How to set minimum & maximum y value?

If you are interested in making sure the view frame doesn't go over or under a certain y value you could do the following,

- (void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{

    CGFloat minY, maxY; //The position in your self.view you are interested in

    UITouch *touch = [[event allTouches] anyObject];

    if( [touch view] == camview)
    {
        CGPoint location = [touch locationInView:self.view];
        location.y = location.y - startY;
        location.y = MIN(location.y,maxY);   //Always <= maxY
        location.y = MAX(location.y,minY);   //Always >= minY
        location.x = startX;
        camview.center = location;
    }
}