Determining Ideal Distance On Soft box

[smoke665]

I know with a square or rectangular soft box you can use the Pythogorem Theorem, but what about an octabox. Would you calculate it as a square?

 

[tirediron]

I use a 1.5 - 2 x the diagonal as my rule of thumb; for an octo or polygonal modifier, just measure across the face and use that distance... BUT.. don't get caught up in that. I typically place lights in an approximate position based on the desired end-goal and then move around 'til the light "looks good" and if that's within the 1.5 - 2x, great, if not... oh well.

 

[smoke665]

@tirediron that would make it very close to the same thing I do now, though it seems better toward the 1.5x number. Thanks!

 

[mrca]

As tirediron said, the ideal distance is the distance that gives you the look you want. Softer shadow edge transition, closer. harder, further away. Also, moving it in closer also speeds up the fall off per the inverse square rule. I like soft so I like it in close. However, watch the size of the catchlight. Do you want one half the size of the eye then having to screw around in post to try to reduce it? Another consideration is feathering and my main is often about 90 degrees to the subject and the rear edge slightly ahead of subject. With an egg crate, it does 2 things, gives soft light and keeps spill of my background so I can control it's tone or the color of gels precisely. I can roll a 6x6 black scrim across from it to minimize light bouncing around the set. I set up with my bust of Julius Caesar so raise the light height til the modeling light starts throwing a shadow under the eye brow then lower slightly then roll it around to get the nose shadow where I want it. Take a test shot and fine tune. This isn't a "numbers" thing, it's a results thing. Since every face is different, there is no one size fits all. I often find my distance is dictated by the small space in which I am often working. Sometimes it I live with my back against a wall and my lights jammed against a side wall.

 

[smoke665]

I like soft so I like it in close. However, watch the size of the catchlight. Do you want one half the size of the eye then having to screw around in post to try to reduce it?

Yeah, I like mine in close and deal with the catch lights on the Octabox. It's not as bad in close with the Beauty Dish.

I have an egg crate on mine as well, but I've only had limited experience with feathering. Generally get rushed and don't have the time to adjust to that fine of degree.

I set up with my bust of Julius Caesar so raise the light height til the modeling light starts throwing a shadow under the eye brow then lower

I was using an old teddy bear (same size as granddaughter), till my DW threw it out when I wasn't looking. I've struggled ever since. LOL

there is no one size fits all. I often find my distance is dictated by the small space in which I am often working

I realize that, my question was more curiosity. I was reading an article on portrait light placement, were he mentioned the Pythagorean Theorem, to arrive at the distance for a rectangle or square softbox, but no mention on an Octabox.

 

[enezdez]

Good Stuff Thanks @smoke665 for the conversational topic!

 

[Derrel]

There is no "ideal distance" for a light placement, except the one that most closely matches your desired lighting result. There is a LOT of on-line nonsense about lighting, promulgated mostly by talking heads on YouTube,and in blogs, but the real test of light placement is the actual result. If the light looks good, then it is good. Seriously.

You have to be aware of the Inverse Square Law, and how rapidly light falls off when the light is placed close to a subject; there must be 10,000 videos where some id'jot says that, "Light is soft when it's placed close to the subject, so position the light very close to the subject for the softest light." Well, okay, but, uh...that also means that the closely-place light's intensity falls off at an almost astronomical rate, and less than two feet from the "bright side" of the subject, the lighting could easily be three to four stops darker! So...yeah...How far away the light is positioned depends....on a lot of factors. YOU get to decide how far to position the light from the subject, and higher-level mathematics are not the way to evaluate how far away the light ought to be.

Not trying to poke too much fun, but applying the Pythagorean Theorem to light placement is a boneheaded thought. Euclidean Geometry and photographic lighting using studio lighting gear...kind of like applying Newton's law of Motion to the speed at which one ought to lift a beer glass to one's lips...what is the ideal amount of force and speed to pound down that beer but good???

 

[smoke665]

kind of like applying Newton's law of Motion to the speed at which one ought to lift a beer glass to one's lips...what is the ideal amount of force and speed to pound down that beer but good???

As with certain other things one should use slow and steady motions when drinking beer. To much speed can cause things to slosh out of control.

Agree with you on the exact placement of the light. It's possible my title didnt convey the question correctly, but as I said earlier I was curious as to the application of the theorem to an octabox vs a square or rectangular soft box. I think all agree the exact placement is the one that fits for your shot. While I don't calculate or use math, the spot I first instinctively place my light happens to be very close to the theorem results and using Tirediron's low estimate of 1.5 would also be very close. As you say the final location may or may not be in that spot.

 

[Derrel]

The actual look and "feel" of lighting changes, based on the distance from the light, to the subject. The same
light modifier can give a variety of lighting "looks". Distances between three feet and 12 to 15 feet can make a lot of good photos with many
Modern modifiers. Reducing the distance to a simple 1.5x formula leads to one, specific, generalized
Lighting effect. Always using a 4-foot softbox at 6 feet is the height of playing things safe.