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#### Parabolic Light Modifiers (PLM)

Hi guys, can someone explain to me exactly what a parabolic light modifier does? What's the difference between a PLM and say, a Softlighter? What is the difference between a PLM with silver lining and a shoot-through PLM?

Many thanks,
Rhys
A PLM is designed to throw light onto a small area from a large source—think soft but restricted light.

They are best used with studio strobes or bare-bulb flashes.
Thanks, Ben! So, I'm assuming the ones with silver lining produce harsher light than the shoot-though?
Benjamin: +1

The flash comes from the 'focal point' of a dish (umbrella) and illuminates all of the surface of the umbrella. The curve of the umbrella is designed such that all light from that point is reflected in parallel beams towards the subject - but the beams don't spill out. So you get a large light source (therefore 'soft') but with a controlled and aim-able 'beam'...

Look at this en.wikipedia.org/wiki/Parabolic_reflector and then imagine that instead of beams coming 'into' the reflector and being focussed on a point, the beams start at the point (the flash) and are reflected back out of the reflector/PLM...
Thanks, Paul! That was incredibly helpful.
Shoot-through PLM? That doesn't make sense, although I may be missing something.
Ben, I'm probably the one missing something. I was looking at the Alien Bees website and they had some PLMs that were black and lined with silver, and then they had some that were white and had a cover over the back. Maybe I misunderstood.
Good link, the diagram on that page does a good job of picturing it...here's a diagram of the Paul Buff PLM:

Read the descriptions, and you'll understand. Same size light source, different spreads and properties.

Basically, the silver PLM is the one that will produce that narrow spread (and therefore high output) that is so cool.
Thanks!
Easy way is to think of it is how you focus a MAG light or similar flash light but on a bigger scale. Focusing and unfocusing creates a slightly different look. I don't have a PLM so I don't know how well it works in the focusing.
A PLM is part of a system. It's (the white umbrella) designed to be used as a shoot through umbrella, and a regular umbrella and with a diffusion panel, a lightbox.

There are black panels (2) available to eliminate light spill from the side you aren't using.

The silver have only the white diffusion panel available to have it double as a box.

Silver is more reflective and will produce a hotter light. Both are really efficient modifiers.

A parabolic umbrella will focus the light to a point by collecting and directing it. If the focus point is behind the subject the light will wrap the subject and minimize shadows behind.

Softlighters are similar, but they don't offer the black panels.

I own a few PLM'S. 64" white, 64" silver and 86" silver.
The newer 2nd generation ones from PCB appear to offer an Elinchrom speedring mount. As an Elinchrom owner, that's cool. Anybody with Elinchrom strobes and PCB PLMs that can share satisfaction/dissatisfaction with these?
The newer umbrellas have 3 piece center rods. Remove one and bolt the Elinchrom adapter (it's like a cage). It centers the center rod on the unit.

Don't have Elinchrom gear but I have the adapter. It's the only way it comes
Actually the silver is quite nice... not at all like the harshness of a silver umbrella. It has to do with the way the light is spread and the minimal amount of specular produced. Silver umbrellas are so specular for me... I use them for backgrounds and hairlights, but never on skin. Silver PLM works well on skin and overall.
Here is a through review of the Paul Buff PLM system at Rob Gailbraith's site. Shows what you can do with them.

www.robgalbraith.com/bins/multi_page.asp?cid=7-10046-10396
I really dig my PLM, in fact I made most of these portraits with the configuration below. I love the way it concentrates the light. For the money it really can't be beat. Now if only they'd come back in stock....

MOD
I'm not sure why you labeled this OT, it seems perfectly on topic to me. Please feel free to edit the thread's title. :-)
Nionyn, I labeled it OT because given the amount of OT threads and threads that have nothing to do with Strobist, I honestly don't know what is truly considered off OT. Title edited, thanks.

