Everything you need to know before buying a memory card
Today there is a wide selection of memory cards1 available in the market. You can find many different brands, types, capacities, and speeds for every digital camera. In Figure 1, you can see a sample of what is available. Choosing the right memory card becomes even more complicated when looking at all the symbols and abbreviations manufacturers put on them, as seen in Figure 2.
Figure 1. A sample of memory cards available in the market.
So, which memory card should I buy?
There is no clear-cut answer to this question, but there are a few steps that can help you make the right choice. In this article, you will find out everything you need to know before buying a new memory card. In the footnotes, you can find in-depth information if you are interested in more technical details.
1) Memory Cards are electronic non-volatile (meaning they retain their information even when the power supply is turned oﬀ) devices used in portable electronics such as Digital Cameras and smartphones.
- 170 MB/s (Megabytes per second: This is the maximum (theoretical) Read speed of a card.
- V30, U3, C10: all are related to the speed
- 256 GB (Gigabytes): is the storage capacity of the card.
- SDXC: is a SD family card.
A roadmap to choosing the right memory card for your camera
Step 1- Consider Compatibility
Your camera has one or two card slots, so you need to find out which type of card fits in each slot as well as the specifications of each card. This information will help you take full advantage of your camera’s capabilities. You can find this information in your camera’s manual. For instance, Nikon D850 has two card slots, one for an XQD card and one for a Secure Digital Card (SD card). In Table 1 you can see the approved memory cards for Nikon D850 as described in the camera’s manual.
This information is quite helpful despite the technical terms and abbreviations. If you take the manual to your local camera store, they will certainly offer you XQD or SD cards that meet the specifications. Still, there are many cards with different storage capacity and different speed that meet those criteria, and they come with different price tags. Which one shall I buy?
2) SD cards are by far the most commonly used memory cards in digital cameras and are supported by all leading camera manufacturers. Hence, we will discuss this type of cards in more details.
3) On the left side of the SD card in Figure 2, you see a lock symbol and a tiny slider above it. When this slider is positioned as it is shown in Figure 2, you can use the card for Write and Read. If you place the slider on the lock position, then you can not do any changes in the content of the card (it will be protected from deleting or Writing). You can still Read the card’s data.
Table 1. Approved memory cards for Nikon D850 as described in the camera’s manual.
The camera can be used with XQD memory cards. Cards with write speeds of 45 MB/s (300×) or better are recommended for movie recording; slower speeds may interrupt recording or cause jerky, uneven playback.
The camera supports SD, SDHC, and SDXC memory cards, including SDHC and SDXC cards compliant with UHS-I and UHS-II. Cards rated UHS Speed Class 3 or better are recommended for movie recording; using slower cards may result in recording being interrupted.
Step 2- Consider the use
The use you have in mind for your memory card is essential because it will help you determine:
- the appropriate storage capacity
- the right speed of the memory card
Ask yourself the following questions
- Do you have a full-frame or a cropped sensor camera?
- What are the Megapixels of your camera sensor?
- Are you shooting in Raw or JPEG4 ?
- What is the average size of each file?
- Are you shooting in single release or burst mode?
- Are you shooting professionally or as a hobby?
- Do you also make videos?
Your answers to these questions will help you determine which card meets your requirements.
Step 3- Verify Storage Capacity
In Table 2, you can see the SD card groupings and their maximum storage capacities, but this information doesn’t help you determine the storage capacity that you need. For instance, Nikon D850 is compatible with SD, SDHC, and SDXC cards. But what would be the right choice? A card with 32 GB, or a card with 2 TB storage capacity?
4) If you wish to know more about Raw and JPEG read my previous blog.
Table 2. Storage capacity of the common types of SD cards56.
|Type of SD card||Maximum Storage Capacity|
|SD (Secure Digital)||Up to 2 GB|
|SDHC (Secure Digital High Capacity)||Over 2 GB to 32 GB|
|SDXC (Secure Digital eXtended Capacity)||Over 32 GB to 2 TB|
|SDUC (Secure Digital Ultra Capacity)||Over 2 TB to 128 TB|
An experiment about storage capacity
Let’s take, for example, a single 64 GB (SDXC) memory card. If you insert this in a 45,7 MegaPixel (MP) full-frame Nikon D850 you can read on the camera’s display the average number of images you can save on this card (raw and jpeg). Now, let’s insert the same card into a 24 MP, cropped sensor Canon EOS M6, and repeat the experiment. You can see the results of this experiment in Table 3.
Table 3. The number of images (Raw or JPEG) you can save on a single 64 GB SD SanDisk7 card when shooting with a full frame vs. a cropped sensor camera.
|Camera||Sensor size /Megapixels||Average no of images in Raw||Average no of images in Best quality JPEG|
|Canon EOS M6||Cropped / 24 MP||1802||7267|
|Nikon D850||Full frame / 45,7 MP||633||1500|
This experiment makes it clear that the number of images you can save on a single memory card depends on factors such as
- the size of the sensor
- the megapixels
- the format of the image
- the scene you are photographing
If we consider shooting both photos and videos, then the numbers in Table 3 will of course change.
