Types of LVAs Flashcards
What properties of hand mags are available?
Aspheric or spherical lens
Illuminated or non-illuminated
Pocket sized
Insets/multiple lenses (stronger for spot reading)
Most ambidextrous
Some clip into a stand
What are the advantages of a hand mag?
Cheap compared to other aids
Acceptable cosmetically
Acceptable WD
Can be illuminated
Easy to transport
Ok on uneven surfaces
Most are battery operated
What are the disadvantages of a hand mag?
Not good for poor grip/shaky hands
One hand in use while using
Limited mag (12.5x max)
Poorer image if spherical
Needs to be used at correct focal point
What are the advantages of a stand mag?
Higher mag available than hand mags
Steady
Easy to use
May be able to tilt (lower mags)
Even illumination
Easier to keep at correct WD
Hands free compared to hand mags
Good price
What are the disadvantages of a stand mag?
Poor FOV at high mag
Bulkier and heavier than hand mags
Have to work out distance from eye (depends on reading add and system vergence)
Small working space underneath (esp if higher mag)
Needs a flat, stable surface
What specs should be used with most stand mags in the UK?
Reading specs
If a stand mag has a shorter working distance than its power requires, what are the solutions?
Lift mag higher (pre-presbyope)
Distance specs (presbyope)
What are the advantages of a neck/chest mag?
Adjustable distance
Hands free
Useful for hobbies with not much detail
What are the disadvantages of a neck/chest mag?
Limited mag bc of large size
What is the max mag of dome/bar mags?
2x
What is the definition of a telescope?
Two or more lenses separated by a gap which causes an increase in the incident angle of incoming light
What are the advantages of a telescope?
Only form of non electronic distance (angular) mag
Can be binocular
Longer near WD
What are the disadvantages of a telescope?
Max 3x mag for distance on spec telescopes
Expensive
Poor cosmesis
Heavy
Restricted FOV
Training needed
Increases any tremors due to weight
What are the properties of a Galilean telescope?
Positive objective lens
Negative eyepiece lens
Erect image
Eyepiece stronger (numerically)
Length = focal length of o-e
Mag = eyepiece power:objective power (2-3x)
Wider FOV than astronomical but smaller focusing range
Exit pupil has with movement
What are the properties of an astronomical telescope?
Both lenses positive
Eyepiece stronger
Image inverted - prism reverts
Better image quality - exit pupil coincident with px pupil
Mag up to 10-12x
Heavier and longer than Galilean
Exit pupil has against movement
