fine Tune

Autofocus Fine Tune test shot for Tamron 70-200mm f/2.8 Di VC USD lens at 200mm, f/2.8, ISO 100, 1/200-second with flash and Nikon D610 AF Fine Tune set to OFF (Bill Ferris)

Autofocus fine-tune test shot for Tamron 70-200mm f/2.8 Di VC USD lens at 200mm, f/2.8, ISO 100, 1/200-second with flash. AF fine-tune is turned off. (Bill Ferris)

Choosing the right autofocus (AF) mode can be a real challenge. You could leave the driving to the camera and go with Auto-servo AF (AF-A) mode. If you go that route, don’t expect that dumb box of a camera to make the right choices. It will make choices but they’ll probably not be the same choices you would make.

Being the risk-taker that you are, I’m sure you spend most of your time shooting in either Single-servo (AF-S) or Continuous-servo (AF-C) mode. These allow you greater control and, when good choices are made, a higher success rate making keeper images. Among those choices, is deciding which one or more AF points to use. Do you use one, nine, twenty-one or all the AF points on your camera’s sensor? If just one, do you go with the center point or an outer point? If you choose a group of points, which group? Do you allow the camera to have a say in which AF points are used? So many choices.

Let’s assume you’ve chosen an AF mode, and selected the number and location of the AF points that will be used. The next challenge is to successfully place at least one AF point over your subject and acquire focus. When it all comes together, it’s a beautiful moment. The shutter clicks open and the image swiftly, silently, gets encoded as a collection of 1’s and 0’s on an SD card.

Later, when you look at the photograph in Lightroom and realize it’s still not in focus, that moment of joy becomes frustration. What happened? Why is the eye just ever so slightly soft?

Of all the factors than have the potential to cause an out-of-focus image, arguably the most pernicious is a camera/lens combo that is ever so slightly miscalibrated. Despite your mastery of the camera’s AF system, your successful effort to track the subject and the presence of mind to make an exposure at the decisive moment, that slight miscalibration wreaks havoc. Focus is not set on the eye beneath the AF point. Instead, focus is slightly in front of or just behind the eye. The result is an out of focus image that ends up being deleted rather than marked as a keeper.

Autofocus fine-tune is a tool offered by many professional and high end consumer cameras. It allows you to adjust where focus is set to compensate for a miscalibrated lens. How does it work?

In the above images, the blue shaded portion of the semitransparent square overlay represents an out-of-focus area of the black and white image. The portion of the black and white photo visible within the blue shaded overlay represents the area of the face falling within the focus plane and appearing to be be in focus in the image. TOP: This illustrates a properly focused image. The eyes, brow and mouth fall within the focus plane and appear in-focus. MIDDLE: This represents a back-focused image. The ears an temples are within the focus plane and appear sharp. However, the eyes are above the focus plane and look soft. BOTTOM: This represents a front-focused image. The tip of the nose and chin fall within the focus plane and appear sharp. However, the eyes are behind the focus plane and look soft.

In the above images, the blue shaded portion of the semitransparent square overlay represents an out-of-focus area of the black and white image. The portion of the black and white photo visible within the blue shaded overlay represents the area of the face falling within the focus plane and appearing properly in-focus.
TOP: This illustrates a properly focused image. The eyes, brow and mouth fall within the focus plane and appear in-focus.
MIDDLE: This represents a back-focused image. The ears and temples are within the focus plane and appear sharp. However, the eyes are above the focus plane and look soft.
BOTTOM: This represents a front-focused image. The tip of the nose and chin fall within the focus plane and appear sharp. However, the eyes are behind the focus plane and look soft.

In the above illustration, the focus plane of the camera is represented by the semitransparent, blue square overlay. While all photographs have at least a minimal depth of field, for simplicity, I’m illustrating the focus plane as a two-dimensional, flat zone. With large aperture, small focal ratio lenses being popular for portraiture, the shallow depths of field produced by such lenses leave little margin for error when it comes to achieving accurate focus. If focus is not set on the eye or within a few millimeters of the eye, the resulting image will look “soft” and out-of-focus. There will be portions of the subject’s face that look sharp and in-focus, but if the eyes look soft, the overall impression will be that the photo is soft.

