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What visual artifacts should we expect from the images that will be released from the James Webb Space Telescope? Specifically, do we expect 3-pronged diffraction spikes (any preview how they would look?)? Do we expect any artifacts due to the honeycomb-like structure of the main mirror?

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    $\begingroup$ There won't be only mirror-like artifacts like A. Leistra stated, but additional every instrument will have their own artifacts, e.e. due to imperfect correction from flatfields, and also depending on the filterwheels/gratings used. $\endgroup$ Feb 19, 2016 at 20:26

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Are you asking about the PSF (point-spread function)?

There are some simulations & basic images available as well as a downloadable package you can use to compute the PSF for a particular instrument and wavelength. Since the telescope hasn't been fully assembled yet these are based on simulations.

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The JWST images will have various artifacts. I found a web page that summarises the situation for the Near Infrared Imager and Slitless Spectrograph (NIRISS).

The image below (taken from that webpage) shows simulated point sources as they would appear on the detector (including the sampling by the 0.0656 arcsec pixels). The greyscale is on a logarithmic scale of brightness. Each postage stamp corresponds a 77x77 pixel region around the point source, imaged through filters at different wavelengths (identified by the code in the top left, where 090 corresponds to 0.9 $\mu$m etc. and the W or M corresponds to wide-band or medium-band).

NIRISS simulated PSFs, with 0.0656 arcsec pixels JWST NIRISS PSFs

Then there is a further web page that gives the equivalent information for Near Infrared Camera (NIRCam), which has a short-wavelength (SW) and long-wavelength (LW) channel, as well as several filters associated with each of these.

NIRCam SW simulated PSFs, with 0.031 arcsec pixels NIRCam  SW PSFs

NIRCam LW simulated PSFs, with 0.063 arcsec pixels NIRCam LW PSFs

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