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Write Speeds – Cameras and Cards

This guide is about the write speeds of cameras and the read speed of cards. You don’t want to pay more for a card than the camera can handle. Equally, you don’t want to slow down the camera by having a slow card. Slow cards slow you down if you are shooting wildlife or portraits in continuous shooting mode.

You press the shutter and take the shot. In that 1/500th of a second, or whatever the shutter speed is, a lot happens. The light hits the sensor, which is made up of millions of micro lenses pasted onto a sensor the size of your thumbnail.

Each of the millions of micro lenses in the sensor reacts to the wavelength of the light falling on it and the amount of light falling on it. The information from all the micro lenses is combined and processed by the processor. Then the information is sent to the card.

The Lens and the Processor

The quality of the information sent to the card comes from two things – the lens and the processor.

Every lens draws the subject differently. This is quite separate from the distance of the lens to the subject or the focal length of the lens. There may be only three pieces of glass that make up the lens, but that’s unlikely with modern lenses. Modern lenses might have ten or twelve individual pieces of glass in them.

The way the lens draws the subject depends on the curvature of the pieces of glass in the lens, the quality of the polishing of the individual pieces of glass, the quality of the coating, and the accuracy of the placement of the different pieces of glass in the lens.

Then there’s the processor. Every camera manufacturer has its own skill in processing the image after the light hits the sensor. I like Fuji colours and Olympus colours. I also like Nikon with a neutral profile. I don’t know Canon, so I can’t comment.

The Humble Card

So all this magic has been done and then the information gets sent to the humble card. Having zapped its way through all that glass and circuitry, the information has to write to the card.

Each camera has a maximum speed at which it is able to transmit information to the card. That’s its maximum write speed, or readout speed.

The speed is important because the camera has to clear the decks to make way for the information coming from the next shot.

Different cards, different speeds

Different cards have different read speeds. You see that information written on the card. And generally, the faster the read speed, the more expensive the card.

Of course, none of this matters if you are the kind of shooter who photographs slowly and methodically with a several second gap between each shot you take. But if you are shooting wildlife or anything fast moving, and you want to get off as many frames as possible in a short high-speed burst, then the speed of the camera matters and the speed of the card matters.

And you absolutely want a card that can read as fast as your camera can write. On the other hand, there is no sense in buying a card that can read faster than your camera can write to the card. That’s just throwing money away.

Or maybe you do want a card that’s faster than your camera can send information to it: After all, cards last a long time and they can outlast your camera. And the next camera you buy will probably have a faster write speed.

If I were to shoot video, I might want a 300MB/s, 512GB card, but that’s very fast, and I don’t need that speed or capacity and I don’t like to put all my eggs in one basket. I would rather spread the risk over a number of cards.

The Goldilocks card

On the other hand I wouldn’t want to be changing cards all the time. So for me, a good compromise would be a 32GB or 64GB card. Now the question is, what read speed?

The slowest of the Extreme Pro Sandisk card reads at 95MB/second. I know my Fuji X-T2 can write to the card twice as fast as that, so I wouldn’t choose a 95MB/second card if I wanted to be able to shoot high speed bursts for wildlife photography.

If I were a slow shooter then the price would attract me – £13.44 for the 32GB card on Amazon UK at the time of writing.

But I would have to ask myself why I would hamstring myself when the the step up to a fast read speed for a 64GB card is not even twice the price for twice the capacity.

I think the sweet spot is the SanDisk Extreme PRO 64GB card (Amazon affiliate link). It reads at 170MB/s, and it’s £23.99 on Amazon UK at the time of writing.

Nikon Cameras

Sandisk Extreme Pro 300MB/second UHS-II SD card

For wildlife shooting, the D7500 and the D500 are probably the cameras that most people will gravitate towards unless they are professional photographers.

The Nikon D7500 is UHS-I, which means the maximum speed it can write to a card (its BUS speed) is 104MB/second – so there is no point in getting a faster card and a 95MB/second card will be adequate.

On the other hand, the D500 supports UHS-II so it can write to a card at nearly 300MB/second such as this SanDisk Extreme Pro 300MB/s 64GB card (Amazon affiliate link). And it can use the new XQD cards, and supports the latest XQD 2.0 specification.

The only between SDHC and SDXC cards is their maximum capacity.

SDHC is an abbreviation for Secure Digital High Capacity, which is for cards up to a maximum of 32GB. SDXC is an abbreviation for Secure Digital eXtended Capacity, for cards of 64GB and over.

So what to do? Go for a 64GB card, or split the risk over two 32GB cards? What would a statistician say? Is there twice the risk of failure with two cards?

Here’s the 32GB card. And now that I have made my own decision and bought a D500, I have to decide whether to go for one bigger card or two smaller cards. The fact is that I don’t even know how big a card I need for the kind of shooting I plan to be doing on a specific trip my wife and I have lined up. More about that in a little while.

For the moment though, here is what I weighed up in my mind when deciding between the D500 and the D7500.

Of course, price is the first difference. If they were the same price I would opt for the D500 in a heartbeat. It’s got a faster frame rate, two card slots, better autofocus and buffer size.

The differences in the frame rates between the D7500 and the D500 is 8fps versus 10fps. I think that is significant for that once in a lifetime moment. In one second you have two more frames of information to pore over on the computer and choose.

If you read around the Web, you will hear the D7500 slammed because it only has one card slot.

The controversy reminds me of something a commentator mentioned. He was on a flight, and the captain announced that they were trialing WiFi in the cabin during the flight. After a short while, the WiFi failed, and the man sitting next to the commentator complained aloud.

The commentator’s observation was that ten seconds earlier, the man didn’t know the feature existed, and now he was complaining about the service.

I think it is a bit like that with the single card slot in the D7500. I have only ever had one card fail on me. But… now that the ear worm has had its fifteen minutes of fame, it’s hard not to worry about the lack of an extra card for those once-in-a-lifetime opportunities. And the second card slot for the D500 is XQD, which is said to be super reliable. So I plan to use it as a backup – and it will probably be a 64GB card.

How to recognise a UHS-II Card

reverse of a UHS-II card showing second row of pins

UHS-II cards have a second row of contacts below the first row of contacts on UHS-I SD cards. The first row of contacts allow legacy support up to UHS-I speed in cameras without UHS-II pins.

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