File Size - Buffer Size - Write Speed

[dbaldock]

I've been looking at upgrading from a Nikon D90 to a Nikon D7000.

While looking at the D7000 Manual, I see on page 319 that the SanDisk Ultra SDXC 64 GB card is supported. Currently, the Ultra 64 GB is only available as a Class 4 (15 MB/sec) device. (The NOTES on the SanDisk site say, "Up to 15 MB/s read speed; write speed lower") The SanDisk Extreme Pro SDHC 32 GB is available as a UHS-1 (45 MB/sec Read & Write) device. And, while it's not listed in the Manual, Lexar has a Lexar Professional SDXC 64 GB Class 10 (20 MB/sec) device. (The NOTES on the Lexar site say, "Minimum 20MB/s read transfer, write speeds lower") Both of the 64 GB cards are approximately the same cost (~$110 - $115).

On page 320 of the Manual, it shows the file size for the different combinations of image quality, image size, bit depth, and compression type. It also shows the number of images that the camera's buffer will hold (between 10 and 100). For the NEF (RAW) images:
14-bit, Lossless Compression = 19.4 MB File = 10 Images in Buffer
14-bit, Lossy Compression = 16.7 MB File = 12 Images in Buffer
12-bit, Lossless Compression = 15.5 MB File = 11 Images in Buffer
12-bit, Lossy Compression = 13.6 MB File = 15 Images in Buffer

Only one of the four NEF (RAW) file sizes is less than 15 MB (12-Bit, Lossy Compression), which may allow it to be written from buffer to card in less than a second using the SanDisk card that's listed on page 319. Several of the NEF (RAW) file sizes may be small enough to write to the Lexar card in less than a second.

Due to the size of the buffer, and as long as I'm not planning to shoot NEF files at the maximum 5 or 6 fps, do I really need to worry about the difference between using 15, 20, 30, or 45 MB/sec cards in the camera? I understand that there will be differences when using them in an external card reader.

Thanks,
David Baldock

[soymilk]

I have a few sd cards I've been playing around with. The biggest difference in the cards is the time it takes to clear the buffer when you fill up the buffer. With my new sandisk uhs-1 the time is noticeably shorter than when I use a class 4 card.

In most cases I don't ever hit the buffer with the type of photography I normally do. But this past weekend when I took some action shots of shamu at seaworld, I did hit the buffer a few times. Luckily I had the uhs-1 card (45MBps) and the buffer cleared up pretty dang fast. I think the only time it really matters is if your plan on using the card for video. Some of the slower cards might not work for full hd 1080p video.

[Richard_B]

Nikon recommends class 6 (or better) cards for the D7k largely for reason of video recording. What is misleading is the very low performance standard for class 6 or 10 cards.

The buffer of the D7k is rather small and fills up in a hurry. Until it clears the frame rate plumets to less than 2 fps. I have used a variety of cards and the new Sandisk cards make a worthwhile improvement in my experience when shooting action things. If you do not shoot under such conditions most any card will do.

In answer to the question you did not ask, have you heard that the D400 is rumored to be released in the Aug-Sept time frame? It might be of interest to you. Even if it is not, a lot of D7ks should be coming on the market by people who are interested in the D400.

[dbaldock]

Thanks for the replies!

From my research over the last couple of days, it appears that several manufacturers (SanDisk, Panasonic, Kingston, TopRAM, Delkin) are now selling the UHS-1 type of SDHC or SDXC cards, up to 64 GB in size.

The best price I found on Google for the 32 GB cards is ~$110 (SanDisk), and for the 64 GB cards is ~$200 (TopRAM). The 32 GB cards do have a higher sustained write speed of 45 MB/sec vs. 35 MB/sec for the 64 GB cards.

Originally Posted by Richard_B

...

In answer to the question you did not ask, have you heard that the D400 is rumored to be released in the Aug-Sept time frame? It might be of interest to you. Even if it is not, a lot of D7ks should be coming on the market by people who are interested in the D400.

I hadn't heard anything about the D400. But looking at the rumors, they say it will have a 24 MPixel sensor, so I expect it will be another $2000+ camera. As a hobbyist photographer, that's a bit too expensive for me --- the D7000, at ~$1200 is just barely in my range.

Thanks again,
David Baldock

[soymilk]

i'm about to order some 30MB/ps sandisk cards. BH and adorama is having a decent sale on the cards at the moment.

I'm the type that doesn't like having all my eggs in one basket, so i opted for multiple 8 and 16gb cards. You also might wanna look into getting the cheapy but goodie transcend card off amazon. Its been working pretty good for me so far, i can tell the difference in upload between the uhs-1 sandisk vs the transcend. But not so much from actual use. Unless you tend to shoot off 8-9 14bit raw files off in rapid secession.

[mdurisseau]

Honestly, if you don't want to worry about the buffer, use CF cards. Like for like in terms of size, they're available in faster speeds. Just have to make sure your camera can use it. Ron Galbraith has a good comparison chart: Rob Galbraith DPI: CF/SD Performance Database

[dbaldock]

So far, the camera I have (Nikon D90) and the one I'm considering (Nikon D7000) both use SDHC (or SDXC) slots. I haven't actually looked at any that use CF slots - the Nikon ones are too expensive.

Take Care,
David Baldock

[soymilk]

The D7000 has 2 sd card slots. So you might want to consider 2 of the 32gb uhs-1 cards. But since you said you dont do much burst shooting, why get these cards at all? Why not save a bit of money?

I'm cheap, I usually have (2) 16gb cards in my d7000. Off the top of my head that gives about 450 shots per card. 900 is usually more than enough for me, since I usually keep spare cards or a laptop handy for unloading.

[dbaldock]

Well, after pricing the large, fast SDHC Cards, I'm seriously considering buying a Netbook PC that will fit in my camera bag (I believe the bag is a Pelican PCS-1522).

An ASUS Eee PC 1215B-PU17-BK 12.1-Inch Netbook is about $440, and has a 320G H/D in it, so I don't have to worry about buying enough Memory Cards to hold all of the photos I'd shoot during a trip to the UK.

I think 2 to 4 of the 32 GB cards will work just fine for a day's shooting, saving the images as NEF's using 14-Bit, Lossless Compression (~19 MB per image).

Take Care,
David Baldock