Yes, I know you won't get the speed. But, if you didn't have an XQD card or didn't want to start in a new format will the SD card work in the slot ?  If is does work, are their any downside to using it ?

Thanks.

No.  You cannot put an SD card in an XQD slot.  They are completely two different card and slot sizes.  It's kinda like sticking a cassette tape in an 8-track tape slot.  Yes.  I'm old.

Ahh, Saturday morning cartoons...  I giant bowl of sugar masquerading as cereal and H.R. Pufnstuf!  That was the life!

No!!!

Obviously you are asking about adapters. XQD cards are overall physically larger than SD cards, but they are nearly the same length. I'm not sure it would be physically/electronically possible to build such an adapter. And given the performance benefits of XQD over SD I don't know if there is enough demand to make such an adapter economically feasible. As/if/when the XQD user base grows such a beast might pop up on eBay via a 3rd party vendor.

I'm fairly sure that you could get an SD card into an XQD slot. It wouldn't work, and you might never get it out again, but I am fairly sure it could be forced into place...