Vincent was a confessed match-fixer who admitted criminal offences, such as accepting bribes.
Despite this, he was not investigated or charged for the crimes he confessed or formally given immunity from prosecution.
A jury would normally be told if this happened to give them the "full picture" about a witness' credibility.
Instead, the judge issued a formal caution to Vincent that he did not have to answer questions which might incriminate himself of crimes.
After Vincent finished giving evidence, police emails were produced in court which showed Vincent was in no danger of being prosecuted for the crimes he had already admitted in police interviews.
Had he known the true position, Justice Sweeney said he would have issued a different warning to Vincent.
This would only have covered self-incriminating answers of crimes beyond what Vincent had already told the police.
"Any impression given that he was in peril of prosecution was wrong and should not form any part of your considerations," said Justice Sweeney.
"With those warnings firmly in mind, what you make of his evidence in the end is entirely a matter for you."
To find Cairns guilty of perjury, he explained, the jury must be sure of the evidence of at least two of the three witnesses accusing the 45-year-old of match-fixing.
Just one of Vincent, his former wife Ellie Riley and Brendon McCullum was not enough to convict him on the first charge.
They also had to be sure two of the witnesses were independent of each other, with no collusion or even innocent contamination of the other's evidence.
If they acquitted Cairns of perjury, the judge said the jury must also find Cairns and Andrew Fitch-Holland not guilty of perverting the course of justice.
This charge is in relation to the Skype conversation between Fitch-Holland and Vincent.
If they found Cairns guilty of perjury, the jury must consider three steps before they convicted Fitch-Holland of perverting the course of justice.
They must be sure Fitch-Holland knew Cairns was involved in match-fixing and secondly that he knew Vincent was involved in match-fixing.
Thirdly, the jury must be sure Fitch-Holland was asking Vincent to provide a false statement.
If the Crown did not convince them of all three steps, Justice Sweeney said, Fitch-Holland must be acquitted.
Cairns could only be found guilty of perverting the course of justice if Fitch-Holland was also convicted - and the jury was sure the friends jointly conspired to ask Vincent to provide a false statement.
The burden of proof rests with the Crown, which Justice Sweeney said must reach the threshold of "beyond reasonable doubt" - the jury must be sure of the defendant's guilt. If they were not sure, they must find the defendant not guilty.
Justice Sweeney asked the jury to give "cool, calm, careful and dispassionate consideration of evidence.
"And the courage to bring a true verdict with whatever the consequences may be."
Justice Sweeney will continue on Monday and the jury is expected to start considering verdicts on Tuesday.