Mapping fish-eye-lens images to lat-long

Dear HDRI list members,

I use HDRShop to convert between mappings for environment maps, e.g., from mirror ball to lat-long, etc.

I use a Sigma 8mm 180 degree field-of-view fish eye lens on a Canon 1Ds Mark II camera to take fish eye lens (FEL) images of the sky.

In HDRShop I use the "mirror ball closeup" option when I convert from FEL image to lat-long mapping, but through experiments I have determined that the mapping is incorrect. The FEL imaging geometry does not conform to "mirror ball closeup" and the resulting lat-long mapping is incorrect. For example: when I take FEL images of the sky, and manually measure the elevation of the Sun above the horizon, the elevation matches if I interpret the FEL image as a hemispherical mapping. If I convert (using the mirror ball closeup option) the FEL image to lat long in HDRShop the elevation is not correct anymore (e.g, 7 degrees in lat-long map, 20 degrees in reality).

I am searching for a program that can convert my FEL images (produced with the Sigma 8mm FEL) correctly into lat-long format. Can anyone help?

Or put more precisely: I wish to convert hemispherical images into latitude-longitude format.