A miscalibrated camera/lens combo may give every indication of making a properly focused exposure. However, despite the fact that the focus point may be directly over the subject’s eye, the camera will set focus slightly in front of or behind the eye. If you are shooting with a fast f-stop, that slight miscalibration can result in unacceptably soft images. Autofocus fine-tune allows you to compensate for this problem.

In the Nikon D610 menu system, AF Fine Tune is found in the Setup Menu. (Bill Ferris)

In the Nikon D610 menu system, AF fine-tune is found in the Setup Menu. (Bill Ferris)

Entering the AF fine-tune menu, the first option is where you select, ON or OFF, for this control. The second setting is the Saved Value for the lens. (Bill Ferris)

Entering the AF fine-tune menu, the first setting allows you to select, ON or OFF. The second setting is the Saved Value for the lens. (Bill Ferris)

Entering the Saved Value setting, select a positive or negative number from +20 to -20. Positive numbers move the focus point farther from the focus plane to compensate for front-focused images. A negative setting moves the focus point closer to the camera focus plane to compensate for back-focused images. (Bill Ferris)

Entering the Saved Value setting, select a positive or negative number from +20 to -20. Positive numbers move the focus point away from the camera to compensate for front-focused images. A negative setting moves the focus point toward the camera to compensate for back-focused images. (Bill Ferris)

Nikon cameras recognize Nikkor lenses and many third party lenses, and are able store AF fine-tune settings for up to 12 different lenses. (Bill Ferris)

Nikon cameras recognize Nikkor lenses and many third party lenses, and are able store AF fine-tune settings for up to 12 different lenses. (Bill Ferris)

The above series of images illustrate how to use AF fine-tune to add an adjustment to compensate for a lens that consistently front-focuses or back-focuses when used with a specific camera body. AF fine-tune settings are not transferable. A setting on one camera may not be needed on a different but same model body. The setting is unique to that specific camera/lens combination.

Also, Nikon bodies do not allow you to define multiple settings for the same lens. For example, when working with a zoom lens, you are limited to one setting for that lens. If AF fine-tune is engaged, the adjustment will be applied regardless of the focal length used. I recommend you test a zoom lens at the focal length at which it will most likely be used.

The below series of images illustrate my approach to testing a lens to determine if an AF fine-tune adjustment is needed. Right click the below images to open a full-size JPEG in a new window.

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF Fine Tune at OFF. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF fine-tune turned off. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF Fine Tune at +2. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF fine-tune at +2. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF Fine Tune at +4. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF Fine Tune at +4. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF Fine Tune at +6. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF fine-tune at +6. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF Fine Tune at +8. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF fine-tune at +8. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF Fine Tune at +10. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF fine-tune at +10. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF Fine Tune at -2. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF fine-tune at -2. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF Fine Tune at -4. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF fine-tune at -4. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF Fine Tune at -6. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF fine-tune at -6. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF Fine Tune at -8. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF fine-tune at -8. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF Fine Tune at -10. (Bill Ferris)

Photo made with Nikon D610 and Tamron 24-70mm f/2.8 Di VC USD lens at 70mm, f/2.8, ISO 100, 1/200-second with flash. AF fine-tune at -10. (Bill Ferris)

The above series of images is a real world test under real world conditions. When shooting portraiture with the D610 and Tamron 24-70 f/2.8 Di VC USD, I typically shoot wide open with a mix of ambient light and flash at 1/200-second. If you’re going to test a lens to determine an appropriate AF fine-tune setting, test the lens under the same conditions in which it will most likely be used.

AF fine-tune is turned off for the first image in the series. The next ten images were taken with AF fine-tune turned on. A +2 adjustment is applied in the second image. Images three through six have adjustments of +4, +6, +8 and +10 applied, respectively. A -2 adjustment has been applied to image seven in the series. The next four images have adjustments of -4, -6, -8 and -10 applied, respectively. At each setting, I took five handheld exposures with vibration compensation (VC) engaged. The above series includes the second exposure in each five-exposure set.

Reviewing the exposures at 1:1 in Lightroom, all five exposures with AF fine-tune turned off were acceptably sharp at the focus point. Two of the five in that set were a bit shallow in focus, displaying minimal in-focus depth of field in front of the focus point. The set which most consistently produced sharp images with good depth of field both in front of and behind the focus point is the set with an adjustment of -6 applied.

