Kenneth Thomson agreed yesterday he initially formed the view the shot was a near contact wound.
But he changed his opinion after digitalisation of relevant photographs improved their quality.
The earlier photographs were very dark, Dr Thomson said.
Their improved quality meant the contrast was better and it was possible to see "small purple marks" not visible in the originals.
He believed the marks were powder abrasions, tiny bruises caused by powder hitting the skin.
Such marks were not consistent with the defence theory of a close contact wound, he said.
Last week, Dr Thomson told told the High Court in Christchurch Robin Bain was probably shot from a distance of about 20cm, an intermediate range.
The defence says Robin Bain committed suicide, by holding the .22 Winchester rifle against his head, having earlier used it to kill his wife, two daughters and younger son.
Dr Thomson's opinion differed from that of Alexander Dempster, the pathologist who carried out the postmortem on Robin Bain.
And it was also at odds with the opinion of two eminent pathologists the defence would be calling, defence counsel Michael Reed QC said during his intensive cross-examination of Dr Thomson on the 24th day of the trial of 37-year-old David Bain on five charges of murder.
The Wellington-based forensic pathology specialist said although the wound to Robin Bain's head had some factors consistent with a close contact shot, the presence of what he believed to be powder abrasions led him to conclude the wound was not a close contact one.
And he did not think the marks were skin imperfections, as suggested by defence pathologists.
A close contact shot would have shown signs of searing, as found with the wound to younger daughter Laniet's left cheek.
And Dr Thomson said he believed a black substance around the wound to Robin Bain was not soot, as Dr Dempster thought, but rather something known as "bullet wipe".
Although he agreed that, as the pathologist who carried out the postmortem on Robin Bain and who said he saw searing and soot in the wound, Dr Dempster was in the best position to assess the wound, he had made an error, Dr Thomson said.
He confirmed his finding that of the three wounds inflicted to Laniet Bain's head, the first was a survivable wound to her left cheek followed by two other wounds, one a hard contact shot to the top of the head, the other a close contact wound above the left ear, and both potentially causing almost immediate death.
If a ballistics expert gave evidence to say a bullet fragment found on top of some clothing on a chair about 2m from Laniet's head was from the bullet that went into the top of her head, he could give no explanation.
As to the "gurgling" sound heard from Laniet's room, Dr Thomson said he did not believe the shot to the top of Laniet's head could have been the first shot fired at her because he did not believe she would have been capable of making any noise at all after receiving that wound.
"She'd be dead".
But he agreed with Mr Reed if Laniet was still gurgling after the shot to the top of the head, then she would still be alive.
And while he agreed people could survive even horrendous gunshot wounds to the head, and that no-one "could be dogmatic" about such matters, he went on to say it "stretches the grounds of credibility to have survival for any length of time from either of those wounds".
Asked about the opinion of another pathologist who considered Robin Bain had committed suicide and that injuries to his hands provided evidence of a recent fist attack, Dr Thomson said the injuries all looked "remarkably trivial" and dried.
He would not say any of them had been actively bleeding in the period before the body was removed.
And if a specialist facial surgeon was to say faint marks on Robin Bain's hands were teeth marks, he would "respect his opinion but not necessarily agree".
He had seen a large number of injuries from fights and "these don't amount to much", Dr Thomson said.
If the other doctor saw a pattern of the imprint of teeth, he would be "surprised if they were".
But such injuries were not his "area of expertise", he told Mr Reed.
