Biopolis Dresden Imaging Platform

The Devil is in the Detail

Depth of Field and Depth of Focus

Theory

Hands-on

Depth of Field and Depth of Focus

Concept demonstrated

Show students how to properly align their microscope for parfocality by teaching them the concepts of depth of field and depth of focus.

 

Materials

Any microscope with adjustable eyepieces and several different magnification (air) objectives will do. For demonstration purposes, a stereoscope/microscope with a continuos magnification changer and adjustable eyepieces is most suitable.

 

Practical Setup

The students stand around the demo-microscope while teacher explains and shows how to set the microscope up for proper parfocality. Then they should repeat on their student microscopes (or in turn on the demo set up).

How to:

  • Go to the highest magnification and focus using the focus the sample using the focus knob of the microscope (Depth of Field).
  • Then change to the lowest magnification and DO NOT touch the focus knob anymore. The image should now be brought back into focus by adjusting the eypieces one after the other (Depth of Focus).
  • Take care to always leave both eyes open for optimal results! If you have troubles concentrating on the image of one eypiece with the other eye open, simply hold a piece of paper above the not used eypiece.
  • You should now have achived parfocality, meaning as you change magnifications the sample should stay in focus.

 

Idea/Implementation

Peter Evennett, Jan Peychl

Objective Reading

Theory

Hands-on

Objective Reading

Concept demonstrated

Most students have no idea what all those numbers on  microscope objectives stand for. The idea is to present them with a range of different objectives and help them understand them.

 

Materials

  • A range of different objectives: different vendors, magnifications, NAs, working distance, contrasting methods, immersion method, coverslip thickness, working distance etc.
  • Have at least enough objectives so that each student has one.

 

Practical Setup

  • The students get one objective each and are told to study it for a couple of minutes.
  • They are then to introduce their objectives one by one to the rest of the group, explaining all it's features with the help and by discussing with teacher and the other students.

 

Idea/Implementation

Peter Evennett, Britta Schroth-Diez, Silke White

Digital Image Sampling

Hands-on

Digital Image Sampling

Concept demonstrated

Helps students to get a feeling for pixel sizes, resolution and the correct sampling.

Materials

for each student:

  • several checkered sheet of paper/cardboard (every sheet showing differently sized squares)
  • differently sized "samples": eg. sesame seed, sunflower seeds, gummibears,..

Practical Setup

  • students "throw" the samples on the sheets of paper
  • discuss with which sizes of squares they can "resolve" which of the samples.
  • How does that translate into digital microscopy?
  • discuss different scenarios: Can you resolve the biggest samples (eg Gummibears) with the smallest squares chequered board? Yes. But is that a good idea?
  • Which other parameters next to resolution should you consider?

Idea/Implementation

Dan White, Britta Schroth-Diez, Jan Peychl