Half Peak Angle definition

[koimystic]

Basic question that google search didn't turn up many results - what exactly is half peak angle? I am familiar with beam angle and field angle. The reason I ask is I just bought the Arri S60c light intensifier panel and understand it reflects the light a certain direction, but don't understand it's statement of half peak angle of 74 degrees.

 

[Gobokat]

Without looking up Arri's specs for myself I would think the description of "half peak angle" would be analogous to "beam angle" which is 'half the maximum luminous intensity" - and now I've looked up the product and am going to stick by my first reaction that this product, rather than being a pure diffuser, is a polymer prismatic beam reshaper and directs more energy to the front than just letting it spread out the "sides" so effectively redirects enough edge emitted energy to the front to say that you'll hold up to half the emitted light within the 74 degree spread from the fixture.
Anyone who deals more regularly with studio fixtures please correct me.

 

[Dionysus]

Yeah I'm pretty they just 'invented' that term to mean beam angle... Accurate in description but confusing to those who actually know the more classic terminology.

 

[cbrandt]

1/2 peak angle is frequently used by manufacturers, as it is generally part of the standard photometric reports that they receive. It can give you a good idea of how flat the field is.

 

[BillConnerFASTC]

Half peak angle and tenth peak angle are simply other terms for beam angle and field angle, seemingly to be more common in UK and Europe. It does seem clearer than beam and field, and has been around for quite a while. Consider that the beam angle of an early ERS might be much less than the field angle, and today - with the S4 to some degree (ha!) and a lot of LED profiles - there isn't much difference between tenth and half. Plenty of room for both terms.