Parabolic softbox/umbrella in practice?

Started Dec 11, 2017 | Questions thread
MayaTlab0
MayaTlab0 Senior Member • Posts: 2,754
Re: Parabolic softbox/umbrella in practice?
21

vett93 wrote:

I have seen lots of YouTube videos explaining the benefits of parabolic softboxes and umbrellas. My takeaway from them is that they would yield more focused light and the light has less spray.

In practice, do you see enough differences to justify buying them when you already have regular ones?

95% of the modifiers sold as "parabolic" simply aren't, and 95% of the videos on Youtube about parabolic modifiers are complete BS in many regards.

I've written a long boring post in another forum, which doesn't exactly answers your questions and may contain plenty of mistakes, but may still be helpful (and probably is a lot more than a lot of videos and articles on the web) : http://www.fredmiranda.com/forum/topic/1508979

It's still, unfortunately, an over-simplification.

I've re-arranged it a bit here :

a) Regarding the term "parabolic" : it has a precise definition that entails a precise result, and most modifiers sold as "parabolic" simply aren't shaped at all like a paraboloid and aren't even trying. Parabolic doesn't mean that the modifier is deep, it means that it conforms to a specific mathematical definition of the arc shape - wikipedia's article on the matter is explicit enough in that regard.

As a result, NONE of the deep umbrellas on sale today are parabolic modifiers, because their arc shape is nowhere near the definition of a parabola. In fact, a shallower Paul Buff PLM is closer to that definition.

A perfectly parabolic reflector with a perfect mirror finish has a focal point, and if a light source is at this focal point, it will reflect the light rays from the light source in a perfectly parallel beam, like this :

@Parabolix

An example of a modifier that tried to get as close as possible to that definition is the Broncolor Satellite, and it's very shallow:

As a result, a shallower Paul Buff PLM can send light at a rather tight beam angle. Below, a Chinese copy of the extreme silver PLM vs a 20° grid:

b) White materials will scatter the light in all directions, regardless of the angle of the light ray that hits them. A perfect mirror will bounce the light at the opposite angle at which the light ray hit it, a bit like a ping pong ball (without spin :D). Silver materials are, in a way, imperfect mirrors. They vary in terms of reflectiveness. Some of them are quite reflective and won't scatter the light much, others are designed to scatter it a bit more. To sum it up in a over-simplified way :

The result of this is that :
- there isn’t such a thing as a white parabolic modifier. Since the main property of a parabolic modifier is its ability to re-direct light rays in a specific direction, a material that scatters light rays in all directions negates the interest of the paraboloid shape. Some would argue that Paul Buff’s soft silver PLMs aren’t parabolic reflectors either as the material scatters light too much, but I have a less finite opinion.
- Moving the light source inside a white reflector will not change much the beam angle of that modifier : it’s always going to scatter light in all directions. Differences will be marginal.
- On the contrary, silver reflectors are more or less heavily relying on where the light source is positioned relative to them. Moving the light source relative to the umbrella, either laterally or closer/further out, can very significantly change the beam angle, or the effective size of the modifier (from the subject’s point of view). The more scattering the silver material is, the less sensitive it is to light source position.

Paul Buff used to sell the exact same umbrella shape (the PLM) in white, and two silver materials, with different scattering properties, soft silver, and extreme silver, to benefit from the different characteristics of each material.

Broncolor’s smaller 88 and 133 paras use a slightly more scattering material than their bigger ones, because it improves the quality of the illumination from the subject’s point of view and most people don’t really like the look of a really hard parabolic modifier anyway.

c) Adding diffusion over a parabolic, pseudo parabolic, or deep silver reflector will instantly negate a good chunk of its directional aspect, since diffusion scatters light rays. Here is, on the left, an extreme-like silver umbrella, without diffusion, and on the right the same umbrella, but with Paul Buff’s front diffuser :

Some diffusion materials might be weak enough that they will scatter the light only a little bit. The Paul Buff fabric above is quite dense. Broncolor sells different front baffles for their paras, with different optical densities, precisely to vary the impact of the diffusion material.

d) effective modifying size and appearance from the subject’s POV (i.e., what it will look like on your subject in terms of specularity, shadows, etc.) can be different from the physical size or appearance the modifier.

With silver reflectors, since they bounce and re-direct light, only the areas of the umbrella that effectively re-direct light towards your subject will directly contribute to the light quality falling on your subject. From the latter’s point of view, these areas will be illuminated. The areas of the umbrella that re-direct light somewhere else, or don’t receive light in the first place, will look dark from its point of view. With deep umbrellas, what you get usually is this (compared here a Profoto deep with a shallower PLM-like silver umbrella) :

The result is that for most intents and purposes, deep silver umbrellas are much smaller effective modifiers then shallower pseudo-parabolic umbrellas like PLMs. There are a few exceptions (for example if your subject is so close that it's nearly touching the shaft, and you've shoved a strobe with an omnidirectional flash tube all the way in), but in practice they're rare. In most scenarios the outer area, even if it's struck by light coming from an omnidirectional flash tube, isn't oriented in such a way that it can bounce back light towards the subject.

