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(Software-Videos)

Olivier NIVOIX
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Lhoumeau Sky System
BEAMER
LSS-BLOC
CONDENSOR
ADJUSTMENT
TRUNCATED
Lhoumeau Sky System - module condenseur simplifie  
SIMPLIFIED CONDENSOR UNIT


This versatile mount permits to get an hemispheric projector at low cost. The quality of the projection depends primarily on the choice of lenses and care in optical alignments. Even if the result isn't worth a condensor type Heligon Rodenstock, we tried to get a result as close as possible. We don't need to use the fisheye diaphragm with this model, which was essential with the basic installation based on camera lens (but with loss of light). Compared with the Heligon, we get small chromatic abberations but it's only an expert eye critics.
 

The optical assembly includes achromatic doublets, mounted like a Plössl eyepiece, i.e. 2 achromats opposed. 
 
To reduce optical aberrations, it's better to build a baffle at the entrance of the condenser.


Characteristics

Values can differ slightly from 10% for the focal length, and even more in diameter, without fundamentally changing the process.

Doublet 1: F1 = 200mm approx. Diameter from 40 to 50 mm
Doublet 2: F2 = 60 mm diameter from 25 to 40 mm
The distance between D1 and D2 must be adjusted using the projector and the angle of view desired. Do not attempt systematically to obtain a field of 180 ° because the optical adjustments are more critical with very large fields.

Distance (d) D1-D2: 80 to 120 mm typically, adjust for the "zoom effect" wanted

Focal length = (f1 * f2) / (f1 + f2-d), typically around 80mm

Baffling: to be tested empirically based on the quality of the lenses used, between 20 and 35 mm in diameter for what we tested. It must be placed before the doublet D1; it can be sticked to the lens. 



Assembly

One of the difficulties  is to keep all optical components with a perfect alignment. A proposal:

-The condenser should be assembled as a 2 inches eyepiece, just pushed into a diagonal.
-The centerpiece is a 2-inches diagonal.
-The fisheye is screwed within a specially designed adapter ring to replace the original 42mm filletage in the inside, and 50.8 mm (2 inches) at the outside.
-This ring shall be 3-4 mm thick.


Settings


the optical unit is placed in front of the projector, recoilless.
The focus is done either by moving the focus of the projector, or by sliding the condensor unit.
The zoom is set to get the better field and the better adjustment. It can be hard to master a good adjustment as it'll change each time the position of the bloc compared to the exact position of the beamer's carriage of lenses which is moving diagonally (if your beamer don't produce a straight image).
 

Yves LHOUMEAU
© 2016 LSS Group - Yves LHOUMEAU & Lionel RUIZ