5) SDHC cards were introduced in 2006 and SDXC cards in 2009. Hence, most today’s cameras with a SD card slot will support these two types of cards.
6) In addition to their storage capacities that you will see immediately on the cards, there are other diﬀerences in the background. For instance, FAT 16, FAT32, FAT32 /exFAT, and exFAT are the file systems used in SD, SDHC, SDXC and SDUC cards, respectively.
7) On the website of card manufacturers you can find also tables indicating estimated number of images you can save on a distinct card.
Real-life case study
Let me give you an example from my own experience. When I go for a photo walk with a full-frame camera to take photos (in Raw) and make a few videos, two 64 GB cards are certainly enough. When I shoot at a wedding, I may take up to 2000 photographs (in Raw). So, much larger storage capacity is needed in this case.
Let’s continue with the wedding example. Saving 2000 images (in Raw) roughly takes 256 GB storage based on the data in Table 3. One option would be to buy a single card of 256 GB for all images. But would it be a wise choice? Although a single card of 256 GB would be sufficient, many professionals prefer to use more than one cards of smaller capacity. This is just a precautionary measure to be on the safe side in case something goes wrong. It is possible to lose a full memory card or experience card failure8. If you are using more than one cards, you will only lose a fraction of your work, and still have photographs left. Hence, shooting at a wedding, I would choose to save the images on memory cards with 16 to 32 GB storage capacity – smaller cards will require more frequent exchange with the risk of losing some beautiful moments.
If you were to do the same assignment with a cropped sensor camera, then this calculation would change dramatically. As you can see in Table 3, you can save up to 1802 Raw images on a 64 GB card if you shoot with a Canon EOS M6. In this case, you could spread your images over memory cards of 8 to 16 GB.
Step 4 – Check the speed of the memory card
Let’s explain the Write and Read speed of a memory card.
- Write speed (W) is the speed at which the images are transferred from your camera to your memory card.
- Read speed (R) is the speed at which the images are transferred from your memory card to your computer.
Now let’s see where we can find this information on a memory card and how this can help us. On most Sony memory cards, the theoretical9 maximum Read (R) and Write (W) Speeds are clearly depicted. In Figure 3, you can see that the speeds are R: 300 MB/s and W: 299 MB/s. In this case the Write speed is very close to the Read speed. However, in most cases the Write speed is not as high as the Read speed.
8) Now a day SD cards with larger capacities come with a software to retrieve lost datas.
Figure 3. Speed related information you may see on a memory card.
In Figure 3 you can see that the maximum Read speed for SanDisk is 150 MB/s while for Lexar it is 250 MB/s10. On the Lexar card there is also the number 1667X11 12 . This is just another way to state the maximum Read speed of 250 MB/s. Do you wonder why the card manufacturer depicts both numbers? Well, it is a marketing strategy to make sure no potential customer is lost.
9) In practice the Read and Write are slower than these numbers and are related also to the camera and card reader (or computer) you use.
10) When you see only one speed on a card, similar to SanDisk and Lexar cards in Figure 3, this is the maximum Read speed. You can find the write speed in the card’s manual.
11) This was related to CD-ROM drives. A standard drive read speed is 150 KB/s (or 0.15 MB/s) and this is considered as 1X. Hence, when you see this exhibition of speed, you can multiply it by 0.15 to obtain the speed in MB/s. So, 1667X multiply by 0.15 = 250 MB/s)
12) Although we won’t see an example in this article sometimes in your camera manual or elsewhere (in particular in relation to video recording) you may see another way of indicating the speed, which is Mb/s or Mbps. This stands for Mega bites per second. To convert Mbps to MB/s simply multiply it by 0.125. For instance 360 Mbps is equal to 45 MB/s (360 Mbps multiply by 0.125 = 45 MB/s). Hence, 1 MB/s is equal to 8 Mbps.
Which Write speed should I use then?
If you are shooting with a full-frame camera, in Raw format, with an average file size of 50 Megabytes (MB), and you are shooting in single release mode, then the Write speed of the card is not essential13. Since there is a time-lapse between taking photographs even the slowest card on the market will save the image before you photograph the next one.
What happens if I take action photos?
If you want to take action photos and you switch to burst mode, your camera will take more photos in a second. As an example, if you shoot with a speed of 5 fps (frames per second) then within 1 second you create 250 MB of data (5 images of 50 MB = 250 MB). This means that you need a card with a Write speed higher than 250 MB/s to ensure that you can keep shooting without interruptions (due to the time required for transferring your images to your memory card). Among the SD cards pictured in Figure 3, only the Sony card may offer the necessary Write speed. Keep in mind that the actual Write speed might be quite below the indicated 299 MB/s. In case the actual Write speed of the card does not allow you to shoot Raw images in burst mode uninterrupted, you may consider shooting in JPEG, or opt for a memory card of even higher speed.
Which Read speed should I use?
