Hi, I am researching several historic eras of the early universe and part of what I need to find is at what redshifts these events occurred. I have z = 1100 for the recombination era and z = 15-20 for the reinonization era. I haven't been able to turn up this info the "Dark Ages" yet. Any help is appreciated. And I'd be grateful if someone could point me to a good site (beginner level) on how these redshift numbers are calculated. Thank you.