How do you do that Spotlight/Light Beam effect

Started 3 months ago | Discussions
tugwilson Senior Member • Posts: 2,924
Re: How do you do that Spotlight/Light Beam effect

Rico Tudor wrote:

Projection attachments like the Dedolight DP1 and the Godos SA-P have kob which lets you tilt the front of the projector to correct the distortion in cases like this.

DP-1 cannot be tilted. A perfectly circular spotlight when hitting the b/g at an angle can be achieved with an elliptical gobo although the focal plane will not fall correctly for sharp edges all around. DOF can be increased by pulling the fixture way back but illumination efficiency will suffer the inverse-square law.

I think you are right. My memory played tricks, The screw is there to allow the image it be in focus on a slanted surface using the Scheimpflug principle.

The beam is almost parallel. So the falloff is very gradual because the virtual point source is a long way behind the light. The inverse square law applies but you measure from where the light appears to come from not the front of the light.

Ed Shapiro
Ed Shapiro Regular Member • Posts: 339
Re: How do you do that Spotlight/Light Beam effect

tugwilson wrote:

Ed Shapiro wrote:

I suspect it is a post-processing job. If it was done with an optical spot to light and the subject AND background the circle on the background would no be concentric or perfectly round. The shadows on the background indicate that the main light is coming in at about 30-degrees0 that would cause a more elliptical pattern on the background. To get a perfect circle, the optical spot would have to be coaxial to the subject and hide behind her.

Projection attachments like the Dedolight DP1 and the Godos SA-P have kob which lets you tilt the front of the projector to correct the distortion in cases like this.

If the circle was a cutout, adhered to the background, how do y'all account for the falloff of light? You can see the subject's legs and the cove in the cyclorama at a different rate of opacity. If the spotlight was hidden behind the subject, you would need adequate depth of field to render the edges sharply- and you would need more distance between the subject and the background- the shadows indicate that she is very close to the background. Looks like an overlay? To get a definite circle you would need a focusable optical spotlight with a carrier to hold gobos at the proper distance from the condensers.

I had similar doubts about these images but the OP says that there's a BTS video showing the shoot.

Yeah- Interesting. an optical spot with a tilt/shift mechanism or an elliptical gobo that goes "round" when it is skewed. All I have here in the shop is an old 500-watt B&M optical spot with a focusable track and a diaphragm--32000K Tungsten- it that lamp ever burns out, I don't think there are any replacements for it- it was made in 1949

I'd like to see that  Utube thing- I'll look out for it.--

Ed Shapiro- Commercial and Portrait Photographer. Ottawa, Ontario Canada

RobzLondon Junior Member • Posts: 35
Re: How do you do that Spotlight/Light Beam effect

Rico Tudor wrote:

Projection attachments like the Dedolight DP1 and the Godos SA-P have kob which lets you tilt the front of the projector to correct the distortion in cases like this.

DP-1 cannot be tilted. A perfectly circular spotlight when hitting the b/g at an angle can be achieved with an elliptical gobo although the focal plane will not fall correctly for sharp edges all around. DOF can be increased by pulling the fixture way back but illumination efficiency will suffer the inverse-square law.

Inverse square law does not apply to focused or collimated light!

https://www.parabolixlight.com/debunking-the-inverse-square-law

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Ed Shapiro
Ed Shapiro Regular Member • Posts: 339
Re: How do you do that Spotlight/Light Beam effect

RobzLondon wrote:

Rico Tudor wrote:

Projection attachments like the Dedolight DP1 and the Godos SA-P have kob which lets you tilt the front of the projector to correct the distortion in cases like this.

DP-1 cannot be tilted. A perfectly circular spotlight when hitting the b/g at an angle can be achieved with an elliptical gobo although the focal plane will not fall correctly for sharp edges all around. DOF can be increased by pulling the fixture way back but illumination efficiency will suffer the inverse-square law.

