Lens train functionality

[JChenault]

Oh, so the second focal point is after the gate, which is why the gobo must be inserted upside down?

Er No
The gobo must be inserted backwards because when you project an image through a lens it reverses the image (depending where the image plane is in relation to the focal point) The image in your camera is reversed. When you look through a telescope the image is reversed when you put a slide in a slide projector ( remember slide projectors ) the image is reversed.

Take (say) a 6x9 lens. Hold it 9 inches from the floor, see that it is projecting an image of the lights on the ceiling, note that the image is reversed.

If you remove the reflector from an ERS, and put in a gobo and focus the light ( we don't need no stinking foci points ) it will be dim, but reversed.

If you look at a focused ERS in a smokey environment, you notice the beam narrows then expands. ( usually within a foot or two of the unit) If you focus the image on a screen before you get to the narrowing of the beam, it is not reversed ( but very small) After the focus point, it is reversed

 

[derekleffew]

...If you remove the reflector from an ERS, and put in a gobo and focus the light ( we don't need no stinking foci points ) it will be dim, but reversed.

I just tried this, and by golly, you're correct! So the picture in post#9 above IS accurate, after all. I apologize for the confusion.

Everyone should try this at home/school/shop. You don't actually need to remove the reflector, just use a 360Q (or pre-SL Strand Lekolite), open the hinge to let the rear body hang down out of the way, and hold the lamp cap approximately where it would be if the reflector were there.

 

[icewolf08]

I just tried this, and by golly, you're correct! So the picture in post#9 above IS accurate, after all. I apologize for the confusion.

Everyone should try this at home/school/shop. You don't actually need to remove the reflector, just use a 360Q (or pre-SL Strand Lekolite), open the hinge to let the rear body hang down out of the way, and hold the lamp cap approximately where it would be if the reflector were there.

Almost correct, but not quite. Yes, it is the lens that flips the image, but the reflector in an ERS unit is designed such that the secondary focus is not only before the gate, but also far enough away from the gate such that as the light diverges from the focus it passes "exactly" through the gate. (Ok, that was a poorly constructed run on sentence which I hope conveys the point) The lenses are then sized and placed to "fill" the beam after it passes the gate. You will notice that on a 36˚ source 4 fixture the first lens in all the way at the back of the tube and is smaller, whereas in an 19˚ the lens is at the front of the tube and basically fills the tube diameter. This allows the lenses to collect all the light (assuming 100% optical efficiency) coming through the gate.

I don't really have the patience to draw a diagram right now, but I can if people want.

 

[mstaylor]

That's what I was referencing when I said take it out and watch how it works. We used to do it outside with the sun. We would demonstrate how the two sizes differed but also how the flip works. Then we would open a fresnel and show why it didn't.

 

[Esoteric]

Almost correct, but not quite. Yes, it is the lens that flips the image, but the reflector in an ERS unit is designed such that the secondary focus is not only before the gate, but also far enough away from the gate such that as the light diverges from the focus it passes "exactly" through the gate. (Ok, that was a poorly constructed run on sentence which I hope conveys the point) The lenses are then sized and placed to "fill" the beam after it passes the gate. You will notice that on a 36˚ source 4 fixture the first lens in all the way at the back of the tube and is smaller, whereas in an 19˚ the lens is at the front of the tube and basically fills the tube diameter. This allows the lenses to collect all the light (assuming 100% optical efficiency) coming through the gate.

I don't really have the patience to draw a diagram right now, but I can if people want.

I would love a drawing of the working of the lens train and I would link back to your blog if you produced one!

Mike

 

[derekleffew]

...I don't really have the patience to draw a diagram right now, but I can if people want.

Yes, I believe a scaled, dimensionally accurate drawing IS in order. The only dimension I'm sure of is the gate diameter of a Source Four is 3.12".

If it helps, here are the EFL s of various fixtures' optics
Source Four 90º 2.13"
Source Four 70º 2.67"
Source Four 50º 3.3"
Source Four 36º 4.8"
Source Four 26º 6.8"
Source Four 19º 9.3"
Source Four 14º 11.05"
Source Four 10º 17.8"
Source Four 5º 25.5"

 

[icewolf08]

I would love a drawing of the working of the lens train and I would link back to your blog if you produced one!

Yes, I believe a scaled, dimensionally accurate drawing IS in order. The only dimension I'm sure of is the gate diameter of a Source Four is 3.12".

I'll see what I can do, but it will take a few days to be that detailed. I have a few big events happening in the coming week, so I am pretty busy. What would really help is if someone actually had an accurate CAD/VW drawing of a source four to work with. That and I will have to brush up on the maths to calculate the reflection angles off the reflector. It may need to be fudged a little...

 

[MPowers]

Technically, an axial ellipsoidal is so-called because the lamp is mounted 'on axis' with the reflector. While the Selecon Pacific's lamp and reflector are not physically axial to the optics (90 degrees perpendicular, actually), the cold mirror positions the reflected light on axis with the optics. The lamp still protrudes through the center of the reflector, while a 'radial' ellipsoidal sees the lamp entering at the radius of the optics through the side of the reflector.

