The virtual image you see when looking in your microscope is not quite the same as the real image you would see with your eye. For one thing, it is bigger. For another thing, the orientation of the image is different. The two lenses in a compound microscope reflect the original image two times, in two different planes, while magnifying it. So what you think of as the “top” of your image is really the bottom, and what you think of “right” is really left. Usually this is not an issue at the microscopic level, but it is important to understand how the microscope is rearranging your virtual image.
Lab 4 Exercises 4.4
- Get an “e” slide. If it is already under your microscope, rotate the lowest-power objective into place, use the coarse focus to lower the stage, and remove the slide.
- Look at the unmagnified “e” on the slide by eye. Rotate the slide around in your hand so that the “e” is right side up. Now clip the slide onto the microscope stage with the stage clips so that the “e” is facing you right side up when you look at it with your unaided eye.
- In the right-hand circle below, draw what the “e” looks like when you are looking at it right side up. Assume the circle below is the size of the entire coverslip. Draw the “e” you see unaided in the correct proportion to the coverslip. (The unmagnified “e” will take up a tiny portion of the coverslip area.)
- Clip the slide into your microscope stage so that the “e” is still facing you right side up. Follow the checklist in Lab Exercise 4.3 to ensure you are setting up the microscope properly for use, but stay on the lowest power objective. Get the “e” into your field of view and in focus.
- In the left-hand circle above, draw what the “e” looks like when viewing it through the microscope under the lowest-power objective. Under the circle, write the total magnification of the image.
- When viewed under a microscope, how is a specimen rotated?
- Look at the stage and slide directly (not through the eyepieces.) Move the stage control knob that causes the slide to move away from you on the stage, then move it back to its original position.
- Now move the stage control knob the exact same way you just did, but view the “e” through the eyepiece. When the stage is moving away from you, what direction does the virtual image appear to be moving?
- Again, look at the stage and slide directly (not through the eyepiece.) This time, move the stage control knob that causes the slide to move to your right, then move it back to its original position.
- Now move the stage control knob the exact same way you just did, but view the “e” through the eyepiece. When the stage is moving to your right, what direction does the virtual image appear to be moving?
- The field of view is the entire area you can see when looking through an eyepiece. Use the stage control knobs to move the virtual image of your “e” to one side of the field of view. Keep most of the “e” in the field of view, but move it to one side or the other.
- Now switch to the next-power objective. (Do not skip.) To get to the next-power objective, and not the highest-power objective, which way did you have to rotate the objectives, clockwise or counter-clockwise?
- Using only the fine focus knob (you do NOT use the coarse focus knob on any objective other than the lowest objective), get the “e” in focus.
- When moving to the next objective, which part of the field of view do you zoom in on?
- Move away from the eyepieces and look at the distance between the slide and the bottom of the objective. Rotate back to the lowest power objective. Now rotate to the next objective (do not rotate to the highest-power objective by accident). Now rotate to the third-highest objective. What happens to the distance between the slide and the bottom of the objective as you rotate to higher power objectives?
- With the third-highest power objective still in place, how space is there between the slide and the bottom of the objective?
- Notice there is a danger of smashing the objective lens into the slide if you were to use the coarse focus. Why are you instructed to only use the coarse focus with the lowest-power objective?