And thanks, guys, I really appreciate your wealth of information. I've been wondering about PLMs for quite some time. I didn't anticipate such a generous response. Thanks again!

Rhys
If anyone knows anything specific about the availability of these from PCB, please update the thread. Thanks.
MOD
No probs. :-)
Basically, if it's about off-camera flash or something on the Strobist blog it's on topic. Off-topic posts are allowed, but they do at least need to be directly and specifically lighting or photography related. And it's nice and polite if they're labeled 'OT'. :-)
Hope that makes sense.
i'm always trying to figure out the plm too. given the "soft yet focused" light source everyone describes it as i'm very interested. My question is isn't a gridded softbox or more so a gridded octa also a "soft yet focused" light source? can anyone explain how a gridded octa would be different than the plm? Is it that the plm is higher output than a gridded octa because of the layers of diffusion fabric on the octa?
The PLM, when used with a bare-bulb flash or studio strobe, provides perfectly even light on a small area from a large source, with practically no loss in power.

That's why they are so cool.
A gridded diffuse light source is still a diffuse light source, the light still spreads in all directions allowed by the grid.

A parabolic reflector is the reflective equivalent of a transmissive lens, it has a focal point and by moving a light source backwards and forwards around the focus you can generate a diverging or converging beam of light. Sort of like a Fresnel lens on a spot light except much bigger.

EDIT: exactly the same equivalence is seen in telescopes. Refractors are limited in size, whereas reflectors can be made much bigger. In their case large apertures are the aim, but principles are the same.

Bill.
@dmourati- I had to wait 5 months for the new version PLM. I'm sure it can't be like that now.

I'm getting pretty impatient waiting for them to become available. Does anyone have any info on the knocks off version? Should I just wait?
MPakt: I just bought a Parabolic Umbrella from ebay from seller CotswoldPhoto - he's based in the UK, but I believe he can ship to the US (though you'll need to confirm that!)

Same item as this: cgi.ebay.co.uk/64-162cm-Silver-Black-Parabolic-Type-Umbre...

I've bought several items from him in the past, and he's reliable and very quick in delivering. The Parabolic is strong, well made and well packaged, and from a very quick 'self portrait' test at the weekend it works well. I haven't had chance to upload the shots, but I intend to write a quick blog comparing it with other modifiers at my disposal (24" pop-up softbox, also from CotswoldPhoto, bare flash, standard white shoot thru etc)

My first impressions are really positive - the only disadvantage is the size of it! I don't have the luxury of a studio, and the ceilings in my house are only ~8' high so it's not physically possible to get this thing as high as I'd like sometimes!
Adorama also sells the knock offs:

So far one poor review because the umbrella arrived in a poor state. No other reviews I've been able to dig up.
"the only disadvantage is the size of it! I don't have the luxury of a studio, and the ceilings in my house are only ~8' high so it's not physically possible to get this thing as high as I'd like sometimes"

I completely agree. I have the 86" and have ten foot ceilings, but even that is too low. Don't bite off more than you can chew. I just use it as very low fill from behind camera.
@Kris This Is
Holy crap! I want that 12 foot brolly in your photostream. What was that being used to light?

obeychad: What was that being used to light?

Obi-Wan: "that's no 12 foot brolly - that's a space station"

;o)
aperture-priority: sweet. thanks for clearing that up! :)
FYI, on Oct 19th got this from PCB:
PLMv.2 parts are continuing to arrive from our vendors daily and we are attempting to fill all backordered umbrellas as quickly as we can. We hope to have all backorders for silver PLMv.2 umbrellas filled in order to begin shipment of new orders in late November.

Unfortunately, there will be additional delays on white PLMv.2 umbrellas as we have been forced to change fabrics in order to meet our high standards for quality control and performance. The fabric that we were using originally was a Nylon-based fabric that has a higher water absorption rate and has been found to cause some dimensional change from low to high humidity. As the unique design of the PLM depends on complete dimensional stability, we have had to find an alternative Polyester-based fabric. While this new fabric maintains 100% stability and passes our rigorous quality control testing, having to switch fabrics has regrettably caused additional delays. When the new fabric arrives, we will do our best to assemble and ship the backorders as quickly as we can.

