Conventional Fixtures - PC lanterns

[IlyaSmirnov]

So, after looking through about a dozen lighting books (mostly college texts) and even more websites, I still can't find a definitive explanation of PC lanterns - everyone has their own term that PC stands for, and the beam has been compared to both Fresnels and ellipsoidals, and it's a relatively uncommon instrument, at least here in the States... Can someone set the record straight?

What exactly does "PC" stand for? (I've seen plano-convex and "pebble-convex" most) What is the beam and light quality like? How would one compare to a similarly sized Fresnel? Finally, aimed more to those outside the States, how common are they? Would it be worth getting a pair for our school auditorium (if nothing else, to learn about their distinct characteristics), or are they essentially relics from the past, not in common use?

Thanks in advance, looking forward to learning more about them!

[MNicolai]

From the Selecon website: Selecon Lighting - What is a PC?

What is a PC? PC stands for ‘plano-convex’ which describes the lens used in this luminaire. This type of lens has a smooth surface and outward curve and is used when the beam of light must have a hard or well defined edge.

Plano-convex luminaires use a similar optical system to that of a Fresnel. With a ‘crisp’ beam and less light scatter than the Fresnel the PC provides a wide range of beam angles useful from onstage, side stage and auditorium lighting positions.

The narrow spot achieved with Selecon PCs is near parallel and very efficient, ideal for dramatic highlights while the flood angle (60°) will cover a large stage area from a short throw distance.

The incisive quality of the beam contrasts with the ‘softer’ quality of the Fresnel and can be used for dramatic effect. The addition of a light diffusion (eg Hamburg Frost 114) alters the beam of a PC to that of a Fresnel.

Mid to flood focus beams can be shaped using the barndoor accessory.

The beam is a cone of light so the size of your lit area increases as the throw distance from the PC to that area increases. However, the beam angle of this light cone can be altered by a focus knob that changes the distance between the lamp and the lens. As the lamp (with its reflector) is moved towards the lens, the beam becomes wider, and as it moves away from the lens, the beam becomes narrower.

This adjustment is accomplished on Selecon PCs using a unique posi-slide lamp and lens focus system located on the left hand side (looking from the front) of the luminaire using a focus knob which simply slides back and forth.

I'd say it's basically a fresnel in the sense of the spot <=> flood focus mechanism, but without the trademark fresnel lenses. Here's the fresnel info.

Selecon website: Selecon Lighting - What is a Fresnel?

What is a Fresnel? Fresnels are the workhorses of stage lighting and the most common luminaire (light) used on stage. They are called a ‘Fresnel’ because they use a ‘Fresnel’ lens, recognised by the characteristic ‘stepped’ moulding on one face and the texturing on the other, named after its designer, Augustin Fresnel.


This Fresnel lens produces a very even light that is soft at the edges and tends to project a soft shadow. Because the edge of the light is soft, it is not absolutely precise and will blend easily with the edges of other Fresnels to give smooth stage coverage.

SOFT EDGE = the centre of the beam of light is bright and gradually darkens towards the edges.

The beam is a cone of light so the size of your lit area increases as the throw distance from the Fresnel to that area increases. However, the beam angle of this light cone can be altered by a focus knob that changes the distance between the lamp and the lens. As the lamp (with its reflector) is moved towards the lens, the beam becomes wider, and as it moves away from the les, the beam becomes narrower.

This adjustment is accomplished on Selecon Fresnels using a unique posi-slide lamp and lens focus system located on the left hand side (looking from the front) of the luminaire using a focus knob which simply slides back and forth.

A detailed knowledge of light’s behaviour and measurement is not required to light a production however you will need to know about the


INVERSE SQUARE LAW:

When a beam of light leaves a spotlight, the area illuminated by the beam increases as it goes further away from the spotlight. The same quantity of light must illuminate larger areas. If the distance from the light source to the surface (otherwise known as ‘the throw distance’) is doubled, the intensity drops to ¼ of the original. This happens because the illuminated surface is now four times bigger.

The images showing the lenses are the best way to show the differences between the two.

