Contents: DSLR | MegaPixels for print size | Sensor Sizes | Lens info | Glossary | Reviews | Links | Picture Taking| Filters | Accessories | On-line stores and dealers

DSLR: Digital Single Lens Reflex (SLR) cameras
SLRs are larger and more expensive ($600+) than than point-and-shoot (P&am;S) digicams, but offer many advantages:

• Interchangeable lenses:
  Although a full-range zoom lens (18-200 mm) on a SLR is still about the range of 10x optical zoom on a digicam, you can also get super wide angle (12 mm) and super telephoto (400+ mm) lenses. You can also get lenses with low f-stop values (f/1.4-2) for "available" light situations and macro lenses for taking life size images of small objects.
  Lenses range in price from $100 to $2,500+
• A variety of filters (e.g. polarizing, haze, ..) which attach to the lens.
• Accurate, large, and bright optical viewfinder.
• Faster - Startup, focusing, continuous shooting, less than 1/2 sec. shutter lag.
  DSLRs usually use Phase Detection type autofocus sensors which which can determine correct focus immediately rather than Contrast Detection sensors used in most P&S models which must adjust the lens and compare contrast at different positions.
• Larger pixels on the larger sensors improve image quality, especially in terms of noise and dynamic range. They practically eliminate noise at ISO 400 and 800. The Canon 5D mkII ($2,700) with a full frame sensor goes up to ISO 25,600, or 6 stops above ASA 400.

The Megapixel Myth:
A 2007 article/blog "Breaking the Myth of Megapixels" by NY Times columnist David Pogue started a lot of discussions on the need for more MP.
A 3 MP image pretty much looks the same as a 6 MP image, even when blown up to 8 x 10, because you are limited by printer resolution and the physiology of the eye. A small 40% increase in resolution pixels per inch will result in a doubling of the MP count (because the the total is proportional to the square of the resolution), so it is easy for the manufacturers to increase the count a lot, and generate hype that will suck consumers into buying an upgraded camera.
However, there are some advantages to more megapixels:
- You have more flexibility in cropping a picture (selecting a small area) and still getting a good image.
- You can get the effect of a longer lens, by cropping a small area. More Megapixels may be cheaper than a $1,500+ 300 mm lens. On the other hand you can get a 2x tele-extender for $250 but you get a light loss of two stops, so must use larger apertures or slower speeds.

A computer screen only shows 72-115 ppi.

Joe Holmes' limited-edition 13 x 19" prints of his American Museum of Natural History series sell at Manhattan's Jen Bekman Gallery for $650 each. They're made on a 6MP D70.

Printing at 300 ppi requires 4x (2x horiz. x 2x vert.) the pixels as 150 ppi

Aspect ratio 4:3 - point and shoot, 3:2 - SLR

DPI means dots per inch, and has to do with just how much ink your printer lays down when it prints a photograph. Printers with higher DPI settings can produce more detailed photographic prints.

DPI and PPI are used interchangeably a lot of the time, but are not the same thing. For example, you can print an image on your 300dpi printer at 72ppi, 100ppi, or 300ppi. Changing the ppi affects the size of the printed photograph.

However the number is a bit misleading since it's not always measured in the way you think it might be! Printer settings of 360dpi, 720dpi, 1440dpi and 2880dpi are often found. However the difference between then is subtle at best. Most people probably couldn't tell the difference and 360dpi usually looks great. Changing DPI does not change the size of the print. See also:
The Megapixel Myth at SLRgeek.com Sunday, 14 December 2008
Imaging in Tech
Megapixels at best-family-photography-tips.com.
The The exception to the digital cam scam (a.k.a. When megapixels actually matter) David Berlind blog on zd|net.
Imaging in Technology

Anti-Shake:
The popular thing now is anti-shake technology which allows you to take pictures at slower shutter speeds without a tripod. I.e. it compensates for movemenet of the camera when you snap the shutter. It does not compensate for moving objects as in sports photography where you still need faster shutter speeds to stop motion.
Image Stabilization (Canon) and Vibration Reduction (Nikon) are incorporated into lens with a gyroscope and floating elements. Sony,, Pentax and Samsung use a floating sensor in the camera. In camera stabilization is not as effective as in-lens and it isn't very effective for long telephoto lenses, but it does work with all lenses, which saves you money in lenses.
Lens stabilization will get you 2 stops. (see F-number at photography) i.e. 1/15 instead of 1/60th for minimum handheld speed.

