Softboxm umbrella, octabox comparative sizes....

When comparing sizes of octaboxes or umbrellas. It is easy to determine that (given the same distance from modifier to subject) a larger unit will produce a softer light than the smaller unit. In other words, a 45 inch octabox will produce a softer light than a 32 inch or 24 inch octabox.

However, does this hold true for softboxes?

I realize that a 45 inch by 45 inch softbox will produce a softer light than a 24 x 24 inch softbox. However, in general use, would a 24 x 36 inch softbox produce a softer light than a 24 x 25 inch model. Or will it just produce the equivalent softness over a greater area?

RPCrowe wrote in post #18658236
When comparing sizes of octaboxes or umbrellas. It is easy to determine that (given the same distance from modifier to subject) a larger unit will produce a softer light than the smaller unit. In other words, a 45 inch octabox will produce a softer light than a 32 inch or 24 inch octabox.

However, does this hold true for softboxes?

I realize that a 45 inch by 45 inch softbox will produce a softer light than a 24 x 24 inch softbox. However, in general use, would a 24 x 36 inch softbox produce a softer light than a 24 x 25 inch model. Or will it just produce the equivalent softness over a greater area?

distance of diffused light source from subject determines the amount of light that can be "wrapped" around the subject to soften and widen transition zone from highlight to shadow. So, at same distance bigger will result in more wrap. That is one reason I like big, and feathering, which is a way to control where the light strikes the subject. Grid on the modifier will also help with control.

Ignoring the scatter of uncontrolled light reflecting off walls and ceiling etc. a 36" umbrella is just as soft a source as a 36x36" softbox or a 36" Octobox or a 36"x36" white reflector panel...only the reflected catchlights vary in appearance

RPCrowe wrote in post #18658236
When comparing sizes of octaboxes or umbrellas. It is easy to determine that (given the same distance from modifier to subject) a larger unit will produce a softer light than the smaller unit. In other words, a 45 inch octabox will produce a softer light than a 32 inch or 24 inch octabox.

However, does this hold true for softboxes?

I realize that a 45 inch by 45 inch softbox will produce a softer light than a 24 x 24 inch softbox. However, in general use, would a 24 x 36 inch softbox produce a softer light than a 24 x 25 inch model. Or will it just produce the equivalent softness over a greater area?

I was always told to look at the diagonal measurement, so theoretically it is softer
mike

Yes size is relevant to subject distance, but it is also relative to orientation of subject and light.

Take it to an extreme and consider a strip box or long rectangle. The light provided with a 90 degree rotation would be vastly different ((tall vs wide).

So corner to corner measure is only relative to objects and shadows cast along that plane. Same for edge to edge width. In reality however, I doubt you'd see much difference with area and all other things being equal ... which is pretty much impossible.

dpe wrote in post #18658961
I was always told to look at the diagonal measurement, so theoretically it is softer
mike

Academic debate. Consider that a long narrow light source is only like a 'large source' in one dimension only, and is a 'small source' in the other dimension. That contradicts the diagonal measure, does it not?!