For 12 minutes, the teenager was recorded walking naked to the shower, showering, then putting on her underwear.
About eight seconds after she left the bathroom, the man went in and stopped it.
He kept the video for nearly a month before his partner found it and made a complaint to police. However, the couple are still together.
The man admitted his offending and pleaded guilty but sought a discharge without conviction, saying the consequences of a conviction would outweigh the offence.
However, Judge Mathers said while she accepted the man had real remorse he and his partner were in a position of trust at the time he made the recording.
"This was no sudden act of anger leading to unwarranted violence. It was a premeditated act. It required the placing and hiding of the cellphone.
"It required getting the victim to take a shower and it led to a twelve-minute recording of a 13-year-old girl preparing to shower, showering then dressing."
Judge Mathers said she considered "the deliberate and pre-planned filming of the victim" to be high-level offending.
"Children need protection. This invasion of a child's privacy was serious and totally unacceptable."
The man had already lost a job after telling his employer about the charge, he had not told his new boss about the charges and feared he would suffer the same fate if he did, she said.
A considerate employer should be understanding of the conviction and may not automatically dismiss the man because of it, she said.
She also accepted his likelihood of reoffending was low and that he had suffered real consequences from the criminal proceedings.
But the judge said the decision about whether to grant a discharge without conviction was "difficult" but ultimately the consequences did not outweigh the gravity of "surreptitiously filming a 13-year-old girl".
"Such a child is entitled to security and privacy and to the recognition by the courts that such offending is totally unacceptable."
The girl remains unaware that the recording even happened.
However, Judge Mathers said a conviction for making an intimate visual recording would be punishment enough, so ordered him to just pay court costs of $135.