Microscopy of a dandelion seed: exploring depth of field and focal plane

This resource supports students to build confidence in using microscopes by exploring the concepts of depth of field and focal plane. Understanding depth of field and focal plane helps students to understand why they should begin observing a specimen with the lowest power objective and why they should use the focus knobs slowly and carefully. Because it is a relatively large specimen, students can be encouraged to relate what they see under the microscope to what they can see with their naked eye. They should notice that the sections of filaments that are just moving out of focus and those sections that are just about to come into focus are noticeable but blurry and that sections of filaments that are very far away from being in focus are not noticeable in the image at all. It should also be clear to students that although the filaments appear as separate objects when viewed at some levels, by adjusting the focus it is possible to see that they all join together at the centre of the pappus.

This resource was developed as part of the series of articles Teaching Microscopy Using Plants published in School Science Review. To find out more about how this resource can support use students to become confident, independent microscopists, read the first article What does a microscope show me? available from the Growth Hub.