Forget about lenses. The glasses and control of the melts is best left to the professional. Casting or slumping mirror blanks is within the capability of the amatuer. Bubbles are not a problem unless very large or near the surface. Casting pyrex, the materiel of choice because of its low expansion characteristics, can be melted into molds at the temps you mentioned but it takes time for the pyrex to flow into the mold and even longer for the bubbles to work their way out. Slumping is far more practical. Less than 1500 deg. is needed to slump. Annealing and strain relief are a much greater problem. Precise temperature control is required as are long time periods at the required temps (1050 deg. for anneal and 950 deg. for strain relief). Other glasses such as plate etc. can be worked at lower temps but pyrex is the best choice. Water white plate can be slumped for Maksutov corrector blanks but the glass should be checked for stria.