# Two card slots?



## Ozarker (Jun 28, 2015)

In the next week or so I'll be ordering a 5D Mark III. The prices as of late are fantastic. My question has to do with the dual card slots. Are there two slots in case of card failure? Does a CF card do a better job with photos than an SD card? I notice that some of the CF cards are hundreds of dollars. There must be good reason, right? Honestly, I do not know. Maybe the write speeds, size, etc. Hoping someone can educate me. Thanks!


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## Don Haines (Jun 28, 2015)

CanonFanBoy said:


> In the next week or so I'll be ordering a 5D Mark III. The prices as of late are fantastic. My question has to do with the dual card slots. Are there two slots in case of card failure? Does a CF card do a better job with photos than an SD card? I notice that some of the CF cards are hundreds of dollars. There must be good reason, right? Honestly, I do not know. Maybe the write speeds, size, etc. Hoping someone can educate me. Thanks!



It's mostly for redundancy. Card failures are rare, but if you are getting paid for the job and you loose the day's images that's a blow to your reputation and you also don't get paid.... It's hard to get brides to re-enact the wedding.... sports teams to re-play the game... Nasa to re-launch that rocket...


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## Ozarker (Jun 28, 2015)

Don Haines said:


> CanonFanBoy said:
> 
> 
> > In the next week or so I'll be ordering a 5D Mark III. The prices as of late are fantastic. My question has to do with the dual card slots. Are there two slots in case of card failure? Does a CF card do a better job with photos than an SD card? I notice that some of the CF cards are hundreds of dollars. There must be good reason, right? Honestly, I do not know. Maybe the write speeds, size, etc. Hoping someone can educate me. Thanks!
> ...



Makes perfect sense. Thanks Don. Is there a reason to use the CF slot over the SD slot?


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## Don Haines (Jun 28, 2015)

CanonFanBoy said:


> Don Haines said:
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> 
> > CanonFanBoy said:
> ...


It really depends on the cards you have... The fastest CF cards are faster than the fastest SD cards, but the SD cards cost considerably less. Realistically, unless you put the camera into burst mode and hold the shutter down for several seconds it really does not matter if you have fast cards or if you have the fastest cards.

My CF card is a Lexar 800X speed. You have to be careful with Lexar because they only tell you the read speed... That 800X card has a read speed of 120MB/sec but the read <edit> _write_ speed tops out at 75MB/sec. Their 1066X cards are bit more balanced at 160MB/sec read and 155MB/sec write. The write speed is the important number as that is what determines how fast you write to the card. They also have a 1000X card, but the write speed on it is about 90MB/s.... not really that much better than the 800X cards.... if you need speed, go for the 1066X and leave the 1000X cards alone. The Sandisk cards are a bit more honest and they tell you the read and write speeds. Both are roughly comparable in price... 

My SD card is a Sandisk Extreme Pro card.... it has a speed of 95MB/sec read and 90MB/sec write.... it is faster than my CF card..... That's about as fast as SD cards come. I really don't recommend going with the slower cards (less than 45MB/S write speeds) or bursts will take forever to clear. Beware the posted speeds with cards... everyone seems to only report the read speeds.. with the exception of Sandisk...

Remember, it is write speed that is important and you are only as fast as your slowest card....

Cards like that should do you for all but the most insanely demanding occasions.


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## Ozarker (Jun 29, 2015)

Don Haines said:


> CanonFanBoy said:
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> > Don Haines said:
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Thank you for such a good explanation Don. My SD cards keep up well with bursts on my 70D so should do fine with the slower 5D MK III. I'm no pro, just a guy that likes camera gear and taking pictures, learning for now. Just using the one slot should do me fine. It will be interesting to see the difference in IQ between the 70D and the 5D MK III and I think the two cameras will work for me for a long time. I'd really like to have a 1DX rather than the 5D MK III, but just don't know whether I could raise that kind of cash. Still need a Canon EF 24-70 f/2.8L II. Sold all my EFS lenses (Except for my STM lens) because the 70D will be strictly for birds and such. 

