After years of postponement and dilly-dallying, I have set my mind upon the purchase of an
Image Capture Device. I have shortlisted three such devices, as candidates for purchase.
Magic Mirrors
Film Cameras
Digital Cameras
I would have settled on Magic Mirrors, but due to the fact that all witches and wizards who used to manufacture
such image capture devices have either been burnt at the stake or have died of old age, I had to focus on the other
two contenders. Film cameras(35 mm film) are great, but the fact remains; they are old technology, and improvements
if any would be imperceptible. In contrast digicam(excuse the euphemism) technology is getting better every day. Add
to the that the freedom from replacing film, developing the shots and tediously scanning the shots for publication on
the web, digicams seem to be much superior and hassle free. Some may contend that the image quality is much better than
35mm film, but
research has shown that the new 11 Megapixel
digicams offer much better picture quality.
But how do I go about buying a digicam? Well, I decided to do some research on this. I started out by identifying,
what features one should look at, while making a decision about which camera to buy and which not to buy. Basically, one
should concentrate on most if not all of the following features
Batteries
Pixel Count(Megapixels)
Pixel Size
Sensors
Lenses
Timing Lags
Memory Storage
Killer Apps
I delved into each of the above mentioned criteria in detail and came up with a checklist for each.
1. Batteries
There are certain things one should look at while deciding what kind of batteries are desirable. I have listed down most
of the features that any potential digicam owner would be interested in a battery to power his digicam.
Reusability
Technology
Size
Cost
Ruggedness
Standards
The Green Factor
Reusable batteries are desirable and lead to lower cost of ownership, in the long run. But they are expensive to start
with.Disposable batteries on the other hand are comparatively inexpensive to purchase. So if one is not planning on
doing a lot of photograhy with the digicam, disposable batteries are the best bet. Also there are issues with disposable
batteries like enviornmental friendliness and safety of disposal. Alkaline batteries are the most popular disposable
batteries that are in use. NiCad, NiMH and Lithium ion technologies are very popular in the sphere of rechargable
batteries. NiCad is the oldest technology and has a lot of drawbacks, and hence digicams with NiCad batteries should
best be avoided.Among the other two contenders, Lithium ion scores better compared with NiMH.For one, the
technology is relatively new and has a lot of scope for improvement.Also lithium based batteries are lighter, are
free from problems such as memory, a problem with Nickel based batteries and have half the rate of self-discharge
as Nickel based batteries do. On the flip side, they are slightly steeply priced and are also prone to ageing. Another
feature one should look into is whether the battery form factor and design is propreitory. Batteries which conform
to standards are always better than those that are produced by a single manufacturer, in terms of choices available
to the customer.
 |
|
 |
|
 |
| Propreitory form factor |
|
Standard form factor |
|
Disposable lithium batteries |
1.1 Links
A description of Lithium ion technology
2. Pixel Count
Pixel count is expressed in Megapixels. It determines what size prints one can get at a good resolution. One should
look at the number of active pixels rather than the total pixel count. But manufacturers noemally dont specify these.
Based on the size of the prints one is aiming at, one should look at a digicam a specified Megapixel count. This table
should help you to make a good choice.
| Megapixels |
Print Size (Inches) |
| 1 |
4 x 5 |
| 2 |
5 x 7 |
| 3 |
8½ x 11 |
| 5 |
11.7 x 16.5 |
| 6 |
13 x 19 |
| 11+ |
16 x 24+ |
If you are planning to shrink the shot to a smaller size, then the pixel count doesnt actually matter. Needless to say,
the Megapixels are probably the easiest but not the correct indicator of the resolution of the camera.
2.1 Links
All about Pixels
3. Pixel Size
Before I encourage you to read on, I warn you that what follows is not for the faint hearted. It is highly
technical and I didnt understand a word of it during my first read.The casual reader may prefer to skim rather
than break her head over jargon and terminology that one is wiser without.Ok, here goes . . .
Pixel size is not easy to figure out straight from the camera specs. It is closely related to pixel spacing.
This is how a typical sensor of a digicam looks like.
The table below lists typical pixel spacings for different breed of cameras.
| Category |
Spacing in microns |
| Inexpensive and Compact |
2.6 |
| Prosumer Cameras |
3.4 |
| DSLR Cameras |
6.8 - 10 |
The thing that matters here is the
Active Pixel Area.It has relation to noise and sensitivity.
