You need a proper reflective filter that stops most of the light before it reaches the lens, I use a Thousand Oaks
http://www.thousandoaksoptical.com/ full aperture for my 25cm Newtonian telescope and it works well. Its got a few pinholes in it these days, its over 20 years old, but still works fine. It gives a yellow/orange sun.
The cheap way out of it is to use a Mylar solar filter, if you dont mind a blue Sun. Either of these will let you see darker sunspots and some other markings on the face of the Sun.
http://science.nasa.gov/ssl/pad/solar/feature1.htm
Talk to the guys at Binocular and Telescope Shop in Sydney to find out what is suitable for your setup.
https://www.bintelshop.com.au/ search for solar filter... but you will still have to talk to Mike or other staff about your exact requirements. (tell him I sent you
)
Hydrogen Alpha (H alpha) filters are the expensive filters Steve was thinking of, the narrowest of them (thousands of A$$$) give a bandpass only about 1 Angstrom wide and let you see all sorts of wonderful solar surface details, flares etc, and prominences reaching out into space beyond the limb of the Sun. Less expensive ones with a bit wider bandpass will let you see the same thing, but with a lot less contrast.
My Transit of Venus pics are at:
http://members.ozemail.com.au/~loomberah/transit.htm
The animation pics are a bit dodgy, I had some light leaking in the back end of the scope and was in a rush to get the animation made, so didnt have time to burn all the light leak areas and blank areas from image rotation out of the images.
***DO NOT TRY AND USE AN ND FILTER BEHIND A FAST LENS!!!***
Gordon
http://science.nasa.gov/ssl/pad/solar/feature1.htm