Again, thank you very much for your help.


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## neuroanatomist (Jun 29, 2015)

Don Haines said:


> My SD card is a Sandisk Extreme Pro card.... it has a speed of 95MB/sec read and 90MB/sec write.... it is faster than my CF card..... That's about as fast as SD cards come. I really don't recommend going with the slower cards (less than 45MB/S write speeds) or bursts will take forever to clear. Beware the posted speeds with cards... everyone seems to only report the read speeds.. with the exception of Sandisk...
> 
> Remember, it is write speed that is important and you are only as fast as your slowest card...



Or your slowest card slot. If only the 5DIII's SD slot supported those high speed cards. Alas, it does not.


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## Mt Spokane Photography (Jun 29, 2015)

I typically write raw to the faster CF slot, and jpeg to the SD card. I often use a eye-fi card for unimportant photos or temporary ones, and they are on my device (Phone, tablet, or computer) when I finish taking photos. In the event that I want to develop a higher quality image, I have the raws on the CF card. The SD also acts as a backup.

There is no right or wrong way to use the two slots. You can use them to expand memory capacity by filling one, then switching to the other, its done automatically.

Just be aware that the SD slot is slow, and can drag the CF speeds down when writing to both cards.


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## Don Haines (Jun 29, 2015)

neuroanatomist said:


> Don Haines said:
> 
> 
> > My SD card is a Sandisk Extreme Pro card.... it has a speed of 95MB/sec read and 90MB/sec write.... it is faster than my CF card..... That's about as fast as SD cards come. I really don't recommend going with the slower cards (less than 45MB/S write speeds) or bursts will take forever to clear. Beware the posted speeds with cards... everyone seems to only report the read speeds.. with the exception of Sandisk...
> ...


good point!

Also, if you are shooting RAW and jpg, yow can save one to CF and the other to SD and it should clear the buffer quicker


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## dolina (Jun 29, 2015)

CF cards are superior in write/read speeds vs SD UHS-I.

The inclusion of the SD slot can be attributed to the following reasons

- EyeFi WiFi card size is SD
- popularity of SD cards
-- today 3 out of all EOS bodies have CF slots
-- today 3 out of all Nikon bodies have CF slots
-- There was a time that CF cards could be found on Rebels like the 300D


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## Ozarker (Jun 29, 2015)

Thank all of you very much. I appreciate your help. Have not shot much in the last six months due to recovery from rotator cuff surgery and a torn Achilles tendon. For about four months I couldn't even raise my hand to the shutter button on my camera.

Respect all of you very much. Thanks again for the help.


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## rpt (Jun 29, 2015)

I use the SD slot for MagicLantern.


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## Mt Spokane Photography (Jun 29, 2015)

dolina said:


> CF cards are superior in write/read speeds vs SD UHS-I.
> 
> The inclusion of the SD slot can be attributed to the following reasons
> 
> ...



And before that, even entry level cameras had CF slots. My old Nikon CP990 has CF and so does my Canon S3IS. Then, I've also had cameras with PCMIA with a hard drive inside, Smart media, MMC, memory stick, etc. I still have some of each just in case I find a ancient camera that I want to buy and play with.


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## dolina (Jun 29, 2015)

My PowerShot A40 from 2002 had CF slots. First Canon digital camera I ever used. Before that it was a Kodak DC20 from 1996.


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## Valvebounce (Jun 29, 2015)

Hi Don. 
I see you listed them in order of difficulty, hardest to easiest! 
Let's face it NASA will be launching another one shortly, but it may not be as spectacular! ;D
In all seriousness, I hope the next one goes without a hitch, the costs must be horrendous, and people are depending on one getting there! 

Cheers, Graham. 



Don Haines said:


> It's hard to get brides to re-enact the wedding.... sports teams to re-play the game... Nasa to re-launch that rocket...


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