List of Questions

D

DCATTechie

Active Member
Was thinking the other day of some of the terms and procedures that I don't know and thought "What better place to ask than CB?" So here they are:

1. What is a baffle and what is its purpose?
2. What is a louver and what is its purpose
3. What is a concentric ring and what is its purpose?
3. How exactly to doughnuts make a gobo appear sharper?
4. How does "power work" for a touring rig. How is it distributed and with what types of cable?
5. How is data distributed in a touring rig situation?
6. What exactly is three-phase power, and how does it work?

Thanks!
 
I'll take a stab at it (and most likely be corrected by someone far more knowledgable):

1, 2, 3a: no idea
3b: they block the light that is coming from sharp angles
4: assuming you're talking about how is the rig powered... There usually is a company switch which the electrician will tie in with either cams or tails. This then goes to a distro which supplies circuits for dimmers, movers, ect. In some cases dimmer racks are tied in without using a distro. For example the way it worked at my old high school was there was a 60A 3-phase company switch (with cams). Our (professional) LD/ME would tie in the cams to the distro. From there I think some were straight runs to the units, and some were some type of breakout. Don't remember for sure. The dimmers were also separate b/c they were permanent.
5: DMX cables. I believe they sometimes use looms and special truss which the fixtures stay on.
6: 3-phase usually (in the US) has 3 hots @ 120V, a neutral, and a ground. The neutral is often larger because it can carry more current than a single phase if there are imbalances. 3 phase needs to have the loading as even as possible across the phases. Each phase is 120 degrees off from the others, creating a 208V potential across 2 hot phases. The 3 phases can also be used together to make 240V. As far as the 208V, graph a sine wave with A=120 and look at the max difference between the waves-- it will be about 208V.

Of course always get a qualified professional for electrical stuff...
 
4: there is a source of power, either a company switch or some other power tie in, or a generator. Depending on the venue and the show, there could be combinations of multiples of these. Type SC feeder cable with camlock connectors is ran from the power source(s) to dimmer racks and power distribution units. These can range from small boxes to large racks. From the power distribution units, portable cables such as SO cable and socapex cable supply power to the loads.

6: the answer to that question can turn into a long discussion as there are several types of three phase power. Basically the three phase power usually used in our industry is 120/208Y. There are three hot legs, a neutral and a ground. Between any hot leg and neutral you get 120v. For example with a 200 amp 3ph supply, you can get 600 amps worth of 120v. Between any two hot legs you get 208V (used to power moving lights and other higher wattage loads)
 
Most of these questions could also be answered using the search function. There has been an significant amount of discussion about 3 phase power. Concentric rings are a part of lenes and can be located that way. I am by no means trying to stifle your inquisitivness, just saying you might be well served by the search function.

Those sure do sound like essay questions........
:think:
 
Footer said:
Agreed. Don't bring your homework here for us to do for you. Sounds like questions I used to right when I taught....
Click to expand...

These are not questions for an essay or for my homework. They are purely for the advancement of my lighting knowledge, and I believe that that is the point of this site, to answer questions and to help others gain more knowledge. Even if these HAD been for a homework assignment(WHICH THEY ARE NOT), I don't see the problem in asking for assistance. If I didn't know what a term was and I found it in the CB Wiki, would you say that the Wiki had done my homework for me? I would not. I would say I was using my resources. If I asked a teacher for assistance would that mean said teacher would have done my homework? I believe he would be teaching and doing his job. If I don't know the answer to a question, I feel the logical thing to do would be find the answer, not just leave it blank because I didn't know it. Just because the questions I asked were similar to ones that you had used for your class does not mean that they are questions used in a class of mine.

And I did use the search function and the CB Wiki. Terms like louvre, baffle, and concentric rings were not in the Glossary. Also, the thread about Three-Phase power was over my head, so I asked for it to be explained in a simple way so I could understand the basic idea of it, although now I'm starting to think that it was a mistake.

I feel like I'm being chastised a little for asking questions. If I'm breaking the TOS please let me know, but I do believe that asking question is well within the acceptable things to do on this site.