If the Write speed is not an issue for you – you use it for photography only – and you choose a memory card that is not fast then you better make yourself a cup of coffee and enjoy the time it takes for your images to get transferred into your computer. The process will be slow!
If you, on the other hand, choose a high-speed memory card, you need to make sure that your computer or card reader is compatible with this speed class. Otherwise, the read speed will be reduced to the speed class supported by your computer or card reader.
What if I want to record videos?
In case you want to record videos, your camera manufacturer gives you a clear description of the card(s) you need for best video quality as seen in Table 1. When filming, a certain number of frames per second are created, and consequently the memory card should have a certain minimum guaranteed Write speed14 that you can record videos without any issues. If the Write speed of the card is slow, then your camera may stop recording, and you may lose some frames. This is called ‘frame drop’ and it will become apparent to you as you playback your video.
There is an exponential improvement in video quality – you may not have yet a 4k device while 8Ks are coming – so the Write speed for videos is more and more critical. Moreover, there are many differences in speed among the various brands. This makes it even more difficult for the consumer to determine which card will surely provide the sustained Write speed that is required. This problem is addressed by introducing different speed classifications (Table 4) for SD cards15 which are:
The relevant speed class symbol is visible on the SD cards. In Table 4, you can notice some overlapping between the classifications. For instance, C10, U1, and V10 all indicate a minimum Write speed of 10 MB/s.
13) This example is valid for any other camera (full frame or cropped sensor) or file size and format.
14) you may read elsewhere: Minimum Sustained Write Speed, Minimum Sequential Write Speed and so on.
15) This issue is less critical for XQD cards. XQD cards are currently the fastest cards on the market and are using PCI Express interface, allowing them to provide exceptionally fast data transfer.
16) The UHS Bus speed (basically an electronic circuit allowing data transfer) interface contains 3 families; UHS-I, UHS-II, and UHS-III, which allows the bus speed interface to be increased from MB/s in UHS-I to up to 624 MB/s in USH-III. This increased speed is accompanied by some manufacturing changes. For instance on the rear side of a UHS-I, you see only one row of pins (gold-ish colour on the top), while the UHS-II and III has two rows of pins for faster Write and Read performance. UHS-I, II, and III are available for SDHC, SDXC and SDUC cards. There is also a futuristic SD express bus speed (available for SDHC, SDXC and SDUC cards) that would allow a data transfer speed up to 985 MB/s, and uses PCI Express interface.
17) Video Speed Class is introduced to answer a demand for high resolution and high quality 4K and 8K video recording and it also has an important feature to support next generation flash memory such as 3D NAND.
Table 4. Speed class and corresponding video format.
|Minimum Sequential Write Speed||Speed Class (it is indicated as a circle with a number inside)||UHS Speed Class (it is indicated with an U and 1 or 3 inside inside it)||Video Speed Class||Corresponding Video Format|
|2 MB/s||C2||SD video|
|4 MB/s||C4||HD video|
|6MB/s||C6||V6||Full HD video|
|10 MB/s||C10||U1||V10||Full HD video|
|30 MB/s||U3||V30||4K UHD video|
|60 MB/s||V60||8K+ Video|
|90 MB/s||V90||8K+ Video|
Be careful of marketing tactics
Looking back at Figure 3, you realise that on the card by Lexar, a slower speed class like C10 is marked on the card as well as the faster speed class of V60. Why is that? C10 guarantees a sustained Write speed of 10 MB/s, while V60 guarantees a speed of 60 MB/ s! Which one is correct? Both! This card provides a minimum Write speed of 60 MB/s, as well as a minimum write speed of 10 MB/s. So, why the manufacturers do this? Again, it’s a marketing strategy.
If you read in your camera’s manual that it supports C10 class, you expect to see it on the card before buying this more expensive card. Hence, the manufacturers provide this speed class on their cards next to a higher speed class to expand their market. Wise for the manufacturer, but not value for money for you. If you buy this card, you will not be able to benefit from the faster speed of 60 MB/s, since your camera doesn’t support it.
Where to buy? Which brand?
There are many brands to choose from, but unfortunately there are also a lot of counterfeit memory cards on the market. It is important to be careful! I would recommend buying your memory cards from your local camera store or a trusted webshop. Reputable manufacturers of memory cards are SanDisk, Toshiba, Panasonic, Sony, Lexar, Samsung, Kingston and Transcend.
If – like me – you intend to shoot mainly in Raw, use low speed burst mode, record videos occasionally, and also use your cards on assignments, then for a Nikon D850, the cards depicted in Figure 4 are excellent choices. These two cards are compatible with the camera, and they meet the specific criteria.
Figure 4. Compatible cards for Nikon D850, matching intended usage described above.
Your personal choice might be totally different based on your camera and your intended use. Whatever your photographic venture, make sure to follow these 4 Steps.
Step 1- Consider Compatibility
Step 2- Consider the use
Step 3- Verify Storage Capacity
Step 4- Verify the required speed
I hope this was helpful. Should you have any question please feel free to send me an email.
Triangle Photo Academy