Digital Negative's capture interface has a live histogram and allows for manual focusing.

Digital Negative for iOS is the latest app aiming to appeal to more serious photographers by claiming it works "like the negatives from a film camera" by saving and editing images as DNG files.

In the app description in iTunes, the Digital Negative team explains its methodology: 

Digital Negative is the first app that captures uncompressed images that retain all of the information recorded by the camera sensor. These Digital Negative (DNG) pictures are much like the negatives from a film camera, and the serious photographer can use standard raw editing programs or Digital Negative’s built-in raw editing tools to develop the photograph and display all of the features in the image.

If you're a little suspicious, you should be. True RAW is the output from the sensor’s pixels, prior to demosaicing, white balance or gamma correction (i.e. tone curve application). Digital Negative outputs DNG files with a TIF extension that are 28.5MB each. They show up as compressed 48-bit files (16-bit each channel for RGB), so have been demosaiced at least, and probably white-balanced and gamma corrected too.

Digital Negative is not the first app that claims to offer this type of super high-quality file output from a smartphone. We debunked 645 Pro's raw TIFF option last year with a side-by-side comparison of the giant TIFF file and the compressed JPEG. Even though the TIFF files were bigger, their overall image quality was not discernibly better than the maximum-quality JPEG output. KitCam also added similar functionality in an update last week, and Pure Shot, by the same makers of 645 Pro, also boasts "dRAW TIFF output."

We spent some time playing with Digital Negative and its output and could not get Adobe Camera Raw to interpret the DNGs correctly at all, but the in-app "Dark Room" offers some interesting options – white balance correction, highlight recovery, NR adjustable in 10 levels among other parameters. The problem is that not much of this seems to be working properly at the moment. On the iPhone 4S white balance and highlight recovery just generates nonsense output. This again suggests we're not looking at the same type of raw files that we'd expect from a DSLR. On the iPhone 5 we discovered an additional problem. The aspect ratio of the preview image is different to that of the captured image which makes it virtually impossible to correctly frame an image.

So while Digital Negative offers some interesting functions users should be aware that it is not generating "real" raw files. More importantly though it is simply not working very well in its current state which is reflected in the overwhelmingly negative app store ratings. Nevertheless in principle Digital Negative looks like a nicely designed app with an interesting feature set. We are hoping to have another look at it once the bugs have been fixed.