Lenses:
The following refers to interchangeable lenses for digital SLRs.

Sensor Sizes:
Most DSLRs use image sensors (APS sensors) which capture an area smaller than that of a film camera, which gives the lens a longer Equivalent Focal Length (EFL) (the ratio is referred to as a cropping Factor (CF) typically about 1.5x.
e.g. a 50 mm lens on a DSLR with an APS-C sensor will be the equivalent of a 75 mm lens on a film camera.

A full frame (35 mm) sensor the same size as 35 mm film is 36x24 mm.
APS-C sensors are nominally 23.7 x 15.7 mm. Many variants exist. APS-C film measures 25.1 x 16.7 mm, Sony's APS-C measures 21.5 x 14.4 mm, Nikon "DX" sensors measure 23.7 x 15.7 mm (CF=1.5), while Canon has several (smaller and larger) variants, e.g. 22.2 x 14.8 mm (CF=1.6) and 28.7 x 19.1 mm.

Camera	Desig.	factor	aspect ratio	size mm	CF
Point and Shoot cameras
Minolta XI	1/2.7"	.167x	4:3	5.3 x 4.0
Nikon Coolpix 995	1/1.8"	.22x	4:3	7.2 x 5.3
Canon Powershot S500	1/1.8"	.22x	4:3	7.2 x 5.3
Canon Powershot G7	1/1.8"	.22x	4:3	7.14 x 5.36
Olympus C-8080	2/3"	.28x	4:3	8.8 x 6.6
interchangeable lens cameras - Mirrorless DSLRs
Sony Alpha NEX ILC*	APS-C	.65x	3:2	23.5 x 15.6
Nikon 1 V1 ILC*	CX	.36x	3:2	13.2 x 8.8
Olympus PEN E-PM1 ILC*	Four Thirds	.54x	4:3	17.3 x 13
Samsung NX20 ILC*	APS-C	.65x	3:2	23.5 x 15.6
Single Lens Reflex CamerasSLRs
Olympus Four Thirds *	Four Thirds	.54x	4:3	17.3 x 13
Canon 50D, EOS Rebel	APS-C	.62x	3:2	22.2 x 14.8	1.62
Nikon D70	APS-C 1.8"	.65x	3:2	23.7 x 15.7	1.52
Full Frame		1x	3:2	36x24

CF - Cropping Factor - Effective increase in lens focal length.
Desig - The type designation harks back to a set of standard sizes given to TV camera tubes in the 50's. These sizes were typically 1/2", 2/3" etc. The size designation does not define the diagonal of the sensor area but rather the outer diameter of the long glass envelope of the tube. See DPReview.com.
Factor - Ratio of vertical size to 24 mm (full frame)
* The Four Thirds system is a standard created by Olympus and Kodak for DSLRs. Lens design has been tailored to the requirements of digital sensors. The size of the sensor is slightly smaller than for most DSLRs and this implies that lenses, especially telephoto lenses, can be smaller. Olympus, Panasonic, and Leica make DSLR cameras that conform to the Four Thirds System.

ILC - interchangeable lens camera - Smaller than SLRs with no mirror.

Lenses - Focal Length / Angle of view.
Angle of view can be vertical (27%deg; for 50 mm), horiziontal (40%deg; for 50 mm) or diagonal (47%deg; for 50 mm).

 
See: DSLR Sensor_size_and_image_quality at wikipedia.

