derekhawkins wrote:
>Russell Shaw wrote:
>> derekhawkins wrote:
>>
>>>>Russell Shaw wrote:
>>>>Without the reflector and beam collimation, you'll need a bigger
>>>>globe for the same exposure time.
>>>
>>>This is more to do with focus than collimation. Parallel rays would be
>>>better than divergent rays but convergent rays would even be better
>>>than parallel rays if shortest exposure time was the only goal.
>>
>> That's just a roundabout way of saying you get the fastest exposure by
>> focusing all the light to a smaller area, maximizing the power density.
> If you remove the reflector and put a collimator in front of the lamp
> you'll get your collimation without focus. Yes, nice low intensity
> parallel rays.
If you put a collimator (lens) in front of an isotropic light source such
that the cone of interception is 90 degrees (quite efficient for a lense setup),
then you'll only collimate 15% of the light (the other 85% is lost).
My cylindrical parabolic reflector intercepts light 270 degrees around the globe,
so 75% of the light is reflected. Because it is only parabolic in one axis, more
light is not collimated in the other axis, so hits the box sides.
Because the globe is laying horizontal and there is no light emission along the
axis of the globe, then not as much efficiency is lost.
The efficiency is certainly triple that of a lens collimator of similar area.
"Yes, nice low intensity parallel rays."
The intensity of parallel rays does not decrease with distance.
By using 24" of distance, the divergent rays from the globe is quite low
and the parallel rays are much more intense.
>> I designed the reflector to give parallel rays, and the result shows as
>> an even power density of the size larger than an A4 sheet.