You didn't tell exactly which iPad so here's the usual link:
http://smallbusiness.chron.com/wipe-ipad-factory-settings-passcode-55572.html
While using my iPad Mini (OS7?) as camera a fault appeared where the screen image suddenly showed only the large time numerals. Eventually I got a very large passcode panel but no keypad. (The two small icons for "do not disturb" and "location service", were visible beside the battery indicator.)
Eventually the keyboard appeared after much screen massage, but was too large and too unstable to use. Pinching the screen had no effect. By juggling it was possible to get passcode in but on opening any app there was a momentary correct size image which immediately enlarged and was unresponsive.
In an effort to turn the iPad off I could not get the necessary slider to appear.
I'd be very grateful for any suggestions.

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