Birds, Camera, Camera lens, digital cameras, Digital single-lens reflex camera, Gordon Wiltsie, International Organization for Standardization, iso, Nick Wiltsie, Nikon, Nikon D700, Photography, physiological tremors, shutter speed, Single-lens reflex camera
One stubborn source of pride for me has long been my ability to get good pictures with simple camera bodies and a small assortment of lenses that I almost always focus manually. People attending photo seminars I teach have often snickered to see my gear, which includes at least one bruised and battered lens that shows every hardship of its 20+ -year lifespan. I, in turn, used to secretly sneer at amateurs who actually believed that the mere purchase of vastly more expensive cameras and lenses would automatically help them to create better pictures.
Then – embarrassingly late in the game – I finally bought an [almost] up-to-date Nikon D700, a lighter version of the company’s heavier and pricier D3, which, itself, was first unveiled in 2008.
I already knew that both cameras could shoot at higher ISO’s than anything before them but had not viscerally experienced how profoundly its radical new light sensor had really changed the game. No longer do I believe that technological leaps in camera function are really just tricks to bypass genuine know-how. Instead, the actual workings of this camera (and subsequent models by several companies) didn’t just make basic functions easier, but actually enabled shots that were once almost impossible.
I really ate crow when I first tried it out on flying birds. Until I got the D700, pictures of moving objects that I shot with my manual focus 400mm lens – the only one that is really light enough to carry around — often disappointed me. No matter how great a raptor might look as it soared through my viewfinder, the end results were often out of focus because I had too little depth of field (a function of the f/stop,) or blurred because my shutter speed was too slow.
Because of the limited light-gathering capacity of either film or earlier digital sensors this dilemma between f/stop and shutter speed has always been a fundamental and inescapable function of physic and chemistry. At any ISO higher than 400, film grain has always gotten huge and at the same speed even my faithful Nikon D200 starts generating pixelated “noise.” This makes any telephoto longer than about 300mm very hard to use.
First, the longstanding rule of thumb for hand holding a lens is to choose a shutter speed faster than the reciprocal of its length (in mm.) In other words you have to shoot a 400mm lens faster than 1/400 second (1/500 second in traditional settings.) Even that can be shaky, though – especially if it’s cold, the wind is blowing, or you have to frame something quickly. Just to be safe, I double it to 1/1000 second. Furthermore, if my subject is moving or I am shooting from something like a boat, I double it again to, say, 1/2000 second. (See note at the end.)
The math of everything means that even with a marginal ISO of 400, shooting at 1/2000 second the wide opening of f/4 to get an optimal exposure. This, in turn, gives you almost no room for focusing errors. If you shoot slower you may get camera shake and motion blur.
This whole formula changed, however, with Nikon’s pioneering new sensor. Unlike anything before them, these can suddenly gather light quickly enough for usable ISO’s as fast as 6400 – or even more. The pictures I have shot at ISO 3200 include even less digital noise than the often-pleasing grain I got with erstwhile Kodachrome 200. Even my tests at 6400 are way better than anything I used to get at “just” 800.
Now, if I want to push my exposure all they I can get an either four extra f/stops for hugely more-forgiving focus, or shoot sixteen times faster! (Each doubling in ISO doubles is equivalent to doubling the shutter speed or increasing one f/stop.) So, instead of shooting at f/5.6, I can use f/16. Similarly, when the light gets dim, I gain the same advantages. If a landscape image, for example, meters at f/5.6 at 1/60 second – a picture that would demand a tripod with a 400mm lens – you could comfortably hand hold it at 1/1000.
Now, when a creature starts running or flying, I almost always get the pictures – even with manual focus.
Given my long-standing dismissal of “non-essential” innovations such as autofocus and matrix metering that, in fact, simply make camera option easier (or even dumb it down) cameras like the D700 opened whole new horizons for me. Now I wonder how I ever worked without them!
The pictures in the accompanying portfolio were all taken with my new camera (and venerable 400mm lens) in just the last two months since I got it. Every one of them appeared by surprise when I was assigned to shoot something else.
IMPORTANT NOTE: Just as I thought I was catching up with technology, Nikon has now introduced the D800, which delivers the same ISO’s, but triple the megapixels, and exciting video capabilities. I won’t wait so long to get one of those!
AN INTERSTING ASIDE:
After I showed a draft of this to my son Nick, who is wrapping up a master’s degree at MIT, he responded with a paper he just wrote that “proves” the reciprocal rule of shutter speed. It’s a bit hard to understand, but it does add up!
Nick bases his premise on contemporary research about “Physiological Tremor, ” or, as he puts it: “a ubiquitous, involuntary, and irregular oscillatory movement present in the neuromuscular systems of all humans.” In layman’s terms, this basically means that muscles in our extremities are never motionless.
Here the most interesting part of the paper:
3.2 Camera Optics
Single-lens reflex (SLR) and digital single-lens reflex (DSLR) cameras operate by having the lens focus the scene onto the 36 mm wide x 24 mm tall film strip or sensor. The important measures in this case are the focal length of the lens and the exposure time of the image. Photographic lenses define the focal length, L, as the distance between the ”intersection point” of the light rays and the sensor; a 50 mm lens focuses as if it were a single lens located 50 mm from the sensor. The exposure time or shutter speed, δt, is the length of time the shutter is open.
As can be seen from Figure 10, a single light ray entering a camera that is rotating at angular 8
Figure 10: Diagram of key geometric parameters of a 35 mm camera.
velocity ω will move linearly across the film surface. This blur length, b, can be measured as:
b = ω · L · δt (1)
Enlarging a photograph from a 36 mm x 24 mm exposure to a 8” x 10” print requires a 7x enlargement. As the minimum permissible circle of confusion is 0.2 mm for the purposes of this experiment (as shown in Section 3.1), the maximum permissible size of b is:
bmax = 36 mm (2) Cmax 10 inches
bmax ≈ Cmax ≈ 0.028 mm (3) 7
The general rule-of-thumb used in handheld photography is that the minimum shutter speed to prevent image shake is the inverse of the focal length; for example, a 200 mm lens has a minimum shutter speed of 1/200 of a second. Mathematically, this is:
|δtmin[s]| = | 1 | (4) L[mm]
Combining Equations (1) and (4) with the calculated amplitude of bmax, the maximum allowable angular velocity of the camera becomes:
ωmax = bmax [mm] = 28 · 10−3 rad/s. (5)
Read the full paper here: