Frequently Asked Questions...
These are the technical FAQs for the ABTT forum. It condenses some of questions which have been asked on the Green Room Forum and their replies. If you want to expand or amend an answer to a question, or have information on other technical subjects which you want to add to the FAQ then send your contribution to [email protected] or to the Green Room Forum. The ABTT publishes this information in good faith but no responsibility can be attached to the Association or any of its members or employees for its accuracy or for any liability therefrom. Opinions expressed are not necessarily those of the Association.
Should we fit 16amp fittings when refitting a theatre space?
Posted by Gareth Hughes
Unwise, IMO. Consider how many lanterns, extensions and multicores you currently own, and which I assume you'll be keeping. Each one has a plug and/or socket which needs changing. Then there's any equipment which you might have cause to hire in - this will be supplied with 15A connectors, necessitating the use of 16/15 jumpers. Any companies which tour into your space with their own equipment will bring similar problems. Gareth.
Posted by Brian Fairchild
Except for those of us in TV land.
Posted by Gareth Hughes
Which is generally irrelevant as far as those people who work in small/medium venues are concerned. Generally, the only resident LXs who are likely to come into contact with TV LX types are those who work in large venues which host televised events, or in venues which host conferences and the like. In fact, when I worked at a venue where Plaid Cymru and the Welsh Labour Party held their annual (televised) conferences, the Lee Lighting boys would, as a matter of course, turn up with 15A adapters for every piece of their kit.
Posted by Rick Armitage
I agree with the others, plus I can tell you that as a manufacturer, the most popular socket outlet by far is still the 15A. I also work in a similar sized venue which has 5A outlets on it's IWB's, causes no end of hassle with hire gear.
Posted by Andy Broomsgrove
Don't do it, Gareth is 100% correct in what he says. It'll be years (if ever) before 16A becomes any kind of accepted standard.
Posted by Brian Fairchild
Unless you're starting from scratch on the LX side, stick with the 15A, as Gareth said it'll be easier. There is no technical reason to change.
What is the best type of gauze to use for back projection?
Posted by Gareth Hughes
For back projection you really need a back projection screen rather than a gauze. If you back projected onto gauze, all you'd see is the light from the lens through the gauze, and nothing much in the way of an image. You can rent small to medium sized BP screens (NOT the same as a standard projection screen, which are more opaque) from any major LX or AV hire company, but if you want anything bigger you might have to go to someone like Samuelsons or Gearhouse (or are they the same company these days??).
Posted by Ken Coker
I agree with Gareth.. however, sharkstooth might work for gobos. Joels in Halifax do very inexpensive BP screen.
What is now the convention for numbering and or labelling cues between whole numbers?
Posted by Kevin Fitz-Simons
I was brought up on A,B,C, and now ( apologies to Chris Ellis if he reads this mea culpa.) have come to prefer the point system ( .1, .2, .3).
Posted by Richard Grevers
To my mind, if you end up with lots of intermediate cues for the SM to call, the plotting session has not been used properly. My personal system is that I make sure that any cue which is called by an SM has a whole number. This is in defiance of a supposed "convention" that a succession of related cues (e.g. a scene change should have the same base cue number. Any cue that the SM doesn't call (e.g. automatic links, invisible cues to do things with wagglies) I use a decimal for. If I am marking up cues in a script or a prep sheet prior to plotting/levels rehearsal, I'll do so in page references, and then the SM and I will assign numbers during the tech. I also work in with my SM's personal preferences - neither call House or warmers cues as numbers, so I plot those as decimals, and one SM insists that the first scene build is LX1, so everything up to then is a decimal (hopefully fewer than 10 cues) Cheers from sunny (32�C today) New Zealand
Posted by J. Diamond
I would have thought that now that we are in the computer age and being in a world dominated by computer controlled LX operating systems that mainly do not have alpha keyboards, meaning that only numbers are available that .1,.2,.3 etc would be easier for the DSM to call with out the need for the LX operator to decipher!
