memory card speeds

[pwnage101]

Does the speed of a memory card really matter? I plan on getting the Nikon d80 which supposedly has a maximum write speed of 9.5 MB/s. I was looking into getting the a Sandisk extreme III SD card (class 6) with a max speed of 20mb/s. Will cards like these really help? Will I see much difference between a $10 US dollar class 2 card and the $30+ Sandisk extreme III ?

[Colin Southern]

As a brand, Sandisk is one of the few that I trust. As I understand it, the "class" designations refer to the card's write speed, in mb/s - but the catch is (and I've been bitten by this) ... since class 6 is the highest official class, both a 6mb/s "no name" and a 20 mb/s Sandisk are both class 6, but one is a lot faster than the other. As for a class 2, I'd probably give it a miss personally, since it would take 10 to 15 seconds to write a single image from my camera (note: mega-BITS per second, not mega-BYTES per second).

[Bill44]

Actually Colin the classes refer to the "Minimum" write speed. The Sandisk Extreme 30Mb/s Cards (Used to be called ExtremeIII 30Mb/s) are an unofficial class 10 card.

[Colin Southern]

Hi Bill,

I just checked Sandisk's website ... looks like class 10 might be official now. For what it's worth, I have a class 6 A-Data and a class 6 32GB Sandisk SD Card - the first takes about 5 sec per image (compared to around 1 sec per image on my CF card), and my 32GB Sandisk card is around twice as fast as the A-Data.

[Shadowman]

Troy,

I'm might not sure that speed really matters unless you want to transfer within a time deadline (publication) or you have limited power on your hardware such as a laptop.

Does the speed of a memory card really matter? I plan on getting the Nikon d80 which supposedly has a maximum write speed of 9.5 MB/s. I was looking into getting the a Sandisk extreme III SD card (class 6) with a max speed of 20mb/s. Will cards like these really help? Will I see much difference between a $10 US dollar class 2 card and the $30+ Sandisk extreme III ?

[Blazing fire]

I agree with Shadowman.

Write speeds aren't that important because your camera has a buffer which acts like a RAM. It stores the captured pictures temporarily before writing into the memory card. How many photos the buffer can store depends on the type of camera, and quality of picture (compression ratio, RAW and/or JPEG, ISO etc.). A Nikon D700 for instance, can store about 17 14bit lossless compressed RAW files in the buffer.

Some regard read speeds to be slightly more important than write speeds, because it affects how long the photos take to be donwloaded. A slow memory card coupled with a slow card reader can be so excruciatingly slow that you may resort to downloading the entire card, then view the photos from the HDD. Having a fast card and fast reader could therefore speed up the workflow and increase efficiency by using a shorter, more direct method of viewing photos straight from the card. This is not that important because you can make coffee while waiting for the pictures to be copied to the HDD.

So the wite and read speeds of a memory card isn't that important unless time is of essence, or you need to take photos continuously. Bear in mind that even sports/action photographers rarely require long burst of shots. You would however, benefit greatly from the extra speed if you're downloading pictures onto a laptop that is running on battery power. Imagine the agony of watching the battery slowly draining away while a cards takes 45minutes to transfer files.

[Colin Southern]

Write speeds aren't that important because your camera has a buffer which acts like a RAM.

I agree - although - it depends on what you're shooting. When shooting RAW (25mb per shot) my 1Ds3 is limited to 12 shots and it can only write about 1 image per second to the CF card - so if I'm shooting sports and I want to a 4 or 5 second burst of action at 5 fps, I can't do it (I have to slow the camera down to around 3fps).

In terms of reading files - personally - I just chuck the card in the card reader - crank up the DNG converter - and let it copy the images to my HDD converting and renaming them as it goes. There's ALWAYS something else I can do with that time (check my gear over - go have a shower - go have a meal - go watch a TV program I've recorded - go check CiC )

[Blazing fire]

Ah yes, that's somthing I've missed out!

I like to use this water tank analogy to illustrate why FPS and memory card affects the number of shots taken. The size of the buffer is represented by a water tank. Beneth it is a tap (write speeds). Above it is an opening to allow water to enter. This water similar to the data to be writen.

A high FPS means more water is being poured into the tank, and it would fill it up faster in a shorter period of time.
A fast card means more water can be drained out faster per unit time. A fast memory card can therefore indirectly increase the number of shots you can take in a burst.
A large tank means it can contain more water.

So besides the size of buffer and image size, FPS plays a part in determining how many shots can be taken before the buffer is full.

