Recommended start point for sharpening RAW Images

Things are worse than you imagine. Not only is there no ideal sharpening for an image taken by a specific camera and lens combination, with lens set to a specific aperture, the correct sharpening depends on the output medium and the viewer or photographer's taste. Sharpening is therefore as subjective as anything can be. So the answer is sharpen to taste according to what you see in the final output medium at the desired size.

Image sharpening is a very subjective matter. It is very dependent on a myriad of factors, including output factors (medium size, resolution) as well as camera factors (sensor size, sensor pixel pitch, low pass filter strength, sensor noise level), etc. Even your subject magnification and the size of the finest element of detail in-frame relative to the spatial resolution of the sensor can matter. These factors will all affect how much sharpening you "need", as well as how much sharpening you may "want", relative to an original unsharpened image. Some sharpening might need to be "intrinsic", providing a base degree of sharpness to your image in general, while other sharpening may be "targeted" to a given output...and if you have multiple outputs (i.e. computer screen and print at multiple sizes), then each output will probably need its own unique sharpening tuned for the output medium.

There are no hard and fast rules about what makes for good sharpening and what doesn't. When sharpening for screen, you can often get away with minimal sharpening, or even none at all. The more your subject fills the frame, the less likely you'll need any sharpening. The smaller your output target relative to the native image size, the less likely you'll need sharpening. When you need to crop more, or when your output target is closer to the native image size, you might need more sharpening. The relative resolutions of output medium and working medium also play a role. Print, for example, tends to utilize considerably higher pixel densities than computer screens, by a factor of 3x at a minimum (when using a 100ppi screen) to more than 6x (when using a 72ppi screen or printing at very high resolution, such as 600ppi). When sharpening for print, you can usually apply much stronger sharpening settings with a larger radius than you can when sharpening for screen.

The size of subject detail relative to the size of a pixel can also affect how you sharpen. This can change for the same subject depending on how large the subject is relative to the frame, pixel density of the sensor, and even the resolving capability of your lens. If you use a high quality lens and fill the frame with your subject (whatever it may be, even a landscape taken with a narrow aperture or T/S lens to maximize DOF), you will probably find that you need much less sharpening than if you are using lens of lower quality. When your subject fills a fraction of the frame, you will often need more sharpening to bring out what little detail there may be. That offers the first tip to sharpening....make sure you can fill the frame with your subject (allowing for the artistic addition of negative space where necessary), and avoid the need to sharpen at all.

Another key factor to sharpening, and the ability of sharpening to have an appropriate impact, is image noise. The more noise in your image, the more likely you will enhance noise (rather than detail) with "default" or "canned" sharpening settings. If you have no option but to use a high ISO setting that results in high noise, even if you can fill the frame with your subject, you will probably find you need to use different settings (such as a larger sharpening radius) than when you use a lower ISO setting or have less noise. In the same grain as enhancing noise, sharpening has the tendency to add "halos" around edges and key objects. The stronger the sharpening applied, the stronger the halos will be. The only way to avoid this is to produce a sharper image in camera.

There are no general rules for sharpening. All the technical stuff above aside, ultimately how much sharpening you apply really boils down to your personal aesthetic taste. To some people, a given photo might need sharpening, where as to others, the exact same photo might seem perfectly sharp strait out of the camera. There are also a variety of ways to improve perceived sharpness. The standard sharpening tools of Lightroom are not the only way. The "Clarity" tool, which affects microcontrast, is an alternative or complementary way of improving sharpness without actually needing to apply a high degree of standard sharpening, mitigating the potential impact of haloing while achieving stronger results. There are also a variety of high- and low-pass filtering methods to sharpen photos in a tool like Photoshop which offer different results that may be more appropriate to different subjects.

Sharpening is really a matter of taste, so its best to experiment for a while and find out what works for you. Make it a part of your style.

Here's what I'd start with.

For an image to be displayed on the screen, 100% for amount and 1.4 px for radius. View at 100% when making adjustments.

For a 5x7 print at 300 dpi, 200% for amount; 8x10, 300%.

For standard prints (i.e. not canvas), judge the amount of sharpening by looking at the image at 50%. That will get you in the ballpark. If you're looking at a file destined to print output at 100% on the monitor, it should look over sharpened.

Depending on the subject, you might need to mask what's being sharpened. Grass and some foliage doesn't take well to the sharpening.