Posted by Mic Pool
Our system goes like this: * LX Cues have point cues to separate them, o .3, .5, .7 etc, as this is how the desk displays them and how they are programmed. * Sound Cues have a start, which is the whole number e.g. SQ 1, but any action relating to the same piece of sound gets a letter. i.e.: o SQ 1 - Start Thunder track o SQ 1A - Build o SQ 1B - Fade Out etc etc... * I also differentiate between a sound cue and a music cue, this means that when you are doing a one person op. you can have a better chance of getting the right button pushed. Some DSMs raise an eyebrow at the MQ idea. * Followspot cues follow the A & B system. Anyway just a thought.... Two problems exist with the above numbering system. With regard to the sound cue labelling system; this is fine for a simple sequence but gets absurdly complex in a sequence with a great many overlapping effects. If using any form of show control or just using a database or spreadsheet to compile cue lists a sequential numbering system is essential. I use a decimal numbering system for the computers but these translate the cue numbers to a,b,c etc on cue lists for the stage manager. This is because the instruction SQ2a uses one less syllable than the instruction SQ2point1. The cause of inaccurate cueing is often that the DSM is devoting more effort to getting the cues called than getting them in the right place. Two decimal places are useful as a numerical database sortable convention for follow ons. i.e. SQ23.12 would indicate the second follow on to sound cue 23A and when sorted using a standard numerical sort would appear in the correct position in the list.
Posted by Matt Savage
Two problems exist with the above numbering system. With regard to the sound cue labelling system; this is fine for a simple sequence but gets absurdly complex in a sequence with a great many overlapping effects. Sorry, but we usually try to avoid the 'absurdly complex' sound effect plot, relying more on a bit of skill and preparation time to get a good result, with a good director and MD with a stopwatch. Our sequences fortunately stay simple, for ONE person to do as our staffing budgets are tight. If using any form of show control or just using a database or spreadsheet to compile cue lists a sequential numbering system is essential. I use a decimal numbering system for the computers but these translate the cue numbers to a,b,c etc on cue lists for the stage manager. Surely two sets of numbers / letters is more confusing? This is because the instruction SQ2a uses one less syllable than the instruction SQ2point1. The cause of inaccurate cueing is often that the DSM is devoting more effort to getting the cues called than getting them in the right place. The cause of inaccurate cueing is often the DSM does not understand the effect or the reason for its presence. Two decimal places are useful as a numerical database sortable convention for follow ons. i.e. SQ23.12 would indicate the second follow on to sound cue 23A and when sorted using a standard numerical sort would appear in the correct position in the list. 23.12 hmm....I'll stay with my letters....but thanks for the suggestions.
Posted by Dave Whiting
I find more and more people are calling memory numbers for lighting cues, which doesn't seem to me to be a major problem (I can already hear cries of "Heresy!"). Light cues not generated by the board (switching of independent circuits etc.) do not occur so frequently as to become a headache, and the DSM and board op. can quickly agree on mutually acceptable names for those cues. As to extra cues, I personally prefer using the decimal system for extra cues,(and credit for that belief goes to Peter Streulli!) rather than a, b, c etc. It is easier to add extra cues, for example if your first extra cue is called 1.5, then another extra cue before it can be called 1.2 (or 1.1,1.3,1.4) and cues after it can be called 1.7 (or 1.6, 1.8, 1.9). In my experience it is hardly ever necessary to go to two decimal places! Yes I agree, with the dominance now of 'memory' lighting desks it seems to me that the decimal system has superseded the a,b,c, by default. It's simple to use just allocating .1, .2, etc. between each whole number cue, unless of course you're using one of the crazy breeds of board which tell you what point number you can use. A daft idea if ever I saw one! By the way if you have to go to TWO decimal places then me thinks that the communication between the LD and the producer etc. was not too good in the first place!
Posted by Jacqui Leigh
What is the "form"?. Because we should be training our future DSM's at college. If we are all on the same story life would be easier. However having been trained the old way with ABC. I am too finding that it should tally with the lighting boards, i.e. LX Q1.1.Are there other drama schools who are having to change their ways?
