I teach Lightroom and I got tired of asking students who convert to DNG why they were doing so and never getting a good answer except they read to do somewhere. I decided to put together my own David Letterman (United States reference) Top Ten Reasons Not to Convert to DNG:
1. Precludes you from using OEM software You will never be able to use your camera manufacture’s software again. Ever. Features that are specific to certain cameras (like Nikon’s Active D-Lighting and Picture Control) are not supported in the DNG format. Do you really think that Adobe knows everything that’s in every proprietary RAW file format it supports?
2. Backing up images will take longer In Lightroom, many of the changes you make can be stored in small XMP sidecar files that accompany raw files, and are only a few kilobytes. When you convert to DNG, changes are made directly to the file, so when you back up your images (hopefully daily) the whole file, typically 20 MB or more, needs to be backed up instead of just the small XMP sidecar files.
3. Metadata can’t be read by other software XMP data, including keywords, stars, and metadata that you may have changed in Lightroom is not available if you want to use another program that can read XMP sidecar files but not DNG files.
4. Longer downloading times from your memory card If you convert images to DNG upon importing to Lightroom, processing times increase since Lightroom must import and convert all the files to DNG.
5. File sizes One argument is that DNG file sizes are more efficient and are up to 20% smaller. In 1956, the first IBM Model 350 hard drive weighed over a ton, cost $329,928 (in 2014 dollars) annually to lease, and stored 3.75 MB of data. It would have taken over 20 of them to hold a single Nikon D810 (36 MP) 14-bit RAW image file. Today, a 3 TB hard drive (formatted) holds the equivalent of 725,333 of the Model 350 hard drive and costs $100. The equivalent storage capacity, using the IBM Model 350 hard drive, would cost $14.9 billion to lease the same capacity (not to mention the 11.6 million square feet to store them, or the cost of electricity to run them.) I’m not concerned about the size of native RAW files!
6. Load times DNG files supposedly load faster in the Develop module. With faster processors and Smart Previews, RAW files load very quickly in the Develop module even from an external drive USB 3.0 drive.
7. Ability to read RAW file in the future. One of the other main arguments in favor of converting to DNG files is that if a camera manufacturer stops producing software that can read their RAW files, then their RAW files would be unreadable. I don’t think Nikon, Canon, or Sony are going away anytime soon, and even if they were, you could use their software to read their files. Worst case, you could always convert them to DNG.
8. DNG is not an industry standard, it’s Adobe’s standard. As much as Adobe would love the DNG format to become the industry standard, it’s not. It’s Adobe’s standard. While a few camera manufactures produce camera the shoot DNG file as their native RAW files, most do not. DNG requires a lifelong allegiance to Adobe.
9. Camera brand not easily identified. Converting all your files to DNG makes it harder to quickly identify the camera manufacturer when looking at the file name since the suffix will be a generic DNG, and not one associated with your camera.
10. No obvious benefit. For all the reasons touting the DNG format, perhaps the biggest reason not to convert is that there is no obvious benefit. DNG files don’t contain more information (maybe less), are negligibly smaller, don’t load appreciably faster, take longer to download because the must be converted, and ties you to Adobe forever! They simply are, understandably, a greater benefit to Adobe than you, and have not been embraced as a standard format.