Optics - Magnification and Telescopes Flashcards
What type of image does an Astronomical telescope produce?
Inverted
With telescopes how do you calculate the magnification?
Mag = D eyepeice / D objective
Which telescope is longer: Astronomical or Galilean?
Astronomical.
What type of image does a Galilean telescope produce?
Upright.
Give examples of Galilean telescopes?
- Surgical loupe when used with add
2. Magnification in slit lamp and operating microscope
How do you calculate the length of a Galilean telescope?
Focal length of eyepiece - focal length of objective
How do you calculate the length of an Astronomical telescope?
Focal length of eyepiece + focal length of objective.
What type of lens make up a Galilean telescope?
A small (+5) PLUS objective lens and large MINUS (-55) eyepiece
What type of lens make up a Keplerian telescope?
PLUS lenes
How is the distance of a Astronomical (Keplerian telescope calculated?
By the SUM of the focal lengths of eyepiece and objective lens.
The lenes of a Galilean telescope is separated how?
By the DIFFERENCE of their focal lengths.
What is Aniseikonia and what causes it?
It is the difference in perceived image size between the two eyes.
Causes: unequal refractive errors - monocular aphasia or pseudophakic surprises; retinal problems; occipital lobe lesions.
(Rule of thumb for spectacle correction is that 1D of changes the retinal images size by 2%)
What is Knapp’s Rule?
That the proper corrective lens placed at the anterior focal point of an eye will produce retinal images of the same size no matter what amount of axial ametropia exists.
An Indirect Ophthalmoscope acts like what type of telecscope and produces what type of image?
Astronomical with the patient’s cornea acting like a + objective lens and the 20D + lens as the eyepeice. Real, inverted image
What are 4 ways to minimize meridonal magnification?
- Minmize the vertex distance
- Grind the cylinder onto the back of the lens
- Decrease the power of the cylinder
- Change the axis towards 90 or 180