Posted by Peter Webb
WELCOME ANORAKS! They didn't get this much response when they asked the Scots and Welsh to vote on the referendum (except, of course the Pattern Numbers question!!!!!) Most computerised boards of any worth are able to re-number point cues to whole numbers at the push of a button, and if numbers are your preference, then user support of the desk manufacturer should be able to write ABC cues as an option for your machine (I know ours would) But, all this aside, we are a receiving house (80 plus pro shows per year and 40 plus student shows) and we have found, in almost every case, that no matter what preconceptions companies arrive with, when push comes to shove, those that matter don't mind, and those that mind don't matter! On a personal note; if you're a producing house and you're writing your cues up in anything else other than your portable word processor (pencil and rubber) certainly before the first week proper is over.......then you deserve all you get) If you're touring it, then your crew should be fully au fait with the operating procedures whereby the S/M operates; if you're a one man octopus tour....then you can use whatever system you damn well like!
What is dimmer ghosting?
Posted by Nolan
A dimmer regulates the electric current going to an instrument. When a dimmer is 'off' it should not let any current through. When a dimmer is ghosting it allows some current to pass through even though it is at zero percent (off), and the lighting instruments hooked into that dimmer will be on at a very low level - 'glowing' if you will. The term ghosting (I would presume) is related to the much debated "ghost light" that many theatres have.
Why do dimmer racks bleed?
Why do our dimmers bleed light through. The lighting board does not necessarily have to be set up for this to happen it seems to be something the dimmer does on its own. Different companies have expressed several opinions, the most common seems to be that because the dimmer is warm when it gets put in the lorry in the evening and remains in the normally cold climate until it is pulled out again the next day ready to be used for the show, it is a problem with condensed water?. The dimmer is a no nonsense type (LD1222) it has no special features. It isn't something that happens extremely often but strikes when we least expect it!. )
Posted by bob
I have seen this in the LD1222 before. Do you have a power matrix supply? If so this would run over the sub level and the DMX, with no return, would take over as their own level. Try using A DMX anz. and see if you have a sub system running for back up if not, try repositioning your Relist poles. This could also be in the control relay in the rack, If that was the case it just needs some tuning. or they could just have gotten wet from rain or moisture build up, and then they just subsided.
Posted by Simon
Quite often the "pre-heat" needs adjusting - i don't know your dimmers but there is often just a pot that needs adjusting either on the front or inside the unit - but if you're unsure get an electrician to open the unit as the best way to adjust it is with the mains on,
Posted by Mike Savage
You can adjust the 'zero' position of most dimmers by altering potentiometers inside for the relevant channel. It could also be caused by the Triacs on that channel are giving up the ghost. If the light bleeding problem gets worse as the dimmers get warmer this could be a sign that this is the case. If the triacs or other semiconductor is giving up then they will need to be replaced.
Posted by Ant Peter
Far be it from a techoignorant such as myself to submit an authoritative view to you, but have you had the dimmer packs serviced recently?
Can you trim J.T.M. Dimmers so they do something between 0 to 20% and 80 to 100%?
Posted by David Ripley
JTMs and STMs, from memory, have dimmers with S curve outputs i.e. they don't do too much to start with and then dim, after which the fade flattens out. I don't think you can change the curve but obviously you can trim the pots to prevent bleeding, reduce voltage at 100% to save lamp life etc. The modern digital dimmers have selectable dimmer curves.
How do you trim old Strand-Electric PTM60 dimmers?
Posted by Mark White
The traditional method of trimming these dimmers was to connect a true RMS meter across the output of the dimmer (the 70 series Fluke is adequate) and set the trim pots as follows: * With the control voltage at zero, adjust VR1 (the bottom end setting pot) to give 6-9 volts output. Anything higher than about 12 volts makes the filament glow. * Then increase the control volts to 90% of full which will be say -9 volts on a -10 volt system and set the output to say 220 volts by means of VR2 (the top end setting pot). This is no job for the faint hearted or the inexperienced, those heat sinks are live! You are working on live equipment and all adequate precautions have to be taken to satisfy the Electricity at Work Act amongst other requirements.
Where does the term "GOBO" originate?
Posted by Jonathan Badger, D Hughes and David Lawrence
'Go betweens' - image cut outs placed in front of luminaires, used in film industry (US). Similar sort of use as Linnebach Projection.
