• The maximum focusing point is beyond infinity
• Is it a default?
• The lenses move with the temperature…
• …and the manufacturer has to compensate that
• Summary

The maximum focusing point is beyond infinity

You turn the focusing ring until it stops, and then, you realize with the signometer that you’re not focusing at infinity, but slightly beyond.

Is it a default?

Is there a problem with the lens? Is the focusing screen on my camera misaligned?

None of that. It’s perfectly normal.

The lenses move with the temperature…

Depending on the temperature, the metal casing holding the lenses expands and contracts.

Consequently, the lenses move closer to or further from the sensor depending on the temperature. This explains the slight shift you’ve observed.

…and the manufacturer has to compensate that

To anticipate these movements, lenses have a tolerance in their focusing range.

This means they all extend slightly beyond infinity to prevent you from being unable to focus at infinity because you are blocked by the focus ring’s stop.

Summary

If your lens focuses slightly beyond infinity, it is not a default but a deliberate decision by the manufacturer to ensure your lens is usable under all temperature.