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Additional Bonnette Galilee
Reference: BV20.U

Additional Bonnette Galilee

Public price (Tax incl.) 52.50 €

General conditions
Delivery: 2-3 working days
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Galilean system - Principle:


  • The Galilean monocular is an afocal magnifier, meaning the image is formed at infinity.
  • The point of this system is simply to magnify for distance vision.
  • For near vision, simply add a cap lens to the front.
  • Note: its power determines the working distance, which will be at its focal length.


Monocular:

  • Body made of anodised aluminium, very stable.
  • Very light.
  • Achromatic telescope.
  • Wide field of view. 24° for the 1.8x
  • Anti-reflective coated.


Telescopes focused at infinity ∞

1.8 x

2.1 x

2.5 x
Ø Objective 20mm 20mm 20mm
Field 24° 20° 16°
Weight 10 gr 12 gr 16 gr






  • You can:
    • Buy a trial case with 3 monoculars that fit the optician's standard trial frame
    • Rent a trial case for a one-off sale.

Our add-on lens holder lets the optician find the wearer's optimal magnification using the trial box.

  • Universal: you only need one telescope with a trial ring.
  • No more need for huge stocks.
  • Placed on the trial frame, it lets you add the patient's prescription to assess the benefit of correcting.
  • The trial is done in real conditions.
    • With a reading chart or a newspaper.
    • On a computer screen.
    • For intermediate vision, a TV screen.
  • To find the add-on lens power, divide 100 by the eye/object distance (in centimetres).
  • Choose a large "panto"-style frame.
    • The optical centre must be the near vision centre.
    • The optical centre-to-frame distance must be at least 19mm.
    • Mark the optical centre (near vision) and check it.
  • For a monocular fitting, order:
  1. The chosen 1.8x, 2.1x or 2.5x telescope (Code BV20.Gxx ?).
  2. The add-on lens determined with the trial box. Code (BV20.Axx ?)
  • Option: pre-sized ophthalmic lens, to be edged to 21mm.
  • The plain mounting ring (Code BV20.B24) or prescription mounting ring (Code BV20.B20), depending on the option above
  • A mounting disc to be edged. (Code BV20.D30)
  • A large case. (Code BV20.E01)
  • For a binocular fitting, order:
    1. 2 chosen 1.8x, 2.1x or 2.5x telescopes (Code BV20.Gxx ?).
    2. 2 add-on lenses determined with the trial box. Code (BV20.Axx ?)
    • Option: 2 pre-sized ophthalmic lenses, to be edged to 21mm.
  • 2 plain mounting rings (Code BV20.B24) or prescription mounting rings (Code BV20.B20), depending on the option above
  • 2 mounting discs to be edged. (Code BV20.Dxx ?).
  • A large case. (Code BV20.E01)
  • A mounting kit. (Code BV20.D34)

    • Or simply mark the near-vision optical centre on the glasses and LESA FRANCE takes care of everything..............Code BV20.MONT

      • Simple, isn't it?........

    How to proceed

    Removable cap lens conversion table

     

    Telescope magnification

     

    1.8 x

    2.1 x

    2.5 x
    0.5 D 2 metres Watching TV 2.00 2.40 2.80
    1 D 1 metre Watching TV 2.25 2.60 3.10
    1.5 D 66 centimetres Looking at a screen 2.50 2.90 3.40
    2 D 50 centimetres Looking at a screen 2.70 3.10 3.75
    3 D 33 centimetres Looking at a screen, reading 3.10 3.60 4.30
    4 D 25 centimetres Looking at a screen, reading 3.60 4.20 5.00
    5 D 25 centimetres Looking at a screen, reading 4.00 4.70 5.60
    6 D 17 centimetres Looking at a screen, reading 4.50 5.20 6.20
    8 D 12 centimetres Looking at a screen, reading 5.40 6.30 7.50
    10 D 10 centimetres Looking at a screen, reading 6.30 7.30 8.70
    12 D 8 centimetres Looking at a screen, reading 7.20 8.40 10.00
    14 D 7 centimetres Looking at a screen, reading 8.10 9.40 11.20
    16 D 6 centimetres Looking at a screen, reading 9.00 10.50 12.50

    How to choose the telescope magnification?


    • Look at the table above.
    1. Suppose the patient has useful acuity with a Galilée 1.8x and a 12D cap lens: the working distance is 8cm.
    2. With a 2.1x telescope, the working distance goes from 8cm to 10cm for the same magnification (±≈).
    3. With a 2.5x telescope, the working distance goes from 8cm to 12cm for the same magnification (±≈).
  • You gain distance on one side but lose field on the other; testing is needed to find the best solution.


    • The Galilean telescope.
     
     
    Telescopic systems are multi-lens systems that allow both distance and near vision.
     
     

    How does it work?

    Its basic principle is that of binoculars.
     

    Binoculars are a Keplerian system.
     
    • It consists of a convex objective and a concave eyepiece..
    • When the 2 focal points coincide, the system is said to be afocal.
    • The magnification of such a system is the ratio of the objective's focal length to the eyepiece's.
    • So with an objective of 80mm and an eyepiece of 40mm focal length, the magnification is 80/40=2.
    • The total length of the system is then 120mm, and the image is also inverted.
    • Rather hard to mount on spectacles.

    The Galilean telescope is the most convincing alternative.
    • It consists of a convex objective and a concave eyepiece.
    • When the 2 focal points coincide, the system is said to be afocal.
    • the 2 focal points coincide; since the eyepiece is negative, both lenses are in front of the focal point.
    • The total length of the system is then 40mm and the image is upright, so no erecting prisms are needed.
    • The drawback is that the eyepiece focal length is very long for a negative lens, which limits magnification to 3x at most to keep a good image.
    • That said, the system is compact and light, so it can be mounted on a spectacle frame.

    Vision up close.
    • Adding a lens in front of a telescope makes the system's focal length that of the add-on lens.
    • The magnification is the telescope power multiplied by that of the lens.
    • For binocular vision, angled mounts are used.
    • The limit for a binocular fitting is 5D.
    • To correct ametropia, a prescription lens is placed in front of the eyepiece.
    • Our company can carry out the complete fitting.

    In summary.
    • The system is light and can be mounted on a frame.
    • A Galilean telescope without a lens gives vision at infinity with corrected ametropia
    • Near vision at the focal length of the add-on lens.
    • Without corrected ametropia the image is still fine; only the focal distance varies up or down.
    • High astigmatism must be corrected.
    • To correct ametropia, a prescription lens is placed in front of the eyepiece.
    • By design, our telescopes have a pinhole effect.

    The big advantage.
    • Allows hands-free work.
    • Allows watching TV with additions below 1.
    • Lets you read a whole screen just by moving your head.

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    Characteristics:

    Reference BV20.U
    Net weight 10 g
    Public price (Tax incl.) 52.50 €