How can you make gobos yourselves?
Posted by wac
Through experience in theatre please don't make your own gobos as they are really annoying in use and tend to stab fingers.
Posted by Frank Wood
It's not that hard, if you can find the materials. That's probably the hardest bit. When I last did it, I used the thinnest copper sheet I could get. Then, you have to make the artwork. After that, you have to make the masks. You need two identical ones, preferably made on film designed for the purpose. Kodalith is ideal. one should be physically reversed. RS do a spray-on photo-resist. Make sure that you have an even coating on both sides Assemble the two negatives as though you were trying to make a double-sided PCB. Then etch it using your usual process. Trim the edges with a needle file, and you have your gobo. The etching always leaves ragged edges. I shouldn't do this for anything other than very bold goboes. But it works.
Posted by Hans van Bemmelen
You can use transfer sheets. You photocopy or laser print the design onto the sheet, in mirror reverse. Next you put the sheet, image down, onto the material (thin brass or stainless steel) you want to use for your gobo (template). A hot iron is then used to transfer the toner + binder which make up the image to the metal. The other side of the metal is covered with self-adhesive film or lacquer. The metal is then etched. Holes will be etched where the metal is not protected by the image . Even if the transferred image does not look completely black the transparent binder may still act as a resist. Just try and see how well it works. The transfer sheets may be available from electronics shops, they are also used for making printed-circuit boards. Alternatively try the transfer sheets used for printing onto T-shirts. This process is very simple but the quality of the transferred images leaves something to be desired. However, it is well worth having a try.
Where can I get panels that emit light when a current is fed to them?
Posted by Brian Fairchild
I'm not sure if this is the stuff you want but you can get thin flexible sheets of electroluminescent material from Farnell Components. (who almost certainly have a web site)
Posted by Jester`
Look into some stuff called Light Sheet. It's an American product, and can be quite expensive, but this is probably what you are looking for.
Posted by Colin Winslow
Contact 'Illuminati', 3 Gladstone road, Colchester CO1 2EB Tel: 01206 798076 Email: [email protected]
Where can I put two mac 250's for the schools annual musical festival, on the ceiling! or on the stage it self ?
Posted by Andy Briggs
You need to ask yourself the question "why am I using these fixtures" - 2 intelligent pieces of kit are not really going to create an awe inspiring lighting design. Everybody watches huge lighting extravaganzas on the box or on a show and so very few people are impressed by moving/changing colours unless a lot of thought and planning goes into the design process (which is why we employ LD's) If you have the things anyway, I would suggest putting them in the air at the rear of the stage set focusing through the haze towards the audience. Very few people will actually see any gobo's etc. which are focused onto the stage floor in a small venue, but most people will see the effect through the haze. Secondly "less is more" - don't use them all the time - it's boring, they are a lot more effective when used in short well thought out sections.
Posted by Phil Edge
One question that may help the design process, Are the Audience in a flat hall, or are the seats banked. The reason behind my question, is the Macs do not move as fast as the moving mirror stuff like the 918, so a lot of the great effect you get from the MAC 250 are from moving Gobo's around rather than the flashing and high speed movement of the 918. So if the Audience can see the stage floor you have a great area to put the MAC's to work projecting on, if they can't see the floor, then you are projecting onto the back wall or as beams through the Haze.
Posted by JJ
I agree with both Andy and Phil, my only additions would be, Masterpiece, forget it, find something else, anything else!
How does Peppers Ghost Work?
Posted by Pat Nelder
See http://analog-press.com/Pepper04.html for good documentation. I don't ever remember seeing references to the use of the illusion in an actual production, as opposed to a staged demonstration - though that's not a very clear distinction for the 1800's! There would clearly be problems about size of glass plate and sightlines in anything approaching a full size theatre, even a Richmond or a Bury St Edmunds.
