B size Glass gobos - which profile works best.

[paulears]

Supplied recently with a B size glass gobo, I was somewhat unimpressed with the performance, and the light output from the Source 4 was pretty poor and worse, trying one in a Cantata cracked the glass. The show tours the gobos and I couldn't get any brightness from the Source 4 zoom, and while the Cantata was a bit brighter - wrecking the gobo was embarrassing - what did I do wrong?

[gyro_gearloose]

Source four glass gobo holders go in the iris slot, not the metal gobo holder slot don’t they? Maybe the lamp peak needed adjusting because the glass gobo was in a different focal plane to metal gobos?

[alistermorton]

Did you use the correct holder for the cantata? Might be a silly question but the holder for a metal gobo and a glass gobo have the tabs in different places, and forcing a glass gobo into a metal holder will do damage.

[timsabre]

Also S4 has a dichroic reflector which removes a lot of the infrared / heat from the light beam so it's kinder to glass gobos than a cantata. As Gyro says the peaking control on the S4 can make a massive difference to brightness.

 

And you need to put a glass gobo in the right way round with the pattern side towards the lamp if I remember correctly, otherwise they are likely to crack.

 

You probably already know all this, sometimes glass gobos do crack for no apparent reason. I was doing the launch ceremony for Hull's 2017 City of culture bid and the organisers had splashed out for a colour glass gobo (just the one) to shine onto City Hall for the event which local BBC were carrying live. It cracked and partially fell out of the holder about 2 minutes before event start, very embarrassing.

Edited August 28, 2021 by timsabre

[gyro_gearloose]

Acetate gobos in a Selecon Pacific might be more reliable if you need detailed/coloured gobos.

[Shez]

Pre-heating the gobo in the couple of cues before it's needed is a good idea to lower the thermal shock it experiences if subjected to a sudden 100%.

[paulears]

Hmm I’m not remotely experienced with glass gobos in these but I did not adjust the peaking in the S4. In the cantata the gobo was in facing the lens not lamp. I’m wondering if the gobo was just a little tight in the holder and the heating bent it a little? It’ll probably be another ten years till we get given another do no opportunity to experiment sadly. It was apparently sharp and clear in an s4 at the next venue!