As others have said: Use SAFE dedicated solar film or SAFE dedicated solar glass filters for the Sun:
With such filters you may get this at 600mm f/11 with ISO = 100 and t = 1/125s:
Pentax K200D with Tamron Adaptall-2 SP 300mm f/5.6 lens and 2X Tamron SP F-Series teleconverter.
Without this filter (Optical Density, D=5) I would have needed an exposure time of 1/125s divided by 100,000!!! Are you sure you got a
black rather than a
blank image?
Of course, during totality things are very different and you must take off the filter - but ONLY DURING TOTALITY.