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ALL soft boxes have the same throw whatever the size,
whatever the shape whatever the make.
The only differences are three:
— a larger box will better wrap at close range
— some shapes will have other spot, spread or fall off
— smaller boxes will give smaller catchlights.
So, any soft box of given shape but different size will differ
only in the wrap. The bigger, the better the wrap. A smaller
soft box at ten feet will cover from head to toe but a bigger
one will wrap a bit more at the same distance and much bet-
ter at three feet!
Not really accurate, although the innacuracies that I see may be down to nothing more than language.
I interpret "Wrap" to mean "Wraparound". Wraparound is not entirely dependent on size, but is dependent on
relative size, e.g. a small softbox can produce a wraparound effect on a small subject such as an orange, but a big one is needed for a large subject, assuming that the same effect is required.
Obviously, any type of light source will illuminate the part of the subject that it points at, but if the light source is small then the light will be stopped by anything that it hits that's sticking out - a nose, cheekbones etc - and this light blockage causes shadow.
Wraparound occurs when different parts of the subject are illuminated by different parts of the light source, e.g. the nose and other parts of the subject may be lit by the centre of the softbox, but light from the edge areas will light areas that would otherwise be in shadow simply because the light is coming from different places.
The lighting intensity will not be even because of the effects of the inverse square law, for example with a large softbox, placed at a distance of 1m from the subject, some of the light will only be travelling 1m, other light (from the edge areas) may be travelling 3m so the parts of the subject that are 3m from the light will receive a lot less light.
Moving the softbox further away will produce a very different type of lighting because the ratio of light fall off will be very different, i.e. if the light from the nearest point is now travelling 3m, the light from the edges is now travelling 5m so the fall off of light will be much less apparent.
So, to get a more rapid fall off of light, regardless of softbox size, simply place the softbox closer. In fact, because of practical difficulties, quite often a smaller softbox can be a lot better than a larger one because it simply isn't possible for a larger one to be used very close to the subject - of course, all this assumes that soft light, and wraparound light, is good and that hard light is bad, which is a very big assumption and it is really a beginner assumption - beginners who, up to now, have only shot with tiny light modifiers then find themselves with a studio flash and a fairly big softbox and they light the soft light that this can produce and from that point onwards they want bigger and bigger softboxes
- until they progress to the point where they find that hard light is the right approach for some subjects.
I'm the first to admit that although life can be a lot easier with a wide choice of softboxes (and other light shapers), up to a point the people who have a deep understanding of how light actually works can use this knowledge to limit the range of sizes and shapes that they need.
As for whether or not really large sofboxes are actually needed, this can depend on the style of the photographer. For example, we have a
140 x 27cm strip softbox, I use it all the time to create rim lighting, including full length. In theory it isn't long enough for that but simply moving it a m or so away spreads the light perfectly, but of course at that distance, partly because it is behind as well as at the side of the subject, it just produces a fairly hard strip of light - which is what I want. But, if I wanted to photography someone who is 2m tall and wanted the softbox to be really close, then to get the same effect with that person that I can (if I want to) get with a smaller model, I would need to use a larger strip softbox, and we now have one that is
2m long. Frankly, so far I've only played with it and I may never actually need it, for the type of shots that I personally like to create - other people may find it indispensable.
Another potential problem with large sofboxes is space, although this comment doesn't really apply to our new strip softbox because it is typically used vertically and almost touching the ground - big softboxes (or at least the ones that work) are deep, they need to be, and they take up a lot of space, which matters when the space is limited. Typically, they are used high, and limited ceiling height makes them unsuitable for home or garage use, unless the subject is seated - I've lost count of the number of people who have bought 1.5m octa softboxes without thinking it through, only to find that when it's touching the ceiling the centre of the softbox is
below the face...
Sometimes though, the carefully crafted and well thought out lighting arrangements that we all like to use just aren't practicable, and when this happens it can be a good idea to use a larger softbox from further away. And they same thing applies to other types of light shaper. For example, we now have
60cm folding beauty dishes (which, when a diffuser is fitted, become softboxes) and in a perfect world, this is what I would normally used for glamour portraits of the right model - but it only produces the right result in perfect situations, and when photographing a model who is constantly moving, and flirting to camera,
a larger one allows a lot more flexibility - but again there is a downside, because the larger one needs more ceiling height to maintain the correct angle.
