There are lots of emails asking the same question: “When will you publish an iPhone or iPad version of Sofortbild?”
Short answer: This is technically impossible without dedicated custom hardware.
Slightly more elaborate answer: In order to get admitted to the iOS App Store, apps written for iPhone/iPad need to adhere to the official SDK published by Apple. Using this SDK, it is not possible to directly communicate from iOS to a camera in the way needed. There are two workarounds: 1) The USB library of iOS could be ‘hacked’ to perform as needed. Given the disclaimer outlined above, such an app would never be allowed on the App Store and therefore nobody could get it. End of story. 2) One could create a piece of hardware that mediates between iOS and the camera. Creating custom hardware is not something a small independent developer can do.
Fortunately, hardware solutions exist on the market, e.g. The CamRanger. We have no affiliation or experience with this product. Feel free to check it out.
There have been a lot of requests for a Windows version of Sofortbild. There is something that might be interesting for you: Bernd Peretzke has written a similiar application for Windows XP and Vista called DCamCapture. Bernd is using the Nikon SDK as well, his application has a similar feature set and it is also free.