DoctorStar Posted December 10, 2009 Share Posted December 10, 2009 Evening folks, I was trying a little exercise today with our volunteer students techs at school where we were lighting 4 evenly spaced stools on the stage using 4 Selecon acclaim zoom profiles (650W). The spots were on a FOH bar 6m from stage and 5 metres higher. Each lantern was set to the same angle, spots were overlapped a little to give smooth coverage between stools and as a starter each spot pointed straight at the stool in front of it...I.e. no fanning. Sooooo, why were some spots dimmer than others: even the year 7 commented on it. Faders were all up to 11. Is it likely to be a cleaning issue or a bulb(s) on the way out? I cannot believe that any minor difference in throw/beam angle would cause such an obvious difference (or perhaps I'm wrong) <What should I try first? Thank you in anticipation, DocStar Link to comment Share on other sites More sharing options...
themadhippy Posted December 10, 2009 Share Posted December 10, 2009 Did you check the lamp peak adjuster thingy? Link to comment Share on other sites More sharing options...
mark_s Posted December 10, 2009 Share Posted December 10, 2009 Dusty and dirty lenses and reflectors can reduce the output of a lantern by a fair bit. I can't really comment on the effect of an ageing (incandescent) lamp though - I'd imagine it to be a fairly negligible factor, if at all. Also have you considered the dimmers? None of them have a topset or anything set, do they? Link to comment Share on other sites More sharing options...
DoctorStar Posted December 10, 2009 Author Share Posted December 10, 2009 lamp peak adjuster.....tell me more?? DocStar Link to comment Share on other sites More sharing options...
gareth Posted December 10, 2009 Share Posted December 10, 2009 Profiles have a lamp adjuster which allows you to adjust the lamp through a limited range of movement forwards and backwards within the reflector. This will let you adjust the beam from a flat field (even illumination from edge to edge) to a 'peaky' beam with a hotspot in the middle. If it's been set too far the other way it's quite possible that you've got a "doughnut" beam with a dark hole in the centre - worth checking to see if that's the cause of your crappy light output. Other than that, check the cleanliness of the optics - as someone's already mentioned, a coating of crud on the lenses and reflector will play havoc with the output of the lantern. Edit to remove duplicate post Link to comment Share on other sites More sharing options...
vinntec Posted December 10, 2009 Share Posted December 10, 2009 1. First there were two different versions of Acclaim profiles - Axial (which take 600W lamp) and conventional which takes up to 650W. I believe the Axial is noticeably brighter if properly adjusted?2. If they are all the same 650W type, then check that all have the same lamp fitted precisely - T26 for 650W I believe. If an incorrect lamp is fitted, so that filiament does not align with reflector, this will be significantly darker (or not focus properly). Also some clown might have fitted a 500W lamp?3. Check there isn't a gel or frost in the gel frame of the darker lamps!4. Have the lamps been properly aligned (we only have axial so not sure how much control older ones have)?5. If lamps are not on full, have the dimmers all got the same profile? if you are not sure, reverse the circuits and check if fault moves or not.6. Are the zoom lanterns all the same model (eg 18/34)? This is less of an issue if the beam sizes are roughly the same.7. If you are still stuck, get a pair of different lanterns to ground level and focus them at a wall - typically sharp focus of smallest possible spot. If they still look different, check for anything else which is different (such as focus knobs being in different places, reflectors at different heights, etc). That's about all I can think of... Peter Vincent Link to comment Share on other sites More sharing options...
DoctorStar Posted December 10, 2009 Author Share Posted December 10, 2009 Thanks folks, I will "get logical" with these 4 spots tomorrow. BW DocStar Link to comment Share on other sites More sharing options...