[IlyaSmirnov]

Originally Posted by MNicolai

I'd say it's basically a fresnel in the sense of the spot <=> flood focus mechanism, but without the trademark fresnel step lenses. Here's the fresnel info.

The images showing the lenses are the best way to show the differences between the two.

So based on that, and also what I've seen elsewhere, a PC essentially has a sharper beam than a Fresnel, and I'm guessing would be a bit brighter, too, at the same wattage, because the lens is a bit more efficient, right? So it sounds as though you could imitate a PC with an out-of-focus ellipsoidal/leko... or would something else in the light quality prevent that?

Would these differences justify having a couple around, or is this too subtle of a difference to make it worth having both in one's inventory?

[gafftapegreenia]

The biggest justification for owning PC's is their wide angle range. Whereas ERS's are often fixed, and zoom ERS's can't zoom over the entire practical range, the PC can. It's a very flexible fixture with a harder edge than a Fresnel, so it's great for specials and front light where shuttering isn't so important. So, beyond that, you are now getting into the debate of fixed ERS vs. zoom ERS. However, a PC is still not an ERS by it's very nature, and thus has characteristics all its own. This might be considered too subtle for the "average" or majority of users, who feel that all you need in this day and age is S4 PARS and ERS's, and while that may work, when a educated designer wants the quality of light found from a PC, only a PC will do. What this really means is for most of us we get along fine with S4 everything, but for those such as Broadway designers, who understand light in a way I can only currently dream of, it matters. I think this is where the real conversation of what constitutes the "art of lighting" begins, and one I don't think I need to explore much further.

The beam of a PC is indeed sharper than a Fresnel, but softer than an ERS, basically, as you said, an ERS is soft focus.

The reason you've seen pebble-convex is that modern PC fixtures has a stippling on the back of their lenses, just as Fresnel lenses are stippled. This helps soften the beam, make it smoother, and reduce prismatic affects around the edges of the beam. All of these were considered problems with the older styles of PC's. It was the older style of PC, once so common in the US, that gave PC's a bad name and thus they went the way of the the footlight.

I wish your poll had one more option: "No, but I'd like a few to play with"

And one more thing, a Fresnel is not a Step Lens. A Step Lens is a Step Lens.

[waynehoskins]

Of course, historically the PC came first, and then the Fresnel lens was modified to it, making the Fresnel PC spot.

I'd like a couple of PCs. I'd like a couple of BPs as well; they're another fixture that's so blasted simple and unique that's also gone the way of the dinosaur.

[Grog12]

Originally Posted by waynehoskins

Of course, historically the PC came first, and then the Fresnel lens was modified to it, making the Fresnel PC spot.

I'd like a couple of PCs. I'd like a couple of BPs as well; they're another fixture that's so blasted simple and unique that's also gone the way of the dinosaur.

.....really?

Can you cite a source?

Am I just this tired from packing that that sounds wrong?

maybe i wanted a website too

[derekleffew]

Originally Posted by waynehoskins

...I'd like a couple of BPs as well; they're another fixture that's so blasted simple and unique that's also gone the way of the dinosaur.

LD Roy Bennett spec'd. about 30 Beam Projectors on Madonna's 2004 tour. Personally, because of the way they were used, I didn't see any reason they couldn't have been PAR64-NSPs.

[waynehoskins]

Originally Posted by Grog12

.....really?

Can you cite a source?

Am I just this tired from packing that that sounds wrong?

maybe i wanted a website too

Not readily .. I've read it in old books in years past. The Fresnel lens and step lens are of course ways to make a PC lens take up less glass for a given focal length, and therefore less weight. PC lens came first; PC spot came first. Take a PC spot, change the PC lens for the lightweight Fresnel lens, and you have a Fresnel spot.

[soundlight]

Here are your BPs: Wybron, Inc. - Products - Fixtures - BP-2

[waynehoskins]

Originally Posted by soundlight

Here are your BPs: Wybron, Inc. - Products - Fixtures - BP-2

I think I actually saw those at USITT '05, and made a point to pick up the brochure. It may have been Selecon, I forget, though the more I think about it I'm more sure it was Wybron.

Pretty light. Need to get a couple.