***I always thought "axial" referred to within the same axis as the optics (lenses), but the WIKI states that axial means within the same axis as the reflector. By this definition, the Selecon Pacific is an axial ellipsoidal.

Axial ERS means that the axis of the reflector is the PRIMARY axis. However, the axis can be redirected at one or more points. As long as the beam/picture image remains centered along that line, the unit is axial. Example is the old Kodak slide projector with a MR-16 lamp (variation of PAR reflector) focused through a mirror and then through the slide to the screen. Point source, axial reflector. The light bends and reflects along the way, but stays centered around the center axis of the light reflected from the original source. Kind of like an automobile drive chain with "U" joints. The end result is not exactly in line with the source of power, BUT, the end result is a wheel rotation around an extension of the axis of the engine. Axial is exactly that, around an axis. Doesn't matter if the axis changes direction or not.

 

[derekleffew]

...That and I will have to brush up on the maths to calculate the reflection angles off the reflector. ...

Oh that's easy. Angle of Reflection=Angle of Incidence. But I suspect you already knew that.

http://www.etcconnect.com/docs/docs_downloads/miscdocs/S4-19-views.zip

 

[kicknargel]

I have to say I have a problem with many points in the article that are either opinions or misunderstandings and are presented authoritatively as fact.

"These are by far the most versatile units in any lighting designers arsenal. They can do literally everything. Perfectly controllable front light, back light, side light, put gobos in them and you can put down a beautiful pattern wash or use a single unit to add depth to a scene. Shins, mids, heads in dance. Need a prefectly even color wash? They can do that as well, just lay down a wash and soften up the focus. Need a hard edged spot? Sure. They can also function as follow spots. They can wash scenery or cycs. Anything you want to do with a light they can do it. The only drawback? Price. They cost three times as much as a fresnel and six times as much as a PARCan. But you get the ultimate in flexibility. This unit can literally do it all."

I think you will be hard pressed to find a lighting designer that, given the option and unlimited budget, would use only ERS fixtures. They are a versatile fixture, but cannot fill all the functions of PARs, fresnels, etc. No one would light a cyc with ERSs if far cycs were available.

Sorry for the rant. I'm just a little terrified some high school administrator will read this and decided to buy only ERSs for their new auditorium.

 

[Esoteric]

I have to say I have a problem with many points in the article that are either opinions or misunderstandings and are presented authoritatively as fact.

"These are by far the most versatile units in any lighting designers arsenal. They can do literally everything. Perfectly controllable front light, back light, side light, put gobos in them and you can put down a beautiful pattern wash or use a single unit to add depth to a scene. Shins, mids, heads in dance. Need a prefectly even color wash? They can do that as well, just lay down a wash and soften up the focus. Need a hard edged spot? Sure. They can also function as follow spots. They can wash scenery or cycs. Anything you want to do with a light they can do it. The only drawback? Price. They cost three times as much as a fresnel and six times as much as a PARCan. But you get the ultimate in flexibility. This unit can literally do it all."

I think you will be hard pressed to find a lighting designer that, given the option and unlimited budget, would use only ERS fixtures. They are a versatile fixture, but cannot fill all the functions of PARs, fresnels, etc. No one would light a cyc with ERSs if far cycs were available.

Sorry for the rant. I'm just a little terrified some high school administrator will read this and decided to buy only ERSs for their new auditorium.

Why not? If given the choice I would do 90% ERS units with 10% PARs (in fact I have worked at several professional theaters here in Dallas with that exact setup). If I have the proper angle to do it, I would rather use Source4's as the rep cyc lights (there is a theater here in town who's cyc is lit by 6 Source4 90 degree units with Seachangers on them, it is the most beautiful cyc I have ever seen), and if I don't want to use the cyc, I have units that are actually useful for something else.

But beyond that, there is no claim this is the only or even best way to do that. But you can not deny that an ERS can do everything any other light can do, AND it can do things that only it can do! It IS the most versatile light in theater, that can't be realistically disputed. There isn't any opinion in there really. ERS units can do all those things.

 

[DuckJordan]

Really? Can it get as punchy as a par? Can it have the nice diffuse spread of a fresnel? And does it have the even fill of a true cyc unit? Can it create a nice single beam such as a beam projector... and all of those are just from the top of my head. I'm not saying the ers doesn't have its place but claiming it can replace other units entirely is a fallacy that just creates bad designs.

Sent from my ADR6300 using Tapatalk

 

[Esoteric]

Really? Can it get as punchy as a par? Can it have the nice diffuse spread of a fresnel? And does it have the even fill of a true cyc unit? Can it create a nice single beam such as a beam projector... and all of those are just from the top of my head. I'm not saying the ers doesn't have its place but claiming it can replace other units entirely is a fallacy that just creates bad designs.