Type	Focal Length	35 mm or full frame DSLR †				APS-C
		Angle (diag)		Field of View @ 10'		1.6 CF Canon			1.5 CF Nikon
		diag	horiz	diag	horiz	diag	horiz	Field (horiz.)
8 Fish Eye	8 mm	180°	180°	inf.	inf.	180°		457
15 Fish Eye	15 mm	180°	142°	inf.	58	112°		21
Ultra Wide angle	11 mm	126°	117°	39	33	101°	91°	20.2	21.5
Super Wide angle	14 mm	114°	104°	31	26	87°	77°	15.9	16.9
Super Wide angle	17 mm	104°	93°	25	21	76°	66°	13.1	13.9
Super Wide angle	18 mm	100°	90°	24	20	73°	63°	12.3	13.2
Super Wide angle	21 mm	92°	81°	21	17	65°	56°	10.6	11.3
Wide angle	24 mm	84°	74°	18	15	58°	50°	9.3	9.9
Wide angle	28 mm	75°	65°	15	13	51°	43°	7.9	8.5
Wide angle	35 mm	63°	54°	12	10	42°	35°	6.3	6.8
Standard or Normal	50 mm	47°	40°	8.7	7.2	30°	25°	4.4	4.7
portrait	70 mm	34°	29°	6.2	5.1	22°	18°	3.2	3.4
portrait	85 mm	29°	24°	5.1	4.2	18°	15°	2.6	2.8
Telephoto	105 mm	23°	19°	4.1	3.4	14°	12°	2.1	2.3
Telephoto	135 mm	18°	15°	3.2	2.7	11°	9.4°	1.6	1.8
Telephoto	210 mm	12°	10°	2.1	1.7	7.3°	6.1°	1.1	1.1
Telephoto	300 mm	8.2°	6.9°	1.4	1.2	5.1°	4.2°	0.7	0.8
Super Telephoto	400 mm	6.2°	5.2°	1.1	0.9	3.8°	3.2°	0.6	0.6
Super Telephoto	600 mm	4.1°	3.4°	0.7	0.6	2.5°	2.1°	0.4	0.4

A fisheye such as Canons 15mm f/2.8 produces a 180° diagonal field of view with a full frame sensor, but results in dramatically curved images.
A rectilinear lens such as Tamron's 11-16mm f/2.8 produces a more normal image (straight lines are supposed to stay straight).
You need an external flash with ultra wide angle lenses because the lense will cast a shadow.

† As of 2007, only a few current DSLRs have full-frame sensors, including the Canon EOS-1Ds Mark II, the Canon EOS 5D, and the Nikon D3

See: Canon Field of View

Digicams:
Most digicams (compact 'point-and-shoot' digital cameras) use sensors known as 1/2.5", whose area is only 3% of a full frame sensor (5.8x4.3 mm). Even high-end digicams such as the Canon PowerShot G9 or the Nikon CoolPix P5000 use sensors that are approximately 5% and 4% of the area of a full frame sensor, respectively.
Their angle of view without zoom is about the equivalent of 36 mm lens on a full frame camera. My Nikon Coolpix 3500 (3M pixels with a 5.6-16.8 mm lens) has a field of view of 9.7' at 10'.

Because most of the digital image sensors (CCD or CMOS) are smaller than image produced by the lens they add a telephoto effect and the effective lens length is increased by about 1.5 (Nikon) - 1.6 (Canon) compared to a typical 35 mm film camera lens. e.g. a 50 mm really acts like a 75 mm on a film camera. More expensive DSLR's (e.g. Canon 5D and Nikon D3) have full frame sensors so this is not the case.
See: Sensor Sizes at DPReview.com
Angle of View at Wikipedia

More Lens Info:
Zoom:
Most cameras come with an optional wide angle zoom lens, usually 18-55 mm.
Make sure the shortest focal length of the lens is the equivalent of 28 mm or less, enough for landscapes or tight shots of groups.

Lenses are also rated by the maximum aperture (smallest f-value = largest opening). Lenses that are capable of very large openings like f/2.8, f/1.8 or even larger are called "fast" lenses (or fast glass) because they let in a lot of light enabling fast shutter speeds in low-light conditions. Lenses with higher minimum f-values (e.g. ≥5) are sometimes called "dark" lenses.
Zoom lenses have a range of maximum apertures. The min f-value goes up as you zoom out.

Wide angle 14-55mm
Mid 18-85 mm
Tele 55-200
Full range 18-200

F number:
The F stop number is the focal length divided by the aperture diameter.
Is a measure of light gathering capability which depends on how wide the opening in the lens is.
Typically the minimum ranges from f/1.2 - f/4.5.
They go up in steps by a factor of √2 e.g. 1.4, 2, 2.8, 4, 5.6, 8,11,16,.. You will also see half stops 1.8, 2.5, 3.5, 5.0 Zoom lenses usually list two values; 1 is the minimum at wide angle the other is the minimum F value at full zoom. Look for one whose widest aperture setting at its maximum zoom (the second, larger figure of the two f-numbers usually given in lens specs) is below f5 or, even better, below f4.
A lower number will let in more light for shooting in low light situations without a flash.
The lower the f stop the less depth of field (distance where objects will be in focus). Many photographers use this for effect to blur the background and concentrate on the subject of the photo.
A maximum f-number of f22 or greater is critical for shots that demand a great depth of field.

