Why would you under-expose a RAW image? You should always expose so that the bar graph on the histogram is not quite touching the right hand side, this is so you can have as much image data as possible in the first stop which contains the brightest tones! Read this!!!
http://www.luminous-landscape.com/tutorials/expose-right.shtml
and this!!
http://www.luminous-landscape.com/tutorials/optimizing_exposure.shtml
It is never a problem to reduce the exposure in Lr or whatever software you use you will find that you get less noise etc

Good Morning,
Raw contains all the info that was recorded when you clicked the shutter. Very good to have that but not in all cases.
When shooting something important where images have the possibility of being printed large then one should shoot in RAW. If one is shooting something that will ONLY be used for snap shot purposes one can easily get away with jpegs.
However one thing to think of is RAW conversion only takes a few minutes so it is easy to convert so why not let yourself to have one less thing to think about and shoot everything in RAW.
Someone stated that .dng files were proprietary to Adobe and that is wrong. Hundreds of applications use this file designation.
philb
benton, ky

The RAW file format provides more image information giving more elbow room for later image development. A larger file size results.

The JPEG file format derives from the RAW file while in camera according to camera metering and settings. This in-camera pre-processing discards some image information. But this discarding gives a smaller file size.

That said, some experienced photographers will shoot in the JPEG file format when they can control lighting and color calibration to produce a well-exposed image.

Photographers who shoot many pictures of an event (like a wedding) will use the JPEG file format to minimize processing time in order that they may write an invoice sooner.

Please know that shooting in RAW requires more processing afterward, first in the RAW software and then in the photo editor to finish the photograph. You will spend more time and effort going this route but potentially will have more control over results.

You could try shooting with your camera set to RAW + JPEG. This setting will give you two files, one in each file format.

Of course, with this setting, your images will then take up more space on the hard drive, yet consider the very low cost of computer storage these days. You could just buy, say, a 4 terabyte external hard drive to save all your photo files.

Finally, please consider one day when you have gained more experience in shooting and in image processing, you may wish to return to your earlier images to process them for their value in light of the passage of time. You will thank yourself for having a RAW file of those precious images.

A RAW file contains all of the information that the camera recorded. If the camera converts this to a JPG file, some of that information is adjusted to correct exposure, contrast, color, etc. Some of the information may be lost and irretrievable, such as detail in the highlights and shadows.

If you don't want the camera to make arbitrary decisions for you, work with the original RAW file and make your own adjustments. It's a little more work and you might not want to do it for all of your images but it provides you the most control over your image.

Most current photo editing software can start from a RAW file but if you are not using a Nikon or a Canon, try before you buy.

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Hi, jmcD,

Here's another "take" on the " jpg -RAW comparison" that some of my students and workshop participants have found useful:

The RAW data collected by your camera at exposure is not an image data file comparable to the JPEG file that your camera selects, copies, and "cooks down" from that original, inviolate sack of RAW data.

The 12 bit or 14 bit "RAW FILE" your camera delivers is simply a guarantee that that sack o' RAW data can be repeatedly "worked" by the RAW converter of your choice to come up up with a practically unlimited number of raw versions/ interpretations in a 16-bit environment , each with multiple thousands more options of interpretation than posessed by that little 8-bit RAW file that,admittedly, doesn't look too bad straight-out-of-camera (SOOC) but which is served up as a small "medium-well-done" hamburger rather than with all the glorious inate potential of a whole side of RAW U.S.D.A. Prime beef that never looses weight as new entrès are prepared from it!
Damn...now I'm hungry...salivating...prime rib, please -medium rare!

Dave in SD