Inverse square law does not apply to focused or collimated light!

https://www.parabolixlight.com/debunking-the-inverse-square-law

Are they claiming that with their reflector design you will set up your flash unit in one of their reflector models and make a meter reading at say 8 feet away than another reading at 12 feet away and there will be no loss of light? And...what does that have to do with an optical spotlight?  Sounds interesting!

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Ed Shapiro- Commercial and Portrait Photographer. Ottawa, Ontario Canada

Rico Tudor Contributing Member • Posts: 831
Re: How do you do that Spotlight/Light Beam effect

Inverse square law does not apply to focused or collimated light!

Unless you deal with point sources (not available in this reality) the light cannot be collimated. Laser light is, of course, collimated but not by refractive means, and is rather impractical for head shots! With a projector, the "spotlight" is the imaged stop of the optical train, and where you might place a gobo or iris. As distance increases, the diameter of the projected optical stop enlarges linearly—simple geometry. With increased distance, a particular spotlight framing around the subject can be maintained by closing down the iris but flux density has nonetheless been reduced by the inverse-square law. This flux reduction can be eliminated by using a longer projector lens with same f-stop (iris open).

For a mathematical treatment of inverse-square, search for "flux as a surface integral" on Wikipedia. Salient concepts are "orientable" and "divergence".

For pedagogical insight, shine a Maglite on the wall. The central blob is the (imaged) bulb. Yes, the back reflector is a crude paraboloid! With increasing distance from the wall, the blob enlarges. If you remove the Maglite reflector by unscrewing the head, you can project the naked bulb with a photographic lens onto a far wall and make out the tungsten filaments: they will be much larger than life-sized and dim.

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tugwilson Senior Member • Posts: 2,924
Re: How do you do that Spotlight/Light Beam effect

RobzLondon wrote:

Rico Tudor wrote:

Projection attachments like the Dedolight DP1 and the Godos SA-P have kob which lets you tilt the front of the projector to correct the distortion in cases like this.

DP-1 cannot be tilted. A perfectly circular spotlight when hitting the b/g at an angle can be achieved with an elliptical gobo although the focal plane will not fall correctly for sharp edges all around. DOF can be increased by pulling the fixture way back but illumination efficiency will suffer the inverse-square law.

Inverse square law does not apply to focused or collimated light!

https://www.parabolixlight.com/debunking-the-inverse-square-law

That's an oversimplification and not a good explanation of the physics.

The inverse square law applies to light emitted by a point source. In the real world we never have a point source so the inverse square law is an approximation to the effect we can observe. In general it's a very good approximation but in some cases the nature of the light source produces affects which seem to break the law (it doesn't break the law).

An ideal parabolic reflector will have a point source of light at the focus and the reflector will produce a set of parallel beams. The is equivalent to having light emitted by a point source infinitely distant from the observer. The inverse square law still applies but is the source is infinitely far away you get no dropoff. In practice things are lots messier than this and if you try an model the behaviour you end up with a very large number of point sources at various distances and positions behind the reflector and you do get measurable dropoff as we all know.

With most modifiers the effect on dropoff is quite small. In the last couple of years LED light manufacturers like Namlite have produced reflectors designed for specific lights which are dramatically effective. These are faceted reflectors and I don't quite understand the physics behind them. I imagine they are tuned to the size and shape of the COB.

Projectors are a special case too. Lights like the Dedolight have a focusable emitter and a set of very high quality optics that produces a beam of light with a precise spread. It does this with very little light loss. From an inverse square law point of view the light comes from a point source at some distance behind the light and that distance can be changed by using lenses of different focal length in the projector. The effect of this is that you can throw the light surprisingly long distances with very little falloff. However they don't violate the inverse square law.

TheGrilledCheese Regular Member • Posts: 111
Re: How do you do that Spotlight/Light Beam effect

Shoot against a green screen and then put whatever you want behind the subject and add a shadow. That's the easiest way if you want some flexibility in post. Otherwise you're stuck with what you shot.

