It is best practise to not have sharpening applied in camera but to adjust after. There are two reasons to sharpen, firstly it is to correct losses of sharpness due to the process and the other is to optimise the image for the final medium. Sharpening for print and web is different.
This is a difficult skill to master as each individual image will have differentqualities which may or may not take to being sharpened. The size of the size of the image will affect the levels and the medium on which it will be printed also has an effect. My own personal experience has shown that I had to sharpen images more for printing on the Epson Archival paper than with gloss or semi gloss.
This task had to be completed to make me more familiar with sharpening procedures, I use Photoshop and the Unsharp Mask, adjusting the values on the Amount, Radius and Threshold, and always view at 100% so I can see the changes that occur.
For this task I had to take an image, ideally a portrait and save a reference image that has had no sharpening applied. Three more versions were then produced each with a different degree of sharpening. All four images then had to be printed, compared to each other and with the 100% magnification images on screen.
a couple of useful links
Guide to Image Sharpening
How To Sharpen An Image - Advanced Photo Sharpening | PhotoshopSupport.com
Once again I returned to the portraits I had taken for the workflow exercise. I have screen printed the processes but obviously the results will be tricky to see on a monitor based on screen prints with diluted resolution ;o). All images were printed out at 6 x 4 as this is the only photographic paper I have, also it is using up some Kodak paper which was given to me, not ideal with an Epson printer, but was ok for this exercise and also showed how important to is to have the correct paper profiles when you print. Also showed I think I need to check my print head allignment.....
The first image to be printed out was the unaltered image and was a little soft as it was on screen.
|1px @ 50%|
|1px @ 250% Threshold 10|
For my own interest I printed a fifth shot without altering the threshold, on the whole the image seemed to be able to take the strong sharpening without and major detrimental effect, although I would like to print the images larger at a later date to so the effect that size has on sharpening. I know from previous experience that when printing A4 and on archival paper I had to sharpen quite aggressively to get the sharpening effects I required, printing a few trial runs before I got there. In conclusion different subjects can take different tolerances of sharpening and each individual image will vary, the amount of sharpening will show on screen but not so markedly in print, to get an acceptably sharp print the majority will look over sharpened when viewed on a monitor.