You can also notice that both umbrellas are illuminated in a bicycle wheel pattern. That’s because of two things :
- the silver material used in both of these umbrellas is quite reflective, and
- because they are 16 sided fabric modifiers, they are imperfectly shaped, and only the middle area of the fabric between the ribs is effectively in the right orientation to be able to re-direct light rays towards the subject.
The result is that catchlights might exhibit this bicycle wheel pattern, and you may see multiple, stepped shadows appear. Basically, instead of behaving like one light source, they behave like 16 elongated light sources.

Paul Buff’s soft silver umbrellas use a silver material that’s just scattering enough that this bicycle wheel pattern doesn’t appear. It will look like this (extreme on the left, soft on the right) :

But since the material scatters light a little bit more, it isn’t quite as directional as its extreme silver cousin (extreme on the left, soft on the right) :

That being said, you can still see in the above shot that the soft silver can be configured to produce a hot spot that more or less corresponds to the area lit by the more extreme version, with the head in the same position. So some of its pseudo parabolic DNA is still there.

It still remains quite a lot tighter than, for example, a white umbrella (soft silver on the left, white - BTW a deep one - on the right) :

All of these comparisons were made with the light modifier on axis with the camera’s lens (i.e., the subject), but you may very well want to feather the light (albeit with highly directional silver umbrellas, there isn’t much feathering room to be honest). when you feather the light, you will see the effective modifying area of the umbrella change, move to the side, etc…

Since white reflectors scatter light in all directions, their fabric doesn’t have to be in a precise orientation to re-direct light towards your subject. As a result they don’t suffer from this bicycle wheel pattern look. But how your strobe is positioned, how its flash tube is designed and which reflector is used can still matter in terms of illumination evenness.

e) "Spill" / "spray" can have various origins, but one of the most common causes with umbrellas is bare flash tube spill, i.e. when the flash tube is visible from the sides. In the following photo :

- the blue arrow corresponds to the area that's illuminated by the light reflected by the umbrella,
- the red arrow to the area that's illuminated by the strobe's bare flash tube if it hasn't been properly killed by a spill kill reflector or by other means. Very often people say that umbrellas, even silver ones, have massive spill, while they don't bother to effectively kill the spill from the bare flash tube,
- and the green arrow to the area that's illuminated by the light reflected from the subject (if your subject is a white wall, it will matter).

That's been taken with a Profoto B2 without a spill kill modifier, and with the Cactus umbrella slightly forward from the head (hence why you see a streak of light coming from the bare tube). If I had used a flash with an external flash tube and without a spill kill modifier, bare tube illumination would be massive and cover a much wider angle.

Bare flash tube spill can be useful, for example if you want to benefit from the flash tube’s exposition to use a bounce reflector in addition to the umbrella. But it’s a good thing to eliminate it properly, at least when comparing spill from different modifiers :D.

So to answer more precisely your question :

Regarding fabric modifiers, the main benefit FOR ME of attempting to reach a shape that's as close as possible to a paraboloid, is that you can reduce the amount of scattering a silver material requires to avoid an uneven or bicycle wheel illumination pattern when looking into the modifier, which can produce unwanted results (such as stepped, multiple shadows). So you can get both a rather precise beam of light, and a reasonably even and trouble-free illumination pattern. The Broncolor 88 and 133 are pretty good in that regard, for example. And in a diminished capacity, since it isn't quite as well shaped (but still far better than any other silver umbrella, particularly the deep ones), the Paul Buff PLM soft silver is pretty good too, as you've seen above.

In more general terms high-end paras are mostly prized for their versatility. But some of the effects they're famous for (such as the ring of light in the defocused position) are less a result of them being parabolic than of them being designed in a specific way. For example, regarding the ring of light, it's just because their outer area is in the right orientation to bounce back light towards the subject at most common distances while the centre isn't in the right orientation to do so.

The great news is that most people don't need an exacting parabolic modifier. Personally as long as I have reasonable directionality and a reasonably even, spoke-less illumination, I'm happy. A Paul Buff PLM soft silver meets my personal sweet spot but there are plenty of other interesting solutions, most of which aren't parabolic, and don't even have to be to prove satisfying.

A modifier doesn't need to be parabolic to already be quite versatile and provide a variety of different light qualities.

So I'd focus less on trying to find a parabolic modifier than on finding a modifier that suits your needs. Apparently it's about getting a tighter beam angle, and that doesn't necessarily require an exact parabolic shape, nor does it require a deep one. Depends on where you want the trade-offs to be :D.

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