Program Exposure on the Nikon N6006

Dan Knight

The Nikon N6006 (F601 outside the U.S.) has two program exposure modes, P and Pm. This article will compare the two and explain why you should probably never use the P setting.

Program Mode P

The Canon A-1 (1977) was the first 35mm SLR to offer program mode. This program took a very simplistic approach to choosing a shutter speed and lens opening: starting at 1/1000 sec. and f/16, it reduced the shutter speed by one step and opened the lens by one stop in a linear fashion.

As other makers added program exposure to their lines, they tended to follow Canon's lead. It wasn't until the Minolta X-700 (1981) that someone devised a better program.

What Was Wrong With Canon's Program?

The problem with Canon's program mode was low light photography. One of the first rules of 35mm photography is that you should avoid hand-holding exposures below the reciprocal of your focal length -- that would be roughly 1/60 sec. with a 50mm lens or 1/125 for a 135mm telephoto. In low light, that often meant shooting your normal lens (most often f/1.4-1.8) wide open or close to it.

Canon's program, which Nikon essentially duplicates with the N6006's P mode, doesn't do that. It's not intelligent; it won't open an f/1.4 lens all the way until the shutter speed reaches 1/8 sec. Knowledgeable photographers would be shooting wide open by 1/30 or 1/60.

Put another way, at EV 7 (EV is a standardized light level) the program would choose roughly 1/20 sec. at about f/2.4, which could easily lead to camera shake showing up in the picture. A smart photographer would shoot at 1/60 and f/1.4 if his lens was fast enough, 1/45 and f/1.8 if that was all his lens allowed.

With program shift and several exposure modes to choose from, a savvy photographer can override the default program settings. On the other hand, the whole point of program mode is that the camera is supposed to choose the best setting for you.

Until the Minolta X-700, program mode was counterproductive to low light photography. Minolta gave the whole thing a bit more thought and devised a program that (a) would shoot "wide open" by 1/60 sec. and (b) chose even higher shutter speeds with tele lenses with sufficient light. Thus was born the multiprogram mode.

Nikon's P Program

The standard P mode in the N6006 and earlier Nikon SLRs was based on Canon's model, but extended to 1/2000 sec. and f/22 on cameras and lenses that allowed those settings. It's a simple step-for-step, stop-for-stop program that's okay in bright light but bad news in low light.

Program Mode Pm

The multiprogram mode (Pm) in the N6006 follows Minolta's lead -- and then goes beyond it. In all cases, if a lens goes to f/22, the Pm mode will set 1/2000 and f/22 at EV20. But after that, all bets are off.

Nikon's Pm mode follows some rules that are based on the focal length of the lens you are using and their probable application.

  1. The lens will always be wide open at the reciprocal of the focal length: 1/30 for a 28mm lens, 1/50 for a normal lens, 1/200 for an 80-200 zoom at 200mm. This guarantees the highest possible shutter speed in low light conditions.
  2. If then lens is faster than f/2.8, the camera will use the reciprocal speed between f/2.8 and wide open. This provides the extra depth of field most trained photographers would choose in that situation.
  3. Between f/2.8 (or the maximum aperture for slower lenses), Pm mode closes down 2 stops for each step of shutter speed. In the case of a 28mm f/2.8 lens, than means 1/60 @ f/5.6 (EV 11) and 1/125 @ f/11 (EV 14). In the same light, the 50/1.4 lens would be set at about 1/90 @ f/4.8 and 1/180 @ f/9.5, respectively.
  4. In the case of the 28mm lens - and this probably applies to other wide-angle lenses as well - once Pm mode reaches f/11, it switches to two steps faster shutter speed for each stop. Reasons for this probably include the luxurious depth of field and a desire to avoid the smallest apertures, which tend to be less sharp than medium ones. (For most lenses, best optical performance ranges from about two stops from maximum to about f/8.)

Instead of a "one size fits all" program mode, Nikon engineered a program mode based that accounts for focal length and the way trained photographers typically work. Where Minolta's dual program X-700 had been a real innovation, Nikon's Pm mode fine tunes it for better performance with any focal length lens.

Visual Aids

As photographers, we generally believe a picture is worth a thousand words. On the other hand, some people are intimidated by graphs, so I wanted to explain in words just what these graphs illustrate. Except for the 105/2.5 chart, these are copied from the N6006 manual.

This graph shows exposure settings with a 28mm f/2.8 lens. Note that with this slow a lens, both the P (red line) and Pm (green) programs are wide open at 1/30 sec. Also note that Pm provides more depth of field when light permits.

This graph shows exposure settings with a 50mm f/1.4 lens. Note that the P program (red) begins to close down the aperture at 1/8 sec., while the Pm program (green) waits until 1/50 sec. to do so. This will minimize camera shake. The Pm program then closes down the lens without changing the shutter speed until it reaches f/2.8. From there, it soon provides more depth of field than the P program.

This graph is extrapolated from the above rules and the chart in the N6006 manual. It shows the exposure settings we can expect with a 105mm f/2.5 lens. Where the P program (red) begins to close down the f-stop at about 1/20 sec., the Pm program (red) keeps the lens wide open until about 1/100 sec. to reduce camera shake. Except in bright conditions, this program will use a wider aperture and higher shutter speed than the P program.

This graphs shows exposure settings with a 500mm f/4. The P mode (red) would begin closing down the lens at 1/60 sec., which is obviously unholdable using a 500mm lens. If I read the chart correctly, the Pm program (green) waits until about 1/700 sec. before it starts to close down the aperture, leading to consistently higher, more hand-holdable shutter speeds.

Using the rules above and the graphs in the N6006 manual, you could probably create your own charts (as we did for the 105/2.5) for such interesting lenses as the Sigma 20mm f/1.8, 300mm f/2.8, and others you might own - even variable aperture zooms. If you understand the dynamics of shutter speeds, f-stops, and hand-holdability, I think you'll agree that the Pm program is vastly superior to the P program for general use.

As I said above, you should probably never use the P program.

Go to Nikon N6006/F601 page.

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