From left to right: Focus graycode encoder, focus scale for the user (meters in white, feet in yellow, magnification in orange), gray main focus barrel with main focus cam, then a black secondary focus barrel with cam and just at the right edge of the image the innermost, third focus barrel.
<a href="//commons.wikimedia.org/wiki/User:Phiarc" title="User:Phiarc">Phiarc</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>