Canon EOS 40D CompactFlash Memory Card Compatibility

The Canon EOS 40D uses Compact Flash memory cards. 128GB is the largest card memory size that can be used.

A card over 128GB will not be recognized or the EOS 40D will display an error. The camera will not work.

Compact Flash cards are more expensive than SD cards. If you already have an SD card that is 128GB or smaller, you can use a SD to CF card adapter.

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SanDisk Extreme 64GB CompactFlash Card

• Write speeds of up to 85 MB/s for faster shot-to-shot performance.
• Transfer speeds of up to 120 MB/s for increased efficiency.
• Video Performance (VPG-20) for Full HD video recording.
• RTV silicone coating protects card from shock and vibration.

Lexar Professional CF Card 64GB

• High speed performance—leverages UDMA 7 technology to deliver a read speed up to 1066x (160MB/s).
• Supports the VPG-65 specification for professional-quality video.
• Captures high-quality images and extended lengths of stunning 1080p Full-HD, 3D, and 4K video.
• High-speed file transfer to dramatically accelerate workflow.

SanDisk Extreme Pro CF 128GB

• Records and captures cinema quality 4K and Full HD video.
• Transfer speed of up to 160MB/s (1067X) read speeds.
• Industry leading shot speed performance of up to 150MB/s (1000X) write speeds.
• Designed for professional photographers and videographers

Card Reader

The UGREEN 4-in-1 card reader is what I use with my CF cards.

The UGREEN reader is USB 3.0 compatible. Transfer speeds over USB 3.0 will be quicker than the Canon EOS 40D.

The card reader can read these memory card types:

• CompactFlash Cards
• SD, SDHC, and SDXC Cards
• Memory Stick (MS), MS Pro, MS PRO-HG, and MS XC DUO
• MicroSD, Micro SDHC, and Micro SDXC Cards

SD to CF Card Adapter

These adapters work great. They aree limited to a maximum continuous write speed of ~20MB/s.

I have been happy with the two I own. CompactFlash cards are multiple times more expensive than SD cards.

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Compact Flash Card Type I vs II

CF Memory cards come in two physical sizes, Type I or Type II.

They have the same width and length. The only difference is how thick they are.

• Type I - 3.3mm thick
• Type II - 5mm thick

The Type II spec was for Microdrives. They were a small mechanical hard drives.

That’s how new Compact Flash was when the Nikon 40D was released. People used tiny mechanical devices that were prone to failure because of how badly they wanted 1GB of storage.

Avoiding Card Read Errors

One of the most common problems with cameras that use CF memory cards are bent card slot pins. If a pin is bent, you might see a ‘unable to use card’ error message.

To avoid bent pins, don’t force a Compact Flash memory card into the Canon EOS 40D. The extra space for a Type II card allows a CF card to be out of alignment.

If the CF card will not effortlessly slide into the slot, take it out and check the alignment of the memory card. Also, check to see if the memory card is damaged.

If everything looks good, carefully align the CF card and try again.