/rant
 
As I stated, no offense or quashing of your inquisitiveness intended. Apparently being the hot-spot of some learning institutions has created a hair-trigger response on my part for "homework" thing. List of well phrased questions which have mostly been covered, usually equals someone looking for homework answers so please forgive my jumping to conclusions. You did not state that you had searched and did not understand the 3 phase power discussion.
Obviously, No it is not against the TOS to ask questions it's what we at CB encourage however, each of the questions you listed could very well be it's own thread. By all means break them up and post each in it's own thread or this will become a VERY confusing thread. Do not be alarmed if others post links to existing threads on the subjects then grumble about using the search function. The Search is great but it can require some finesse, just because the term "concentric ring" isn't on the wikki, doesn't mean the terms "Fresnel, Lens, Step and photo-metrics" are not. < honestly baffles and louvers are much more of an architectual reference and one might not expect to find them referenced here. >
 
DCATTechie said:
I don't see the problem in asking for assistance. If I didn't know what a term was and I found it in the CB Wiki, would you say that the Wiki had done my homework for me? I would not. I would say I was using my resources. If I asked a teacher for assistance would that mean said teacher would have done my homework?
Click to expand...

Us giving you the answer is not reasearch. If you find the answer, thats a different thing. If you ask someone what 2+2 equals, they give you the answer, and you write it down on your homework you have not gained any knowledge.

If you have a question ask, ask it. If you have a list of questions, ask them separately.

Like Van said, most of the questions have answers on here already. For the ones that have not, give us some context as to what you want to know about them. I am not crazy about answering completely cold questions. Give us some reason as to why you are asking the question.

This list did look like a homework assignment that I would have given out. It is not unreasonable to assume that it was. That being said, I don't like to do peoples homework for them. My time is worth more then that. I don't mind helping someone get out of a jam for a real show, but I don't want to answers questions for someones 100 level stagecraft class.
 
check out the city theatrical website as they will show you examples of baffles, rings etc.

Donuts work by reducing the field of view from the lens to remove light that comes from the filament sections which are not located at the optimal point of the reflector. This can be demonstrated with a a pencil, protractor and a ruler. Draw an ellipse and mark the two focal points. One is where the lamp is and the other is the gate before the lens train. Ideally all the light comes from one focal point and will pass through the other. However if you draw another focal point slighty to the side of the ideal one and then drew a line to the reflector and ensured that the reflected ray is a tangent to the reflector you will find it misses the other focal point. This produces light that is slightly out of focus and cannot be corrected by a bench focus however a donut in the colour runners will clean it up at the expense of some loss of light output. This is why the optics in projectors and cameras are much more complex beacuse they inlude features to address this.
 
Van said:
As I stated, no offense or quashing of your inquisitiveness intended. Apparently being the hot-spot of some learning institutions has created a hair-trigger response on my part for "homework" thing. List of well phrased questions which have mostly been covered, usually equals someone looking for homework answers so please forgive my jumping to conclusions. You did not state that you had searched and did not understand the 3 phase power discussion.
Obviously, No it is not against the TOS to ask questions it's what we at CB encourage however, each of the questions you listed could very well be it's own thread. By all means break them up and post each in it's own thread or this will become a VERY confusing thread. Do not be alarmed if others post links to existing threads on the subjects then grumble about using the search function. The Search is great but it can require some finesse, just because the term "concentric ring" isn't on the wikki, doesn't mean the terms "Fresnel, Lens, Step and photo-metrics" are not. < honestly baffles and louvers are much more of an architectual reference and one might not expect to find them referenced here. >
Click to expand...

Thanks Van. After looking over my post, I do realize that it looks like I'm fishing for answers for an assignment. I should have made myself more clear about my intent and prior searches. I grouped all these questions together because I thought I would catch more flack from creating 6 different threads when each could be answered fairly simply without the need for multiple posts. Next time I will definitely break up my questions as I can see how this way of formatting it could get very confusing.

I do apologize for ranting in my previous post. I realize that you and the others had the best intentions and didn't want to be giving out free answers. I will try to search function more thoroughly next time. Forgive me for my sarcastic reply, it was uncalled for.
 
church said:
check out the city theatrical website as they will show you examples of baffles, rings etc.