Posted by Andy Gale
I can find two written references for "pepper's ghost" :- French Theatrical Production in the Nineteenth Century [J.P.Moynet / L'Envers Du Theatre - translated by Alan S Jackson & M Glen Wilson - published by the American Theatre Association] Effects for the Theatre - edited by our own Graham Walne - published by AC Black Or, if neither of these suffice, grab an old stager ... after about half a dozen pints you will get a completely coherent explanation which [unfortunately] you will not be able to remember the next day...
Posted by Howard Bird
As an old stager I have used Pepper's Ghost for a production of the Scottish play. It was fine if you happened to sit slap bang in front of the set but viewing diminished noticeably as you moved left and right. We used UV paint and lights. it seemed an awfully good idea at the time....
Posted by Nick Taylor
I can remember being taken to see TV studio recordings where this "Peppers ghost" concept was used. I guess this might have been up to 30 years ago. Cameras could be lined up just so, in the audience you didn't really see much of an effect. From memory it was to make a human small on table top. A trick more easily done these days!!!
Posted by Dorian Kelly
There is a very good example of a peppers ghost effect in London at the moment at the Shakespeare's Rose Theatre exhibition. Designed by Bill Dudley, this consists of a piece of glass, with an applied layer of 3M quarter-silver film. This is suspended at 45 degrees tilted toward the audience. Above this suspended parallel to the floor is a large piece of rear projection screen on which is projected some video images. The image is reflected into the glass. The idea is to watch both the image and the background beyond at the same time. It works very well, and is fairly bright because of the quality of the projector used, but the angle of view is severely limited. I have some images of Victorian use of this effect.
Posted by Colin Winslow
"The True History of Pepper's Ghost" (A reprint of the 1890 edition) - Price �5.95 "The Ghost, The Ghost, The Ghost" by John Phillips - Price �4.75 "Randall Williams King of Showmen" by Vanessa Toulmin - Price �6.95 are all books on the subject published by Stephen Herbert in the 'Projection Box' series. His telephone number is 01424204144 Email: [email protected] Pollock's Toy Theatres Ltd at 1 Scala Street, London W1 (tel: 020 7636 3452) also stock them.
Are there any regulations prohibiting or limiting the use of more than one phase supply on a lighting bar. If so what are they?
Posted by shane guy
The formal regulations changed with the 15th edition IEE regs. (It was prohibited before then). There is a guidance note that suggests it's not a good idea it's code number is PM50, but I can't remember it's title.
Posted by Keith Yarwood
I do not think that there are any regulations as such, only the requirement to operate safely. We used to maintain so far as possible 2m separation, and never more than one phase on a bar. But I think that if you are working with equipment which is tested for proper eathing, there is really no significantly increased risk. A 240 volt shock to a person on a ladder would, in any formal risk assessment be rated so badly that a 415 volt shock could hardly be worse. There are certainly regulations requiring regular testing, which for ordinary lanterns and cables we take to be annually. This regime seems to be far safer than what was the case before.
Posted by Ian Evans
Under the 16th Edition Wiring Regs The voltage range of 50v - 1000v ac is classed as low voltage and can therefore be treated with the same care and regard as for 230v. as stated by Mr Keith Yarwood all equipment should be maintained in accordance with the Electricity at work act 1989, this should ensure the integrity of the wiring, Also all hard wired systems throughout the theatre should be Tested once a year for compliance with Theatre licensing. This being the case there would have to be approximately six or seven situations occurring (e.g. Live wires touching metal work, earths disconnected etc)for someone to receive a 400v shock (just a little note to say that the Voltage supplies in the UK are 230V single Phase and 400V three phase +10% and -6%)
Where you can get hold of stencils for the most common types of lantern?
Posted by Gilly, Jackie and rw
Most Lighting suppliers do them at both 1:50 and 1:25. Strand make their own. Futurist Lighting (Harrogate) do stencils with Strand symbols on. Whitelight do a standard 1:25 with symbols suitable for pretty much everything, a 1:50 version, and a moving light stencil. And Stage Electrics sell them.
Where can I get information on old Strand lights?
Posted by Snid
There is a Strand Archive website which I think you will find useful at www.ex.ac.uk/drama/strand
Are there any laws on using strobe lights?
