Glance at the summary firstThe summary from the end of the lesson, as a road map before you start reading.
Memory cards cause trouble most often because of a corrupted file layout, physical damage, counterfeit capacity, and cells wearing out over long use. The markings in a U, a V and a circle on the card show the minimum write speed, while the big number on the front usually shows the read speed; in burst shooting the camera pauses when the buffer fills up, and a slow card lengthens this pause. Setting up a rotation with numbered cards, marking the full card, formatting after backing up the photos, and pulling an unreadable card out of use right away and trying data recovery also secure that short moment when faces of every skin tone catch the light in dim light.
Learning goal
You will be able to explain why a memory card can fail and how to reduce this risk. You will read the speed class markings on a card and tell write speed from read speed; you will explain why the camera pauses during burst shooting through the relationship between the buffer and card speed; you will recognize a counterfeit or suspicious card and test the capacity of a card you have bought; you will set up a card rotation that numbers cards and uses them in turn; and you will know what to do and not do in the first minutes when a card can't be read, to raise the chance of getting your photos back; you will also see why, in dim light, the moment when faces of different skin tones catch the light is often hidden inside a sequence.
The question
You are at a village festival. In the square a circle line dance is going on, evening has fallen, and the only light comes from bulbs hung on poles and a fire burning in a corner. The old woman leading the dance, dark-skinned, in a headscarf edged with needle lace, turns waving her handkerchief, and on every turn her face enters the firelight for a moment. You shoot in bursts; but at the seventh frame the camera pauses, an hourglass appears on the screen, and the moment when the woman's face is fully lit slips away.
The next morning, when you put the card into the computer, something worse happens: the screen says "card cannot be read." Why do memory cards fail? And how does a card's speed explain why the camera paused that evening? In this lesson we will talk about what is inside a card, the markings on it, and ways of using cards safely in the field.
Context
In Lesson 3.7 we saw formatting the card in the camera, not removing it while the write light is on, and splitting the risk across several cards. That lesson told the care before going out into the field. This lesson looks more closely at the card itself, the writing on it, and the causes that make it fail.
In the previous lesson we saw that a RAW file is many times bigger than a JPEG. This size asks two things of the card: more capacity and a higher write speed. Choosing the card correctly makes it possible both not to miss the moment in burst shooting and to know the risk when you entrust a whole evening to a small piece of plastic.
Simple explanation
Why do cards fail?
Memory cards are a kind of flash memory that stores information in small memory cells. Each of these cells can be written and erased a limited number of times; with very long use, the cells wear out. But most cards cause trouble for other reasons before they wear out. The most common reason is the file layout being corrupted: removing the card while the camera is writing a file, the battery dying, or a card being moved from one camera to another without being formatted can mix up the list that shows what is on the card. The photos may still be on the card, but the camera or the computer can't find them.
Physical damage breaks cards too: bending, getting wet, extreme heat, and the contact points wearing or getting dirty. Another cause is counterfeit or low-quality cards. Some counterfeit cards report a much bigger capacity than they really have; when the card fills up it silently writes over the old files, and the problem is only noticed when the photos won't open. A high-capacity card sold far below the market price should always raise suspicion.
What do the markings on a card say?
There are a few kinds of speed markings on cards. The number 10 inside a circle, or the numbers 1 and 3 inside a letter U, show that the card guarantees a sustained write speed of at least 10 or 30 megabytes per second. Markings like V30, V60 or V90 likewise tell a minimum write speed of 30, 60 or 90 megabytes per second, and were defined especially for video. These markings tell the speed the card can write at even in the worst conditions.
The so-many megabytes per second written in big letters on the front of the card, on the other hand, is usually the maximum read speed; that is, it shows how fast the card will transfer to the computer, not how fast the camera will write to the card. Cards are also made with different connection types; faster cards with a second row of contacts on the back reach their full speed only in a camera that supports it. When choosing a card, looking at the minimum speed class recommended in the camera's manual is the safest start.
Why does the camera pause during burst shooting?
When the camera takes a frame, it first writes it to a small and very fast internal memory called the buffer; from there it moves it to the slower card. When you shoot in bursts, frames fill the buffer faster than the card. When the buffer is full, the camera holds off taking new frames and waits for writing to the card to finish. Because RAW files are big, the buffer fills up with them much faster; a slow card also delays the emptying of the buffer.
This pause is especially annoying when photographing people in dim light. In low light, the moment a face looks good is often a short one: the moment the head turns to the light and a glint falls into the eyes. On a dark-skinned face this moment can be the only frame where detail comes out of the shadow; on light skin, on the other hand, the frame where the fire or the lamp hits directly can be the frame that blows out the forehead. The right frame is often hidden in the middle of a sequence. A fast card and knowing how many frames the buffer takes let you land the sequence on the right moment.
