2 Photographic Equipment
This chapter provides detailed descriptions of the photography gear that is required to obtain high-quality medical images. It discusses acceptable options for cameras, lenses, flashes, light meters, and associated accessories, as well as endoscopic imaging systems. The terminology related to this equipment is explained thoroughly, as are the features that are relevant to selecting the best equipment for the specialized demands of medical use.
DSLR, digital single-lens reflex, endoscope, equipment, flash, lens, light meter, mirrorless, resolution, sensor, speedlight
Digital photography equipment is practically ubiquitous in the modern era. Nearly everyone carries a camera of some kind, most commonly in the form of a smartphone. While a well-trained photographer can usually maximize inferior equipment to obtain acceptable results, the proper equipment will allow a photographer to reliably create high-quality imagery. The authors of this textbook do not specifically endorse any particular brand of equipment, and note that outstanding results can be obtained with products from any brand: the limiting factor in image quality is usually the photographer’s skill. This chapter discusses the fundamentals of camera equipment, with attention to the features that matter for medical applications.
The camera body contains the imaging component of the digital camera, the sensor. There are two primary factors to consider when evaluating a camera’s sensor: resolution and physical size. Resolution is typically represented in megapixels: higher numbers mean better resolving power. A resolution of 12 megapixels or greater is sufficient for printing in high quality at standard sizes, and many consider a resolution greater than 24 megapixels to be wasted. However, increased resolution allows very large prints to be generated or more aggressive image cropping.
The most common standard sensor sizes are full frame, APS-C, and Micro Four Thirds. While larger sensors yield slightly better image quality (especially in terms of reduced noise), excellent images can be produced regardless of the sensor size. The most noticeable effect of sensor size is a change in field of view: larger sensors result in a wider field of view at a given focal length. Full-frame sensors are approximately the same size as 35-mm film, and lens focal lengths are usually referred to in relation to this size. APS-C sensors result in an effective focal length multiplication of 1.5 times, and Micro Four Thirds in doubling. Thus, a 50-mm lens on full frame behaves roughly like a 75-mm lens on APS-C and a 100-mm lens on Micro Four Thirds. In this book, all focal lengths are listed as 35 mm equivalent.
There are three main types of camera bodies: point-and-shoot, DSLR, and mirrorless (Fig. 2.1). Smartphones, while superficially most similar to point-and-shoot cameras, will be covered in Chapter 6. To be acceptable for medical use, a camera must feature manual exposure controls, be able to shoot in RAW format, have a configurable focusing system, be compatible with suitable lenses, and be able to synchronize with external flashes.
Point-and-shoot (hereafter P&S) cameras are compact and have an integrated camera body and nonremovable lens. While they have the advantages of being cheap, easy to use, and lightweight, most lack the requisite features listed above for medical photography, and as such are not recommended. However, there is a small but growing segment of full-featured, high-end P&S cameras that can be considered although current models are probably not the optimum choice.
Digital single-lens reflex cameras, or DSLRs, are the usual choice for professional photographers. They feature a large optical viewfinder and interchangeable lenses. The viewfinder works by a mirror-and-prism system to allow real-time preview of the exact image composition. Modern DSLRs also have a Live View function that allows the user to use the rear screen as a viewfinder to display the digital image from the sensor in near real-time.
DSLRs are the most technologically mature form of digital camera, and the major brands have a wide selection of lenses available. High-end bodies feature full-frame sensors, while a variety of mid-range to entry-level models feature APS-C sensors. The main differences between entry-level and more advanced cameras relate to ergonomics as opposed to image quality. Professionally oriented bodies will have easy access to critical functions via physical knobs and buttons on the exterior of the body; lower-end models often have fewer controls, and thus require operation of menus to accomplish the same tasks.
Almost any modern DSLR, even entry-level models, will be able to provide satisfactory results for a medical photographer, as all of the requisite features listed above are included with every current-generation camera. Battery life is usually quite good, often enough for an entire day of shooting. The only downside of a DSLR is the larger form factor, which is not a major consideration for medical applications.
Mirrorless cameras are a newer category beginning to emerge in competition to DLSRs. They are available with the full range of sensor sizes, from full-frame to Micro Four Thirds. Mirrorless cameras are similar in shape and feature set to DSLRs, with the notable omission of the optical viewfinder, relying instead on a Live View function on the rear screen. Some mirrorless cameras also feature an eyepiece with a small internal screen. This results in a smaller form factor but some diminution in battery life and autofocus performance. One advantage of mirrorless cameras is their flexibility in lens choice, as the mirrorless design allows for adapters to be used so that lenses from DSLRs or other brands of camera can be mounted, although this sometimes results in decreased performance or loss of autofocus capability. Mirrorless cameras are rapidly evolving and have not yet reached maturity—in several years, it is possible that they will have surpassed DSLRs.
Lenses are the most important component of a photographer’s system, and lens technology has remained largely stable for several years (Fig. 2.2). In general, the lens is the limiting (equipment) factor for image quality, and high-quality lenses are to be used at all times.
Lenses are referred to by their actual (not effective) focal length and the minimum f-stop, such as the 85-mm f/1.8. There are two main categories of lenses: prime lenses and zoom lenses. Prime lenses have a fixed focal length, and because they are optically less complex, they are lighter, smaller, usually have a wider maximum aperture, and usually produce higher-quality images than an equivalent focal length on a zoom lens. Zoom lenses cover a range of focal lengths such as 70 to 200 mm. This is made possible by a mechanism that results in a heavier, larger lens with slightly reduced image quality compared with an equivalent prime lens. The diminution of image quality is not usually apparent in controlled studio conditions.
When choosing a lens for medical use, the two most important criteria are the focal length and the minimum focusing distance. The use of a zoom or prime lens is entirely up to the photographer’s preference, but it is easier to standardize photographs with a prime lens, as the perspective is fixed. Choose an equivalent focal length between 80 and 200 mm. Longer focal lengths require an unacceptably long distance from photographer to subject and may lack sufficient depth of field, even at small apertures. Shorter focal lengths introduce “perspective distortion,” which results in structures nearer to the camera appearing larger and more protuberant, with the remaining features appearing to recede unnaturally. This is a result of the relative distances of the portions of the subject to the camera as opposed to a lens design flaw.