Question regarding softboxes...

[AGellert]

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Mike,

Always a pleasure to see you get into it as well. We would love to have you at a Supershoot. I know you would benefit from the educational value and hands on experience of shooting shooting and more shooting.....

Thanks for the kind words on Kelly. Although no one has to tell me she's beautiful...I get that part,obviously....that's why I keep her around.... ;-)

J T

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JT,

I bet you "keep" her around for more than just her beauty.


Andrew
President, KellyG World Wide Web Fan Club

[Gunfitr]

I've never thought of it as the relationship of the diaganol, but essentially, what happens is that if you have the light closer than the diagonal, you are surrounding the model with total wraparound light and losing the shadow casting ability. (you are so close that the subject is totally bathed in strong light)

As you pull the light back, there comes a point where you will actually increase the shadow ratio and diminish the softness of the box as the lightsource becomes "smaller" in relationship to the subject.

The "perfect" distance is thus the distance that allows you to make full use of the shadow/highlight function of the box.

I use a five foot octobox quite frequently and have found that images have a different look compared to placing the light as close as possible to the model versus pulling it back a great distance or some intermediate distance. Yes, this should be self evident.

I don't know that their is a "perfect distance" to shoot at....the perfect distance is the distance that gives you the look you want.

I would agree that there is a distance that takes maximum advantage of the ability of the light source and mathmatically that would be the ratio between the distance to the model and the widest measurement of the light.

However, different light boxes throw different shadow patterns. ie. same size boxes are not all he same.

In any event, you can set a lightbox at a given distance and then feather it to get different results, so I'm not certain that the distance of the light is as important as simply understanding how to use whatever lightsource you are using to get the effect you want.

Understanding the concept may be a benefit.

Mark

[jtsmith]

Ok, she's actually my boss......I'll admit it... :-)

J T

[jtsmith]

I think you actually got it right... :-)

J T

[Al_Nowak]

Just to reiterate the questions I raised, they were:

1. What is the derivation of the diagonal of the softbox as an "optimal" distance from the model?

2. Has anybody experienced the "pop" the book's author refers to?

Okay, I've read the replies carefully, and here's where I am at with the questions I asked.

Nobody has come up with a definitive relationship between the diagonal of the softbox and the distance to the model, or at least they haven't shown the math behind it.

The "pop" is probably a personal preference for a given lighting condition, rather than a universally observable phenomena.

So here's what I do know... and JT I WAS paying attention, the fact that my eyes were closed and I was snoring softly is due to the transcendental state I enter when deeply absorbing vast amounts of data... yeah, that's it... transcendental state.

1. Softboxes ideally would output even light across their front surface. In reality, it rarely happens that way. The light in the center of the front surface tends to be more directional and a bit stronger.

2. The closer to the front surface the model is, the larger the apparent light source and the less shadow you are likely to see as the light "wraps" the model.

3. "Feathering" the light so that the model is at the edge of the box's surface tends to "wrap" the light a bit more and produces a "softer" light on the model since it is not as directional as the light in the center of the box.

4. Moving the softbox away from the model makes the light falling on her more directional and from a smaller source, and thus darkens the shadows and reduces the transition area between illuminated areas and shadowed areas.

Okay so far? I realize that a lot of these terms are relative, and your definition may not exactly match mine, but bear with me.

There doesn't seem to be a precise mathematical reason for the diagonal to model distance relationship. It may just be that that's where the author of the book feels the light is "right" for him. Other people may feel it's "right" when the model is at some other distance.

Nobody seems to have experienced the "pop" he refers to, or at least they didn't admit it. It probably just a personal preference for a given shadow to illuminated area ratio or transition zone width.

If the diagonal distance works for the book's author, great. Me, I'm going to take some time and play and see what MY preferences are. I have a pretty good idea what they are already and I don't think it's the diagonal distance, but it depends on the type of shot.

By the way, I have specifically avoided mentioning the title of the book or the author's name. If you want a better book, get David Kimber's "Lighting for Glamour Photography", Jon Gray's "The Complete Guide for Beauty and Glamour Photography", or Barry O'Rourke's "How to Photograph Women Beautifully." But that's just my opinion, and it's your money. Trust me on this one.

[jford]

I tend to be a bit more critical about such things as "optimal distances" because in my work as an analytical chemist, I've learned that "optimal" usually refers to a specific set of constraints or desired goals. Change the goals, the "optimal" changes. Frequently, as you say, people use "optimal" to mean "the way I like it."

Just a guess though: if you have a softbox of length l and width w then the diagonal is d = sqrt(l*l + w*w). If you place the object a distance of d away from the center of the softbox, the object is a distance of 1.12d from each of the corners, i.e. about 10% further than from the center. IF you assume a uniformly emitting softbox, then you've got a pretty nearly flatly illuminated object, since it's nearly equidistant from each corner AND the center. If you move it further, the directionality becomes greater, although the uniformity also increases. Closer makes the unitformity decrease.

Frankly, it seems to me to fit "the way I like it" philosophy of optimal.

[RM_Drake]

Also remember that the other lights (if any) and angle of light vs subject vs camera also come into play. If you were to use two softboxs as the light source, place one as close as possible on each side of the lens, set the lens height at the model's nose level with the model facing squarely into the camera, you'd have a pretty lousy picture, regardless of distance. What you'd create is a huge, soft ring light. By design, ring lights are meant to lessen or eliminate shadows, and without shadows, there's no contrast.

If photography could be reduced to a few mathematical formulas, a you could build a machine to take pictures automatically. Wait... they've done that... it's the photo booth in malls. [img]/ubbthreads/images/graemlins/grin.gif[/img] --Randy

[jtsmith]

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There doesn't seem to be a precise mathematical reason for the diagonal to model distance relationship. It may just be that that's where the author of the book feels the light is "right" for him. Other people may feel it's "right" when the model is at some other distance.

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There is always a mathmatical or scientific reason for the way light responds or how an object responds to light but in lamen terms, it is his "sweet spot" in the way he wants it and likes it.

A "POP" is also always going to be subjective.

An optimal distance is also going to be subjective...

There are just too many variables. Model's features for one example and desired effect tastes for another...just to name a couple....

On the main light using the main light only, that modeling light is going to give you a perspective of how it really is going to look when it flashes. You just have to look into it and start reading it from the modeling light. Pay attention to how the light wraps around, how sharp the shadows are, specular highlights on the forehead and cheek, etc. It's there, you just have to read it with your eyes to begin with. Then you will find your very own optimal distance or your clients optimal distance depending on who you are shooting for.

J T