Camera: Fuji X-T1
Focal Length: 1000mm (digiscope)
Filter: Thousand Oaks Polymer Solar Filter
I tried out a new filter the other day for solar viewing, the polymer filter from Thousand Oaks Optical. It had some pros and cons compared with the 2 x stacked ND 3.0 filter approach, notably it is much cheaper than two high quality ND 3.0 filters, but you do get what you pay for as the threads were not well machined and the filter would not smoothly thread onto the optics or another clear filter from B&W. That said, the stacked ND 3.0 filters introduced a slight reflectance in the middle of the image, leading to some aberration and loss of detail, whereas the polymer filter surprisingly allowed me to extract a bit more detail in the surface of the sun around the sunspots. In terms of flux, I estimate that both the stacked ND 3.0 filters and the black polymer filter reduce the amount of light by about 6 log units.
Note: Looking at or imaging the sun can be inherently dangerous, particularly if you are doing it with optics. Any solar filter must be in good repair with no holes in it to allow raw sunlight to get through and the filter MUST go on in front of any optical lenses, else you are risking either a retinal burn or a CCD toasting event. This is of course another advantage of using mirrorless cameras with no optical path from the lens to your eyeball and retina. So, if some catastrophic failure of filtering did happen, your retina would not suddenly find itself in the optical path.