The table of data Mike provided shows clearly what many solar observers know already from experience. Hopefully others will read this thread and think about it before asking the question once again or worse, trying something potentially dangerous. The use of a white light filter for an ERF is just ignoring the data presented above.

The only way a wide H-alpha bandpass filter (with a red glass filter as an ERF) could reveal any prominences would be with a coronograph type design with a stop at the focus to shield the solar disk. For disk details it would be futile as well as dangerous. Many H-alpha nebula filters may be to wide even for this unless you are blessed with exceedingly deep blue skies.

I think the best thing to recommend to new experimentors is to refer them to people who have designed and built solar telescopes from relatively inexpensive materials such as Dave Groski. We can also recommend saving up for an entry level solar telescope or sharing the experience with a local solar observer.

Glenn