Don Allen Posted December 11, 2009 Share Posted December 11, 2009 I copied the specs from Selecons web site, the axial with a 600w lamp is brighter than the base down with a 650w lamp. Axial typical performance 18°-34° at 18° Peak – 108,500 cd Flat – 65,800cd 18°-34° at 34° Peak – 65,000 cd Wide – 36,500cd Axial typical performance 24°-44° at 24° Peak – 95,000 cd Flat – 35,000cd 24°-44° at 44° Peak – 50,000 cd Wide – 25,000cd 650W base down typical performance 18°-34° at 18° Peak – 70,100cd Flat – 58,064cd 18°-34° at 34° Peak – 52,400cd Wide – 38,000cd650W base down typical performance 24°-44° at 24° Peak – 78,600cd Flat – 40,500cd 24°-44° at 44° Peak – 40,500 cd Wide – 34,000cd It takes patience to learn how to adjust the lamp adjust on the axial but it is well worth it. I use a light meter as an indicator of when the adjustment is set correct as it is hard to judge with the eye alone. A lot of people are not aware of the peak/flat adjustment available of profiles, go to the Selecon Products page and look up the Acclaim zoom profiles specs and adjustment procedures in the Axial Operation manual and look up their explanation of peak/flat on page 4 of the base down Acclaim operation manual (international) . For most stage lighting you need a peak adjustment. I think the lamp adjustment is probably the reason for the different light outputs of your zooms. Be VERY CAREFUL when adjust hot lamps, as you can blow them very easily if you jar or shudder them. BEFORE do any lamp adjustments, when the fixture is cold, make sure all adjustments move freely, so you avoid blowing a lamp. Link to comment Share on other sites More sharing options...
Russ83 Posted December 11, 2009 Share Posted December 11, 2009 Other than that, check the cleanliness of the optics - as someone's already mentioned, a coating of crud on the lenses and reflector will play havoc with the output of the lantern.Out of interest how do you go about cleaning a reflector? I had a bad experience years ago when wiping an old reflector with a damp cloth that the reflective coating was coming off. Since then I have been very cautions and stuck to just cleaning the lenses. Should you just wipe it with a duster or what liquids do you use? Link to comment Share on other sites More sharing options...
gareth Posted December 11, 2009 Share Posted December 11, 2009 A wipe with a duster will usually suffice. Link to comment Share on other sites More sharing options...
WiLL Posted December 11, 2009 Share Posted December 11, 2009 Indeed with older reflectors it's best to go with care and avoid using any cleaning agents other than a good dusting cloth. TBH anymore than that shouldn't be needed unless the lantern has lived a really abused life or been used outdoors a lot. I once opened up an old profile which had been used by an amdram company for many years during their outdoor performances to find a toasted moth cremated to the reflector, god knows how it had managed to make it that far inside the lantern! Link to comment Share on other sites More sharing options...
adam2 Posted December 11, 2009 Share Posted December 11, 2009 As many others post, dirt or incorrect adjustment is the most likely cause of the differing light output. Two other possibilities are 1)different voltages on the lanterns, not that likely but possible, especialy with a three phase supply into the dimmers. 240 volts on one lantern and 220 on another will be very noticable. 2) different voltage lamps fitted, a 220 volt lamp will be a lot brighter than a 240 volt one if worked from the same supply. Link to comment Share on other sites More sharing options...
DoctorStar Posted December 12, 2009 Author Share Posted December 12, 2009 Thanks everyone, a combination of adjustments and a duster and I am now the owner of a beautiful, uniform FOH wash. BW DocStar Link to comment Share on other sites More sharing options...
MrBoomal Posted December 12, 2009 Share Posted December 12, 2009 I also had a slighty dim Cantata Fresnel. When I opened it up the reflector was coated with a very pale yellow powder.It was as if it had been attracted with some form of electrolysis. It easily wiped off with a duster. I'm using standard GE T29's. Anyone ever seen anything like this before? Link to comment Share on other sites More sharing options...
mrjammy83 Posted December 14, 2009 Share Posted December 14, 2009 I also had a slighty dim Cantata Fresnel. When I opened it up the reflector was coated with a very pale yellow powder.It was as if it had been attracted with some form of electrolysis. It easily wiped off with a duster. I'm using standard GE T29's. Anyone ever seen anything like this before? has any one being spray painting Link to comment Share on other sites More sharing options...
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