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8.0 Technical topics
Resolution: PPI, LPI, DPI
For more detail, here are three explanations on Dots Per Inch (for printing) vs. Pixels Per Inch (cameras):
»www.rideau-info.com/photos/index.html (spotted by IsaacGolding )
Depth of field will become narrow if your aperture is wide open (f/1.8 or f/2.8) and will widen if you use a narrower aperture (f/8 or f/11)
I've written a tutorial on this:
»[Tutorial] Depth of Field
Fuji decided the standard rectangular layout of pixels on sensors wasn't as good as a honeycomb layout.
The short version: »www.dpreview.com/news/0001/00013···ixel.asp
An independent assessment: »www.extremetech.com/article2/0,3···7,00.asp
Fuji's own site about SuperCCD technology: »home.fujifilm.com/products/digital/sccd/
If you want concise, relatively complete, technical, but not too technical explanations:
HowStuffWorks.com has How Digital Cameras Work, and ExtremeTech.com has Anatomy of a Digital Camera.
It does get very technical, as a good explanation of this topic requires, but it's well illustrated.
Okay, that wasn't much help, but maybe this will be:
Depth of field for digital cameras
This applies only to the small-sensor cameras. If you don't mind a little mathematics, this reference is good for dSLR's, which use larger sensors:
This entry explains how to fix a very common monitor problem--an incorrect aspect ratio. It is particularly useful for CRT (Cathode Ray Tube) monitors, although some LCDs (Liquid Crystal Display) may need it.
The instinctive thing to do with a new monitor, or after changing resolution, is to push the useable area all the way to the edges. Unfortunately, that can change the aspect ratio, causing squares to not be square, and circles to not be round, giving a distorted view of whatever is on the screen.
Standard monitors, using normal resolution settings (640x480, 800x600, 1024x768, 1600x1200, etc) have a 4:3 aspect ratio--width larger than height--derived from traditional TV screens, which also use CRTs.
What if the display isn't standard, or has an odd resolution? Doesn't matter--the method will work with any kind of display or aspect ratio.
Why doesn't zooming all the way out work? Monitors often don't physically match their theoretical aspect ratio, so pushing the viewable area to the edges may cause the actual ratio to be incorrect.
The adjustments are easy:
First step: Center the next graphic on a monitor. The more centered it is, the better, especially if the display isn't a flat screen or LCD. For a large, high-resolution display that needs to be more accurate for CAD or image editing, there is a bigger graphic here.
Second step: Use a ruler to measure the top and bottom. (A soft sewing tape or plastic ruler is best, to keep from scratching the screen.) The measurements should be equal. If they aren't the monitor's geometry is out of adjustment, and may involve some tinkering to get it correct. Find the "trapezoid" (sometimes called "keystone") control. It will look something like this in the monitor's menu, control bar, or manual:
Some monitors don't have this control, and may require a technician for internal adjustments.
Last step: Use the ruler to compare the top or bottom with one of the sides. If they aren't the same length, use the monitor's vertical- and horizontal-size controls until the view fills as much of the screen as possible with matching measurements. This may take a few tries.
When the adjustments are finished, there may be black bars at either the sides, or the top and bottom--very similar to a widescreen DVD viewed on a standard TV. There shouldn't be a black frame all the way around, since this indicates more useable area is available.
Parts of this FAQ were in an earlier thread: /forum/remark,7219730~mode=flat
A monitor's PPI (Pixels Per Inch) resolution only depends on its physical size and display settings. It doesn't matter if it's hooked to a Mac or a PC. Furthermore, a monitor set at 1600x1200 pixels will have a very different PPI value than it does at 800x600 pixels.
If you'd like to know what a display's actual PPI is, measure the length of the graphic below in inches with a soft ruler--a sewing tape or plastic ruler is safest for the screen--and then enter that value in the calculator under it.
Note: For best results, go to this FAQ entry first: »Digital Imaging »Monitor Adjustments, Part I
What happens if you change the monitor's settings? The PPI value changes proportionately. Doubling the resolution doubles the PPI, for instance. A 19" monitor may easily vary from 50 to 100 PPI with different settings.
DPI (Dots Per Inch), which is sometimes erroneously used interchangeably with PPI, has nothing to do with how a graphic is displayed on a monitor. It is used for output to other devices, most commonly printers. One of the graphics below is saved at 10 DPI and the other is at 1000 DPI. Which is which? The only way to know is to download them and check with image-editing software.