Ed Shapiro
Ed Shapiro Regular Member • Posts: 339
Re: How do you do that Spotlight/Light Beam effect

jlafferty wrote:

I have to say it’s surprising how willfully people keep insisting this isn’t done with lighting. The light isn’t at an angle relative to the wall - the subject-shadow separation is due to camera angle. It’s also the case that you can move the light source relative to the subject to increase shadow separation from the subject, while keeping the projector front element parallel to the wall. The light has a crisp edge because they made the face of the projector parallel to the wall, and moved around that. It’s *possible* they also cleaned up the edge in post but my hunch says *not necessary*.

I am not "insisting" or arguing about anything. I am just making an educated guess based on light and shadow in the images and what I observed based on my experience with ordinary equipment.  If, in fact, there's new innovative equipment that modifies light to behave in new and different ways- as I wrote, I find that interesting.  If there is a technique that I am not familiar with, I would like to see it performed- someone mentioned an online video.

Again, IF, there is a light modifier incorporating a parabolic umbrella that defies the inverse square law that can be utilized with ordinary studio-like equipment, not laser or laboratory-generated point light sources, that's interesting too. Otherwise it just interesting topics of scientific conversation that have no practical usage in applied photography.

I love "lighting", I teach lighting, and I study and learn to light so any effect that can be done with lighting and does not require all kind of messing around with in post-processing, appeals to me.

As for the images in the OP's question.  to me, the effect looks artificial.  The edges of the spot of light look unreal. If the effect is strictly the function of lighting via a specialized technique or equipment, I don't feel the technique was applied with sufficient nuance.

This is my OPINION- it ain't carved in stone- I'm always receptive to other ideas and opinions.

Ed Shapiro- Commercial and Portrait Photographer. Ottawa, Ontario Canada

elliotn Senior Member • Posts: 2,312
Re: How do you do that Spotlight/Light Beam effect
1

Ed Shapiro wrote:

I suspect it is a post-processing job. If an optical spot was used to illuminate the subject, it would not be as sharp around the edges on the background- unless she was almost touching the background.

She's clearly very close to the background. But even if she wasn't, why does that preclude getting a sharp edge on the background?

The shadow on the background indicates that the light was coming in at an off-camera angle of about 30- degrees- that would not cast a perfectly symmetrical circle on the background.

It seems to me that the light is only slightly above camera - maybe 5 or 10 degrees off the horizontal axis. That would give the kind of circle we are seeing.

RobzLondon Junior Member • Posts: 35
Re: How do you do that Spotlight/Light Beam effect
2

Rico Tudor wrote:

Inverse square law does not apply to focused or collimated light!

Unless you deal with point sources (not available in this reality) the light cannot be collimated. Laser light is, of course, collimated but not by refractive means, and is rather impractical for head shots! With a projector, the "spotlight" is the imaged stop of the optical train, and where you might place a gobo or iris. As distance increases, the diameter of the projected optical stop enlarges linearly—simple geometry. With increased distance, a particular spotlight framing around the subject can be maintained by closing down the iris but flux density has nonetheless been reduced by the inverse-square law. This flux reduction can be eliminated by using a longer projector lens with same f-stop (iris open).

For a mathematical treatment of inverse-square, search for "flux as a surface integral" on Wikipedia. Salient concepts are "orientable" and "divergence".

For pedagogical insight, shine a Maglite on the wall. The central blob is the (imaged) bulb. Yes, the back reflector is a crude paraboloid! With increasing distance from the wall, the blob enlarges. If you remove the Maglite reflector by unscrewing the head, you can project the naked bulb with a photographic lens onto a far wall and make out the tungsten filaments: they will be much larger than life-sized and dim.

I think you my be confusing terms.

Collimated means the light is parallel - for all practical purposes sunlight is collimated and can also be achieved with lenses, and approximated to by paras etc.

Laser light is in phase or coherent - all the photons have a similar wavelength and the wave peaks and troughs coincide - which is what gives laser light its intensity.

The inverse square law is all about radiated energy (light in our case) spreading out over spherical space - the area of that sphere increases with square of distance (4 Pi r^2), thus the amount of energy per unit area falls off by the inverse amount. Parallel light does not spread out into a sphere, so (its energy) does not fall off in the same way.

