• PPI, LPI, and DPI
• How are images captured with a digital camera?
• Depth of Field
• Digital sensor sizes and focal-length factors
• How are Fuji SuperCCD sensors different?
• How do digital cameras work?
• How do digital camera sensors work?
• How does digital compare to film in image detail?
• How do scanners work?
• Is the depth of field deeper for digital cameras?
• Monitor Adjustments, Part I
• Mac monitors use 72 PPI, and PCs use 96 PPI--Right?
• Focal length, image size, cropping, and enlarging
• Where can I find out about Colorspace?
• Depth Of Field Simulator
• The Rule of Equivalent Exposure
• Even more DOF stuff
• What is Metamerism?
• What is Simultaneous Contrast?
• How does diffraction limit sharpness and DOF?
• A Tedious Explanation of f/stop (in plain English)
• Is there a A How-To Guide For Stock Photography?
• How Much Should I Charge for My Image?

For a quick summary, go here:

Resolution: PPI, LPI, DPI

For more detail, here are three explanations on Dots Per Inch (for printing) vs. Pixels Per Inch (cameras):

Resolution Article
»www.megapixel.net/html/articles/···els.html
Photo.net
»www.rideau-info.com/photos/index.html (spotted by IsaacGolding )

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by Nick edited by tmpchaos
last modified: 2006-06-18 06:49:18

Anatomy of a Digital Camera: Image Sensors at Extremetech.com

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by mikeky edited by climbers
last modified: 2004-02-11 16:39:47

Depth of field is the area which your camera will have in focus when you take a photo.

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

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by Nick edited by climbers
last modified: 2004-07-15 03:40:46

These are some of the more confusing topics in digital photography, and often the camera company doesn't give specifics. A reasonably comprehensive table with explanations is here:

»homepages.ihug.com.au/~parsog/ph···rs1.html

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by climbers
last modified: 2004-04-26 01:00:28

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/

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by climbers
last modified: 2004-02-10 01:48:47

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.

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by climbers
last modified: 2004-02-09 20:01:15

Digital sensor technology is pretty complex. A lot goes on behind the scenes when we press that little button. This gives a good start in understanding how they work:

»www.extremetech.com/article2/0,3···5,00.asp

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by climbers

The most useful reference for this is Image Detail.

It does get very technical, as a good explanation of this topic requires, but it's well illustrated.

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by climbers edited by tmpchaos
last modified: 2011-04-24 06:50:40

Very much like copiers.

Okay, that wasn't much help, but maybe this will be:

»computer.howstuffworks.com/scanner.htm

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by climbers

quote:

---

The depth of field of a digital camera with a lens of the 1:N focal length equivalence ratio at a given F-setting is the same as that of a 35 mm camera with a lens closed down to the aperture number of F multiplied by N.

---

and

quote:

---

For example, an Olympus C-4000Z (1:5 ratio) at F/2.8 provides acceptable sharpness in the same range as a 35 mm camera with the lens closed down to F/14 i.e., 5*2.8 (at the same equivalent focal length, i.e., image angle). The Olympus E-20 has the focal length ratio of 1:4, therefore its lens at F/2.8 provides depth of field of an equivalent 35-mm camera lens at F/11.2.

---

from:

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:

»www.photo.net/learn/optics/dofdigital/

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by climbers
last modified: 2004-02-10 13:07:12

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

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by climbers
last modified: 2004-02-26 12:55:55

No, it's a myth.

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

(JavaScript must be enabled for this calculator to work.)

Length (inches):

Pixels Per Inch:

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.






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by climbers edited by tmpchaos
last modified: 2011-11-02 16:51:56

The definition of focal length is the distance from the center of the lens element to the film (or sensor) surface. This is why a 20mm lens is a little short lens and a 500mm is so long it requires some type of support to hold it steady. A zoom lens has elements that move closer to, or farther from the film surface.

Focal length and magnification are related by the simple equation:

Focal Length X Object size
--------------------------------- = Image Size
Lens-to-object distance

Image size is the actual size of the object at the negative or sensor surface. If you wanted to take a picture of an object that is 5 feet tall, using a 50mm lens, from a distance of 10 feet. The actual size at the negative or sensor surface would be: (convert everything to mm)

(50mm) X (1524mm)
---------------------------- = 25mm
(3048mm)

If you change the lens to a 100mm and take another picture from the same location the object size at the film surface becomes 50mm, or 2X. Note that by convention all magnification factors (for the 35mm format) are relative to a 50mm lens. Therefore, a 200mm is said to be 4X, and a 400mm lens is said to be 8X.

