This is with reference to the Sony NEX-5R. I have gotten into the habit of telling Lightroom to convert all ARW to DNG when I import them, in the hope that DNG, being an open format rather than a proprietary, encrypted one, will let me easily access my photos decades from now. It's a nice bonus that DNGs are little smaller than ARW.

Are there any other factors that would affect this decision? Or am I over-doing the longevity part?

To be clear, I don't want to keep both the ARW and the DNG. I don't plan to convert to JPEG and delete the RAW, either.

  • If your RAW format is readable for a open source program now (dcraw, darktable, etc.) I see no risk in its longevity (hoping there will be no silly patent-bashing problem in the future...) – Rmano Dec 14 '13 at 23:55

The format longevity question is impossible to answer conclusively. But it reminds me a bit of the best advice I've heard for preserving ones' personal artwork: become famous. Famous artists have their work in galleries and museums, and a whole industry exists to support them. Similarly, I imagine that the most popular cameras will have the best chance of ongoing raw converter support, even if it's only as a DNG-converter style program, while others may be lost to the sands of time.

And every camera model has a unique raw format, even if the file extension is common to the entire brand. Software that works with the NEX-5R won't automatically support the NEX-5T, Canon 70D needs to be supported separately from the 60D, and so on. DNG files are much more universal, although each converter will give different results.

One other advantage of DNG worth mentioning: there's only one file per photo. Proprietary raw files can't be modified, so programs like Camera Raw need to create additional files just for keeping track of the changes to be made to the file when it's exported into a pixel-image. These sidecar files that contain all of the editing instructions are unique to each program, and if they're lost then so are the changes. With DNG these editing instructions can be written directly into the DNG file, increasing their portability and making backups and archives more manageable.

But wait, there's more! One reason NOT to use DNG files is that some programs can't work with them. DxO Optics is my preferred raw converter, but it can only do its magic on original raw files, not converted DNG files. That's critical for me today, and who knows what might come along in the future.

So, to make a short story long: convert to DNG on import for your working copy of the file, but also buy a basic external hard drive and check off Lightroom's option to archive the original raw file on it. When that drive's full put it somewhere safe and start another one.

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  • Thanks, mpr. Not having sidecar files is reason enough for me to go with DNG. I don't want to keep both DNG and ARW, as I mentioned in my question. – Kartick Vaddadi Dec 15 '13 at 6:47

I'm keeping my RAW photos in original format. One of the advantages of converting to DNG, that result file will be little bit smaller than RAW. But with current prices for storage it's not a problem. So I'd say it's your own decision which format to choose, but if you are already with DNG, continue with it. I'm not converting to DNG as still able to open my raw files in any program. When I can't, I'll think about converting them to DNG

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Few reasons:

  • While most camera-manufacturer RAW formats are losslessly compressed, you might achieve a slight increase in compression on a computer because the computer doesn't have to worry about processing time. Whether this is worth it depends on how well your individual camera (losslessly) compresses its native raw format. It's like the difference between choosing 'normal' compression and 'ultra' compression when making a zip file: like you said in your question, not a huge difference but potentially 'nice to have' depending on whether the time spent on conversion (during Lightroom import) bothers you.
  • The longevity issue you've already mentioned. You can look at prints of photos you took 20 years ago and (if you stored it properly) get new prints made from the film. Will image processing software in 20 years' time be able to open proprietary Sony RAW files from now? See for example this forum topic on the trouble a user had opening Word files produced on an original iMac (~15 years ago).
  • If you own another RAW-capable camera (DSLR/mirrorless/advanced compact), or might conceivably buy one in the future, then having all your raw files in one format (DNG) makes choosing processing software simpler: you just need to find one that works with DNG files, rather than having to find one for ARW files (NEX), one for PEF files (Pentax), one for CR2 files (Canon) and so on. This may not be a problem now if the NEX is your only RAW camera, but very few people go through their whole lives only buying one camera brand.
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  • -1 because most raw formats are compressed in some way (which is usually lossless). – James Snell Dec 14 '13 at 23:30
  • Most are, but some aren't (Pentax PEF for example) – David Russell Dec 15 '13 at 0:09
  • There is also the issue of how compressed the file is: the camera can't devote an excessive amount of processing time to compression, so a file compressed in Lightroom on a computer will be smaller even than an also-losslessly-compressed image from a camera (the very experience the OP describes in his question). For example when creating a Zip archive in 7zip, I have the options 'Store, Fastest, Fast, Normal, Maximum, Ultra', with increased compression but longer compression time as you go up the scale. – David Russell Dec 15 '13 at 0:15
  • Even if you corrected that to say most raw formats are compressed but that file size could be reduced I'd still keep the downvote in place. Conversion to DNG is not a lossless operation even on cameras where it is offered as a raw format and as a file format it is by no means guaranteed to be readable in future because it can just be a wrapper around a raw file, which it would still need to know how to open. photo.stackexchange.com/questions/6188/… goes into more detail. – James Snell Dec 15 '13 at 0:38
  • Pentax PEF didn't used to be compressed but is now. No, wait. Isn't that it always has been compressed, but Pentax on-campus DNG didn't wasn't (but is now)? – mattdm Dec 15 '13 at 0:47

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