Photography Notes

How A Digital Camera Works, How To Take (Good) Pictures, ...

 

Intro

This page created to remind myself of some things, and maybe help you too.

 

 

 

Background

In the beginning, I shot pictures in Auto mode; if the picture didn't turn out, then it wasn't meant to be. However there are two reasons NOT to use Auto mode:

1. You may not be able to take a good-enough picture, or you may not be able to get the shot at all.
2. You may want the shot to turn out in some special fashion.

Admittedly, many cameras these days have so many scene modes that manual-er modes are often not necessary. Still, have you ever tried to get a good picture of the moon using auto mode?

 

How Digital Cameras Work

Before a Picture is Taken

Camera and/or photographer defines two classes of settings:

1. Those things that affect the raw image produced by the sensor.
2. Those things that are applied to the raw data after the picture has been taken.

Taking The Picture

Shutter opens, light passes through a variable size opening in the lens and hits a sensor for a while which creates an increasingly exposed image until the shutter closes. How long a while needs to be depends on amount of light getting through the opening & sensor sensitivity. Which things are in focus depends on focus distance, zoom setting, and size of the opening. These are the only things that determine the raw image the sensor produces. Everything else is applied by a computer afterward.

After The Picture Is Taken

Class 2 settings are applied. This may be done in-camera, or in higher-end models this step may be postponed until the picture has been copied to a computer. In any case, limited adjustments may be made by computer.

 

Definitions

Class 1 Settings	A term I made up - camera settings that determine raw image, namely: Aperture, Shutter Speed, ISO, Focus.
Class 2 Settings	Camera settings applied to the raw image to make a JPEG. e.g. white balance, color profile, sharpening.
Focus Distance	There is exactly one thin plane of focus at a certain distance from the camera. Everything at that distance will be in maximum focus, everything nearby distance-wise will be slightly out of focus, everything much nearer or much farther away will be way out of focus.
Depth-Of-Field	The rate at which things at growing distances from the focus distance become out of focus. The greater the depth-of-field the slower the rate, meaning more things are more in focus. Depth of field is defined by actual focal length (not equivalent focal length), aperture, and focus distance. Point-n-shoots have much shorter focal lengths, which is why they are biased toward greater depth of field.
Selective Focus	The opposite of great depth of field, meaning as things are further from the focus distance they become out of focus rapidly, so fewer things are in focus.
Point-n-shoot	Compact all-electronic cameras with fixed lenses and great depth-of-field. Pictures are most often shot using the LCD, although some have electronic viewfinders.
DSLR	Digital versions of the old film cameras using Single-Lens-Reflex technology - they have more selective focus. Pictures are most often shot looking through an optical viewfinder, although some allow focusing/picture taking while looking at the LCD.
High ISO	Uping the gain on the sensors pixel amplifiers, resulting in faster shutter speeds, but more noise.
Low ISO	Reduced gain on the sensors pixel amplifiers resulting in cleaner pictures, but reduced shutter speeds.
Aperture	Size of opening in lens through which picture light passes. Note: Lenses perform best in the middle. Wide-open causes chromatic aberration and softening and stuff. Stopping down causes diffraction resulting in softening, loss of light, and stuff. The optimal range depends on the camera and the lens.
Stop Down	Decrease aperture (larger f-stop numbers).
Photograph Quality	After editing, subjective. Measured by emotional response of person viewing. Depends primarily on the shot, and secondarily on image quality and post-processing.
Raw Image Quality	Pre-editing, objective. Measured scientifically. Includes sharpness/resolution/detail, cleanliness/noise, color contrast/saturation/accuracy, dynamic range.

 

Random Thoughts

• Use the light, Luke. Light has so many different qualities its amazing. If you see something and go "Wow! - look at that!!", take a picture immediately - its probably in the best light, then move around for a better shot, if ya feel like it. If it seems like it might be a good shot, but the light doesn't seem to be good, take a picture anyway - in case you're wrong, then wait for the light to change, or try another angle, or supplement it.
• Get as close as possible, instead of zooming, but not too close, unless you want over-sized noses.
• Think 3-Dimensionally. On no camera I know of is depth-of-field more of an issue than a DSLR - use it to your advantage.
• If you really want a sharp picture with maximum depth-of-field, dont be afraid to use the pocket-camera, instead of the big one.
• Remember: Lens is sharpest at middle apertures, fastest wide open, and has most depth-of-field stopped down.
• Dont forget manual focus mode. Skilled application of manual focus can save your key-ster when autofocus is problematic.
• Autofocusing, especially on moving objects, takes practice; so does manual focus. So, practice both!
• Remember: Autofocus mode is really: autofocus to start, with option for manual finish. You can coarse focus first on auto, to aid manual focus, or manually focus first to aid autofocus.
• Trap focus is another thing that can get shots you'd miss if you had to focus with auto/manual.
• Best flash mode: slow/rear. Just remember to use a manual shutter mode to ward away ghosts or down-throttle the ambient.
• Remember to balance for different colored light sources, or not. Read: gels & gobos...
• Flash off-camera is good sometimes, but the best fill flash for removing dark eye-sockets often comes straight from the camera.
• Angle matters. One function of photography is to show perspectives not ordinarily seen in normal life. Get low, get high, get close and angle.
• Put the subject in the corner of the frame for a change, or at the side...
• There's a time to shoot fast, and a time to shoot slow - Know the difference.
• The background is part of the picture - dont neglect it.
• Other little things may also be part of the picture - get rid of the ones you dont want if you can, or add some things to enhance.
• Take lots, keep few. OK, sometimes there are exceptions, but if you're like me, you usually err on the side of keeping too many, rather than discarding too many.
• Think of the sensor as a canvas, the lens as a paint brush, and light as the paint. Open the shutter, paint a while, then close. Shorter shutters to freeze motion and limit exposure, longer shutters to emphasize motion and collect more light.

 

Image Quality

The primary determiners of image quality, assuming you've got the camera steady enough, exposed properly, and properly focused..., are:

• Distance to subject - closer the better, but not too close ;-}
• Lighting
• ISO
• Aperture - Middle apertures are sharpest, and exhibit least optical anomalies.

Secondary things:

• Camera/Lens. You can get better image quality by moving closer, better light, low ISO, and proper aperture, than you can by switching cameras and/or having a better lens, assuming the camera you have is decent and already has a decent lens. Granted, if you already have all those things covered, then a better camera/lens can achieve better image quality.

 

Camera / Lens

Many people have the impression that camera & lens are the biggest factors that determine image quality. That is not altogether true. Under good conditions, try shooting a picture with a $300 compact and also with a $2000 DSLR and compare; the image quality may not be much different. The biggest advantages in a $2000 DSLR over a $300 compact is that you can get a good picture under more conditions; that, and selective focus.

 

RedEye

Caused by reflection of camera flash from back of eye, through the pupil. Humans reflect more red light, deer reflect more blue light, ... same phenomenon.

Assuming there isn't enough non-Flash light to get the picture (consider bringing in more light or upping the ISO and skipping the flash...):

• Best to avoid in the first place:
  • Use off-camera flash so reflection does not enter lens - best solution.
  • Have people look away from the lens - second best - use if you dont have off-camera flash.
  • Have people look at a bright light for a moment to constrict their pupils before taking the picture. This is what red-eye flash mode does, but many people find it irritating, and sometimes causes sour expressions, which is why I dont like it.
• If not avoided, use red-eye reduction tool in post-processing.

 

 

Final Thoughts

Have fun, and let the magic happen!

The End