Here I am going to say it again,
the use of Synthetic Sapphire has more than likely lead to IR leakage. You'll need a filter to get rid of this.
Luckily this is an easy problem to fix and fix cheaply!!😉
Direct Quote:
Sapphire Glass Wikipedia:
One application of synthetic sapphire is sapphire glass. Here glass is a layman term which refers not to the amorphous state, but to the transparency. Sapphire is not only highly transparent to wavelengths of light between 170 nm (UV) and 5300 nm (IR) (the human eye can discern wavelengths from about 380 nm to 750 nm[33]), but it is also five times stronger than glass and ranks a 9 on the Mohs Scale, and much tougher than tempered glass, although not as much as synthetic stabilized zirconium oxide (such as yttria-stabilized zirconia).
One application of synthetic sapphire is sapphire glass. Here glass is a layman term which refers not to the amorphous state, but to the transparency. Sapphire is not only highly transparent to wavelengths of light between 170 nm (UV) and 5300 nm (IR) (the human eye can discern wavelengths from about 380 nm to 750 nm[33]), but it is also five times stronger than glass and ranks a 9 on the Mohs Scale, and much tougher than tempered glass, although not as much as synthetic stabilized zirconium oxide (such as yttria-stabilized zirconia).