2
Digital Imaging with Hasselblad
THE ADVANTAGES OF HASSELBLAD'S DIGITAL IMAGING SYSTEM
You can create digital images with Hasselblad medium-format cameras by simply replacing a film magazine with a magazine for electronic imaging, as shown in Figure 2-1. This design allows you to use the same camera and the same lenses and accessories for film photography as for electronic imaging. You need not invest in a completely new digital camera system and need not familiarize yourself with another camera. You need not learn anything new about creating the ultimate image quality, the use and operation of lenses and lens controls, exposure, composition, use of light, and so on.
Working with the same camera for film and digital photography is advantageous because recording either type of image is based on the same principles and requires the same camera and lens operation. The image is simply recorded on a different medium. The real differences between film and digital photography come after the image is recorded in the camera. That is when you must decide whether to change the image and how to present and store it. Even if you plan to record all your images digitally, you cannot limit your studies to electronic recording principles and the use of computers, scanners, or imaging software. As with film, producing a great digital image requires recording a good image in the camera. You must first learn everything about the camera and lens operation and about the approaches that create great images of the highest quality in your camera. The Hasselblad Manual covers all these aspects.
The comment is often heard that in this digital age photographers need no longer be overly concerned about creating perfect results in the camera because images can easily be changed and improved, and all the faults can be corrected afterward in the computer. It is certainly possible to retouch images and to improve their quality by making them brighter or darker or sharper or by changing colors. You can also add a soft touch, make an image more effective by changing the composition or the background, produce double exposures, combine different images, or make almost any other desired changes. But these manipulations done in the computer are very time-consuming if you want to do them yourself and very costly when done on the outside. The best approach is still to become a good photographer and to try to record an image in the camera that is as perfect as possible so that it needs little or no after work on the computer.
Figure 2-1 Magazines for electronic imaging A digital imaging back can be attached to some Hasselblad cameras in the V system in place of a film magazine. The H camera can also be used with digital backs specifically made for this camera model.
If you decide now or in the future to make digital recording part of your photography, learn the principles of electronic imaging and the possibilities offered by this new recording medium from other photographers, in workshops, or with updated books on digital imaging.
DIGITAL BACKS FOR THE HASSELBLAD
The magazines for electronic imaging are not made by Hasselblad but by several other companies specifically for use on Hasselblad cameras. Most magazines must be used with specific Hasselblad camera models, so study the specifications supplied by Hasselblad or the manufacturer of the digital back. Most backs require motor-driven camera models, with the 555ELD being an ideal model for various digital backs. The 555ELD has Databus connections at the rear of the camera body, eliminating cable connections to digital backs that also have the electronic coupling. The 555ELD has a special release for electronic imaging in addition to the release for film photography.
The Hasselblad H camera system offers the most complete integration for electronic imaging, with digital Databus interface technology between the camera and the electronic imaging backs. The camera's LCD display can show a histogram of a digital exposure. All the HC lenses are also designed for the ultimate image quality in electronic recording. The H camera can therefore be considered the most updated and most sophisticated medium-format camera for electronic imaging.
THE DIGITAL CAMERA BACKS
Because electronic imaging technology is changing rapidly and new and modified products are introduced constantly, I refrain from discussing specific products or recording techniques. Doing so would outdate this manual rapidly, perhaps even before it comes on the market. When you are ready for electronic imaging, study the specifications for the various digital backs. Meanwhile, a few basic points can be made here.
A single-shot back lets you record moving subjects and use flash, and therefore it is suitable for any type of photography. A multishot back can be used only for stationary subjects but produces better image quality. Some backs offer the option of both approaches.
Some backs must be used in combination with a computer (which can be a laptop) when the image is recorded and therefore are more suitable for studio work. Others can be used untethered, with the image being recorded on a media card as done with special digital cameras. This is probably the type you want to consider for location work.
SENSOR SIZE AND FOCAL LENGTH OF LENS
The sensor size varies greatly among cameras made specifically for digital recording, either the point-and-shoot or the professional approach. There are also variations in sensor size among digital backs, but at present most of them are either the 37 × 37mm square or the 24 × 36mm rectangular size. Because these sensors are considerably smaller than the 6 × 6cm or the 6 × 4.5cm film formats, the lenses on the camera cover smaller areas than they do with film magazines. In other words, a wide-angle lens for film photography becomes a standard lens for digital recording, and a standard focal length lens becomes a telephoto lens.
I feel it is most logical to determine the equivalent focal length or area coverage by the difference between the long side of the film format and the imaging sensors rather than the diagonal. The factor is approximately 0.7 for the 37mm square and the 24 × 36mm rectangular sensor and the 6 × 6 or 6 × 4.5 film format. This means that a 50mm lens covers the same area in digital recording as the 80mm lens does on film. The 80mm standard focal length becomes a telephoto, covering the same area as a 120mm lens on film. If you work with a monitor or if the back has one built in, you can see the covered area on the screen. If you want to see the composition on the focusing screen of the camera, you must mask it down. Some backs come with a focusing screen, with the digital area coverage clearly marked.
IMAGE QUALITY
The digital image is formed on the sensor in the camera by pixels that are light sensitive to either green, blue, or red. The number of pixels is indicated in a specification sheet, either by the number of pixels along either side of the sensor or by the total number of pixels on the entire surface (or both). The specifications may perhaps read 3120 × 2060 pixels, which adds up to 6.4 megapixels. The number of pixels is directly related to the image quality produced in the camera. The higher the number of pixels, the better the image quality (provided that everything else is equal, especially the performance of the lenses). Lenses of questionable quality limit the image sharpness in digital recording just as they do in film photography.
