I was just looking at this picture :
and wondered why no Corona or trace of the little explosions on the surface of the Sun are visible ...
How should the Sun be photographed to see those details on its surface ?
by Paul Cezanne
It's because that image is only capturing the visible spectrum. Most of the images you see of the sun are capturing the ultraviolet spectrum, where you see some really impressive explosions and coronal ejections:
That image was taken from space with a highly specialised scientific camera, but you can capture some details, including prominences using a DSLR in conjunction with an appropriate filter:
image (c) Kevin Lewis, source: http://www.photosbykev.com/wordpress/photography/pst-solar-imaging/
The filter used in this case was an Hα filter, designed to let through the frequency of light produced when an electron in a hydrogen atom changes energy state (it would be an understatement to say that there are a lot of hydrogen atoms in the sun). Note this is a multi exposure image with one exposure for the main disc and a separate longer exposure for the prominences (flares coming out of the sun).
Spontaneously I would say they are just too small - compared to the sun's size. You can't see mountains from the ISS on earth either.
But I could be wrong....