Golf professionals teach that the player must keep his eyes exactly above the ball, when he aims a putt. For this reason, golf players usually stand very close to the ball when they putt, and they lean their chest forward, to have their eyes precisely over the ball.
Minigolf players rarely have their eyes exactly over the ball. In fact, it is often impossible for a minigolf player to have his eyes over the ball -- for example, when your ball has stopped on the other side of an eternite lane. To play the putt while having your eyes over the ball would require that you stand in the middle of the lane -- and that is forbidden by the rules.
Because minigolf players don't have their eyes over the ball, they suffer from some optical illusions, which golf professionals want to avoid with their strict "eyes over the ball" rule. Minigolf players sometimes see the hole in a different direction than where it actually is... an optical illusion! One of the minigolf lanes where this has most significant effect is when putting at the Volcano (lane number 8) of beton courses. The volcano illusion.
If you look at the picture above, the first picture shows what a golf player would see, when he aims for a putt at the Volcano lane of beton minigolf, having his eyes exactly over the ball. The second picture shows what a minigolf player with right-hand putter might see in the same situation. The + sign is the center of the putting green (on ground level) -- the direction where the player needs to aim the putt. But the minigolf player sees the hole __in a different direction__ than where the center of green actually is, because of a perspective distortion, which is caused by the fact that the player does not have his eyes exactly over the ball. If the minigolf player aims at the hole, rather than at the center of green (which is not in the direction where he sees the hole!), he will probably miss the hole on the right side, when he plays the putt.
If the putting green were made of glass, and a + sign were painted at the middle of green on ground level, it would be easy to notice this optical illusion, and always aim at the + sign, rather than at the hole. But the putting green is made of solid material, and the player cannot see the center of green on ground level.
Some minigolf players try to avoid this optical illusion, by taking an aiming mark between the ball and the hole, some 20 cm in front of the ball. This aiming mark will not be much above ground level, so the optical illusion will be smaller. My personal choice is more simple and straightforward: As a right-hand player, with my eyes quite far behind the ball, I always aim the putt some 2 cm to the left of center (or whatever the putting map says) at Volcano. With this simple thumb rule I have always found the center of hole reliably when putting at the Volcano, both in small and in large competitions.
When I was the webmaster of Minigolf World Championships 2001 (Vaasa), I asked the coaches of team Finland to give their putting maps, so I can publish them on the tournament website. They refused, because they wanted to keep maximal home field advantage for team Finland. "The Germans would never give any such information to others", they explained. Maybe they had a valid point in their thinking.
In 2008, as I was the webmaster of European Championships in Tampere, I didn´t bother to ask for putting maps from team Finland. I made the putting maps by myself, for publishing on the tournament website. All the 2 x 18 lanes, and I didn´t even have an assistant to throw the ball back to me from the hole. Who needs a gym, when you can train your back muscles by making a putting map?
I cannot guarantee that I was able to 100% neutralize the Volcano illusion from my putting maps, on lanes such as the Volcano on beton, or the German slide and Midhill on eternite. Many teams used my putting maps unchecked at the Nations Cup, and a few times I saw a top player such as Anders Olsson miss a putt at one of these lanes, while reading my putting maps.
Next time when you travel to an important competition, pay special attention to the putting maps of lanes where the hole is above the level where the ball will be when the player makes a putt. The Volcano of beton, the German and Swedish slide, the Midhill. Who made the putting map, was it a right-hand or left-hand player? What happens when a left-hand player reads a putting map which was done by a right-hand player?