[pwnage101]

If that is so, blazing fire, how are the "number of shots" definitively measured if they are subject to a changing variable: memory card speed? Perhaps they are not definitive?

[Shadowman]

The camera manufacturer designates the shooting speed at full resolution and the camera should perform at a faster rate when in continuous mode. How fast they are recorded onto the memory card should be designated by the card manufacturer. As stated earlier RAW records more information therefore at a slower speed.

If that is so, blazing fire, how are the "number of shots" definitively measured if they are subject to a changing variable: memory card speed? Perhaps they are not definitive?

[pwnage101]

so when I read 6 raw frames in a Nikon d80 dpreview, that can change with a faster/slower card?

[Blazing fire]

If that is so, blazing fire, how are the "number of shots" definitively measured if they are subject to a changing variable: memory card speed? Perhaps they are not definitive?

I'm not exactly sure, for I don't work in such an industry, but it's logical to assume that they take the memory size of the buffer and divide it by the average size of a photo. In other words, they do not factor in the rate at which data is written into the card.

so when I read 6 raw frames in a Nikon d80 dpreview, that can change with a faster/slower card?

Maybe, maybe not. Depends whether it is the official specs, in which case it should almost always be higher in reality, >6. If you take the data from their "performance" section, it would most likely represent the number of shots per buffer in acutal situations.

In the case of a d700, the actual number of shots taken with a slow card is 17. A fast card increases this value by 2. Refer to the water tank analogy for the explaination.

http://www.dpreview.com/reviews/nikond700/page13.asp

 
 
Burst of RAW images (12-bit NEF)

Timing
Time, secs
(4GB SanDisk Ducati) 
Time, secs
(2 GB Lexar 133x)Frame rate 5.0 fps 5.0 fpsNumber of frames 1917Buffer full rate 2.2 fps1.1fpsNext burst11.0 secs21.0 secs

[Shadowman]

That was a very detailed comparison of all the factors (media, camera mode, image transfer, USB transfer speed, and card reader) that can affect the workflow.

[Blazing fire]

There is 1 more thing that I've missed out... again; That is the write speeds of the camera. You can have an extremely fast card, like a pretec CF 666x but if the camera does not support those speeds, due to different data timing modes, then there is no point buying a fast card for the sole reason of having faster write speeds. There are mainly 2 types of modes, PIO (Programmed Input/Output) and UDMA (Ultra Direct Memory Access). The latter is faster and has many different modes.

Thanks shadowman! You flatter me greatly . It's gratifying to have one's effort recognized.

[Colin Southern]

For what it's worth, I did a back to back test using a Canon 1D3 (fastest camera around a few years ago) between a Sandisk Extreme III and an Extreme IV - in a nutshell, no practical difference (ie the limitation was in the camera, not the card). Why was this important? ... well, a 16GB Extreme III was about the same price as a 8GB Extreme IV; so in terms of price / capacity / performance, I made a bad choice

[Shadowman]

I think this string of discussions is very useful because it highlighted many of the advertised specifications that manufacturers use to market their products and the discussion broke down any discrepancies, presented factual accuracies, and provided potential consumers with additional parameters to use when selecting a camera or accessory. Well worth the time invested.

There is 1 more thing that I've missed out... again; That is the write speeds of the camera. You can have an extremely fast card, like a pretec CF 666x but if the camera does not support those speeds, due to different data timing modes, then there is no point buying a fast card for the sole reason of having faster write speeds. There are mainly 2 types of modes, PIO (Programmed Input/Output) and UDMA (Ultra Direct Memory Access). The latter is faster and has many different modes.

Thanks shadowman! You flatter me greatly . It's gratifying to have one's effort recognized.

[Dave Humphries]

~ a 16GB Extreme III was about the same price as a 8MB Extreme IV;

Colin,

Those Extreme IV's were very small (and expensive) when they first came out

That's still 3-1 to you I think , but I'm glad to see you're following in my footsteps and giving me a chance to even the score

Cheers,

[Colin Southern]

I'm glad to see you're following in my footsteps and giving me a chance to even the score

Well ... actually ... I have both an Extreme IV AND an Extreme III in my camera at the same time (it switches automatically to the "slower" card if the first one fills up)

[Dave Humphries]

Well ... actually ... I have both an Extreme IV AND an Extreme III in my camera at the same time (it switches automatically to the "slower" card if the first one fills up)

Which, at 8 megabits, I guess it will quite soon

[Colin Southern]

Which, at 8 megabits, I guess it will quite soon

Luckily it's 8GB*

* E&OE!