Digital Exposing for the Highlights

It should now be clear that there are important technical advantages to properly exposing digital image files, but using the Zone System with 35 mm cameras always requires some extra efforts.

With roll-film cameras the problem always is: how to apply individual contrast control to frames that must be developed together. That isn't a problem with digital 35 mm frames, but there is still the issue of metering selected areas with built-in light meters.

Since it's so easy to preview digital photographs using the camera's little LCD window, one practical solution would be to take a quick reference meter reading of your subject and note where the histogram falls on the scale from right to left.

FIGURE 100 Camera histogram of underexposed digital image.

If the image is too dark you could simply open up one or two stops using either apertures or shutter speeds until the histogram is as far right as it needs to be to avoid the problems caused by expanding the contrast.

FIGURE 101 Camera histogram of digital image exposed to the right.

Moving the histogram too far to the right would be overexposure and cause the subject's highlight values to fall off the edge of the histogram where they would be lost. The consequences of this will be discussed below in the section The Zone System and Digital Contrast Control.

This is a quick and very simple exposure method (and this is what many digital photographers actually do), but there is one issue that, if you're shooting raw image files, makes this approach less precise than it appears to be.

As I mentioned at the beginning of this chapter, digital camera previews are generated based upon assumptions about how you will eventually want to use the image. One of those assumptions is that you're shooting for JPEG images that are compressed. If you are shooting in raw format, which you should be, this means that the histogram the camera creates won't precisely match the one you will eventually be working with. This issue also applies to the flashing "out of gamma" highlight warnings that are a function of many digital SLR cameras. When your preview is set to this function it can give you the alarming impression that your highlights are blown out when, if you are shooting in raw format, they may be recoverable.

A more precise exposure approach would be one that accurately placed your subject's highlight values where they should be on the Zone Scale. Photographers who are experienced with properly exposing transparency films are very familiar with this variation of the Zone System, which is much more accurate and consistent.

If your in-camera light meter has a spot metering function, or if you have a hand held spot meter:

• Carefully meter the Zone VII Important Highlights of your subject.

• Make note of the meter's recommended exposure for these areas.

FIGURE 102 Meter's recommended exposure-Zone VII on Zone V. Remember that the meter's recommended exposure would render these areas as Zone V or middle gray.

• Since Zone V is two stops darker than Zone VII, opening up two stops from the meter's recommended exposure for the textured highlight will accurately place them on Zone VII.

FIGURE 103 Important Highlight placed on Zone VII.

This will be the perfect exposure for digital cameras!

Chapters 4 and 5 explain the general theory behind this process in great detail.

With compressed 8 bit JPEG photographs you have relatively few pixel levels to work with so the editing required to correct bad exposures can seriously degrade your image.

Although this Zone-System-oriented approach to digital exposure will work extremely well with JPEG images, it's important to not overstate the importance of using this method when you're shooting camera raw files for your general purposes.

As you will see, the conversion process from raw files to tone mapped digital images offers you many powerful tools for manipulating the exposure and contrast of your photographs.

Adobe's Camera Raw converter allows for effective exposure control that can, to some extent, compensate for exposure and contrast problems.

What the Zone System adds to this process is the ability to make consistently precise exposures that require less correction in the conversion stage; it allows you to think creatively about how to use exposure in imaginative ways.

Digital Camera and Digital Photography

Digital Camera and Digital Photography

Compared to film cameras, digital cameras are easy to use, fun and extremely versatile. Every day there’s more features being designed. Whether you have the cheapest model or a high end model, digital cameras can do an endless number of things. Let’s look at how to get the most out of your digital camera.

Get My Free Ebook


Post a comment