|
1– Writing With Light— The Basic Principles |
|
Exposure
Probably the first key to photography is getting the right exposure, or brightness Overexposed photos have areas that are too bright to capture detail (also called “washed out”) Underexposed photos are too dark to reveal detail Sometimes in harsh lighting it is impossible to expose an entire scene correctly, so you have to decide what portion of the photo you want to capture Usually it is better to shoot for the highlights and let the dark areas fall to shadow
This photo is exposed to favor the foreground so Here settings were changed to favor the mountain, the mountain which is in direct sunlight is overexposed so the foreground is underexposed
Three ways to alter the exposure are to manipulate the aperture, shutter speed, and film speed These settings will be discussed here
Aperture / f stop This is a literal hole at the base of the lens that opens to let more light in and closes to let in less light f 2.0 is a wide aperture or large hole and lets in more light f 32 is a very small aperture and lets in less light
Depth of Field- Higher f stops (f32) allow for a deeper range of focus referred to as the depth of field, while a lower f stop (f2.8) makes for a shallow range of focus and tends to blur the background of a photo
Shutter Speed This is the time in seconds(usually fractions of seconds) that the film is exposed A curtain opens in front of the film and allows light to expose the film for a given amount of time
Slow shutter speeds let in more light and are good for darker settings or for capturing blur or motion 1/6 second 1/25 second
Fast shutter speeds are good for sharp photos, sports, stopping action
1/1250 second 1/1000 second
Film Speed (ISO) The ISO refers to the sensitivity of the film to light On digital cameras this is adjustable High ISOs (1600) are more sensitive, and require less light to expose the film, but are more grainy (noisy) Low ISOs (100) are less sensitive and require more light to expose, these are less grainy Because higher ISOs are more grainy, they should only be used when necessary This is why you will notice that many sports photos are very grainy. They use high film speeds so they can use a faster shutter speed and stop action (it’s grainy vs. blurry).
This photo was shot with ISO 1600 because flash was not allowed. Notice the grain up close
This photo was shot at ISO 200 Notice there is no grain in this blow-up
Aperture, Shutter Speed, & Film Speed Chart This chart demonstrates how these three settings can work together and is referred to below
Aperture (f stop) Shutter Speed (time in sec.) Film Speed (ISO/ASA) 2.8 portraits 1’ (1 sec.) 1600 more sensitive film, more grainy 4.0 1/2 (half sec.) 800 5.6 1/4 400 8 1/8 200 11 1/15 100 16 1/30 50 less sensitive, less grainy 22 landscapes/macro 1/60 32 darker 1/125 1/250 1/500 (1 five hundredth sec.) 1/1000 darker Exposure Value (EV) The values in the chart above represent three ways the brightness or exposure of a photograph can be controlled. (A fourth way is to control flash output or ambient light) The amount of light altered by moving up or down the chart by one line is referred to as one EV These values are equal to each other in all three columns (f stop, shutter speed, and ISO) Notice that the values are either doubled or halved as you move up or down. In each case a photograph will become darker as you move down these columns, and brighter as you move up So, three examples of ways to darken your photo by one EV are: 1- Going from f8 to f11 (smaller hole or aperture allows less light in) 2- Going from 1/60 to 1/125 (faster shutter speed, less time film is exposed) 3- Going from ISO 200 to 100 (less sensitive film) Also notice that the same amount of light can be captured if you move up one column the same amount you move down another. The following settings will be equal in exposure(all appear equally bright) but have different qualities in depth of field, film grain, and motion: f stop shutter speed ISO Exposure 1- f5.6 1/500 100 Exposure 2- f8 1/250 100 Exposure 3- f11 1/125 100 Exposure 4- f16 1/60 100 Exposure 5- f22 1/60 200 Exposure 6- f16 1/125 50
*EVs can be broken down by1/2 or 1/3 for fine tuning exposure This is why you may notice many more options in your camera than are included in the chart at the top of the page If you set your camera for 1/3 EV increments, then three clicks on the wheel equals one EV So instead of going from f5.6 straight to f8 (one EV) your camera will read f5.6, f6.3, f7.1, f8 This is the same for shutter speeds, and film speeds
Depth of Field
Depth of Field was mentioned above with aperture, but it is important and there is a little more to it Depth of field is a range that can be in focus in one photo, say from a certain flower to a certain tree About 1/3 of this range is in front of your subject and 2/3 behind Large depths of field can get everything in focus from a flower, to a lake, and include the mountains behind Large depths of field are desired for landscapes Small depths of field have a very little range in focus, maybe not even an entire flower will be in focus Sometimes small depths of field are desired to blur otherwise distracting backgrounds and are often used for portraits