Sent from my ADR6300 using Tapatalk

Why yes, it can do all those things.

 

[DuckJordan]

I'd love to see it, do you have the inventory to do a side by side shoot out?

 

[Esoteric]

Nope. Don't keep conventionals in my inventory. But I have tons of pics on my website of ERS units in all these roles.

 

[jglodeklights]

There are situations where an ERS is not the correct choice. There are situations where a PAR/Fresnel/beam projector/cyc light are not the correct choice. There are situations where you do not have the correct choice. Part of being a good designer is making the best choice with what you have or can get. Example of where an ERS was not at all appropriate- the high school I work with did a production of Much Ado About Nothing in one of their hallways where there was limited power and limited space. I made the mistake of trying to use four S4 50 Degree units to create a two color front wash. OOPS. The distance between where I could place the light trees and actors were performing meant that the ERS just couldn't provide an even enough wash even with a heavy diffusion, and it was also quite dim (for what we needed) with or without the diffusion. Solution? Rented 4 S4 PAR WFL and used AP1500 Tough Frost in them. Was able to get the kick I needed, and a pretty even wash. Yes, same 575watt standard life lamps in the PARs as in the lekos.

Additionally, the larger source size a PAR creates for the light actually makes quite a difference in how we perceive the quality of the light, the same for a Fresnel. Use a Altman Far CYC as a front light with some heavier diffusion (just be sure to use a 1k lamp!) and see the perceptual difference (and actual difference) in the quality of the light and shadows. One can not deny that an ERS is a versatile fixture, but so are the others. It is also situation dependent and to deny that is a HUGE fallacy.

 

[Esoteric]

I partially agree. There are times when, for example PARs can make suitable front light (on a video shoot for example), but in these situations ERS units are also acceptable. But I cringe when I walk into churches that are using PARCans as front light and completely washing out their background. This is an example of when an ERS is appropriate and a PAR is not acceptable. But in any example where you can use a PAR, Fresnel, Cyc Light, etc I can achieve the same results (or better) with an ERS. The same can not be said the other way around.

Part of the problem in the situation that you cite is that you were using the wrong ERS, a 50 degree is not the equivalent of a Source4 PAR WFL. You were diluting your output too far. At similar distances a Source4 50 degree will cover twice as much territory as a Source4 PAR WFL. Now you do get a brighter beam and a substantially darker field on a PAR than an ERS, but that can be altered by adjusting the bench focus on the ERS. The equivalent of a Source4 PAR WFL is a Source 4 36 degree. Then you can throw cyc silk in it (to get the beam shaping if that is what you need) and you get much better output than you do from a Source4 PAR (compare 185fc at 16' to 400fc at 15').

 

[jglodeklights]

Actually, no. A S4 36 would have been more wrong for the situation because the S4 50 was not wide enough to cover the area that needed to be covered in the horizontal direction. A S4 36 with R113 would have spread the beam to cover a decent area, but still not in a way that would have provided even coverage. PAR's, Fresnels, and ERS's have completely different lens and reflector properties and have completely different ways in which the light is transmitted by them. For the power, budget and space I had to work with, the WFL PAR had much more appropriate output qualities. Beam and field angles do not always provide adequate representations of how the light will function in space.

 

[gafftapegreenia]

I still prefer a majority of Fresnels in small storefront and blackbox spaces, as opposed to ERS's. Granted I've never had the chance to use a 90 degree in such a situation, maybe that would change my mind. Probably not tho.

What's so wrong with PAR's as front light? In high school (where I was lucky to even get new gel for every show) Using our six 1K WFL PAR64's as front light was a much more effective solution (both in output and coverage) than trying to use the eight 360Q 6x9's. (Trust me, we kept trying...and trying, because we'd been taught, and at that age, firmly believed "ERS's are the best for front light")

Ok, MAYBE I'll buy the argument that SOURCE 4's can just about do everything that a Fresnel, PAR, Cyc, Flood, Scoop, and Beam Projector can. However, I think the "multi-tool rule" applies. Just because they can do most everything, doesn't mean they are the BEST at most everything.

 

[Esoteric]

JGlo, if you put in the R113 you should get as good (if not better) horizontal coverage than a WFL Source4 PAR. I can't find the numbers right now, but when you look at the starting numbers for each unit, the Source4 PAR has a beam angle of 20 deg x 31 degree, the Source4 36 degree has a beam angle of 27 degrees. I find it had to believe that R113 does not add 2-4 degrees to the beam angle. I will gladly admit if I am wrong (I know there is a Rosco rep around here somewhere) but I don't think that I am.

If you used a 90 degree Source 4 Gaff, you would change your mind. I know I did.

PARs as front light are completely uncontrollable. You just end up with light everywhere, usually washing out the background. There is a reason why you don't walk into most professional theaters and see PARs as front light. Unless you have the prefect angle, you just kill all your scenery washes using PARs as front light.

I will say they are not the cheapest option to perform all those tasks, but they certainly do them at least as well as other, cheaper alternatives.