Brian Arthur Campbell Mathers pleaded not guilty on Tuesday in Brisbane District Court to two charges of making child exploitation material and one charge of possession.
Mathers allegedly committed the offences at a Moreton Bay home between December 2020 and October 2021.
Crown prosecutor Elise Adams told the jury that a 13-year-old girl had been taking a shower on October 19, 2021.
"She noticed a figure and then a phone camera lens within what she described as a leathery phone case in the corner of the open bathroom window," Ms Adams said.
Ms Adams said the girl saw the lens move away from the window after she turned off the water and stepped out of the shower.
Five seconds later, the girl said she heard a laundry door close quietly and Mathers ask her if she was almost done in the bathroom.
Ms Adams said Mathers was the only adult at the home that morning.
Police interviewed the girl and seized Mathers' Samsung phone but they were unable to retrieve any deleted data.
On October 24, Mathers told his wife that he had thought he was filming her and he deleted the video straight away.
Mathers declined to answer police questions about October 19 but admitted filming the girl in the shower some time in December 2020 or January 2021 when she would have been 12 years old.
"His story was one night when he and his wife had been drinking, she told him that she was going to have a shower and he decided to film her," Ms Adams said.
Mathers told police he filmed for about 30 seconds and later realised it was a video of the girl and panicked.
Ms Adams said Mathers told police he moved the file into a "locked application" on his phone.
"He claimed he did not watch the video but 'kind of looked at it and (saw) smoky glass so I could see the outline of her'," Ms Adams said.
Mathers' barrister, Dominic Nguyen, said his client made an "honest mistake" when filming the girl in December 2020 or January 2021.
"(Mathers) did not at any time on October 19, 2021 use his phone to record (the girl) in the bathroom," Mr Nguyen said.
He told the jury they would see a pre-recorded video of the girl testifying and him questioning her over the credibility and reliability of her evidence.
"Carefully scrutinise what she says and, respectfully, treat her evidence with caution," Mr Nguyen said.
He said his client was never knowingly in possession of child exploitation material and  deleted the video when he realised it was not of his wife.
The trial was then closed to the public to allow the jury to listen to the girl's testimony and police interview.
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