Hitchhiking Life: Sankha's Digital Camera Purchase Guide

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

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

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.