Standard or Normal lenses (50 mm on a digital camera)

Highest degree of sharpness.
Natural perspective
Best for flat subjects on copy stands.
No barrel or pincushion distortion.

When a zoom lens says it is macro capable it is not a true macro lens. It will not get you 1:1 life size and the macro capability usually only works at the end of the zoom range and edges will be fuzzy.

Macro-telephoto:
Best for close-up photography of small subjects so you can get further away and avoid shadows.

Recommended combintation:
BobAtkins recommends: "The best low cost solution would be the 18-55 coupled with a 50/1.8 and a 75-300. This gives you one wide-angle zoom, one telephoto zoom and one fast lens ideal for portrait work."

Canon and Nikon say that with an in-lens stabilizer, you can make the aperture four stops smaller without changing the shutter speed, versus about two stops on an in-camera system.

Lens Reviews:
Sigma, Tamron and Tokina are popular 3rd party lenses. Sigma has a wider selection with many good lenses, but has some quality control problems and some auto-focus problems with Canon cameras.

Reviews:
Digital Wide Angle Zooms at kenrockwell.com

Filters:
There are pros and cons to filters. They provide protection in dusty conditions or blowing sand at the beach, and you won't worry about using a tissue to wipe off your filter which is easy to replace, but there are downsides also.
Many times you will be told by camera store clerks or read in books that you should always keep a filter on the front of your lens to protect it. Except in severe conditions like blowing sand, salt spray from ocean breakers, industrial environments, and a few others, this is bad advice. Camera stores often push filter sales because filters are very high profit items.
An extra piece of glass can also produce flare.
There have been cases of a piece of broken glass from a filter scratching the primary lens and situations of filters stuck on because the aluminum threads self seizing.
The downside to using a UV filter as a permanent fixture on a lens, is that you risk abberation, flare and ghosting whenever the light is coming from the front. A poor grade filter will also lower the contrast of your images.
If you must put a filter on the front of your lens, insist on only the very best multicoated glass. Nothing can kill the quality of a great lens faster than a poor quality filter on its front.

A current trend is for "thin" filters. The main reason for using the thin filters is on the wide end of things, to reduce their contribution to vigneting, which will become more obvious if you add a second filter.

Many say a polarizing filter is the most important one, however they reduce light by 1.3 stops or more. UV filters have a very small affect exposure.

* Ultraviolet (UV), skylight and haze filters:
UV light causes a blue tint to film cameras (especially at high altitude), but this is not a problem with digital sensors.
The term "UV filter" by itself usually refers to a neutral (untinted) filter blocking the shorter wavelength UV-B (320-280 nm) and UV-C (10-280 nm) band.
Much of the haze seen in visible light film photographs results from the scattering of UV-A by air molecules, water droplets and particulates. Haze filters block more UV-A (320-400 nm) than regular UV filters but also take a bite out of visible blue. For example, Tiffen Haze 1 reduces excess blue and transmits 29% at 400mm wavelength, while Tiffen Haze 2A provides greater ultra-violet correction than Haze 1 and transmits 0% at 400mm wavelength. They produce a slight yellowish color cast, the 2 more than the 1. They may also require a small exposure correction.

UV or not UV? at photo.net has charts showing transmission % of different filters.

 
Filter  Transmission % at 400-350nm
Tiffen HAZE-1     2.5%  (equivalent to a 5 f-stop reduction of UV)
Tiffen 812       12%  - A warming (shift to red) filter 
Tiffen PL-C      17%  - photo.net says tiffen, but the PL-C is a Canon polarizing filter
Hoya 81B         18%  - A warming filter
Hoya UV          24%
B+W KR1.5        33%
6 Others tested allow 65-90% transmission

Skylight filters are pinkish to cut blue but are no more effective in the pesky UV-A band than regular UV filters.

