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5D Mark III Firmware Update


I went to the Canon site to download the latest firmware for my Canon 5D Mark III, which is version 1.3.5. However, the instructions on the site tells you to verify the size, and no matter what I do or how many times I download the file, the size never matches. The site says the size should be 18.88 MB for EOS 5D Mark III Firmware Version 1.3.5 [Windows]. After downloading and extracting the file it is only 17.1 MB. How do I know if the downloaded file is any good before I apply it to my camera? I don't want to destroy my camera with a bad firmware file. If the file needs to match exactly, what should I do next?



What is the file size pior to exraction?  When I did my 5D mark IV the camera verified the file also, at least that is what I remembered.  Also could be the differance between 1024 and 1000 as 1 K.

Never mind about the differances in 1000K as would not make up for the 1.78K differance.  Sorry I haven't been much help.


I just downloaded the file. After extracting from the ZIP file the .fir file in the folder is 17,975,776 bytes, the same size given in the Canon download page.


2019-01-29 (1).png


Try downloading again.

John Hoffman
Conway, NH

1D X Mark III, M200, Many lenses, Pixma PRO-100, Pixma TR8620a, Lr Classic

Here is the link I went to and it says the size is 18.8 MB,, See the screen shot. I calculate 18.8 MB = 19,713,229, what am I missing?2019-01-29_Canon_5D_Mark_III_Download_Page.jpg

The size given there is the folder size. If you download that folder, unzip it and open it you will have the .fir file and a pdf for the instructions.

John Hoffman
Conway, NH

1D X Mark III, M200, Many lenses, Pixma PRO-100, Pixma TR8620a, Lr Classic

Okay, here's my confusion. In the pdf, 5d3-firmwareupdate-en, it says in "(2) Create the firmware update file" step 4; "4. The name and size of the firmware update file can be checked on the Web site." I cannot find anywhere on the web site confirming the firmware update file size of 17.1 MB.


Obviously, I was reading this wrong. It is actually refering to the download zip file size and not the extracted .fir file size (which I was interpreting as the 'firmware update file'). Okay, I'm going to upgrade the firmware in my 5D Mark III tonight, I'll let you know if it is still working in the morning 🙂


Are there any gotcha's I need to be aware of when upgrading the firmware on my camera?


jhoffman75 thanks for your help, patience and clearing this up for me.


CaliforniaDream, I should have read your post more closely, I think I would have figured this out, thanks for your help as well.

It is confusing. It's in the "Driver/Software Details" link:


2019-01-29 (2).png


Only gotchas are 1. be sure fully charged battery and 2. don't touch any controls on camera until its finished updating.

John Hoffman
Conway, NH

1D X Mark III, M200, Many lenses, Pixma PRO-100, Pixma TR8620a, Lr Classic

Ahh, I didn't notice that it said "Supporting Documents", thanks for pointing that out.



In Windows, at least, the size of a file (assuming the definition thereof to be the amount of space it takes up on the drive) can vary with the block size used by the file system. And that usually depends on the overall size of the drive. Larger drives tend to get a larger block size.


I still have that file (5D300135.FIR) on my server (a Dell GX620 running Windows 2003 Server), and I'm told that its size is 17,555 KB). It's been installed in my camera for more than a year, so I'm pretty sure it works.  Smiley Happy 

Philadelphia, Pennsylvania USA
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