Donuts work by reducing the field of view from the lens to remove light that comes from the filament sections which are not located at the optimal point of the reflector. This can be demonstrated with a a pencil, protractor and a ruler. Draw an ellipse and mark the two focal points. One is where the lamp is and the other is the gate before the lens train. Ideally all the light comes from one focal point and will pass through the other. However if you draw another focal point slighty to the side of the ideal one and then drew a line to the reflector and ensured that the reflected ray is a tangent to the reflector you will find it misses the other focal point. This produces light that is slightly out of focus and cannot be corrected by a bench focus however a donut in the colour runners will clean it up at the expense of some loss of light output. This is why the optics in projectors and cameras are much more complex beacuse they inlude features to address this.
Click to expand...

I don't think I agree with this logic. Not that I am convinced you are wrong, but it is not my understanding.

If you have a lens and an iris, and you close the iris, the image gets sharper / depth of field improves. ( until the iris gets very small - a lot smaller than we are talking about here).

In photography this effect can be observed by taking an SLR camera and looking at the depth of field with the iris wide open, and half open. My photography instructors tell me that a lens is sharpest two f-stops from all the way closed (And I believe I have seen this in my photographs).

In the human eye, you can see this by reading in dim -vs- bright light. In dim light small text can be difficult to read. If the light is bright it is much sharper. This is because the iris in your eye closed down in bright light and you get a sharper image on your retina. (More obvious as you get older and need reading glasses).


My belief is that it is the irising down effect of the lens that makes gobos sharper with a doughnut. With a leko you are effectively making an iris with a doughnut.

As to why irising a lens down makes is sharper, I'm not sure.

Now I don't have any citations as to 'This is how it works in Theatre' - the physics just made sense to me. It's just my opinion as to how lenses work based on my understanding of optics.

Thoughts?
 
Last edited:
As to baffle, louver, and concentric ring -

Not usually used too much in theatre - but in architectural parlance these are things used to cut off the viewing angle, and/or stray light from a fixture. Here are link from City Theatrical.

I did once see Abe Feder use an egg crate baffle in beam projectors. Sigh - I think I am dating myself because I remember beam projectors
 
JChenault said:
My belief is that it is the irising down effect of the lens that makes gobos sharper with a doughnut. With a leko you are effectively making an iris with a doughnut.

As to why irising a lens down makes is sharper, I'm not sure.

Now I don't have any citations as to 'This is how it works in Theatre' - the physics just made sense to me. It's just my opinion as to how lenses work based on my understanding of optics.

Thoughts?
Click to expand...

Why, is actually an easy question to answer. It is all about surface area. Consider that at any one point on the gobo you have an infinite number of rays of light heading towards the lens and stage. Some of those rays will hit the lens and be refracted and land on the stage in the appropriate point in the pattern. Some will hit the stage at some other point in the pattern. Some won't even make it to the lens at all. By using a donut (or irising down a camera lens) you effectively limit the surface area of the lens that is exposed to the stage. By doing this you also limit the light that passes to only the more direct rays hit the stage. You get rid of some of the rays that hit the wrong place.

My explanation is a little awkward, and if I have some time I will draw up a picture.
 
Sam,
No problem at all never apologize for asking questions. Somebody might complain about "that guy that filed six different threads in one day..." but it won't be me. Thanks for the apology, and in return... you should see dome of my first posts here .......:rolleyes:

Oh and concentic rings, Yeah see I immediately went to Fresnel lens then I got to thinking about architectual lighting again and realized that might be what you were refernecing along with baffles and louvers all of which help cut out ambient side light from fixtures whose primary focus < pun> is downlight.
 
icewolf08 said:
Why, is actually an easy question to answer. It is all about surface area. Consider that at any one point on the gobo you have an infinite number of rays of light heading towards the lens and stage. Some of those rays will hit the lens and be refracted and land on the stage in the appropriate point in the pattern. Some will hit the stage at some other point in the pattern. Some won't even make it to the lens at all. By using a donut (or irising down a camera lens) you effectively limit the surface area of the lens that is exposed to the stage. By doing this you also limit the light that passes to only the more direct rays hit the stage. You get rid of some of the rays that hit the wrong place.

My explanation is a little awkward, and if I have some time I will draw up a picture.
Click to expand...


I still don't get it. Consider a point on the gobo where there is a small hole. I want to project an image of that small hole onto the wall.

Why is it that the light from the hole that passes through the center of the lens is sharper than the light that passes through the edges? (or is it just a different focus than the light that passes through the edges?)

If I made a donut that was off center - what would that do to the image. (Humm - I may have to try that)
 
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