Active Pixel Area = Square of Pixel Spacing x Fill Factor
The Fill Factor is the fraction of total pixel area covered by active elements. A little introspection shows that,
the active pixel area can be increased by increasing the pixel size, and consequently the pixel spacing.Small pixels
suffer from increased noise while very large pixel size produces an undesirable effect called aliasing.
3.1 Links
More On Aliasing
4. Sensors
The Law of Sensor Size reads - "Bigger the better".It is very difficult to find out the correct sensor dimensions
because of a really archaic nomenclature used to define the sensor size.The sensor sizes in this nomenclature are defined
as 1/x'.Here x is a real number.The bigger the x the greater the dimensions of the sensor.
The diameter of the sensor would be d=(1/x)*25 mm.If the aspect ratio is given as m:n,
then the width and height of the sensor are respectively m*d/(m+n) and n*d/(m+n) respectively.
4.1 Links
More On Sensor Sizes
5. Lenses
Lenses are the eyes of the camera and are thus are very important in determining the quality of the image.
Before I start, I would like to define certain terms that will be used quite extensively in the subsequent text.
Focal Length
Focal length indicates the distance needed between a lens and an object to make the object
visible and in focus.It measures the field of view of the lens.Short focal lengths tend to be
wide angle
while longer ones tend to be
telephoto.Telephoto brings distant objects closer but suffers from a narrow
field of vision.Wide angle lenses have a wider angle of view.
Zoom
The ratio of the longest to the shortest focal lengths of a camera is called its zoom and denoted by
Nx.
Here N is a number.
F-Stop
It is defined as the focal length divided by the circular aperture opening.It is denoted by
f/N.
The smaller the f-stop, the larger the lens aperture and hence larger the amount of light admitted.
Digital Zoom
Enlargement of pixels by interpolation.Decreases the resolution of the image.Is equivalent to cropping
using software.
A decent digital camera should have at least 3x optical zoom.Also 30mm is considered to be modest wide angle while
135mm is moderate telephoto.Do not use digital zoom as a criterion for evaluating the quality of the camera.The f-stop
determines the speed of the lens.Smaller f-stop cameras have greater speeds, but the optics come at a steeper price.
5.1 Links
All about F-Stop
6. Timing Lags
The total time taken for the image to be stored on the media since the shutter is pressed is called the shutter lag.
Shutter lag includes the time taken for autofocus and the shutter depress.Cameras with lesser shutter lag are preferrable
to cameras with greater shutter lags.Shutter lag should be lesser than 0.5 seconds.
7. Memory
Talking of Memory - "Size Does Matter".The amount of available memory determines the number of high quality pictures
one can store.Memory comes in two types - Microdrives and Flash Memory.A lot of cameras dont support microdrives and
also they are not well suited to high-altitude photography.Flash, with increasing capacity and decreasing costs is a
popular choice.Flash cards come in two types - CF1(3.3mm) and CF2(5.0mm).Flash memory cards are more durable than
Microdrives because the cards contain no moving parts.
8. Killer Apps
Listed below are features that do not affect the quality of the image in any way, but are great value-adds.
Video with sound
Most modern digicams come with an ability to record motion with sound. The length of the recording depends on
available memory. The movies are usually stored in QuickTime format.
Scene Modes
Most good digicams come with a range of preset scene modes.Examples are Potrait, Night, Indoor, Underwater etc.
These are provided to assist with selecting the best focus, exposure, ISO, white balance, shutter speed and photo effect
settings to match the shooting environment.
Anti Shake
Image blurring caused in long exposure cameras can be reduced by Image Stabilization techniques known as Antishake.
Cameras with Antishake produce better images even at long exposures. These cameras have built in gyro-sensors that
compensate for any upward or downward motion during the exposure.
Self Timer / Remote
Any camera worth its casing, should have a self-timer.The self-timer depresses the shutter at the end of a set
time interval.Better models come with a remote that can be used to depress the shutter remotely.
Panoramic Images
Cameras with panoramic image capture allow the use to take a series of images at incremental angles and stitch them up
with software.If one intends to capture wide landscapes, then this feature is a must.
