How Much Memory Do You Require?

How Much Memory Do You Require?
Digital cameras are seldom supplied with memory cards these days, partly because the cards that were once supplied are woefully inadequate for today’s camera resolution levels and partly because many digicams come with built-in memories where pictures can be stored. Unfortunately, these internal memories are often relatively small so new camera purchasers should always buy at least one high-capacity card when they purchase a new camera.
Purchasing a digital camera normally locks you to a specific card type, with Secure Digital (SD), Memory Stick (MS) and xD-Picture Cards most popular among digicams and CompactFlash (CF) and SD cards for DSLRs. A few cameras have two card slots and some models have a single slot that will accept two different types of cards (for example, xD and SD).

Some cameras have dual slots that will accept different types of cards. With more sophisticated cameras it is usually possible to transfer image files between cards and decide which card
Prices of all memory cards have plummeted since mid-2006, making high-capacity cards affordable to even the most cash-strapped photographers. When we went to press you could buy a 1GB SD card for less than $30.
In this chapter we’ll outline typical capacities for a range of memory cards and provide guidance on how much memory you require for some typical shooting situations.

How Many Images Can You Store?
The table below shows the approximate number of pictures popular memory cards can store for digicams of different resolution levels. The figures provided are based on JPEG images from compact digicams, taken at the highest resolution and quality settings.

The actual number of pictures that can be stored on a card will depend on the camera model and how much the JPEG files are compressed. Some cameras apply higher compression ratios that others. Card capacities will be significantly higher when lower resolution/quality settings are used.

Photographers who use DSLR cameras will find they need higher storage capacity – especially if they shoot raw files. For this reason, we recommend at least a 1GB card. The table above gives the approximate capacities for high-resolution JPEG files at a compression ratio of 1/4 from typical DSLR cameras.

Compression ratios vary for raw files, although all manufacturers provide lossless compression. For example, 10-megapixel raw files can range in size from 17.66MB to 9.8MB, depending on the file format used and the degree of compression applied. TIFF files, which are usually uncompressed, are roughly three times the resolution of the camera’s sensor in size (e.g. around 30MB for a TIFF file from a 10-megapixel camera).

How Much Video Can You Store?
When memory cards are used for storing video clips, capacities are measured in time, rather than number of image files. The compression ratio applied by the camera will dictate the size of the video files. Most camera manufacturers put a limit of 4GB on video capacity – or up to one hour of video recording. The table below shows typical video recording times for three different video formats with three card capacities.

Factors Affecting Card Capacity
The actual capacity of a memory card can depend on several factors:

1. How the computer operating system sees it. Most operating systems define a megabyte as 1,024KB (1.024MB), which means a 1GB card’s capacity is 1,048.576MB.
2. How the card manufacturer defines a megabyte. For many manufacturers (and most disk drives), a megabyte is exactly one million bytes.
3. How formatting the card changes its capacity. This varies, but typically around 1% of total capacity is allocated to a ‘security area’.

The last two factors together explain why the actual capacity of most memory cards is slightly lower than it might appear.

How Much Memory Do You Need?
Assuming you always shoot with your camera’s highest resolution and quality settings, it’s easy to calculate the size of the memory card you require. Back in the days of film, most amateur photographers would shoot up to two 36-exposure films in any one day; the equivalent of 72-75 shots. With digital, we’re less conservative, so a better estimate for a day’s ‘normal’ shooting would be 100-150 shots. In photographically exciting places, this figure could safely be doubled – and if you plan to shoot video as well as stills, you will need at least four times more memory capacity.

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CompactFlash cards are available in capacities up to 8GB.
When you’re travelling, we recommend allocating at least 2GB per day if you travel with a laptop computer or portable storage device and can download each day’s shots in your hotel each night. A total of three 1GB cards will provide for one ’emergency’ spare that can be used when you need more capacity. Cards are light and take up very little space in your camera bag. It’s better to have several spares than to be forced to shoot at lower resolution and compromise your ability to make big prints.

Travellers without laptops or portable storage should have at least 4GB of memory card capacity with them and allow a minimum of 2GB per day when they will be in transit and unable to transfer their shots to optical disks. You should be able to find services that will transfer images from a memory card to a CD or DVD in most population centres. We recommend purchasing two copies of each disk: one to keep with you and the other to send home as a back-up (in case the other disk is lost or damaged).

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Take at least two 1GB cards when setting out for a day’s photography.

Do You Need a High-Speed Card?
CompactFlash and SD cards are supplied with a range of speed ratings, typically 40x, 80x and 144x (where x represents a transfer speed of 150 kilobytes per second). These speed ratings can be useful for photographers as they can help you to choose a card which matches your camera’s data transfer speed.

Memory card manufacturers charge premium prices for their high-speed cards but, for photographers who shoot with digicams, fast cards will be of little benefit. Even many DSLR photographers will find standard 40x speed cards will be adequate for most shooting situations. However, they will make a difference in how long it takes to download files to a computer, particularly if you have a fast PC.

High speed cards are also worthwhile for video recording, especially if your camera or camcorder supports the new, ultra-fast UDMA technology (which will be supported in the next generation of DSLR cameras). However, you need a UDMA-enabled reader to benefit from the speed advantages this technology offers when downloading large files to a computer.

The main determinant of memory card speed is how the controller in the card exchanges data with the camera. This can vary by as much as 3-4 megabytes/second from one camera to another. The flash memory itself also determines the maximum speed of different cards and accounts for a sizeable part of the price premium charged for fast memory cards.

Is it worth paying more for a high-speed card? It is if your camera can match the card’s data transfer speed and if you use burst mode frequently. If you take shots one at a time, the speed of the card is irrelevant.

High-speed cards may also be worthwhile if the camera is unable to shoot and write simultaneously, or if your camera’s innate write speed is slow and its buffer memory is small. Otherwise, you may not notice much difference between a high-speed card and a standard one.

Memory Card Tips
Beware of counterfeit cards that appear to be from a leading manufacturer but lack the warranties of the genuine products. Replicated cards with labelling and packaging that resembles cards from leading brands are readily available on the internet. Check card labels very carefully and only buy from reputable re-sellers. If the deal seems too good to be true it probably is.

Treat memory cards with care. Keep them in dust- and water-proof cases while they are not in use. Always carry at least one back-up card in case you run out of memory on a shoot.

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Moving the lock on the side of an SD card down protects all the files it contains against erasure. To delete the files or format the card you simply return the lock lever to its up position.

Don’t open the camera’s card compartment while the files are being written; it will almost certainly cause shots to be lost. Shots may also be lost if the battery fails while files are being written. In most cases these ‘lost’ images can be recovered with file recovery software (which is supplied with some high-speed, high-capacity cards). Many camera shops provide a file recovery service for a small fee.

Always format each card in your camera before you use it, making sure you have transferred the images it contained to an archive folder. Some digital cameras can’t operate with cards that were formatted in a computer or a different camera.

Don’t expect a camera to display images captured on a card by a different camera – even if it comes from the same manufacturer.

Write Protection
Secure Digital (SD) cards have a built-in facility that allows you to lock files stored on them so they cannot be deleted. This is useful when you are using several cards over a period of time and don’t have facilities for downloading the shots. A sliding lever on the left side of the card locks in this write protection. When it is pushed down towards the lower edge of the card, all data on the card is protected. Pushing it up towards the top of the card removes the write protection and allows image files to be deleted individually or collectively. The card can also be formatted.

For other memory cards, write protection can be applied through your camera’s play or set-up menu (indicated by a tools icon). The function is usually indicated by a horizontal key icon. The same menu is used to remove write protection.

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