Shot at f5.6 Shot at f16- Notice the petal in front, and some of background is sharper
There are two ways to change the depth of field: Increasing depth of field Decreasing depth of field Wider angled lenses (12mm) Telephoto(400mm) or macro lenses(100mm) Closing down aperture (f22) Opening up aperture (f2.8)
For ultimate depth of field this was shot at 14 mm, and f 22 Notice that everything is in focus from the subject to the mountains
Problem- So you might think that the sharpest photo would be taken at f22 or f32 But in fact, after you reach a certain f stop, around f11 or f16, a phenomenon called diffraction begins to soften your image For every benefit in photography there is a trade off So for each photo you have to determine your priorities For digital SLRs usually f8 or f11 will give you the sharpest photo provided that you can get everything you want in focus at those f-stops *Some cameras have a depth of field preview button that can be pressed to see what you have in focus for a given aperture
White Balance
Light is measured in degrees Kelvin, each degree expressing different color Our human eyes are able to accommodate for these color changes but film cannot As a result, to get correct colors in different lighting conditions, white balance must be adjusted Non-digital film cameras require different types of film, or the use of a filter to correct for white balance With digital cameras white balance can be adjusted without extra equipment Common WB settings include: Auto- Not bad, but usually not very desirable even in expensive cameras Tungsten/ Incandescent- Light bulb symbol, very blue unless indoors at night Daylight- Identified by a symbol of the sun, very blue, not a favorite Cloudy- Better than daylight for either sunny or cloudy situations, warmer Flash- Lightening bolt symbol, similar to cloudy Shade- What many photographers use most of the time, nice and warm, excellent skin tone for portraits, works well when using the flash Fluorescent- Tube lights, Use if your photos are too green under street lights, halide or mercury lights Custom or preset- Read your manual if you have this option, it helps you get around mixed lighting
In general, people like warmer looking photos so lean toward shade and cloudy for most situations. If you are shooting indoors, it’s usually best to use a flash and set WB to shady, unless you are shooting teeth, then use the flash WB because it will be the truest color rendition (You don’t want the teeth to look warm) *Some Digital SLRs will allow you to change the white balance by altering the degrees in Kelvin directly
Examples: The only setting changed in the following photographs was white balance
Auto Incandescent Fluorescent
Sunny Flash Cloudy
Shade
Flash (Strobes)
This can be one of the more complicated subjects in photography and can take time to master Here we will only mention a few key concepts and save the rest for a more advanced lesson
Points to Remember: 1-Use rechargeable nickel metal hydride batteries, not alkaline These keep a consistent recycle time and die all at once whereas with alkaline you have to wait longer and longer between shots for the flash to recharge 2- Auto- TTL and iTTL TTL stands for ‘through the lens’ With these functions the strobe feeds light into the environment until a sensor near the film picks up what it thinks is enough light. This amount is preset by the manufacturer and is based on the concept of middle or 18% gray. When this level is reached, the sensor then communicates with the strobe and it shuts off. This all happens while the shutter is open (VERY quickly!). Because auto functions rely on the concept of middle gray, they will NEVER be exactly correct for subjects that do not reflect middle gray. So on TTL black objects will be overexposed and appear to light, and white objects will be underexposed and appear too dark. 3- Flash sync- This is the fastest shutter speed a camera can use and still be synchronized with a strobe. Most SLR cameras have a flash sync of 1/125, some are 1/500, and most are 1/250. Below these shutter speeds all of the flash output is realized on the film. With faster shutter speeds a dark curtain will begin to develop on the film because the curtain closes before the flash has completed firing.
The SLR
This stands for ‘single-lens reflex’, and DSLR indicates a digital SLR SLRs are the cameras that allow the photographer to see through the lens and frame a photo properly They have a mirror that sits in front of the film, reflects light up to the view finder, and flips out of the way when a photo is taken SLRs have removable lenses that are unique for specific uses Although there are non-SLR systems available for dental photography, these are the best for many reasons One of the problems(among others) with non-SLRs in dentistry is that we need a very high f-stop (f22 or f32) to get the depth of field we want in the mouth- Non SLRs usually don’t come anywhere near this
|
