Using Your Camera in Manual Mode - Camera’s Sensor and Memory Cards

Introduction

In this post, I’ll review the camera’s digital sensor and memory cards.  I’ll give a brief over of the sensor, with a link to a more detailed well written description of the sensor and how it works.

For the Memory cards, I’ve compiled the most current information from various sources.


Your Camera’s Sensor - Overview

Do you have any idea how the darn thing actually works?  Coming from an analog film background, I initially thought it might be something akin to film in some esoteric fashion.  

Nope, not even close!!  Boy was I wrong.

Did you know a digital sensor doesn’t record/see colour?  That’s correct.  

A digital sensor’s “photosites”, or light cavities (pixels), only record photons of light that enter them.  The photons enter the photoshite and strike a photodiode.  When a photon strikes the photodiode an analog electrical signal is produced.  The greater the number of photons, the greater the analog electrical signal.  The analog electrical signal is converted to a digital signal that ranges in value from 0 - 255, where 0 = pure black and 255 = pure white.  In other words, the sensor’s digital signal only sees the light as series of black to white, or a grayscale of  tones.

How many photsites are on a sensor?  That depends on the sensor size, e.g., a Panasonic Lumix ZS80’s sensor is 1” x 2.3” and has 20,300,000 pixels. A Sony A7Riii’s sensor is 24” x 35.9” and has 42.56 million pixels.

So where does the colour in the image come from?

Colour comes from a Bayer colour filter array that sits on top of each photosite, or pixel on the sensor.

You’ll notice there are more green coloured filters in the array.  The green pixels produces an image which appears less noisy and renders finer image details.

There are two types of digital sensors - CCD and CMOS.  Because of the manufacturing differences, the following details the differences between CCD and CMOS sensors.

  • CCD sensors create high-quality, low-noise images. CMOS sensors, traditionally, are more susceptible to noise
  • Each pixel on a CMOS sensor has several transistors located next to it, the light sensitivity of a CMOS chip tends to be lower.  Many of the photons hitting the chip hit the transistors instead of the photodiode
  • CMOS consumes little power.  Implementing a sensor in CMOS yields a low-power sensor
  • CCDs consumes lots of power, as much as 100 times more power than an equivalent CMOS sensor
  • CMOS chips are simpler to manufacture, so they are inexpensive compared to CCD sensors
  • CCD sensors are more mature and are of higher quality and have more pixels.

Based on the above, you can see CCDs are used in cameras focusing on high-quality images with lots of pixels and excellent light sensitivity, e.g., medium format cameras.

CMOS sensors tended to have lower quality, lower resolution and lower sensitivity.  However, CMOS sensors have improved to where they’re almost equal with CCD sensors today.  CMOS cameras are less expensive and have great battery life.

For a more detailed, yet clear sensor description, click here.  


Memory Cards

OK, Memory Cards don’t really have a lot to do with using your camera in Manual mode.  But I thought the information might be of interest.


Physical size

Most of today’s devices use either SD or microSD cards, which you can determine by looking at the card slot on your camera.  DSLR cameras use Compact Flash memory cards.

The image set below shows a SDHC card 32GB, a SDXC card 63GB and a Compact Flash card 32BB.

Storage Capacity

Storage capacity is simple, it’s represented in gigabytes (GB). I t’s easy to assume that the bigger the number, the better, but in reality, this is not necessarily the case.

Not only can it be cheaper to use multiple smaller cards, you won’t live and die with just one card because they do degrade, get lost or experience data corruption.

Memory cards are not meant as a permanent storage device.  After your shoot, transfer the image files to your computer, or an external hard drive.  Then format the memory card in camera; never format the memory card in your computer.  And always consider using a second external hard drive as a back-up drive for your image files.

How much storage do you need?  Simple answer; it depends.  A 4GB card holds about 280 RAW image files, or about 1,500 high quality JPEG files.  A 128GB card would hold about 9,000 RAW image files.  Whoa!!!!  That’s a lot!  If you shoot video, you’ll definitely need a 128GB U3 card!!


SD vs. SDHC vs. SDXC

The file system being used to store data determines a memory card’s capacity.

SD (secure digital) cards are the oldest, least used and limited to 2GB of storage.

SDHC (high capacity) cards can store up to 32 GB of data.  SDXC (extended capacity) cards can store up to 2 terabytes (2000 GB) of data.  These high capacity cards also come with a much higher price tag.

Older cameras may not be able to use the SDXC format, so make sure your device does support these larger cards before buying one.


Rated Speed

Things can get a bit confusing, as the the card’s speed can be referred to by various designations.  It’s represented in MB/s (megabytes per second), or a large number followed by an “X” or sometimes both.

The X designation is a marketing term — 1X represents 150 kb/s (kilobytes per second), so 600X is the same as a 90 MB/s rating (600 x 150 = 90,000).  This number typically represent the “read” speed, which is generally higher than the “write” speed.

Write speed is how fast the card accepts image files from the camera.  Read speed is how fast the card lets a computer read the image files during download.


Speed Class

This specification is represented on the card as a number inside of the letter “C” to represent the minimum write speed and is most important to those shooting video or very large images in burst mode.

There are four classes — 2, 4, 6 and 10 — which represent the minimum sustained megabytes per second (MB/s) write speed. The higher the number, the faster the sustained speed.

The point of this is to avoid your camera buffering and slowing down the image writing process.


UHS Speed Class

Faster SDXC memory cards will have the UHS, or Ultra High Speed, rating represented by a number inside the letter “U.”  U1 means it’s 10 MB/s while U3 means it’s rated at 30 MB/s.  Use this type of card to capture 4K video.


UHS Bus Class

Different from the UHS Speed Class, this rating refers to the “bus interface” and is represented by a Roman numeral.  Think of the bus interface as the number of lanes on a freeway vs the UHS Speed Class, which represents the speed of individual cars.


Video Speed Class

If you’re trying to shoot extremely high-resolution video (4K or 8K), this class of cards — designated by the letter V and a number that ranges from 6 to 90 — offers the fastest sustained write speed.


SD and MicroSD Cards

Two of the most popular memory cards are SD and MicroSD cards.  That’s because they’re readily available, affordable, and compatible with multiple cameras across many manufacturers.  Their storage capacity and speed have increased dramatically in the last few years, but so has the price for premium cards. 

It was only a few years ago that a 128GB SD card seemed like the pinnacle of the technology, but the new 1TB SD and MicroSD cards surpassed that milestone.  These memory cards are not meant for the typical amateur photographer.  Rather, they’re tailored for “prosumers” and professionals — just check the price tag.  Even with big discounts, the majority of 1TB SD or Micro SD memory cards cost upwards of $300.

While the price may be steep for most, there are some significant advantages, especially if you record lots of high-quality footage.  With 1TB of space, you don’t have to replace your card as often.  Its read/write speeds can also handle most tasks from 4K video to 8K video, in some cases.  Cards with a V60 or V90 rating are best suited for 8K, while V30-rated cards can handle 4K.  For reference, a V30 rating means that there’s a constant write speed of 30MB/second, which keeps video files smooth and stutter-free.

If you have any specific questions, please email me at edward@amindseye.com.  I’ll reply as soon as possible and may include your question and answer in a future post.

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