Of course strictly speaking the inverse square law ONLY applies to the theoretical point light source, but is a good rule of thumb for most photographic light modifiers, but not so good for focused or parallel light.

I happened to read physics for my degree, and although we never covered the inverse square law's application to photographic lighting, we did in relation to other types of radiated energy

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Rico Tudor Contributing Member • Posts: 831
Re: How do you do that Spotlight/Light Beam effect

Of course strictly speaking the inverse square law ONLY applies to the theoretical point light source, but is a good rule of thumb for most photographic light modifiers, but not so good for focused or parallel light.

Laser light is indeed coherent but also collimated—the characteristic required to project a "spotlight" over some distance with sharp edges. Unfortunately, that beam is only pencil wide! Similarly, a theoretical point source could be collimated by a followspot or projector fixture but the beam diameter would equal that of the front element: again, unworkable for human subjects. All lighting instruments for photographic use are very far from providing a point source, and the spotlight effect is created by focussing the optical stop. Inverse square is then applicable in mathematical terms, and demonstrable by simple experimentation. The sun is not a point source, either: shadow edges quickly become fuzzy with distance, and projecting an image of the sun with any lens will obey inverse-square. Try it.

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Ed Shapiro
Ed Shapiro Regular Member • Posts: 339
Re: How do you do that Spotlight/Light Beam effect

elliotn wrote:

Ed Shapiro wrote:

I suspect it is a post-processing job. If an optical spot was used to illuminate the subject, it would not be as sharp around the edges on the background- unless she was almost touching the background.

She's clearly very close to the background. But even if she wasn't, why does that preclude getting a sharp edge on the background?

The shadow on the background indicates that the light was coming in at an off-camera angle of about 30- degrees- that would not cast a perfectly symmetrical circle on the background.

It seems to me that the light is only slightly above camera - maybe 5 or 10 degrees off the horizontal axis. That would give the kind of circle we are seeing.

Yes- this goes to my point of an artificial effect- there is the disunity of lighting- the light on the subject and the light on the background do not coincide. No matter was the off-camera ligt is coming from, it is not coaxial with whatever is lighting the background.

Hey- I can and have done similar effects with a front'projectin beam-splitter system and a retro-reflective (Scotchbright) background screen.  The trick was to make the background visually compatible with the lighting on the subject otherwise, the effect appears artificial.

Ed Shapiro- Commercial and Portrait Photographer. Ottawa, Ontario Canada

Ed Shapiro
Ed Shapiro Regular Member • Posts: 339
Re: How do you do that Spotlight/Light Beam effect

Rico Tudor wrote:

Of course strictly speaking the inverse square law ONLY applies to the theoretical point light source, but is a good rule of thumb for most photographic light modifiers, but not so good for focused or parallel light.

Laser light is indeed coherent but also collimated—the characteristic required to project a "spotlight" over some distance with sharp edges. Unfortunately, that beam is only pencil wide! Similarly, a theoretical point source could be collimated by a followspot or projector fixture but the beam diameter would equal that of the front element: again, unworkable for human subjects. All lighting instruments for photographic use are very far from providing a point source, and the spotlight effect is created by focussingthe optical stop. Inverse square is then applicable in mathematical terms, and demonstrable by simple experimentation. The sun is not a point source, either: shadow edges quickly become fuzzy with distance, and projecting an image of the sun with any lens will obey inverse-square. Try it.

The sun is my favourite light source- at 93-million miles away, it does a heck of a job.  Condensing solar light and heat with a lens was my specialty as a kid going through my  '"pyro" stage. Saved me lots of money on matches for setting fire to cockroaches!  I did have a so-called point light source in a graphic arts enlarger that I purchased second-hand.  Sharp and heck and contrasty for line copy but showed up too much dust and gran- changed it up for a cold-light housing.

