Focusing

[Calder]

100% preheated prior to focusing.

[JDLX]

Depends what your focussing, if its a profile your not going to be directly moving the lamp anyway so there is no harm in focussing on full, I guess a fresnel maybe a bit more sensitive and a par lamp probably wont blow until you start hitting it with a hammer anyway. ;)

[J Pearce]

I often move the lamp tray when focussing a profile to adjust the peak field of the beam.

A gobo special might want a flat field, but a soft edged spot might need a peaked beam.

[andy_s]

I often move the lamp tray when focussing a profile to adjust the peak field of the beam.

A gobo special might want a flat field, but a soft edged spot might need a peaked beam.

 

Quite right.

I recall on my very first focussing session as a "professional" being asked by LD Mick Hughes to tweak the lamp on a T64. (despite the number similarity, this has nothing to do with Parcans). He was very patient while I went to get a screwdriver.

 

It might be argued that tweaking a teapot was a bit of a canute-like exercise ...

[David A]

For 40 years I have always focused at around 80% as the filament is most susceptible to shock at full.Preheating only works if you chant the magic words while you're doing it.But it does little harm as long as you are not paying for all the wasted power.

[Dmx512]

As paulears says you can pop a lamp at 70% just as easily as 100% and you really need to see the full effect when focussing and unless you like climbing ladders you only want to go round the rig once especially if you have many to focus and colours do change with a redder light souce...Dave

[gareth]

For 40 years I have always focused at around 80% as the filament is most susceptible to shock at full.

I'd love to see any evidence you may have of a lamp filament being less susceptible to physical shock at 80% than it is at 100%.

[GRisdale]

Indeed.

 

I've only ever focused at full, and have never been asked to do otherwise. I can remember, like Paul suggests, losing a lamp or two to sticky Minuettes etc, but other than that I've not seen any mass lamp deaths to prompt me to change my ways. Even if I had/did, my first thought would be to be more gentle rather than turn the wick down. I have on the other hand seen the odd lantern on a side boom thoroughly smacked by clumsy performers, having been running at full temperature for a good amount of time - never to the death of a lamp...

 

Other than not-so-then-suddenly-very-slidey lamp trays, or I suppose a tilt lock giving up on a heavy lantern come to think of it, what exactly have people been doing to pop lamps so much to worry? As has been said, if you ever need to fight with a lantern - jammed colour frame or an overly tight wing nut - just ask for the lamp to be turned off or pull the plug.

 

If I'm operating during focusing I've never worried too much about deliberate pre-heating. I tend to wheel lanterns up a smidge as people move towards them just to help them see them in the dark and to let anyone else see which lantern the focusser needs to get to next. If the rig is cold or there are people on stage I might think to wheel channels up to full rather than @@ing them, but that's it. Works for me.

 

Gareth.

[David A]

For 40 years I have always focused at around 80% as the filament is most susceptible to shock at full.

I'd love to see any evidence you may have of a lamp filament being less susceptible to physical shock at 80% than it is at 100%.

 

I have not done a scientific experiment to prove this, however when cold a lamp will withstand great shocks, like in transport without breaking and when fully hot I find they blow easily, so logic and practise tell me that reducing voltage helps.

[gareth]

The difference between voltage or filament temperature at 80% and 100% is so insignificant as to make no difference at all in respect of filament fragility. No matter what level you focus at, if you're rough with the unit the lamp WILL blow.

 

Example - one of the venues at my place of work has a mix of Permus and old STM dimmers. 100% gives an output of between 225 and 230v. 80% gives an output of between 195v and 200v on the STMs (which have a softer curve), and 210v to 215v on the Permus. A modern dimmer with a more linear curve will give a little less output at 80% - but not very much at all.

 

If knocking the level down by 20% makes you feel better when you're focussing, then fill your boots - but knocking perhaps 30 or so volts off the supply to the lamp is not gaining you anything in real terms.

[litemog]

There is I suppose an arguement for focusing at a level closest to that which you anticipate using the lantern at. Particularly if overlapping several units in a general cover for example, where what can appear to be a smooth transition at 100% can look decidely patchy if only used at 60 -70%.

[dbuckley]

I'm not so convinced about filament fragility at different voltages. Lamp life varies by the twelth power of applied voltages, and that seems insane. So maybe focussing at less than 100% does reduce the liklihood of damage.

[andy_s]

There is I suppose an arguement for focusing at a level closest to that which you anticipate using the lantern at. Particularly if overlapping several units in a general cover for example, where what can appear to be a smooth transition at 100% can look decidely patchy if only used at 60 -70%.

 

Not really. The object of focussing is to make sure the light is pointing in the right direction and doesn't hit anything you don't want it to. In my view this is best achieved with the lantern at its brightest. You are right to say that there may be a patchy appearance to a general cover at lower levels, but this is most likely to be caused by discrepancies in dimmers, the age of the lamp in adjacent fixtures, etc, not by the focus of the light, assuming it has been pointed in the right way in the first place. Ways of solving this might include balancing the channels plus or minus a few percent during the plotting session to achieve a more consistent look, or at the worst getting back up to the lantern to adjust barndoors, shutters, , adding frost as appropriate.

 

However, there's plenty of room for individual approaches, so if your method works for you, feel free to carry on!

[GRisdale]

I have not done a scientific experiment to prove this, however when cold a lamp will withstand great shocks, like in transport without breaking and when fully hot I find they blow easily, so logic and practise tell me that reducing voltage helps.

This seems perfect logic when discussing why lamps aren't wrecked every time they go on a truck, but basing assumptions on the difference between 80% and 100% on observations made of the difference between 0% and 100% is rather inductive.

 

Gareth.

[Ynot]

Lamps are most susceptible to vibration damage when they're cooling down. Under a constant current they're weaker than when stone cold, but still fairly robust.