Shipped my 86"silver a week later. So if you want/are waiting on a silver one, should be close.
obeychad Thats a Broncolor Para .

Check out these ads to se it in use:

The second video is a cool set-up and you can see the focus ability.
So, quick question. Can the PLM or softlighter be used with a strobe and have the same desired effect, or would I be better off waiting until I get an Alien Bee?
A (silver) parabolic is specular and more directional than a softlighter. Specular means there's going to be a more abrupt transition from highlights to shadows, and skin has a greater snap and glow to it. I wouldn't call them soft sources.

When you see stuff like this, you know it's a specular source because of how the light feels:

Three great shots that make it even clearer (can't embed them):

Compare it with this, likely shot with a softlighter or similar modifier (octa):

One of the images isn't working for me. I guess I also meant a speedlight, or two sb-28's
Fixed (for now).
But if you're photographing a totally flat (as in non-reflective) objects, there shouldn't be any difference between the light produced by two sources that are the same size and have the same light distribution across the light source, correct?

This is not taking into account any fill or extraneous light that may come from a wide spread of light bouncing off of other surfaces, of course.
Can you tell me which two light sources in the real world are different, yet "are the same size and have the same light distribution across the light source"?

Also, what's a "totally flat (as in non-reflective)" object?
@chad.latta- I usually use a Lumedyne head (barebulb) in my PLM'S and will power down as low as 50ws. I'm sure I would be able to use my SB800 and Metz 45CL-4, I just haven't yet.

Next time out I'll try it and post back to this thread.
@nosamluap paul I've seen that one from cotswoldphoto before on ebay and have been planning on buying it myself. can you tell me if this umbrella can be focused? I mean can the latch on the shaft be placed in several positions or is there only an open or closed position?
From memory, it only has one position
@crphotoboy

It's actually a Briese 3.3 metres, not a Broncolor.

www.solalights.com/light/flash/briese/focus-330
I guess my question is:

Why (and how) is a PLM "more specular" than a softlighter?
Silver interior, no front diffusion (typically), different shape (parabolic instead of standard umbrella).
To understand the difference you need to think about the difference between a collimated beam of light and a diffuse source. It helps to think about the shadows cast by objects placed in the path of the light. A large diffuse source will cast a blurred shadow which becomes weaker as the distance between the object and the background increases. A large collimated source will cast a hard shadow -- you could do shadow puppets for example. Note that a small source of either type casts a hard edge shadow, but the "spill" from a diffuse source will be different.

This effect is not related to the size of the light source, it is due to the way light from the source travels. Light from a diffuse source is equally likely to travel in any non-constrained direction, light from a collimated source all travels in the same direction. The light from a large collated source travels such that rays from the left side fall on the left side of the subject, rays from the right go to the right and top to top, bottom to bottom, etc.. Light from a large diffuse source goes from everywhere in the source to everywhere reachable by a straight line onto a curved subject.

So a large collimated source wraps around a curved subject as if it were a collection of small collimated sources (lots of flashlight beams if you will) whereas a large diffuse source acts like a collection of small diffuse sources each capable of illuminating all exposed subject surfaces.

The key here is that there are two characteristics directionality collimation vs. diffusion and size small vs. large. Both contribute to the quality of a light source and both are independent.

Objects that reflect light have similar characteristics, a diffuse reflection and a direct reflection. Every object has a mix of the two sorts -- a mirror is virtually all direct, a matt surface is virtually all diffuse (skin lies somewhere in between).

The four factors all interact to give what we or the camera sees.

EDITED: to use the correct term for parallel light beams -- collimated.

HTH
Bill.
That does make sense. Thanks for your detailed explanation.
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