Now, it gets complicated. Normally, I would choose the -6 setting for the Tamron 24-70mm f/2.8 VC and leave it at that. However, I also have a Tamron 70-200mm f/2.8 Di VC USD lens but the Nikon firmware does not distinguish between it and the 24-70mm f/2.8 VC. If I leave AF fine-tune turned on with a -6 setting for the 24-70mm f/2.8, the same adjustment will be applied when the 70-200mm f/2.8 is mounted on the D610. So, I’ve also tested the Tamron 70-200mm, using the same approach as with the shorter zoom.

The results of the testing with the Tamron 70-200mm f/2.8 VC were fairly straightforward. The best set of images was taken with AF fine-tune turned off. The set taken with an AF fine-tune adjustment of -6 were among the worst of the lot.

After testing both lenses, I’ve decided to store a -6 adjustment for the Tamron lenses but to leave AF fine-tune turned off. Both lenses make sharp, usable images without an AF fine-tune adjustment. If I remember to activate AF fine-tune when the 24-70 VC is mounted, so much the better.

Now, it’s time to get out and shoot.

Bill Ferris | November 2015

A, Is for Aperture Priority

I don’t recall exactly how long it took before I was able to look at the letters on the menu dial of my camera and see anything other than alphabet soup. It certainly wasn’t overnight after first getting the camera, weeks at a minimum but probably closer to months.

In part this was due to the ability of the modern DSLR camera to auto select settings that produce good photos. Another factor was the menu of scene modes on my Nikon D70. When taking pictures of people, I used the Portrait setting. I also used the Landscape, Sports and Night settings. The names said everything I needed to know about their function and made it easy to explore settings other than Auto. Yes, I was getting all radical with my camera and trying different menu dial positions just weeks after getting it.

But the real experimentation started when I took the leap of faith required to dive into the alphabet soup settings on the menu dial: A, M, P and S. In addition to being an anagram for, spam, those four letters tease and temp a new photographer with hints of the unknown and mysterious. What happens when you choose, A? Will the camera even function?

The Command Dial on most DSLR cameras allows you to choose between a variety of scene and other settings, including Aperture Priority (A)

The Command Dial on most DSLR cameras allows you to choose between a variety of scene and other settings, including Aperture Priority (A) (Graphic used courtesy Creative Commons)

A, is for Aperture Priority, a setting where you manually select the aperture and the camera fill in the other settings. An aperture is an opening that allows light to pass through the lens and fall on your camera’s sensor. If you’re framing a shot at high noon on a sunny day, there’s a lot of light hitting your subject. This abundance of ambient light means your camera’s aperture can be small and still allow enough light to hit the sensor to capture a beautiful image with a short exposure. This brings us to the concept of f-stop or f/ratio. These terms mean the same thing, the ratio of the focal length of your camera lens to the diameter of the lens opening (aperture) allowing light to fall on the camera sensor.

Suppose your shooting with the kit zoom lens that came with your camera and the focal length (zoom) is set to 50 mm (millimeters). Put the camera in auto and take a picture of something. Then, play the photo and look at the information about that exposure. In particular look for the f-number. The number next the f tells you the ratio of the aperture to lens focal length. A picture taken with a 50 mm lens at f/10 had a 5 mm (1/5-inch) aperture. A picture taken with a 50 mm lens at f/4 had a 12.5 mm (1/2-inch) aperture or opening.

So, the smaller the focal ratio or f-number, the larger the aperture. In short, when you shoot with a small f-number, you’re letting more light into the camera to fall on the sensor. Or at least, your camera is trying to let in more light. When we started this discussion, we began by imagining a scenario of taking a picture at high noon on a sunny day. Let’s change the time from high noon to the golden hour, that first hour after sunrise or last hour before sunset when natural light is soft, warm and dramatic. The light quality is better but there’s not as much of it. So, in order for your camera to allow the same quantity of light on its sensor as a shot taken at noon, the aperture needs to be larger.

