あなたのアイデアのためにこれをチェックしてください。このデモは効果を実装しています
http://www.craftymind.com/creating-the-loupe-or-magnifying-glass-effect-on-the-iphone/
メインコードはこんな感じ
- (void)drawRect:(CGRect)rect {
// here we're just doing some transforms on the view we're magnifying,
// and rendering that view directly into this view,
// rather than the previous method of copying an image.
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(context,1*(self.frame.size.width*0.5),1*(self.frame.size.height*0.5));
CGContextScaleCTM(context, 1.5, 1.5);
CGContextTranslateCTM(context,-1*(touchPoint.x),-1*(touchPoint.y));
[self.viewToMagnify.layer renderInContext:context];
}