Canon D7 - CF Memory Card

[essaytee]

I'm about to purchase a Canon D7. I have a question in relation to the CF memory card. Checking out various brand specs and I note that basically for a given gb storage the rated speed is the determining factor in price.

Given that the D7 specs indicate about 8 fps, obviously the faster rated memory cards the better. From what I can gather there are three speed rated cards, 30, 60 & 90 mb/sec. I'm looking at a 32 gb card but the price for the 90 mb/sec model is rather expensive but am not shying away from the price of the 60 mb/sec card.

So, is a 60 mb/sec CF memory card more than adequate for a D7? If my calculations are correct, shooting only JPEG images, each apprx 6.5 mb, equates to (60/6.5 = ) 9.2 fps (not that the D7 will achieve that).

Are there any other factors at play?

[etherial]

I assume you mean 7D rather than D7?

I have the 60mb/s Sandisk cards for mine and they work a treat, the card doesn't hold up the camera.

[Ray Heath]

G'day Steve

I thought internal buffer size was the detrmining factor for multiple shooting speed and quantity.

[essaytee]

Thanks for the replies. Yes, I meant 7D, what was I thinking?

[kevinj]

I use 30mbs in my 7D with no problems.

[Steve Axford]

It depends on the card and the camera. The rated speed refers to read speed, which is not really important in cameras where write speed is critical. Look up the references where they test the cameras and cards together to see which ones work the best. I think DPReview has some tests, but there are others.

[ricktas]

As others have said, the real write speed for 8fps shooting is entirely based upon the memory within the camera. When you take a photo, it is converted from an analog signal to a digital one in the chip on your sensor. That digital data is then forwarded to a buffer (memory) in your camera and from there is it written to the memory card. When shooting at 8fps, the limiting factor is the size of the memory buffer within the camera.

Where you will notice the difference with a faster card, is when you are copying the files to your computer. Also note that other factors come into play. Ie. USB/ Firewire speed when uploading.

[etherial]

But won't a slow card slow things down too? Once the buffer is full if the camera can't write the data to the card quickly enough things will slow down as you are then limited to the card write speed.

I haven't experienced this with my 7D but I certainly did on my 450D if I used a basic cheapo SD card rather than the Ultra 2 I had at the time.

[Steve Axford]

A slow card will slow things down as the speed of writing is based on the camera AND the card. If the card is fast enough it will have no effect, but if it is slow it will have an effect.

[Ray Heath]

But won't a slow card slow things down too? Once the buffer is full if the camera can't write the data to the card quickly enough things will slow down as you are then limited to the card write speed.

Yeh, but that won't affect the burst rate, it will only affect how fast the data is written to the card once the burst of exposures is finished.

Anyway were probably talking a difference in milliseconds which in practice will have little appreciable affect.

If you need to shoot a maximum burst as quickly as possible followed by another burst as quickly as possible I'd suggest your technique has other problems which you need to address.

[Steve Axford]

Ray, this is wrong. The card does effect how fast the camera will recover from a burst. If the card is slow, you will wait for a long time before you can shoot the next burst. If it is fast enough, you will wait for less time - and the difference could be tens of seconds, not milliseconds. It may be of little value to go for the very fastest card, but the very slowest will slow things down - noticeably.

[Clubmanmc]

The other factor is if you want to shoot video, but any card over 30mb/s will suffice...

I have allways used Sandisk cards, (been using them for the last 5 years)
and never had a bad write to one...

M

[essaytee]

Thanks everyone, good info.

What is the size of the buffer? I'm equating the buffer to being similar to computer RAM, which is very fast memory.

[Ray Heath]

Ray, this is wrong. The card does effect how fast the camera will recover from a burst. If the card is slow, you will wait for a long time before you can shoot the next burst. If it is fast enough, you will wait for less time - and the difference could be tens of seconds, not milliseconds. It may be of little value to go for the very fastest card, but the very slowest will slow things down - noticeably.

That is what I wrote Steve. The only point of difference is tens of seconds or milliseconds.

Regardless, you totally ignore my last statement.

[Steve Axford]

That is what I wrote Steve. The only point of difference is tens of seconds or milliseconds.

Regardless, you totally ignore my last statement.

To me, tens of seconds or milliseconds makes a huge difference. Your last statement doesn't make sense as many people want to shoot bursts on quick succession. I certainly do.

[Clubmanmc]

Thanks everyone, good info.

What is the size of the buffer? I'm equating the buffer to being similar to computer RAM, which is very fast memory.

the older Canon 1D models (my 1DII for example) used DDR RAM in them in 2004 and earlier, so i am sure its quite fast.... the buffer is about 350mb or so...

M

[MarkChap]

A slow card shouldn't affect the burst RATE, it will however affect the burst quantity.

A slower write speed will cause the buffer to fill and there fore you will get less shots in the buffer before it is once again full

[Ray Heath]

... many people want to shoot bursts on quick succession. I certainly do.

Why?

Seems to me if you need to shoot that many frames that quickly then your probably using the wrong technique and the wrong equipment. Why don't you just get a video camera?

And what of the other variables that will determine fps rate; shutter speed, image quality, focusing issues.

[MarkChap]

From the Canon web site

"Speed

Shooting Speed
8 fps / 90 shot max burst (JPEG), 15 (RAW)"

So if you are shooting JPEG you will be able to shoot for 11.25 seconds continuously before you fill the buffer, assuming the camera doesn't write a single file to the card.
In RAW you get 2 seconds before the buffer fills up, again assuming nothing is written to the card during that period.

My question is, how fast and for how long do you want/need to shoot continuously??

As for video, Canon, on page 149 of the manual advise that you need a card with a read/write speed of minimum 8 MB/s

[Steve Axford]

Why?

Seems to me if you need to shoot that many frames that quickly then your probably using the wrong technique and the wrong equipment. Why don't you just get a video camera?

And what of the other variables that will determine fps rate; shutter speed, image quality, focusing issues.

That's silly. If I wanted low res, blurred stills I would shoot video. If I shoot wildlife or sport, I want high burst speed and fast refresh time.