Prices vary widely depending on the quality and number of anti-reflective coatings. For example Hoya has 4 levels of UV filters:

You can reduce haze somewhat in photoshop. Applying unsharp masking repeatedly to all channels or to the blue channel alone with very large radius and very low intensity (amount) settings can be surprisingly effective.
See: UV, Skylight and Haze filters from Dr. Ching-Kuang Shene, Mich. Tech. U (Example photos with different filters)
UV, Skylight and Haze filters at DPfwiw.com
UV or not UV? (graphs of Transmition vs waavelength) at photo.net

* Infrared (IR) (dpfwiw.com/ir.htm) Unlike ordinary films, silicon-based CCDs and CMOS sensors turn out to be quite sensitive to the near infrared (NIR) in the 700-1200 nm (0.7-1.2µ) range

* Polarizers or polarizing filters:
Many say a polarizing filter is the most important one, however they reduce light by 1.3 stops or more.
About Polarized light:
Light reflected from non-metallic surfaces is polarized. The amount of polarization is dependent on angle. There is one angle where reflected light is 100 percent polarized; It depends on the index of refraction of the material but is typically about 30 degrees.

Scattered light is strongly polarized perpendicular to its direction of travel from the primary source, so polarizers can reduce haze from scattered light.
However, when taking wide-angle pictures showing large parts of the sky or panning, the sky will appear bluer in a band perpendicular to the sunlight.

Basic polarizing filters are linear, but they cause problem with modern camers's light metering and autofocus systems.
Circular polarizers were developed to solve this problem. They are really two filters on top of one another in a single ring. The first one is a simple linear polarizer (which blocks or transmits light polarized in one direction). The second one (called a quarter wave plate or Kasemann plate) takes the light passed through the first one and converts its linear polarization into circular polarization, or more simply it depolarizes it. This does not lose any of the effect from the polarizer because the light has been fully polarized prior to passing through this depolarizing plate.

Polarizers reduce your lens appeture by 1.3-1.6 f:stops. (A filter factor of 2.5 - 3 i.e. light reduced 2.5 times), more (3-4 stops) in strongly polarized ambient light.

Which brand (Notes from camera forums):
From: Bob Atkins: I've tested filters for optical flatness, distortion, transmission, reflection etc. and I've never found B+W to be any better than Hoya or Tiffen. The only downside to Tiffen is that many of their filters are not multicoated.
"Genuine" Canon filters are (or were) made by Tiffen. Look at the plastic containers they come in...identical except for the logo.
Canon polarizers scratches very easily!

There The Hoya filters are as good as any, and not just the "Pro" series. Any of their multi-coated filters are fine.
If buying HOYA, just stay away from their green label filters, all other series are worth buying depends on your budget.

At dgrin.com
cmason says, "B+W F-pro, is all I use. B+W and Heliopan use exceptional glass in all their filters. Sunpack, tiffen, canon, use generic glass. hoya uses generic in their basic lines, but the S-HMC lines are quite good. So quality recommended: B+W and Heliopan, without reservation. Hoya with S-HMC, and then, nothing else. YMMV (Your mileage may vary)"
racer says, "All glass has optical abberations, no glass if perfect, and they all have these issues. You buy those expensive L lenses because they have less abberations, meaning the glass is better quality and gives a better quality image. A true multi coated filter might do away with even more errors leading to better image quality.
I use Sigma filters, because they seem to be good quality, are multi coated, and cost around $40-$60. I cant tell any difference between the Sigma and more expensive B+W filters."

See: The polarization of the sky at Polarization.com (example of blue enhancement at 90° to the sun.)
Using a polarizer effectively without TTL control
Choosing a Camera Lens Filter at CambridgeinColour.com

* Neutral density (GND) filters
These just decrease the amount of light allowing you to use a larger aperture or slower shutter speed. See Neutral Density Filters at cs.mtu.edu/~shene/DigiCam/User-Guide/filter/filter-ND.html
Graduated neutral density (GND) filters decrease the light at the top more than the bottom to compensate for a bright sky.

