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 p.1 #11 · Anyone use the Fotodiox Pro 88" Para/Parabolic Reflector? | |
hugowolf wrote:
The deeper parabolic reflectors are more forgiving, more efficient with the light, produce less spill, and offer a greater range of focusing. If you look at the edge of the light projected onto a surface from a deep para, it will have a much sharper transition than from a shallow para.
If you look at the first image in this ‘review’, you can see just how well define the edge is from this Profoto deepish para brolly.
http://www.profoto.com/blog/light-shaping-2/light-shaping-tool-of-the-month-umbrella-xl/
The edge isn't defined because of the depth of Profoto's umbrella but because the photographer didn't use a spill kill reflector to hide the bare bulb from being visible from the sides (he's using a ProDaylight Air, meaning a head with a bare bulb). If you look at the umbrella's inside surface head on, you won't see the bulb. But if you don't use a spill kill reflector and move to the side, you may see the bare bulb along an angle that's between the head on axis and the line drawn between the bulb and the outer fabric's edge.
The good news is that, unlike Profoto's recessed heads, he's using what is the only flash tube design / umbrella hole / spill kill reflector mount combination on the market that can be adapted to any umbrella arc shape and position (since the spill kill reflector can be moved back and forth to cover the bare bulb in any situation).
BTW, you can't really use this picture and argue that the modifier is behaving like a parabolic reflector since the illumination covers a nearly 180° circle  . Theoretically, a perfect parabolic reflector used with a perfect point light source should indeed result in sharp edges and project a perfectly even circle of light that's the same diameter as the modifier. That's not what we're seeing here. It's the bare bulb.
In fact, my Profoto 85cm silver deep umbrella is everything but a parabolic modifier since :
1) the arc shape doesn't follow a parabolic curve. Basically, you could say that the inner circle is parabolic, or that the outer one is, but you can't have both of them behave in a parabolic way at the same time.
2) Because it's too deep and the sliding ring that supports the rods is in the way, you can't really reach the focal point for the outer circle. So, basically, from the subject's point of view, the 85cm silver deep will never be an 85cm modifier, but just a glorified beauty dish that you can't put close to the subject. When people say that the deep silver umbrellas from Profoto are more specular, it's not just because it's a silver reflector, but mostly simply because, from the subject's point of view, it's never as big as its real size, unless they are used really close.
3) If you use one of Profoto's recessed heads, even if you could actually reach the focal point, since it would be far inside the modifier, no light would hit the outer circle of the umbrella.
That, is a picture of one of Paul Buff's PLM (the lower one), with spill from the bare bulb reduced as much as possible (there still is some visible on the pillar for example):
https://farm8.staticflickr.com/7271/27610504161_1a427e3639_b.jpg
source : https://www.dpreview.com/forums/thread/4015351
In this picture the beam of light isn't a perfectly well defined circle that's the same size as the modifier, but, as you said, nothing is perfect (and I'm not even sure a truly perfect parabolic modifier would be desirable). But it's as tight a beam as it can get.
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