Q: When should you shoot RAW format?
(b) Always, unless you're running out of space on your last card
(c) When you know you'll be doing some aggressive post-processing
I'm a little amused, at times, by the almost cult-like following that answer (a) has developed. While I do understand the reasons for shooting in raw, and I do use the format myself, I don't agree with the sometimes fanatical obsession that some photographers have with the format.
The argument in favour
There are quite a few arguments raised in favour of saving the raw sensor data for every image. You can salvage a bad exposure! You can convert to black & white! You can apply different colour profiles! You can fine-tune the white balance!
All of these boil down to one single argument: If you have a RAW file, you have 12 or 14 bits of colour depth per channel instead of the usual 8. That means you have more room to mess around in post-processing before you encounter the discretization artefacts that occur when doing math in a lower bit depth.
You can do most of that on a JPEG...
...and nobody will notice. Bumping up the exposure two stops in post-processing will, on a JPEG, leave some banding or posterization in the shadows. That's a pretty extreme adjustment, though, and for most normal post-processing — such as small adjustments to the white balance, burning or dodging, converting to monochrome, or tweaks to the tone curve — it's awfully hard to tell the difference between a raw source and a good JPEG source.
The argument against
If you shoot RAW, you have to do complete post-processing. On every frame. True, you can configure presets in Lightroom, Aperture or similar for your preferred settings, and that speeds up the process a fair bit. Even so, it takes time and effort to turn a RAW file into a usable image.
You also have to convert the RAW files to an archival format that'll still be readable in a few decades. If you don't, you'll essentially lose access to your work once the current generation of cameras becomes unsupported. The conversion process is automated, but it's an extra step that takes considerable time.
There's also the ever-present risk of running out of card space at an inopportune moment, something that's five to ten times more likely in a RAW workflow than if you're shooting JPEGs.
That said, I still shoot RAW...
...when it makes sense to do so. Those situations include:
- Anything with bad or wonky light, where a fair bit of tweaking will be needed to get a good result.
- Anything that'll be printed big and fancy.
- Anything that I know I'll want to fine tune in post-processing, such as portrait work.
For sports, though? Family snapshots? Documenting an experimental setup in my lab? RAW and its attendant workflow are overkill for quite a lot of things. Use it when it makes sense to do so, but let's not worship a file format, OK?