Distance Magnifiers: Telescopes

PLV0

telescopes (TS)

• to view distance object (intermediate w/ reading cap)

• handheld or spectacle mounted

telemicroscopes (TMS)

• for near using auxiliary lenses

TS general concepts

• light amplification

• angular magnification

  • image produced at larger angle

• objective (F1) positive convergent lens: closest to object

• ocular (F2) positive convergent or negative divergent lens: closer to eye

• afocal TS

TS Magnification

• M = -Doc/ Dobj

• M = entrance pupil/ exit pupil

• M = BVA/ TVA (reference/ goal)

TS Tube Length

• d = f obj + f oc

Galilean TS

• (+) obj lens: stronger than ocular

• (-) ocular lens

• virtual exit pupil

• shorter tube length

• erect virtual image

Keplerian TS

• (+) obj lens

• (+) ocular lens: stronger than obj.

• real exit pupil

• longer tube length (images converge in TS)

• inverted real image (include prism to make image upright)

TS FOV

• larger FOV

• FOV = exit pupil (mm)/ TSmag

• limited by diameter of obj lens

TS Weight

• larger obj lens = heavier TS

TS illuminance

• illuminance = exit pupil / pt bright pupil size

• lower mag = brighter

TS exit pupil

• exit pupil = entrance pupil (obj lens)/ TSmag

TS brightness reduction

• brightness reduction = (exit pupil)²/ (pt pupil)²

Hyperope TS

• more magnification with Galilean

Myope TS

• more magnification with keplerian

focal TS

• under near devices