This article describes managing digital image capture to achieve optimal, or at least intended, dynamic range and how to determine the most appropriate camera range settings to accomplish this.
The Zone System
The simplest takeaway from the oft-misunderstood Zone System, is that an image should be exposed to utilize most or all of the range from black to white, without unintended clipping of near-whites, or blocking up of near-blacks. If the image does not incorporate the full dynamic range in a scene, the photographer should have done this by intent.
In digital photography, the most commonly recommended camera settings involve protecting detail in the brightest parts of the image, and correcting everything else in post-processing.
Errors that Affect Image Quality
It’s true that the biggest image-killer is over-exposing the whites, preceded only by the errors of blur and incorrect focus. Please don’t make the mistake of assuming that these last two items are not relevant to this article: camera settings can cause camera-blur, or motion-blur, as well as shorter or longer than desired focal zones. Other errors that are difficult, if not im- possible to correct in post-processing include noise from excessively high ISO settings, and noise in the darks from too short an exposure or too restricted an aperture. High dynamic range cameras and excellent noise reduction software reduce the impact of these problems, but they do not eliminate the importance of using settings that capture cleaner images. In other words, it’s important to “get it right in the camera.”
The opening paragraphs of this article may be a restatement of the obvious to experienced photographers, but they tend to be an eye-opener to shooters who became serious about photography after the digital revolution. “You mean there is more to camera settings than shooting in Aperture Priority, and adjusting exposure bias to avoid highlight blowouts?” Yes, there is. The next question is: how to best determine optimal camera settings, including ISO, white point, aperture, exposure and even choice of lens, in the digital age? Is an old fashioned handheld light meter still needed, or can the camera’s metering be trusted? Is there a third method that should be considered?
Options in Managing Exposure
Well, the title gave it away: it’s not always a handheld light meter. And if the camera internal metering was the solution, then the automatic camera settings would do the trick. Too often they miss or set the needed exposure range at the expense of some other factor, such as a too-high ISO, or a shortened focal range. We need another method of determining settings that will consistently improve results.
Some of you may be familiar with the Datacolor product called the SpyderCube. If so, you have read the descriptions or seen the videos about using it for optimizing adjustments in post-processing, ideally in a RAW converter. However that’s not the only way in which the SpyderCube can be used: it’s also an effective tool for determining optimal camera settings to get it right, in the camera.
Using the SpyderCube
Here are some tips on using the SpyderCube to help with in-camera adjustments. Later on, we’ll discuss how you can use the SpyderCube during a photo shoot with the camera tethered to your computer.
You can use the SpyderCube to set in-camera custom white balance. Simply enough, set the SpyderCube up in your shot, under your lighting. Initiate your camera’s custom white balance sequence, fill the frame as much as practical with the Cube, and set the white balance.
Setting white balance in this way maximizes the usefulness of the LCD display on the camera, which shows you a semi-processed JPEG, not your actual RAW file. Color and density will be more representative of the real thing, and the camera’s white clipping tool (the “blinkies”) will be more accurate. Later on, you will set white balance/gray balance in your RAW converter from the brighter of the gray faces of the Cube, which represents your primary light source. Next, we’ll try to find the “top” of the exposure.
Start in Aperture priority mode, use either spot metering or center-weighted metering, and take a test shot with both sides of the white/gray faces on the SpyderCube showing equally. Examine the on-screen preview−while you are at it, review the histogram, and take a close look at the appearance of the chrome ball and the white faces.
One expects to see the “blinkies” appear on the highlight reflections on the chrome ball; that assures there are spectral highlights, and indicates Zone 10. You don’t want to see blinkies in the white faces−that would mean you’re losing ground in Zone 9 and Zone 8. The highlight detail would suffer in the image−and probably won’t be recoverable in post-production.
You can use the black face of the SpyderCube, and the black trap it contains, to adjust exposure for the shadows, and control of Zones 1 through 3. You’ll want an exposure that lets you clearly distinguish the trap in the black face of the Cube. Not only will this help you to protect shadow detail, it will help you reduce noise in post-production.
Make your adjustments, take note of your exposure settings and switch to Manual mode. You can calculate adjustments to aperture/shutter speed to manage depth of field and control motion-blur.
At this point, you have better control of your exposure. You may now have the option of reducing your ISO settings, as you are controlling your other settings, and not guessing−so you need less buffer or safety margin. Similarly, you have more latitude in choosing your combination of aperture and shutter speed, again because you need less margin for error.
A final consideration is the density of the gray faces. This is best analyzed in tethered mode, or in post- processing, but a quick judgment of whether they are indeed medium gray, not lighter or darker than intended, can increase awareness of image densities, and control whether you are creating a high-key, or a low-key image.
Shooting Tethered To a Computer
It is now possible to tether most advanced DSLRs to a computer while shooting, and manage your exposures with a high level of control. The SpyderCube is ideal for this too. Software applications that support tethering include: Lightroom, Aperture, Phase One Capture One, Hasselblad Phocus, Leaf Capture and others.
You can use the SpyderCube to correct and adjust images, in much the same way that you would in post- production−but you’ll now do this up front, so you can “get it right in camera” and optimize results beyond what post-process alone can offer.
All of these applications provide tools for adjusting the first shots in a session, and applying those adjustments to all of your subsequent shots. The software applies the adjustment set “on the fly” creating image files that are optimized for real-time conditions, not edited after the shoot.
This gives you every advantage possible in creating the highest quality images for yourself or your client. You can manage the nuance of your captures at the outset, protecting highlight/shadow detail and leverage the full dynamic range of your camera. That perfectly creamy tonal range you admire in the work of the experts can best be obtained though this type of attention to settings.
Shoot the SpyderCube when your studio lighting setup is complete. (You may even want to use the Cube in configuring your lighting setup, but we’ll save that for a subsequent article).
When the image appears on-screen, look at the histo- gram to help evaluate your exposure. If you see that that the exposure is incorrect (clipping highlights for example), make adjustments in your setup and exposure and re-shoot the SpyderCube.
You can use the color eyedropper tool to measure the RGB values of each section. Generally, you’ll want to expose so that the brighter white section will measure about 245, and the black face to measure 6 or so.
Use the brighter gray patch to neutralize color, and set midtone values−in sRGB or Adobe 98 RGB (gamma 2.2), middle gray will measure 119.
As in the earlier scenario, you’re protecting the values in the Zones near the margins of your dynamic range −Zones 9 and 8, and Zones 2 and 3, as well as assuring appropriate midtone densities. If your measurements show values that are out-of-bounds, then adjust your lighting and re-shoot the SpyderCube. Lather, rinse, repeat; it should add body and luster to your images!
You can save your ‘adjustment set’ in many of these software applications, and automatically apply these adjustments as you continue to shoot. In other cases, you’ll apply the adjustments in post-production.
The key to success is taking steps up front to protect information in the image−information that, if lost in capture, cannot be recovered without sacrificing image quality. You got it right, in the camera, from the start!
Now, would Ansel Adams approve of this method? I’m not sure I know the answer to that question, but I’ve been working with this method, and the results have been quite good. It’s worth considering for your own work.
My thanks to C. David Tobie, of Datacolor who provided ex-pert technical support for this article.
Resources: Websites: Adobe Lightroom: adobe.com; Aperture: apple.com; Datacolor SpyderCube: datacolor.com; Phase One Capture One: phaseone.com; Hasselblad Phocus: hasselbladusa.com; Leaf Capture: mamiyaleaf.com