Friday, December 30, 2011

Calibration Factors

Note these are 'pre move' measurements.

Confocal Microscope

lens (in Air)
resolution f (um/px)
100x 800x800 0.160767
100x 1024x1024 0.124108
100x 1600x1600 0.079653
100x 2048x2048 0.063535






10x 800x800 1.614726
10x 1024x1024 1.015435
10x 1600x1600 0.808205
10x 2048x2048 0.63066









lens (in water) resolution f (um/px)
100x 800x800 0.16001
100x 1024x1024 0.115274
100x 1600x1600 0.080559




Light Microscope


um/px
50x 0.186104
5x 1.864454




Thursday, December 29, 2011

Microscope Calibrations

This post is to document how and why we calibrate the microscopes. To begin with a microscope's most basic function is to change the size of something (i.e. make it bigger) for us to view. This does not mean the object changes size, just what we see does (the image is bigger). But we may want to use the image to measure a real size or distance. For example, in the image shown below, we might want to know far it is from the bug's belly to the ruler (or the bug's leg length or width or something).


Currently we usually store an image as a digital photograph on a computer, which means the image is stored as a collection of pixels (the far right part of the image above). If I were to measure a distance I would count how many pixels from place to place. Using the example above I might say that the bug's belly is one pixel away from the ruler, at its closest point. The question is what this distance is in the 'real world', i.e. the real distance from the bug to the ruler. To say, I need to know the 'calibration factor' for my microscope.

The calibration factor is a unit conversion, usually from pixels to microns for an ordinary light microscope. To calculate the conversion factor, all we need is a known distance. In the example above, the ruler will have real distances marked on it, so we have a 'known' distance in our image. All we need to do is measure how many pixels are between two markings on the ruler, and note the dimensions of the markings. For example, say I measure 5 pixels between two millimeter marks on the ruler. My calibration factor is then given by: 1000 um / 5 pixels = 200 um / pixel. I can then take this calibration factor and convert the bug-ruler distance: 1 pixel x 200 um/pixel = 200 um. So my bug is 200 um from the ruler.

Group Photo Summer 2011


Here we are! Obviously I am a little behind on the posts!

From the left: Michelle Davis (Summer Student - Mech. Eng.), Katrina Teskey (Governor's School Student), Margaret Rozario (Summer Student - Physics), Bekele Gurmessa (Ph.D. Student - Physics), Andrew B. Croll (Boss).

Background: Batcheller Technology Center.