Posted by Geoff
Have a look at ABTT Update Safety Matters No. 27
Posted by Jonathon Hurley
There are no laws as such for the use of strobes anywhere - only guidance which, as the HSE states, is good practice only... however, if you don't do something to comply with it you could be in trouble if anything happens. As far as the HSE is concerned, the Event Safety Guide HSG195 (mainly dealing with outdoor events) gives the advice on strobes (para. 661ish) - they should be kept at or below 4 flashes per second (4 Hz) and if multiple units are used they should be synchronised. They also suggest that, if possible, the units are mounted as high as possible and that the light is bounced off something else first.
Posted by Ema Quinn
The best people to contact for this information are the British Epilepsy Association. They have all the medical information you'll need - just to note though, strobes affect many people with alsorts of conditions, not just epilepsy.
Posted by OJ
It is commonly accepted that when using strobes the following basic rules should be followed. 1. Display warnings on entrance ways, walls and possibly on tickets and posters (tickets and posters helps you refuse people their money back after a show) 2. Make an announcement over the PA at the beginning of the show or after the interval and consider also making announcements immediately before scenes containing strobes. 3. Don't prolong use more than 15 seconds, after 10 strobes become uncomfortable for many poeple. 4. Dont use a flash rate of more than about 4 Hz, some neurologists say that at a certain rate, everyone will be affected by strobes. These rules are basically all you can do to allieviate problems. If someone is affected by a strobe they could potentially take thousands in court no matter what measures were taken. Local Authorities have enforcement responsibility for most theatres and should(?!) be able to provide this sort of advice .
Posted by TJ
This is second-hand info but as well as a max flicker rate, two universities in the London area restrict strobes to a max 2 mins per show.
Posted by Owen Jones
You must inform (by law) the customers that strobes are to be used during the performance. You can do this by a sign in box office but verbal information is also a good idea for legal resons. If anyone can claim that they were not aware sucessfully then you can lose your license and also be sued for damages. Signs at every entrance are required, it also a good idea to have them on walls around and about. You must announce the use of strobes at least once before curtain up, if you have strobes after the interval you should announce again. Announcements should be made with house lights on and should be followed by ample time for people to leave. In short, cover your back, go over the top with signs and announce whenever you can. It's better than being sued.
What is the best way to create tinkerbell in Peter Pan?
Posted by Colin Winslow
In the original production (and for many years afterwards) a small round mirror (like the one in a lady's powder compact) was used, the operator sitting in the orchestra pit, reflecting a carefully placed light. We used this method in a production at Theatr Clwyd and it worked extremely well - you can get a very effective kind of 'trembling shimmer' with it that you can't achieve with a spot. - And by the way, it is traditional to list Tinkerbell in the programme as played by 'Jenny Wren'. This was Barrie's suggestion, as children asked him why Tinkerbell was not listed in the programme.
Posted by Pat Nelder
As Colin has said a person holding a mirror to reflect a spotlight beam is easily the best Tinkerbell. For that production, we had a Patt 23N pointing vertically down into the orchestra pit, where the operator sat out of view of the audience. I think we left the light on most of the time, and the operator just held the mirror in the beam when Tink was 'on', which saved a huge number of cues. With a similar throw between lantern and mirror to that between mirror and stage, the shape of Tink is determined by the shape of the mirror. If you put the lantern very close to the mirror, you reflect most of the beam rather than part of it, and the shape is set by the lantern and any shutters or gobos you might use. We've done some very good moving fireworks like this, and it's worth investigating for Tink (a collection of small stars?). You'll probably want a very narrow angle lantern.
Posted by tim paver
I worked on a pro version of peter pan and they used a laser pointer from the prompt corner.
How do you project a video onto a back drop but from behind without reversing video image?
Posted by Dave, M.Elphick and Andrew Chesters
Have a look at the menus to see if there is a rear projection option. Every one I have ever used has offered this facility, even if it has been hidden deep inside the menus. Alternatively just bounce the image off a mirror, this also has the advantage of achieving a larger screen image as the distance from the projector is increased _BUT_ make sure the mirror is securely supported, with _LOTS_ of Gaffa holding it on. You will need a large one if it is a three gun projector.
