This is one interesting tutorial about getting “Nokia Camera” on Lumias other than PureView Lumias like 920, 925 and 1020. Nokia Camera app is available as an update to ProCam on old PureView Lumias, but it is not available for other Lumias like 520, 620, 720 an 820. But seems there is certain way in which one can downlaod it on Lumia 520, 620, 720 an 820.
Here are the instructions from Blog “IJSMblog“,
1. Connect to your WiFi and in Settings > WiFi tap your connection.
2. Turn on Proxy and enter 188.8.131.52 in the Server box and 8888 in the Port box. Then hit the save arrow at the bottom of the page.
3. In Settings > Date+Time select any United States time zone.
4. Then in Settings > Language+Region select your region as United States. In the same Settings page hit Restart Phone.
5. After your phone restarts, go to the Nokia Camera page in the Windows Phone Store. This can take some time…be patient.
6. You should now get the option to Install/Update Nokia Camera. Hit Install or Update, but it will probably fail (again may take some time). Don’t worry. Keep the Store window open by hitting the Windows button, go to Settings>WiFi. Tap your WiFi connection and switch off Proxy.
7. Hit the phone’s Back button to get back to the Nokia Camera page in the Windows Phone Store and select Install/Update again. This time it should work.
8. Don’t forget to change your phone settings back to your Time Zone and Region and restart the device.
Since, the app is officially not compatible with these Lumias, it may still not work as smoothly as on compatible phones.
Anyways, do let us know whether you have been able to install app on your Lumia.