* Color Compensating/Correcting/enhancing Filters
These are used because cameras do not have the flexibility of the human eye to automatically adjust to different situations. They include:
- Light balancing ( increase (bluer/cooler) or decrease (redder/warmer) temperature.
See: Light temperature.
- Correction for different types of indoor lighting.
- Increasing contrast
  Yellow - contrast between sky and clouds
  Orange - contrast between reds and yellows for distant outdoor shots
  Red - cloud effects
- Specialty Filters
  Star filter - Star effect from point light sources
  Fog and mist filters
  Diffusion - soft focus filters - GIves a silky-smooth look to textured surfaces

Many filters are identified by their Wratten numbers (1A-Skylight, 2A-pale yellow, ...81A pale oranage, [warming], 82A pale blue [cooling], ...)

It seems to be the general concensus that color filters aren't really needed with digital photography. You can adjust white balance in many cameras for a Blue/Amber and/or Magenta/Green bias to get the equivalent of a color filter.

Quality - Price:
Hoya has 4 levels of polarizing and UV filters:
(Prices for 52 mm circular polarizer)
Standard - 1 layer of anti-reflectand coating - 95% transmission (5% reflection) - $33
HMC (Hoya Multi-Coated) - 3 coating layers on each surface - 97% transmission - $64
S-HMC (Super HMC) - 6 coating layers on each surface - 99.7% transmission - $69
5 mm thin profile to avoid vignetting , but no front threads.
Pro 1 Digital (DMC) - 2 mm glass instead of 3 in others - $98
less reflection from filter edges to reduce internal reflections. See:
Filter Options for digital cameras at Digital Photography For What It's Worth.
Filter Primer at DigiCamera.com
Filters at Gary Black Photography
Tiffen Filters

Tele Extenders or Tele Converters (TC):
Tele Extenders go between the camera and the lens and encrease the effective focal length by a factor of 1.4 or 2. You will loose 1 f/stop with the 1.4 and 2 stops with the 2x and some loss of sharpness. T-cons can NOT be used with all lenses. Only the lenses listed in the charts will physically "fit" the T-cons.
In many cases, the increased f/stop will result in a loss of Autofocus

Forum comments:
So far I've come across the Tamron 1.4X AF Teleconverter for Canon EOS cameras and Tamron SP AF1.4X PRO Teleconverter for Canon EOS. It seems that the SP is a better one, but from its decription it indicates that "When used with lenses with smaller maximum apertures (F/4 and F/5.6, for example), there will be little difference in image quality as compared with the standard Tamron teleconverters."
Both will lose you 1 stop of light (making your lens an f/8 ), but only the SP (Pro) teleconverter will report this fact to the camera. So, on the cheaper TC you will have to dial in +1 EV exposure compensation.
The problem with the more expensive TC is that your camera will refuse to auto-focus, as it requires f/5.6 or better. With the cheaper one it will at least try to auto-focus (since the camera sees f/5.6), although it may not always succeed.

See Secrets of Digital Bird Photography

Other Accessories:
The most popular accessories for digital cameras are:

• A UV filter to protect the lens. Some prefer a lens hood to a filter, many use both.   see Filters
• A lens hood.
  Improves contrast, reduces glare and flare, protects the lens.
  A lens hood doesn't cover all that much when you're using a wide zoom.
  Problems with hoods - Threading a lens hood on top of the clear filter might cause vignetting on some lenses, and since not all clear filters would even have threads allowing a hood to be attached.
  
• A polarizing filter
• A camera bag/case
• An extra battery
• An extra memory card
• An memory card reader. Using a memory card reader to transfer photo's to your PC is more reliable than using the USB interface on your camera.
• A 12 v (car) battery charger
• A cleaning kit - Soft cloth, blower brush, lens fluid (some say don't use fluids because they will remove lens coatings)
  Zeiss Cleaning Tissues bought at Optometry Dept at WalMart, are pre wetted and also they will not damage an uncoated plastic eye glass lens then they will not damage the element of a coated lens, if used properly.
• A tripod or monopod with a quick release plate.
  Slik gets good ratings, Bogen is also popular and Gitzo is a popular light weight high end mfg.
• A remote shutter release allows you to take pictures with you in them and reduces camera shake.

Camera Armor:
OK, controls still accessable, but not with gloves. Lens cap hard to get on and off.
Button cover labels hard to read.

