5d3 4k raw with sd card only when SD hack activated ?

[hamanohashidate]

Hello,

Does someone know if it's possible to record RAW with the preset 'UHD'  or '3.5k' or 3k with Danne's crop magic lantern build (feb 23) ONLY with SD CARD (no spanning or CF inserted) on a canon 5d Mark III ?
I can record only 1s with a Sandisk extreme pro v30 u3 200MB/s class 10
Note that this card works great and has been also tested on my EOSM.

I read that SD card bus is only around 20MB/s on the 5D3...but I guest this is before to apply the SD hack?

I applied the SD overclock 240 Mhz hack in magic lantern so it should be able to record in UHD is'nt ?

Or even with the hack the sd card bus will stay at 20 MB/s ==>so I must use CF ? and so why to implement this hack ?
I would like to understand.


thank you for your feedback

[Walter Schulz]

It is all about bandwidth.If required bandwidth exceeds write performance recording will stop because of buffer overflow.

- Without SD overclocking SDcard will do just about 20 MByte/s
- With overclocking and compatible SDcard and proper settings you should get 90+ MByte/s in benchmark and around 80 MByte/s in recording.
- Using both card slots and fast cards cam is able to do 145 MByte/s continuously. This seems to be a hardware limit.

Now do the math.

Required bandwidth (in Byte/s) = horizontal pixel x vertical pixels x frame rate x bit depth x compression factor / 8
Compression factor is not a constant and varies with scene/exposure. For very rough calculation use 0.5.

BTW: Sandisk Extreme Pro 200 MByte/s comes in different varieties.
256 GB and up: R200/W140
64 and 128 GB: R200/W90

Lower capacity comes with slighty less performance when overclocked.

[hamanohashidate]

"
- Without SD overclocking SDcard will do just about 20 MByte/s
- With overclocking and compatible SDcard and proper settings you should get 90+ MByte/s in benchmark and around 80 MByte/s in recording.
- Using both card slots and fast cards cam is able to do 145 MByte/s continuously. This seems to be a hardware limit.
"

Thank you for these info! It was not clear for me as sometime people just said the SD card is slow without given details ...
Looks like the bus speed is the same as my EOSM.
So you confirm me it's technically possible but just go below 80 MByte/s so maybe I can manage with the bit deph and also the aspect ratio (to reduce data in the black space...) , frame rate...

For the math I got some approx bandwith in Magic Lantern when I choose the preset / dimension.
I did not realize that the 3k or UHD preset in standard(24frps / 10 bits) request more than this 80 MBytes/s !

I will think probably to buy a CF ... but temporaly I can try it and I will just respect this 80 MBytes /s limit.

For info my SDCard is the 64GB ... did'nt know that the difference for the Wspeed was so big compare to the 256GB and up !

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