The begs the question, so what? Why should you care that the aperture needs to be bigger during the golden hour than at high noon? Well, aperture determines the depth of field in a photo. Depth of field is the range of distance within which objects or people will be in focus in a photograph. When shooting portraits, it’s often more pleasing to have a shallow depth of field. In other words, the person who’s the subject of the photo is in focus but anything in the foreground or background will be out of focus. This quality of an out of focus foreground or background is called, bokeh. Bokeh is a Japanese term describing the portion of a photograph that is obviously out of focus. When shooting a portrait, obvious bokeh in the background is typically very pleasing to the eye. The way to create bokeh in your shot is to shoot using a small focal ratio or f-number, the smaller the better.

Northern Arizona's summer monsoon calls forth brilliant yellow wildflowers near Flagstaff, Arizona. (Bill Ferris)

Northern Arizona’s summer monsoon calls forth brilliant yellow wildflowers near Flagstaff, Arizona. (Bill Ferris)

Above, is an example of bokeh. The subject is in focus in the foreground and the background is obviously out of focus. This transforms the background flowers into a pleasingly abstract tapestry of hues and textures complimenting the subject of the photo.

Suppose you’re shooting a landscape at sunset. A wonderful, warm light is painting the temples and buttes of Grand Canyon. For this shot, you’ll probably want everything in your frame to be in focus. You’re not trying to capture just one temple or butte. Everything in your frame needs to be in focus. In this scenario, a shallow depth of field will put much of the frame out of focus. To put everything from the most distant butte to the blooming foreground wildflower in focus, you need to shoot using a large focal ratio. Typically, I shoot at f/9 when doing landscape photography.

 (Bill Ferris)

The last light of day paints Desert View Watchtower on the South Rim of Grand Canyon a deep rusty red. Desert View overlooks the Palisades of the Desert and the Colorado River in eastern Grand Canyon National Park. (Bill Ferris)

This photo of Desert View Watchtower on the South Rim of Grand Canyon was taken at sunset. My Nikon D90 was mounted on a tripod. The camera was in aperture priority at f/9, ISO 500, a lens focal length of 19 mm and an exposure of 1/30-second.

This brings us to the final question of this blog entry. What impact, other than depth of field, will shooting at f/9 have on your photo? As we’ve discussed, the larger the f-number the smaller the aperture or lens opening. If shooting at sunset to capture a landscape illuminated by that gorgeous, soft light, you can compensate for the small aperture by boosting the ISO setting. The same scene that can be captured with an ISO of 200 at high noon, may require an ISO setting of 800 during that dusky time around sunset.

But there is a price to pay for taking this approach. Boosting the ISO to make your camera more sensitive to light adds digital noise to your photo. With higher end digital cameras, images shot at ISO 800 often look very good. But if you’re shooting with an entry-level camera or an older DSLR, an image shot at ISO 800 will often looking grainy and rough. Rest assured, however, there is another solution.

Use a tripod. For landscape photography or any photography where you want to capture sharp, detailed images with good depth-of-field, a tripod is essential gear. Mounting your camera on a tripod allows you to precisely frame the shot. It also allows you to shoot at low ISO’s of 400 or less during the golden hour and still capture great detail. The scene that was perfectly captured with a 1/500-second expose in bright sunlight may require a 1/10-second exposure at a time of day when the quality of the light is warmer, softer and more dramatic.

Now, 1/10-second may not seem slow but trust me, it is slow in photography. As a general rule when shooting handheld, you want exposure times to be no slower than the reciprocal of the lens focal length. OK, in English. Let’s say you’re shooting with a 50 mm lens. If you’re holding the camera in hand for the shot, the slowest shutter speed you’ll want to use is 1/50-second. Faster would be better. Any slower speed will allow the camera to capture the vibration or unsteadiness of your handhold. That vibration will soften details and produce an image that looks out of focus. If the camera is mounted on a tripod, that rock solid platform will allow you to take longer exposures producing crisp, focused photographs.

OK, I’ve rambled long enough. The next time you’re out with your camera, experiment with using the A or aperture priority setting. Shoot the same subject using different apertures. Compare the ISO settings and exposure times for the resulting photos. Most important, compare how the photos look. Which one looks best to you? Write down or make a mental note of those settings and spend the rest of the day shooting with them. You’ll learn a little more about your camera and you’ll get some great shots.

Get out and shoot!

Bill Ferris | August 2013