Visual evidence
You go back to the same festival the next year. You come with two cards that match the write speed recommended in the camera's manual, bought from a reliable seller, whose capacity you tested at home by filling them from start to finish. The cards are numbered; you put in number one, and number two is in the case. When the dance begins, the same old woman again turns at the front. This time you shoot fifteen frames in a burst and the camera never pauses. When you look through the frames, in the ninth frame the woman's face is turned fully to the fire: the lace of her headscarf, the glint in her eyes and the lines on her cheeks can be made out; in the eleventh frame, the face of the light-skinned young girl beside her is in the same light too, her forehead not blown out.
At midnight, when the first card is full, the camera gives a warning. You wait until the write light goes off before removing the card, mark it as full by turning it upside down in the case, and put in number two. When you get home you transfer the photos and back them up, and only after that do you format the cards in the camera. Last year's unreadable card, on the other hand, you had never formatted, but scanned with a recovery program; most of the photos had come back.
Common mistakes
Common mistakeThinking the big speed number on the front of the card is the write speed.
That number is usually the read speed. The fix: when choosing a card, look at the speed class in a U, a V or a circle, and at the camera's recommendation.
Common mistakeContinuing to shoot onto, or formatting, a card that can't be read.
Every newly written file can be written over old files that could be recovered. The fix: take the card out of the camera right away, don't use it, and scan it with a recovery program.
Common mistakeUsing a very cheap, high-capacity card without testing it.
A counterfeit card silently writes over old files when it fills up. The fix: buy the card from a reliable seller, and test its capacity before first use by filling it from start to finish.
Summary
Memory cards cause trouble most often because of a corrupted file layout, physical damage, counterfeit capacity, and cells wearing out over long use. The markings in a U, a V and a circle on the card show the minimum write speed, while the big number on the front usually shows the read speed; in burst shooting the camera pauses when the buffer fills up, and a slow card lengthens this pause. Setting up a rotation with numbered cards, marking the full card, formatting after backing up the photos, and pulling an unreadable card out of use right away and trying data recovery also secure that short moment when faces of every skin tone catch the light in dim light.
Mini assignment
In this assignment you will get to know your own cards and measure your camera's limit in burst shooting.
- Read all the speed markings on your cards and note whether each one is a write or a read speed.
- Find the minimum speed class recommended in your camera's manual and compare it with your cards.
- Put the camera into burst shooting and hold down the button first in JPEG, then in RAW; count at which frame the camera pauses.
- Number your cards, choose a way to mark the full card, and arrange your case accordingly.
Check yourself
- Were you able to tell whether the big number on the front of your card is the read or the write speed?
- Do you know after how many frames the camera pauses in RAW?
- In a sequence you shot in bursts in dim light, were you able to find the frame where people's faces caught the light best, regardless of skin tone?
Glossary
| Term | Short definition |
|---|---|
| Speed class | A marking that shows the minimum sustained write speed a card guarantees even in the worst conditions. |
| Buffer | A small, fast internal memory where the camera temporarily holds frames before writing them to the card. |
| Counterfeit card | A card that reports a bigger capacity than it really has and writes over old files when it fills up. |
| Card rotation | A system of numbering cards and using them in turn to spread the load and tell the full card apart. |
| Data recovery | The process of getting back the files on an unreadable or formatted card with a special program. |
Mini quiz
1. What does the speed number written in big letters on the front of a card usually show?
- A) The maximum read speed
- B) The minimum write speed
- C) The card's capacity
- D) The card's lifespan
2. What does the V30 marking tell?
- A) That the card is 30 gigabytes
- B) That the card will last 30 years
- C) That the card guarantees a write speed of at least 30 megabytes per second
- D) That the card is only for photos
3. What is the reason the camera pauses after a few frames while shooting RAW in bursts?
- A) The battery has gone weak
- B) The buffer has filled up and the camera waits until the frames are written to the card
- C) The sensor has heated up
- D) The lens is hunting for focus
4. What should be done first when a card can't be read?
- A) Format the card in the camera right away
- B) Keep shooting new photos onto the card
- C) Stop using the card and scan it with a recovery program
- D) Leave the card in the freezer for a while
Answers
- A — The big number is usually the read speed; the write speed is written in the speed class markings.
- C — V30 shows a sustained write speed of at least 30 megabytes per second.
- B — The buffer fills faster than the card; when it is full, the camera waits for writing to finish.
- C — Every newly written file can land on top of old files; scanning the card without using it keeps the chance of recovery.
Summary card
- Cards fail: file layout, physical damage, counterfeit capacity, cell wear.
- The markings in a U, a V and a circle are the minimum write speed; the big number is usually the read speed.
- When the buffer fills, the camera pauses; RAW and a slow card bring this on faster.
- Numbered cards, a full-card marker, formatting after backup.
- Don't use an unreadable card; scan it right away. In dim light the right face is often in the middle of the sequence.
Bridge to the next lesson
The festival's two cards are now in the case, one turned upside down. But the photos inside them live only in those small pieces until they reach a computer or a disk. Should you put the card into the computer with a reader, connect the camera with a cable, or send the frames wirelessly? The next lesson talks about the photos' journey from the camera to the computer, and the speed and risk of each of these routes.