Here is a real important point that seems to confuse a lot of people – the above equation says nothing about the film or sensor size – it gives the image size at the film surface. Or stated another way, a 50mm lens produces the same image size regardless of the film or sensor size. In the above example a 50mm lens will produce a 25mm image at the film surface of an 8” X 10” view camera, a 24mm X 36mm 35mm camera, or an 8mm digital sensor. How much of this image is captured on film or sensor depends on the size of the film or sensor.

Cropping and Enlarging:
This is what one does when using a lens designed for 35mm format on a digital camera. Using the example above if the sensor size is say 16mm X 24mm then the most the sensor can record is 16mm of the 25mm image. If the image is then enlarged to 4 X 6 the resulting photograph has a larger image of the object than a 35mm enlarged to 4 X 6. This is not because of greater magnification by the lens – it is because of greater enlargement during printing. However, the end result is the same. The digital image from a 50mm lens enlarged to 4 X 6 will be the same size as a 35mm image using a 75mm lens enlarged to 4 X 6.

FAQ written by stev32k, added and modified by editor.

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by DavisPhotog

Where can I find out about Colorspace?

»www.faqs.org/faqs/graphics/colorspace-faq/ has an entire FAQ devoted to the subject.

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by tmpchaos

Depth Of Field Simulator

For anyone wanting to mentally picture what DOF is and how camera settings affect it.

»www.liquidsculpture.com/dof.htm

More Simulators

http://www.camerasinteractive.com/index.php
http://www.photonhead.com/simcam/

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by Wall9 edited by Nick
last modified: 2004-07-25 12:12:37

The Rule of Equivalent Exposure

It's such a basic fundamental I thought I'd write up a tutorial for our budding photographers or more advanced photographers who are so bored they are reading this right now.

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.

Happy shooting!

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Thank you for this explanation. As a newbie wanna be pro, the settings can get quite confusing especially when trying new shoots that are not on auto, but, rather on priority settings or manual. Not only did it help with the equivalent exposure theory but also on understanding what each settings achieve. Your math and history lesson really helped in understanding and setting it in stone.

2012-05-14 21:23:53

by B52GUNR edited by tmpchaos
last modified: 2005-02-03 19:42:38

Even more DOF stuff

Here's a list of moderately technical articles on DOF--"moderately technical", in this case, means that no more than high school algebra is required. None of them are complete enough to give a full understanding, but if you work your way through the whole set you'll know about as much as anyone does on this topic.

»www.wrotniak.net/photo/dof/
»www.dofmaster.com/dof_dslr.html
»www.oncloserinspection.com/Photo···yths.htm
»www.rags-int-inc.com/PhotoTechStuff/DoF/
»www.photo.net/learn/optics/dofdigital/
»www.vanwalree.com/optics/dof.html
»www.vanwalree.com/optics/dofderivation.html
»bobatkins.photo.net/info/dofdiff.htm
»www.edmundoptics.com/techSupport···leid=288
»www.largeformatphotography.info/···oDoF.pdf
»medfmt.8k.com/mf/dofmath.html

All links were tested at the time of this posting (07-26-05), although some were a little slow....

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by climbers
last modified: 2005-07-26 12:03:14

What is Metamerism?

A thread about this aspect of color theory is here: /forum/remark,13894757

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by climbers

What is Simultaneous Contrast?

A thread about this important aspect of photographic theory:

/forum/remark,13894885

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by climbers

How does diffraction limit sharpness and DOF?

A very easy-to-read explanation:

»www.cambridgeincolour.com/tutori···aphy.htm

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by climbers

A Tedious Explanation of f/stop (in plain English)

This is very readable:

»www.uscoles.com/fstop.htm

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by climbers

Is there a A How-To Guide For Stock Photography?

Well, glad you asked! Of course there is, and a fairly good one at that!
»www.editorialphoto.com/resources/stock.asp

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by Gemologist edited by Edit This
last modified: 2006-12-28 17:51:44

How Much Should I Charge for My Image?

This is a commonly asked question. Most folks don't really have any idea what their image is worth. Well, this website will supply a calculator to give you a close idea of what your Image is worth! Use it and learn how to negotiate a price.

»www.editorialphoto.com/resources/estimator/

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by Gemologist edited by Edit This
last modified: 2006-12-28 17:51:05