Considerations and Justifications for Choice
After testing the microscope set-up, we realised that the LED backlight was too bright, causing difficulty when trying to image the yeast cells on the webcam. An iris diaphragm, located between the stage and backlight, helps to control the amount of light reaching the specimen, resolving the brightness issue.
Prototyping Process: Cycle of Test, Critique and Re-Design
V1
V2
Identified Issues with Previous Prototype:
- There were too many holes
- Holes were spaced too closely
Modifications Made:
- Reduced number of holes to 4
- Increase spacing between holes
- Decrease thickness to 3mm to optimise printing time
V3
Identified Issues with Previous Prototype:
- Aperture did not work effectively at controlling the light
- More specifically, the images would be lit differently as we rotated the aperture.
By allowing all the light (from a sufficiently large aperture) through, the sample would be fully backlight, and this is typically called ‘brightfield illumination’ since the background is mostly white, and the outlines of the cells are a little visible against it.
- Interestingly, by rotating the aperture (or as was done previously, by obscuring part of the light below (but not completely) the image would transition from brightfield to darkfield.
Darkfield illumination occurs when the sample is illuminated without having the light rays from the light source enter the imaging device (in this case our objective lens and webcam).
By obscuring most (maybe over half) of the lamp, the darkfield image is very clear with strong contrast compared to the brightfield image.
- The ‘light’ that was included with the microscope included 3 cool white LEDs under some sort of translucent plastic, with the intensity controllable by pressing down on the top with like 5 levels powered by 3 triple A batteries.
Modifications Made:
- Change to bridge structure — a more permanent blocker for the light (instead of obscuring half of it horizontally, have a circular blocker in the middle) and have a mount
- Coins of different sizes used to block light to different extents