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Ed Shapiro- Commercial and Portrait Photographer. Ottawa, Ontario Canada

elliotn Senior Member • Posts: 2,312
Re: How do you do that Spotlight/Light Beam effect
1

Ed Shapiro wrote:

elliotn wrote:

Ed Shapiro wrote:

I suspect it is a post-processing job. If an optical spot was used to illuminate the subject, it would not be as sharp around the edges on the background- unless she was almost touching the background.

She's clearly very close to the background. But even if she wasn't, why does that preclude getting a sharp edge on the background?

The shadow on the background indicates that the light was coming in at an off-camera angle of about 30- degrees- that would not cast a perfectly symmetrical circle on the background.

It seems to me that the light is only slightly above camera - maybe 5 or 10 degrees off the horizontal axis. That would give the kind of circle we are seeing.

Yes- this goes to my point of an artificial effect- there is the disunity of lighting- the light on the subject and the light on the background do not coincide.

Hmm, I don't understand what you mean by 'disunity of lighting'. Looking at the bottom right image, the shadow of the model's right hand is just below her hand, and the shadow of the model's chin is just below her chin. Both shadows suggest a light that is positioned just slightly above the camera position. Where is the disunity?

And then the shadows around her left hand appear to be formed by the light bouncing back off the illuminated background.

All of this seems consistent with the use of an optical spot.

I guess it could be a photoshop job... but it's quite complicated... why not just use a spot?

S Castle
S Castle Senior Member • Posts: 1,103
Re: How do you do that Spotlight/Light Beam effect

elliotn wrote:

Looking at the bottom right image, the shadow of the model's right hand is just below her hand, and the shadow of the model's chin is just below her chin. Both shadows suggest a light that is positioned just slightly above the camera position. Where is the disunity?

And then the shadows around her left hand appear to be formed by the light bouncing back off the illuminated background.

All of this seems consistent with the use of an optical spot.

I guess it could be a photoshop job... but it's quite complicated... why not just use a spot?

I think so too. It could even be a Spiffy Light Blaster with a circle cutout slide. But it's probably a hot light with an optical snoot attachment.

The OP has not come back with any comments from seeing the IG Stories BTS video. I wonder if it survives anywhere.

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Shane

jlafferty Senior Member • Posts: 1,307
Re: How do you do that Spotlight/Light Beam effect

Tangentially related, with a good demo of collimated light - this guy builds a really good fake sun out of a parabolic reflector and 500w LED:

https://youtu.be/6bqBsHSwPgw

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NormanAllen Senior Member • Posts: 1,032
Re: How do you do that Spotlight/Light Beam effect
1

tugwilson wrote:

amlbenilde wrote:

Hi thanks! I also suspected that it could've been done with post but the photo at the top-left is a screenshot of a behind the scene video from ig stories. I rent a studio with Godox dp400ii strobes. If i were to opt for a continuous light, what would be a good budget light for this setup considering the modifiers you mentioned.

There are only three options I know of for a high quality projection device.

1/ The Aputure Spotlight Mounthttps://www.aputure.com/products/spotlight-mount/

2/ The Aputure Spotlight Mini-Zoom (not yet available)

3/ The Godox S30 SA-P projection attachment (which is a copy of the far more expensive Dedolight DP2 imager)

The first modifier has a Bowens mount but will not work with a DP400II because it has a lens at the rear which gives very little clearance for the tube.

The other two use the Dedolight mount (not 100% sure about the Aputure one but they would be stupid not to make it compatible). Godox make the SA-17 adapter which lets you use the S30 projector on thier Bowens mount continuous lights. They are very clear that it's not intended for strobes and I doubt it would work with the DP400II because of the clearances at the back. Here is a video review of it. You will see that it is pretty inefficient.

People in the know are dropping hints that Godox is working on a solution that allows the S30 projector to be used on strobes but I don't have any details on that.

There are lots of no name projectors with Bowns mounts which do not have rear optics and will fit on strobes. Ones like this with built in optics or like this which lets you use a camera lens. You can compare the price of these with an S30 projector. I had one of these a while ago and they are fun but the optics are dreadful compared with the S30 projector. I also had a light blaster which is an overpriced piece of junk in comparison.

