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2-4.The opening diameter and focal length

The opening diameter and the concentrating diameter of the point heater are the following relation.

1.The concentrating diameter is in inverse proportion to the opening diameter and changes.

→Hotness can narrow down small so that the mirror opening diameter is big, and is obtained.

2.The concentrating diameter is proportional to the focal length (the irradiation distance) mostly and changes.

→Hotness can narrow down small so that the focal length is short, and is obtained.

3.The concentrating diameter is proportional to the light source size.

→The filament diameter of the lamp is proportion mostly in a square root of the electric power.
→The greater the diameter of the opening is large light source (power is large) enough.
→When using the halogen lamp with the big electric power, the opening diameter becomes big, but the power density does not change.

The figure below shows how to calculate a practical relationship. The academic method is inaccurate.

2-4.The opening diameter and focal length

The above is the calculation when narrowing light energy down and getting a small hot point.
The focus diameter above-mentioned is defined as the area which becomes the same temperature as the center.

There are various definitions focus diameter.
When defining it as the area which becomes the irradiation strength of 1/2 at the center, it’ll be more than 2 times of focus diameter of the above calculation result.

When f is short extremely, It do not hold.
Generally speaking, mirror in case of short focus (about half of the focal length the opening diameter), is roughly comparable to the diameter of the focal point of the light source size.

Another way to use it in back and forth from the focal point cheat if it want to heat a wide range to some extent, that “out of focus”.

It is possible to make an exclusive design, but when it is made of the cost and a problem on a due date, it can be shifted from the focus location, and it should be tried whether it can not be used.

(fig1) f=15 at 10㎜

(fig1) f=15 at 10㎜

Focal diameter is larger substantially uniform distribution

(fig2) f=15 at 15㎜

(fig2) f=15 at 15㎜

Just focus position, light beam is narrowed down.
Maximum temperature is obtained.

(fig3) f=15 at 20㎜

(fig3) f=15 at 20㎜

The focal diameter becomes big, but central part is strong a little.

(fig4) f=15 at 30㎜

(fig4) f=15 at 30㎜

Focal diameter increases, substantially uniform light beams.

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