But an ACT Supreme Court jury on Friday cleared Thomas William Johnston of a second count of producing child porn after jurors could not be sure whether a penis shown in photographs belonged to the defendant.

The jury took almost eight hours to find Johnston guilty of creating the pornography and administering a stupefying or overpowering drug, poison or injurious substance likely to endanger life or cause grievous bodily harm.

During the trial, the 51-year-old admitted to deliberately possessing child pornography and told the court he was addicted to adult pornography.

The court heard the chloroform incident occurred when the eight-year-old girl, a family friend, was spending an afternoon at Johnston's house in November 2009.

The girl later told her mother and police that Johnston put a mask on her, causing her to smell a strong odour and making her eyes water.

She said she soon fell asleep and woke up in a different part of the house, and was still feeling nauseous the next day.

Johnston told the court she was coughing so he put garlic on the inside of a mask and got her to wear it before the pair fell asleep watching television, and he later moved her from the couch to the bed.

But when police raided his house several days later they discovered a bottle of chloroform in his bedroom, child pornography on electronic devices and child porn websites in the favourites list of a web browser.

The Crown argued that a series of images taken on his mobile phone depicted a naked child.

Johnston told the jury he had been trying to overcome his problem with pornography, and had intended to throw out a disk full of explicit images, including child porn.

Defence barrister Ken Archer said that the evidence before the court was not strong enough for a conviction. Mr Archer said the number of images of children on Johnston's computer represented a small percentage of the overall - 40,000-plus items - pornography collection. He said the pattern of usage had been distorted.

The court will sentence Johnstone next year.