Glossary:

AF - Auto Focus (Nikon) see EF
AF D-type - Lens sends distance information back to camera to help things
    like fill-in flash. (Nikon)
AF-S - AF with SWM motor
ASPH - Aspherical Lens Element (Lica)
APO - Apochromatic lens
APS-C Advanced Photo System - Classic (refers to old film APS size
   (25.1x16.7 mm) 3:2 ratio
   Many digital SLR cameras  use APS-C sized image sensors.
   which ranged in size from 20.7x13.8 mm to 28.7x19.1 mm
APS-H frame size of 30.2 x 16.7 mm close to the 9x16 1.8:1 ratio of HDTV
     hence the H. Has a 1.3x magnification on EF lenses
    
ASA - Sensitivity of film ((American Standards Association) same as ISO
      e.g. ISO 100, ISO 400
CCD  Charged Coupled Device Image sensor - Traditional sensors
CF - Cropping Factor  see EFL and FLM 
CF - Compact Flash memory card
CMOS Complementary Metal Oxide Semiconductor - Technology used for
     computer chips adapted to digital photography.  Quality is close to CCD
     and they are cheaper and include more functionality allowing smaller
      camera size.
DO - Diffractive Optics (Canon)
DOF - Depth of field
DSLR - Digital SLR
ED - Extra-low Dispersion glass (Nikon)
EFL - Equivalent Focal Length 
EF - Electronic Focus (Canon) see AF
EF-S EF with Short back focus - Canon Lenses designed for camera's with APS-C
     size sensors.  Won't work with camera's with larger sensors.
EI - Exposure Index - Like ASA
EV - Exposure Value Ev (ISO setting) - Sensitivity to light
EVF - Electronic Viewfinder
EXIF - Exchangeable Image File - Meta Data stored in the jpeg or raw image file
       containing information such as shutter speed, aperture, ISO, Date/Time, ...
DC - (Sigma) Designed for digital APS-C cameras
DG - (Sigma) Designed for digital cameras Works with Full Frame cameras
DX - Nikon smaller DSLR sensors 23.7 x 15.7 mm (CF=1.5)
   The DX-format camera can use both types of lenses (DX and FX)  
FLM - Focal Length Multiplier (see CF)
FX - Nikon full frame (24x36mm) sensor and lens to match
HSM - (Sigma) Hyper Sonic Motor (see USM)
IF - Internal Focusing (Nikon) - Front barrel fixed
     focus won't change if camera is tilted down
IS - Image Stabilization (Canon) see VR
ISO - International Organization for Standardization
    (see EV and ASA above) - Sensitivity to light. 
     ISO 5800:1987-Photography - Colour negative films for still photography
M/A - Manual Automatic setting (Nikon)
MLU - Mirror Lock-UP 
NEF - Nikon Electronic Format (Raw mode)
OS - (Sigma) Optical Stabilizer see IS
Prime Lens - Fixed focal length as opposed to a zoom. Usually faster (lower f-number)
SIC - Suer Integrated Coating (Nikon)
SLR - Single-Lens Reflex
SP - (Tamron) Super Performance
SWM - Silent Wave Motor (Nikon) see USM
TC - Tele Converter or Tele Extender
TTL - Thru the Lens
USM - Ultrasonic motor in Canon lenses for faster quieter focusing. see SWM & HSM
VC - Vibration Compensation (Tamron) see IS
VR - Vibration reduction (Nikon) see IS
vignetting -  a reduction of an image's brightness or saturation at the periphery
         compared to the image center.
XLD - Extra Low Dispersion glass (Tamron)
XR - 

Camera Dealers:
There are many discount dealers out there but it is a "buyer beware" market.
See: Mail Order Warning | Photo Dealer Ratings | Mail Order Tips

Popular suppliers with good ratings are:
B&H 800.606.6969
Adorama 800.223.2500
amazon.com/

Ratings and Reviews:
Digital Photogrophy Review dpreview.com
Lenses at dyxum.com
Ken Rockwell
Google search for reviews.

Links:
Photography - Taking Pictures Photography Notes
Photographing Documents and Historical Object Photography at My genealogy site
Sensor Sizes at DPReview.com
Lenses:
Memory Cards
Understanding Camera Lenses at CambridgeColour.com
DSLRs in products
Old camera ratings (2003, 2005)under products. Light temperature
Popular Digital Camera Sites
Lens Rental at borrowlenses.com
Somerset Co. Photography Club