The number of pixels is only part of the quality story. The size of the pixel needs to be considered, and that is determined by the size of the sensor. In a 24 × 36mm sensor that has 2048 pixels along the 24mm side, the pixel size is 0.0117mm, or 11.7 microns (μm). The pixel size on a smaller 15 × 23mm sensor with the same pixel count is only 7.4 microns.
A larger pixel collects more light, and its signal needs to be less amplified, thus creating less “noise,” as it is called in electronic imaging. The result is a better dynamic range in the picture, with a wider range of shades from the deepest shaded areas to the brightest highlights. A file with all this information will also survive postprocessing much better. Whereas the sensors in most digital backs for Hasselblad are not larger than those in professional 35mm cameras, future digital backs for Hasselblad may very well have sensors that are considerably larger than the 24 × 36mm film size.
The present 37 × 37mm sensor is already considerably larger than those in 35mm cameras, and other digital backs with medium-format sensors seem to be on the way.
At this writing, two companies have announced digital backs with large 36 × 48mm sensors. These larger sensors can be used only in medium-format cameras. They cannot be built into cameras based on the 35mm camera design, equipped with lenses designed for covering the 24 × 36mm area only. With all these larger sensors, Hasselblad medium-format cameras will provide in digital imaging the same great benefit of a larger image with better image quality as they do now in film photography.
Some digital backs for medium-format cameras offer the multishot capability, which can also greatly improve image sharpness. In the normal one-shot mode, only 25% of the total pixels record red, only 25% record blue, and only 50% are used to record green. In the multishot mode, all of the pixels (100%) in the sensor record red, 100% of the pixels record blue, and 100% record the green image. A much larger number of pixels is used to record the image, thus producing better quality. Although multishot backs cannot be used for a moving subject, they offer the utmost digital image quality for still lifes, architectural work, product photography, and copying, where utmost image sharpness is a prime requirement.
LENSES FOR DIGITAL RECORDING
Some manufacturers of digital cameras emphasize that lenses for digital recording must have different quality requirements, must be designed to focus the light more directly to each pixel and that lenses designed for film recording do not provide the best or satisfactory quality especially on the edges of the image. While there is some truth to these facts, they apply only to specific sensor designs.
Practically all large camera sensors, 24 × 36mm and larger, which includes the sensors in digital backs for Hasselblad cameras, are at present of the flat sensor type which show a slight loss of quality only with lights rays reach the sensor at an extreme angle of incidence. This is hardly the case on Hasselblad since the incident light angle is reduced due to the sensors not covering the entire 55 × 55 or 55 × 42 image area for which the lenses are designed. Even the 38mm Biogon has proven to produce excellent quality out to the corners on a 36 × 48mm sensor. All other Hasselblad wide angle lenses are of the retro focus design with an associated moderate incidence angle to the sensor corners. Keeping in mind that high resolution is the main requirement for digital lenses as it is for lenses for high quality film recording, we can state that all Hasselblad lenses in the V and H system are an excellent compromise for film and digital work.
EVALUATING THE TONAL RANGE AND EXPOSURE IN ELECTRONIC IMAGING
In electronic imaging with a digital back attached to Hasselblad cameras, you can evaluate exposure and the image in general on a computer monitor or the monitor on the digital back if the back is so equipped. You can do this at any time and so can make adjustments before you record the final image. This approach is somewhat similar to making a test exposure on instant film.
You can use a histogram to evaluate precisely and scientifically the distribution of the tonal values, in the image and in its exposure. This possibility exists when a digital back is attached to the H camera. To make the histogram appear on the LCD panel on the H camera grip, you program custom option 17, SHOW HISTOGRAM, into the camera, as described under Custom Options in Chapter 4. Programmed to YES (the default setting), the histogram appears on the LCD panel shortly after the exposure. It works with various digital backs, but the histogram may look slightly different depending on the back attached to the camera.
The Histogram
A histogram shows the distribution of the tonal values within an image. The values vary from the black shadow areas (shown at the far left) to the pure white highlight areas (shown at the far right), with the middle tones in between. The horizontal spread covers the full potential dynamic range of the camera system. Photographers familiar with the zone system can think of a histogram as showing the tone values from zone 0 (black) on the left to zone 10 (white) on the right.
Figure 2-2 A histogram of a normal contrast scene with correct exposure (1), underexposure (2), and overexposure (3).
The vertical height of the curve indicates the number of pixels for each tonal value. A high curve indicates a large number of pixels for that particular tonal value. The histogram for a high-key image with few or any dark areas has curves mainly or completely toward the right, whereas most of the curves for a low-key image with few or any bright areas are mostly to the left. An image with an average tonal range from white to black has curves all the way from left to right.
Determining Exposure from the Histogram
The interpretation of the histogram is somewhat different for different digital backs, in part because different backs may report ISO values to the camera in different ways. In principle, however, regardless of the contrast range of the image, all the vertical curves must be within the left and right margin of the histogram—that is, within the maximum potential dynamic range (see Figure 2-2). They should never go beyond the left or right margin. If the curves go beyond the right margin, areas in the image will be totally white without any information, and the lens settings must be changed to make them fall within the left and right margin. If the curves go beyond the left margin, the black zone, parts of the image will be totally black, and you must change aperture or shutter speed (or both) accordingly.
The histogram does not show the exact amount of under- or overexposure, but the results of any corrections made in the aperture or shutter speed setting are clearly shown on the new histogram. Overexposure in digital recording must be avoided because details in the overexposed areas are completely lost. This should be remembered especially by photographers accustomed to working with negative films and leaning toward overexposure to obtain sufficient detail in the shaded areas.