If I was trying to reproduce this at the lowest cost I'd use an S30 with an SA-P projector and an SA-06 iris (it's an expensive item but it gives you very fine control over the size of the circle. Perhaps only buy it if you are having issues getting the circle size you want).

Here's a video review of the S20. There's a two part review of the Aputure projector here and here.

Thanks for this information. I looked into it and the Godox S30 with the projector and iris seem to be a good combination that doesn't break the bank for this. Question: are you aware of any strobe-based solutions for this? I don't mind going the LED route, but the S30 seems to drop to 10W when using batteries, which means using it on location is probably not going to happen.

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jlafferty Senior Member • Posts: 1,307
Re: How do you do that Spotlight/Light Beam effect

The strobe option is the Godox SA-P with the AD400Pro and SA-17 adapter; or the same adapter, an S2 bracket and a smaller light like the AD200/300.

The VL300 will get you in the ISO400-800 ballpark FWIW.

NormanAllen wrote:

tugwilson wrote:

amlbenilde wrote:

Hi thanks! I also suspected that it could've been done with post but the photo at the top-left is a screenshot of a behind the scene video from ig stories. I rent a studio with Godox dp400ii strobes. If i were to opt for a continuous light, what would be a good budget light for this setup considering the modifiers you mentioned.

There are only three options I know of for a high quality projection device.

1/ The Aputure Spotlight Mounthttps://www.aputure.com/products/spotlight-mount/

2/ The Aputure Spotlight Mini-Zoom (not yet available)

3/ The Godox S30 SA-P projection attachment (which is a copy of the far more expensive Dedolight DP2 imager)

The first modifier has a Bowens mount but will not work with a DP400II because it has a lens at the rear which gives very little clearance for the tube.

The other two use the Dedolight mount (not 100% sure about the Aputure one but they would be stupid not to make it compatible). Godox make the SA-17 adapter which lets you use the S30 projector on thier Bowens mount continuous lights. They are very clear that it's not intended for strobes and I doubt it would work with the DP400II because of the clearances at the back. Here is a video review of it. You will see that it is pretty inefficient.

People in the know are dropping hints that Godox is working on a solution that allows the S30 projector to be used on strobes but I don't have any details on that.

There are lots of no name projectors with Bowns mounts which do not have rear optics and will fit on strobes. Ones like this with built in optics or like this which lets you use a camera lens. You can compare the price of these with an S30 projector. I had one of these a while ago and they are fun but the optics are dreadful compared with the S30 projector. I also had a light blaster which is an overpriced piece of junk in comparison.

If I was trying to reproduce this at the lowest cost I'd use an S30 with an SA-P projector and an SA-06 iris (it's an expensive item but it gives you very fine control over the size of the circle. Perhaps only buy it if you are having issues getting the circle size you want).

Here's a video review of the S20. There's a two part review of the Aputure projector here and here.

Thanks for this information. I looked into it and the Godox S30 with the projector and iris seem to be a good combination that doesn't break the bank for this. Question: are you aware of any strobe-based solutions for this? I don't mind going the LED route, but the S30 seems to drop to 10W when using batteries, which means using it on location is probably not going to happen.

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tugwilson Senior Member • Posts: 2,924
Re: How do you do that Spotlight/Light Beam effect
1

NormanAllen wrote:

Thanks for this information. I looked into it and the Godox S30 with the projector and iris seem to be a good combination that doesn't break the bank for this. Question: are you aware of any strobe-based solutions for this? I don't mind going the LED route, but the S30 seems to drop to 10W when using batteries, which means using it on location is probably not going to happen.

Godox has the SA-17 adapter which allows the projector to be used on continuous lights like the SL200II. However whist ip performs optically OK the efficiency is very poor.

Godox has indicated they are making an adapter for strobes which may be a better bet.

The battery performance of the S30 is very puzzling. They should have made a dual Sony battery plate and a Dtap cable which should allow it to operate at full power.

NormanAllen Senior Member • Posts: 1,032
Re: How do you do that Spotlight/Light Beam effect

Thank you!

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