jimtrue.com : school : CJT2141 : 07: Microscope
Posted by Jim True on February 26, 2003 6:00 AM. Last Updated October 22, 2006 9:23 PM
Disclaimer for all material noted here is at the bottom of this web page.
Microscope - "small look"
Simplest microsoft - magnifying glass
Bends the light to make things bigger.
Refractive Index in the glass is causing the image to look larger.
1. Stage - Where the specimens go
2. Objective Lens - bigger the objective, more magnification
3. Oculars or Eyepiece Lens - range from 8-10X
4. Arm that supports the ocular & objective lens
5. Body tubes - Where image forms (Body tubes)
6. Light source - illuminates the subject All have some kind of light source
7. diaphragm - controls to allow light onto the specimen
8. Substage condenser - adjust the cone of light that comes in to hit the sample.
9. Base
KNOW THE PARTS OF THE MICROSCOPES AND IDENTIFY ON A DIAGRAM (p.166)
Terms when dealing with Microscopy:
1. Magnification - how much the image is being increased
4x objective and 10x ocular - 40x (p.168) Ocular x Objective
10x x 10x - 100x
Empty magnification - when image is so big it is useless
2. Field of View - circular area, when you decrease the field of view, you are increasing your magnification.
to increase field of view, decrease your magnification.
Fig 7-1
3. Depth of Focus - Not everything looked at on a microscope is flat; round objects
The thickness of the specimen entirely in focus at the magnification is your depth of focus (p.168)
Increase magnification, decrease depth of focus.
Decrease magnification, increase depth of focus.
4. Working Distance - distance between the objective lens and the stage
+ - Magnification
- + Field of View
- + Depth of Focus
- + Working Distance
Binocular - Two eyepieces
Monocular - One eyepiece
Different Types of Microscopes:
1. Light Microscope (Compound or biology)
2. Comparison Microscope (p.169) - Two compound microscopes connected with a light bridge, mirror that allows a split screen view between both microscopes. Microscopic comparison, firearms, hair, fibers.
3. Stereo Microscope (Stereoscope) - lowest magnification, great depth of view; OBJECTIVES offset just a little bit, 3-dimensional view. WORKHORSE in the lab; document examiner, dna, firearms, trace, drugs.
4. Polarized Light Microscope - 2 pieces of polarized film at body tube and substage condenser; light goes through the polarized film (separate out some of the vibrations in light, and look at birefrigence properties under the microscope). p.172
5. SEM - Scanning Electron Microscope: instead of light, use electrons to magnify. Can go to magnifications up to 10 100,000x, DO NOT GIVE UP DEPTH OF FOCUS at higher magnifications. Gunshot residue analysis, can also be connected to an XRay diffractor (XRD). Working distance, you're in a vacuum, so working distance is irrelevant (must be electrically conductive; plated with gold). FDLE has one at Orlando. GSR analysis.
Microspectrophotometer - use microscope as a gun sight (target what you're going to analyze). Hooked up to a UV-VIS. Use scope to target, objectives move out of the way and UV-VIS or IR beam provides result.
FTIR Microscope.
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