We got this problem reported by some of iphone users as they were not happy with the feature that iphone does not allow to zoom in while taking a picture, as some of us know tap to activate the zoom slider while using the iphone camera has been removed in iOS 5. Now if you want to activate the zoom slider in iphone camera you will need to pinch with two fingers while doing the same.
As per previous settings on iphone camera, when ever you tap on screen you were required to tap on screen to activate zoom slide in camera, but the new changes in iphone camera app made it really difficult as using two fingers while capturing a photo can be difficult as you might holding it with one hand. This fix given below for this problem applies only if your iphone is jailbroken, ZoomIsBack tweak on cydia allows you to slide-to-zoom function, that was present in the iOS 4 Camera.app, before you upgraded to iOS 5 on your phone.
If you do, then you will be glad to know with the ZoomIsBack! Cydia tweak you can bring back this functionality while running the iOS 5 firmware.