Telescopes Flashcards
astronomical telescope- keplarian
positive eyepiece positive objective inverted image erecting prisms needed lightweight now, variable focus
galilean telescope/ terrestrial
-ve eye piece, positive objective common shaped fixed focus small, compact upright image
why are telescopes good
can increase angular subtense without a change in wd
who are telescopes good for
people who visual demands of reading- at any D- but just at 1 D
what does a telescope consist of
eye piece lens
and objective lens
in order to enlarge image- eyepiece must be the most powerful
for astronomical this must be a large -ve- but its ok as shows its inverted. and it corrected using prisms
how do u calculate the enlargement of a telescope
- eyepiece power / power of objective
galilean are shorter than astronomical bc of their -ve lens
how do u work out the length of a telescope
Focal length of eyepiece + focal length of objective
how do u compensate for rx using a telescope
wear their distance rx?
add corrective lenses to eyepiece
alter the telescopic length- myopes will make telescope shorter- in a galilean there will be less enlargement but in an astronomical more enlargement
hype ropes make the gallileaon enlargement bigger, and astronomical image larger
how do u adduct a d telescope for N
add a correcting lens
alter the length- increase the length for N- greater range with astronomical
how do u calculate enlargement when an end cap is used
Enlargement of system =
E(telescope )x (End cap power / 4)
whats the exit pupil for a telescope
where the pupil should be placed to view the object through the telescope
how is the exit pupil diameter calculated ?
Fo/ enlargement
how do u know which type of telescope it is looking at exit pupil and movements
if it moves with - gallileon
if it moves against then its an astronomical
if u seen on a telescope 4 * 16 what does that mean?
enlargement and objective lens diameter
how do u get the biggest fov
hold it right up against the eye
and pupil diameter should match the exit pupil diameter
how lens seperation in a galleilion telescope is
posterior focal point of the objective coincides with the posterior focal point of the eyepiece
telescope is focal and produces parallel emergent light from parralal incident light
accom needed for near-
magnification squared * wd in dioptres
which optical performance is the best- telescope
astronomical
even in terms of FOV
Gallelion telescope. The closer the exit pupil to the entrance pupil of the eye the
better the field of view- maximum light intensity and maximum image brightness
gallilean telescopes have a virtual exit pupil due to the -ve lens
white disc that seems to lie anterior to the eyepiece.
exit pupil is within the system so not in the same plane as the entrance pupil of the eye
compromised
– field of view
– light intensity
– image brightness
how lens separation in an astronomical telescope is
posterior focal point of the objective coincides with the anterior focal point of the eyepiece
The exit pupil for the astronomical system
real and posterior to the eyepiece.
small disc that appears to float above the eyepiece lens.
optimise the field of view, light intensity and image brightness by aligning the exit pupil of the system with the entrance pupil of the eye
small exit pupil in an astronomical telescope means
that the telescope has to be held close to the eye and very still
Field of view is reduced when the device is moved from eye
slightest movement- image moving in and out of view as the emergent light misses and then enters the ocular pupil
which are more expensive- binocular or monocular
binocular
