Bullet point draft on microscopes

·         Magnification:

o   we see most clearly what is at the our focal point and at no magnification

o   objects before the focal length appear larger but blurred

o   objects beyond the focal length appear smaller and less clear

o   magnifications extends the focal length by reducing light

o   objects at our usual focal point appear as if held close to the eye

o   objects beyond our focal point appear as if at our focal point

·         Using a camera teaches us that magnification blurs:

o   it extends focal length

o   distant objects seem closer

o   images blur at relatively low magnifications

o   magnification increases or decreases as one adjusts the lenses forwards or backwards

·         (Invisible objects are unlikely to exist

o   they cannot be magnified into visibility

o   anything so small to have no visibility to eye is unlikely to have extension now matter how many there are (ie, they would seem to have a mathematical rather than actual size)

·         Microscope: what one sees  

o   squinting into a dimly lit cylinder extends focal length

o   the lenses of one’s eyes appear in layers near the top of a cylinder, translucent and magnified somewhat beyond what one sees looking into sunlight

o   the cylinder appears to be about three times the length of the lens tube

o   the screen appears bigger (about eight times that of the eyepiece and objective lenses)

o   one’s eyelashes are magnified (not visible when looking into sunlight)

o   there is a similar looking, two dimensional fixed and more shadowy image on the screen at the bottom of the cylinder

o   the image appears not to change if the glass slide is removed or if the lenses are rotated

o   the image appears not to change in size if one moves one’s eye away from the eyepiece

o   the cylinder is poorly lit (requiring a low level of internal lighting either from the batteries/transformer or relatively small objective lenses if lit by the mirror)

o   too much light or too little light will blur the screen or render the cylinder invisible

o   rotating the focal adjustment rotates the image on the screen but not the edge of the image (slight irregularities are visible at the edge of the screen)

o   there appears to be no distortion of the image as one adjusts the focus or changes the objective lenses and the sides appear to be the same diameter at the top and bottom

·         We are unlikely to be seeing the object on the slide:

o   (i) the magnifications said to be needed are unlikely: additional lenses add rather than multiply magnification

o   (ii) we would not be seeing the circle on the glass stage since this would have a larger diameter if magnified so that we could see ‘cells’

o   (iii) we would expect the slide to be placed further from the microscope

o   the magnifying lenses would be too close to the objects for magnification to take place

o   (iv) we would not expect at any one time to see more than a speck on the microscope slide

o   this would be consistent with lighting from the mirror (ie, a beam of light)

o   we might therefore miss, for instance, abnormalities in a sample

o   (iii)light is not shone onto the object either from the objective lenses or from the mirror, positioned below the slide

o   the cylinder must be relatively dark for the object to be visible

o   whether it were to be viewed directly or projected, it seems unlikely that we would view a slide beyond the cylinder and objective lenses unless it were vivid

o   whether or not it is stained (which might distort the image) a magnified speck is unlikely to be sufficiently vivid (ie, it would appear less vivid) [?]

o   direct viewing is unlikely: the darkness of the cylinder and size of the objective lenses means that objects before, or in, the final lens would be more visible than anything outside it

o   projection is unlikely: the beam of light from the mirror might as it passed through the glass of the stage and the lens might damage and would distort any image projected onto a

o   (iv) The screen appearing not to move relative to the objects on it suggests one is viewing an object above (or an object held in place from above by an object such as a fine needle) the cylinder rather than what is on the slide  

o   The relatively fixed image on the screen as one moves one’s eyes nearer or farther from the eyepiece suggest magnification is at the lower end of the microscope

·         What we are likely to be seeing:

o   (i) at the higher end of the microscope we are undoubtedly seeing the translucent image of the lenses of our own eye

o   this can be seen by comparing what we see to what we see when we squint into sunlight or artificial light

o   the magnification is somewhat higher than that achieved by the eye alone as a result of the reduction in focal length when looking into the cylinder

o   (ii) If we look at the objective lenses we can see what looks like a moveable orange rim, resembling the iris of a pigeon, that shifts slightly if we tilt the microscope

o   the image on the screen also shifts slightly if we tilt the microscope

o   the similarity between the image of the lens of our own eye and the material on the screen suggest that we are viewing the object placed directly behind the objective lens

o   looking into the cylinder it appears that one is seeing an object below a moveable glass or magnifier

o   in fact, the cylinder we are seeing magnified looks likely to be only that contained within the focal adjustment itself

o   ie, the screen looks likely to be at the bottom of what we see rotating on the outside if we rotate the focal adjustment

o   it therefore seems likely that the objective lens is projected onto the screen, the magnification occurring as a result of the distance between the object and the screen (as in a projector)

o   the fact that the image appears to rotates might be a result of either the rotation of the glass or it may be attached to the glass in some way, which would also hold the object in place