The relationship with a camera is like any other: if you want to have a good one, you must learn to understand and work on the “relationship." This is orchid related because it makes one aware of light and heightens one’s ability “to SEE”. If you read no further than what is written below, you will at least have an understanding of light and what you see in comparison to what the camera sees! This is almost never mentioned to beginning camera enthusiasts and becomes a never-ending source of consternation for them.
So here's what you need to understand:
Your camera's metering system ALWAYS “ASSUMES” that it is looking at an 18% reflectance gray card which is a tone or value that is halfway between black and white! (Or a tone/value of color that reflects the same amount of light). This is important to know because your camera's meter always assumes it is receiving light reflected off of that “value” or color (If you don't have a gray card, you could use the palm of your hand which is approximately the same as a gray card). If you photograph snow with a normal reflected light setting your camera will assume it is looking at gray and turn your snow into a value that is equal to that middle gray. If you photograph a black dog/cat on a black chair, your camera will “assume gray” and you will get a gray dog/cat on a gray chair. The same is true for photo prints from negatives. The “printing machine” does the same thing as your camera. It will print a white orchid against a white background, assuming it “should be" gray; so, you will get a medium gray flower and background. Since the sensitivity of camera films fall in a compressed contrast range, it is necessary to understand the above information.
The way the metering system in cameras work entails (1) understanding what your eye sees, (2) what a digital camera sees and (3) what the two normal types of film see. Your eye sees a lot wider contrast range than film does! Your eye can differentiate between approximately 1600 f-stops/or steps in contrast from darkest shadow to brightest highlight. But Film compresses what you see to the following approximate ranges: (1) digital sensor is approx. 12 f-stops; (2) negative (Print film) is approx. 4 f-stops; and (3) slide film is 2 ½ f-stops (maybe!). The middle tone or value your camera meter assumes it is seeing, provides the proper “exposure.” It allows the film to record the scene as close to what you visualize the “picture” to be, within the "film's compressed contrast” range.
The term “ISO” refers to the standard rating system given films to measure it’s sensitivity to light. There is an old rule used in Photography for sunny daytime exposures. It is called the “Sunny 16” rule. If it is sunny, you set your f-stop to f-16. Then you use the closest shutter speed to your ISO number of your film. As an example, if you use ISO100 film, the shutter speed would be 1/125 of a second. If you were using ISO 400 film, then you would use 1/500 of a second.
There is another old photographic term to explain exposure. It is called an Exposure Value or "EV." This is a number given to the amount of light available that includes the ISO film speed. If you used the “rule” above, you would get an exposure value number that is an EV of 14.5 (ISO 100) (or in orchid language: 5,382 foot-candles.)
The Aperture or Lens Opening is similar to the iris in your eye. The larger opening allows more light in, a lower the f-stop number. Each increment either doubles or halves the amount of light as you open or close the aperture. The larger the number, the smaller the aperture (or opening) which is counter intuitive. Look at them as fractions (1/16“)! Figure 1
Times are in fractions of a second: They cut or double the amount of time, and therefore the amount of light, getting to film, see Figure 2.
If you want depth of field, (front to back focus) choose a larger f-stop number (smaller aperture). If you want to stop action, you choose a higher number (faster) shutter speed.
To visualize this concept, try to imagine the EV of 14.5 contained in a measuring cup of light and the light could be measured from EV 1-20. For the Sunny 16 rule, the exposure value number of 14.5 with an ISO of 100. So f-16 at 125 of a second is one set of numbers that can be used to get that measure of light on to film. Once you line up f-16 over125 you can then choose any of the other numbers that line up to get the same amount of light (EV) on film. You can choose a small aperture that gives more “depth of field” (front to back focus). But since the aperture hole is smaller, you need more time (slower shutter speed) to "pour all of your 14.5 measures of light" onto the film. If you need to "stop action," you will need to open the aperture (larger hole) it takes less time to get all of the light on to film and therefore, a faster shutter speed.
To have Orchid people understand the relationship between Photography and Orchid culture, You probably know, there are Orchids that require more light to be happy and others that require less light. If you look at orchids as film, those that require more light are “slower “ films (ISO 50/200). Those that need less light are fast films (ISO 400-1600). This light in Orchid jargon is measured in “foot-candles” which can be directly converted to a camera exposure, “EV” and further converted to specific sets of f stops and “shutter speeds”on a camera! So as in film, a happy plant is the same as a "good exposure." It has received the proper amount of light!