How to downgrade to ios 8 using ios 9 backup

Sorry for posting here, sort of new to be apple discussions.

Thanks for letting me know

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So I recently updated my phone to IOS 9, everything was pretty good until my action camera app couldn't work with my phone because of IOS 9. I know this because I tried it on my friends Iphone and it worked fine.

Now I would like to downgrade my phone back to IOS 8, I know you click Restore iPhone then use a backup but the problem is it won't be able to use the IOS 9 backup.

Is there anyway to downgrade my phone to an IOS 8 version using a IOS 9 backup of the phone?

Thanks, Enoc