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Choice and assembly of the mirror

My current mirror is a mirror of security (used in shops) says " quarter of sphere " 57 cms in diameter.

The sites of sale of accessories of security for shops, propose this kind of article:

Spherical mirror 1/4 of sphere, diameter 600 mm

We would be entitled to think that it is about a sphere of diameter 600 mm cut in 4.

In no way!
It is really about a 80 mm sphere (approximately) of diameter from which we extracted half a spherical cap.

The diameter of the skullcap is effectively 600 mm,
But its optical behavior (which imports us) is that of a sphere the radius of which is 400 mm.

We are confronted with this type of difficulty when we divert an article of its foreseen commercial function.
Polymir unbreakable, sensitive to scores, cleaning in the cold water and the sweet rag (4 kg)
The thoughtful coat is outside.
But it is not totally opaque and leaves show the white plastic,
Giving a "a little bit milky" image.

I paid it 119,60€ with the port.
Ordered by internet here
The reference of the mirror is VOLUM 51-57: here: Technical details at the manufacturer: here
PMMA ( plexiglas ) is not unbreakable
The thoughtful coat is inside.
Plexiglas reflector ( acrylic polymer), very sturdy and unchanging material, covered under vacuum with a film on base of aluminium and with chromium then with a varnish of protection époxy.
I ignore on which face is the thoughtful coat.



- The mirror is screwed on a rather thick board to be stiff (it is plastic flexible and deforms). - This board can be partially hollowed out to leave more place with knees.
- It is fixed to a directional support upward or the bottom.
Some remarks:
- The mirror presents an important surface in relation to the dome surface. It reflects the light resulting from the projector towards the screen (It is its function).
But it reflects then the light of the screen towards the screen and the environment!
It countered thus sensible to limit the thoughtful surface to the useful zone (mask or painting).