Defendant appeals from a conviction of criminal mischief in the second degree. ORS 164.354. He contends that the trial court erred in failing to require a witness whom he had subpoened to appear. The trial judge refused to do so on the grounds that the witness, a physician, had informally communicated to the judge that he knew nothing about the matter.

We affirm without reaching the question of whether the trial judge’s reasoning was correct, because it is clear that if the doctor had been present the defendant would have sought to elicit from the doctor only impeaching evidence on a collateral matter— which is impermissible.

Affirmed.