Well, I love a challenge!
The first step for any image hunt is to head to Google images. That's exactly what I did, searching for "Ernie Banks outfield." Lots of pictures of Mr. Cub turned up, but none of him playing the outfield.
I sorta expected that. After all, what are the odds of finding a picture from over 50 years ago from one of only 23 games that season. I did another search, this time "Ernie Banks 1961." It brought up lots of images of his baseball cards from 1961, but no shots of outfielder Ernie.
Next, it was on to Getty Images. I searched "Ernie Banks" and set a date range of May and June, 1961. Nothing turned up. It was then that I headed to the Sports Illustrated Vault. I did find an article that talked about a possible move of Ernie to first base, but no pictures.
Finally, I surfed to the Chicago Tribune archives, and there I struck paydirt!
Ernie's first game as a left fielder was May 23, 1961. The next day, the Trib had an entire article that discussed the move...
According to the article, the move was Ernie's idea. A bum knee was affecting his play at short and he felt he could do the team more good in the outfield. I've got the entire article below.
His time in the outfield lasted only three weeks. He moved to first base on June 16 and two reasons were given....one, that Ernie needed more action to stay involved in the game...it was too boring out there. The Cubs also wanted a young left fielder to get back in the lineup, a kid named Billy Williams.