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How to Select the Right Camera Memory Card

In today’s market if you want to buy a camera memory card, you may find it challenging to select the right one. A card comes with the following criteria; type, speed, price, capacity. If you want to buy a high capacity card with low price it might come with a low transfer speed. If you wish to buy a high transfer speed with high capacity card it may come with a really high price. If you want to strike a balance between both, you really have to compromise on quality.

select the right memory card

What is a memory card?

A small removable memory medium which can be used to store data on one medium and to transfer the data to another medium.

Let’s see each criteria which will help you decide on a memory card in detail.


This one is fairly straightforward, and not a big deal. A 32GB memory card can hold up to about 1000 RAW photographs. Assuming that one RAW file size is 30MB, in general a Canon 5D MKIII will produce a RAW file between 25-35MB in size. Likewise a 16GB card can hold up to about 500 photographs, and so on. If you shoot in jpeg format, then a 32GB card can hold around 3200 photographs, assuming you have your jpeg settings as fine in detail, and large in file size. With that setting a jpeg file will come in at an average size of 10MB on a Canon 5D MK III camera.


There are many types of memory cards available on the market ranging from Micro SD card, SD card, CF card, M2 (from sony). But there are only three type of cards being used primarily in the photography world, Secure Digital (SD) card, Eye-fi card, Compact Flash (CF) card.

Micro SD card

Micro SD card is a miniature version of the SD card and meant to be used in mobile phones. This card has capacity, as well as transfer speed restrictions. That is why it is used primarily in Smartphones where one can store music and apps, or any other relatively less active data.

select the right memory card

Secure Digital card (SD card)

This type of the card is widely being used in digital cameras, primarily in point and shoot cameras and secondarily being used in professional cameras. The constraint in using this card is the capacity of the card. The initial high capacity is only 2GB when introduced in 1999. But as the time and technology progressed a later version as SDHC is introduced with a higher capacity of 64GB in 2006 (HC means Higher capacity). The recent third iteration of SD card been announced in 2009 as SDXC cards (XC stands for extended capacity). This type of card offers up to 2TB and increased transfer speed.

Eye-fi card

These are unique SD cards that come with built-in WiFi. This allows you to transfer the data to your computer or a cloud-based service or even to your Smartphone directly, thus enabling you to clear off the memory as you shoot, without having a need to replace the memory card. It is even possible to geotag your photographs with the available wireless service, but with less accuracy though.

There seems to be a promising future for this card!

Compact Flash card (CF card)

select the right memory card

First introduced in 1994, CD cards have high speed, and high capacity. This is the reason why CF cards occupy the primary card slot in professional cameras. Present SD cards are equalling the speed and capacity of CF cards, but camera manufacturers are not leaving CF cards just yet. They often provide slots for both an SD and CF card, but some photographers wish they would offer two SD card slots instead. This provides some extra space inside the camera and saves money for the photographer (CF cards costs roughly twice that of SD cards). Hopefully they will switch the importance to SD cards in the near future.

As the name suggests this is a flash memory which aids high speed reading/writing speed, and has a higher capacity too.


Speed in SD cards

All memory cards come with speed, either mentioned or not. Speed here means both writing and reading. The one indicated on the card is the maximum speed the card can read, but the most important thing is the write speed. Read speed is the time taken to read the data from the card and the write speed is the time taken to write the data. Simply put read speed comes into action when you transfer the data from the card, write speed comes into play when you shoot. In general the write speed is about half of the speed of read speed in SDHC cards. In few other cards both the read and write speeds are about the same.

select the right memory card

The speed of cards have been classified into classes by the SD Association, which are referred to below. The speeds are primarily meant for video recording, where sustained recording (write) is required and it is supposed to be the minimum worst case scenario speed.

You really need to give weight to this one single-most important factor, when you buy a memory card. All SD cards have a class noted on them. Check the attached diagram below:

ClassMinimum Speed

Later, in 2009 another class, UHS, was introduced by the SD association and is designed for SDHC and SDXC memory cards. UHS utilizes a new data bus that will not work in non-UHS host devices. If you use a UHS memory card in a non-UHS host, it will default to the standard data bus and use the “Speed Class” rating instead of the “UHS Speed Class” rating. UHS memory cards have a full higher potential of recording real-time broadcasts, capturing large size HD videos and extremely high quality professional HD.

Courtesy – SanDisk website.

UHS ClassMinimum Speed

Speed in CF cards

When it comes to CF cards the speed is often mentioned as X times and in many cards it’s been mentioned as MB per second, which is pretty straight forward. Whereas when the speed is mentioned as 600X or 1066X what exactly does it means? X means 150Kb per second. It is a standard brought over from optical media recording. Now to find out what exactly the speed is of 600X – to find this multiply 600 by 150 and divide the result by 1000. The final result is in MB per second. Eg., a 600X speed card is capable of 90MB per second read speed (600?150/1000).

The latest CF cards come with the UDMA 7 which improves in clearing the camera’s buffer memory quickly, which allows the camera to get ready for the next burst. Firmware upgrade is required for the Canon 5D MKIII (yours may require it also, check with the manufacturer) camera to make full use of UDMA 7.


When it comes to price, the fastest card is the primary criteria which decides the price. The next deciding factor is capacity of the card. An SD card is 50% of the price in the same capacity CF card. So, if you want to buy a high speed card with same capacity you will need to pay more. On the other side if you want to buy a high capacity card at a lower price, it is possible to do so but you’ll get a lower speed card.

select the right memory card


  • If you use two cards at different speeds, the lowest speed is the deciding criteria for the burst. For instance if you use a CF card at 90 MB/sec in one slot and an SD card having the capacity of 45MB/sec (and you set RAW files for both cards) then you won’t get the advantage of 90MB/sec and the possibility of missing the shot. You have to use both cards at the same speed.
  • If you do not upgrade to the latest firmware for the 5D MKIII camera, the host memory will perform for UDMA 6 which significantly consumes more time in clearing the buffer memory.
  • I wish the camera manufacturers would switch to SD cards completely for both slots. The speeds of the SD card already matches with the CF cards, there is no point paying twice the price, and we’d get the added bonus of saving space inside the camera.
  • In few cases the SD card speed is higher than CF cards. For instance SanDisk Extreme Pro speed is 280 MB/sec but from the same manufacturer the CF card’s maximum speed is 160 MB/sec.

Hope you have gotten a bit of information from this article. Do share your thoughts in the comments.

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Navan Viswa
Navan Viswa

is from India residing in Chennai now. He does weddings, products, industrial projects and travel photography. He studied as a Civil Engineer and worked as one for 12 years, found that the job not of interest and his passion was aligned towards photography. So he quit his job and is now roaming with his camera for commissioned and non-commissioned works. You can see more of his writings on his blog and more photographs on his web page as well as 500px.

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