Focal length and magnification are related by the simple equation:
Photography is Greek for writing with light (phos,phot=light + graphos=writing). In a nutshell, photography boils down to writing with light. All the film or CCD captures is light reflections. Thus, it is imperative that the correct amount of light reaches the recording surface. This is called exposure. Modern cameras have built in meters that do a pretty outstanding job at recording the light entering through the lens and adjusting exposure settings accordingly. In most cameras this is called "Program". However, program is a middle-line exposure and sometimes you don't get the effect you want. For instance, you may want motion to stop or even blur some or you may want maximum depth of field. If your camera has an aperture or shutter priority setting (on Canon they call this Av and Tv, Nikon, Minolta and others usually may have "A" and "S" on their exposure mode dial, check your manual for your camera's specific settings).
By selecting aperture or shutter priority, your camera does equivalent exposure for you, eliminating the guess work. If you need to stop motion, you set your camera to shutter priority, set the speed to fast enough to stop the motion and the camera sets the aperture. Conversely, in aperture priority the opposite occurs. You tell it what aperture you want and it sets the relative exposure with the shutter speed. That's pretty neat and makes it easy, but what if your camera doesn't have aperture or shutter priority or you want to shoot in manual exposure, then all you have to remember is that as the aperture opens, the shutter speed must increase to maintain equivalent exposure.
F-stops are fractions of the opening of the diaphragm compared to the diameter of the lens, so f/2 on a 50mm lens means that the aperture will be open 25mm, 1.4 means it will be 35mm, 1.0 means it will open as wide as the lens is. F-stops are also multiples of the square root of 2 (1.4142135623730950488016887242097), but we'll use 1.414 for this exercise.
So, starting at 1, this is the full f-stop scale (rounded):
1 1.4 2 2.8 4 5.6 8 11 16 22 32 45
f/16 lets in twice the light of f/22 and half the light of f/11.
OK, so now we know some of the math behind f-stops, the other factor in the equation is shutter speed.
Shutter Speed range (typical):
15 30 60 125 250 500 1000 2000 4000
As with f-stop, each step increases or decreases the light by a factor of 2x. So 500 is half as much light as 250 but twice as much as 1000. Remember that shutter speeds are usually reciprocals of 1 second, so 500 is 1/500th of a second.
The final part of the equation is your camera or film's ISO rating. ISO (sensitivity) ratings:
25 50 100 200 400 800 1600 3200
Again, each move in ISO is a factor of 2, so ISO 200 is twice as much light sensitivity as 100 and half of 400.
Ok, now that your eyes have glazed over, a quick review: exposure (the capture of light) is related to 3 things: aperture, shutter speed and ISO settings.
Now onto the rule of equivalent exposure. And that is: as one thing changes, the other(s) must change as well. ISO may or may not need to be adjusted.
So, lets say your camera says at ISO 200 f/11 and a shutter speed of 30 your image will be properly exposed (yes, I am over simplifying, but this a conceptual lesson). However, you want the shutter speed to be faster for whatever reason, we'll say 1/125th.
So, moving from 1/30 to 1/125th is 2 steps. Thus, you have to open your aperture by 2 stops from f/11 to f/5.6 in order to maintain equivalent exposure and retain the ISO 200 sensitivity setting.
The reverse is true, if you want to go from 1/125th to 1/30 you have to close the aperature by 2 stops.
And if you open the aperature by 1 stop, you need to increase your shutter speed by 1 step (i.e. 1/60th to 1/125th) and if you close the aperature by 1 stop you need to slow down your shutter by 1 step (i.e. 1/125th to 1/60th)
If you changed the ISO on your camera to ISO 800 you will find the camera will adjust either the aperture or the shutter speed to compensate. However, the price with higher ISO is more noise and possibly loss of detail. Also note that in Program, the camera will decide what to adjust to maintain the equivalency if you increase the ISO, so keep that in mind. Normally, ISO doesn't play a large part in equivalent exposure, unless the lighting is insufficient to achieve your desired result so you have increase or decrease the ISO setting of your camera.
Just remember that for equivalent exposure as one aspect increases, the other must decrease and maybe your camera's ISO may need to be adjusted.
If you increase the aperture without decreasing the shutter speed (or vice verse), you aren't doing equivalent exposure, you're bracketing.
To further confuse things, a lot of cameras adjust exposure in 1/2 or 1/3 stop increments and likewise may have intermediate shutter speeds, but that doesn't negate the concept, you just have to adjust for it.
All links were tested at the time of this posting (07-26-05), although some were a little slow....
This is very readable: