Strand SL cool beam profiles

[vinntec]

We got some Strand SL zooms last year and thanks to help on here have managed to sort out one which had an arcing lamp base. On a recent show the LD says that they were noticeably bluer than the Selecon Acclaim Axials which have exactly the same lamps. The only differences are the more advanced optics in the SL and that the Acclaim reflector is solid whereas the SL reflector allows IR and heat through so the beam is cool - but does this remove some of the red and make it look "whiter"? Or is this complete nonsense?

[ianknight]

My understanding is that the Acclaim Axial has a hot mirror which lessens the Infra Red going in to the beam whereas the Strand SL doesn't - whilst the SL reflector is glass it was done more for efficient light gathering (because being cast the facets would be more precisely aligned to each other) I think. You certainly wouldn't wish to touch a gobo from an SL until it had cooled for a while. :P

 

The perceived difference in the optics will likely be down to the lenses used in the SL and their overall thickness - whilst the lantern design itself was a new (and half decent attempt) by Strand at the time to grab back the profile market - the lenses are still cast and polished borosilicate to withstand the heat passing through them. The difference in the composition of the lenses between the SL and Acclaim (and the thickness to achieve the required focal length) will probably account for the colour "difference" the LD saw and I'm surprised he wasn't more surprised by the fringeing around the circumference of the beam from the SL. I avoid using the SL's & gobo's at the theatre I light because of the fringeing.

[gareth]

It might possibly be nothing more than the effects of age on the glass reflectors in the SLs. They really don't age well at all, and have a tendency to develop a noticeable colour cast over time. We have almost 100 SLs in our lantern stock, the vast majority of which are pretty long in the tooth (they must be getting on for 20 years old now, come to think of it) - a lot of them are developing an irritating colouration to the light. Mostly they seem to be turning green (so I guess your perceived blueness might be this phenomena), although we do have some which are going a rather fetching shade of pink as well. It's recently got sufficiently bad that we've got to the stage of sometimes having to swap units out at focus time if the colour cast is particularly noticeable.

 

You say that the optics in the SL are 'advanced' - personally, that's not quite the word I'd use ;-).

[vinntec]

Two very interesting responses. Perhaps I had better clarify - the light from the SLs (all 6 of them) seemed to be "whiter" than everything else which looks slightly yellow by comparison (so SLs look bluer) including (so the LD says) the Acclaim Axials which have the same lamps. We are doing annual maintenance next week and I want to see it for myself as I have had the SLs and Acclaim Axials mixed in a fan in the past (when we only had 5 SLs) and didn't notice any difference between them then. My suspicion is that he was comparing them with non-axial Acclaims which take a T26 lamp which has a different colour temperature:

 

GKV 3200K

T26 3050K

 

I don't know how significant this difference is and whether or not it is relevant as I light for the human audience not TV. So outcomes might be:

• SL and Acclaim Axial have same "colour" light (to human eye)
• GKV lamped lanterns and T26 lamped lanterns have noticeably different "colour" so where it matters we need to add colour correction in one or the other (if this is the case suggestions for gel welcomed)
• All 6 SLs have same noticeably different "colour" light to Acclaim Axial due to optics so different colour correction might be needed.
• Some of the SLs are different to the others and caused the concern

Or some combination of the above.

 

I am puzzled with the fringing mentioned, as we bench focused all of them when they arrived and their gobo projection was rock solid, far better than our axial Acclaims. For normal use they are hard focused then have a mild frost to diffuse the light and they overlap beautifully like this. Hats off to White Light - whose former stock these are - as they needed very little attention when we received them. So I was more than a little surprised to hear there was a problem with them.

[GridGirl]

On an unrelated note, watch out for cracked reflectors - in a previous job we had something like 36 SLs and 32 of them had cracked reflectors. Some were OK - Strand said that cracks less than 25mm were "normal and expected" but didn't have an answer when I asked them about the one which had split into three pieces in my hand...

[adam2]

If one type of lantern has a mirror that passes infrared light, but reflects visible light, then I consider it likely that the mirror also passes some of the visible red light, there is after all not a perfectly defined boundary between far red and near infra red. If some red is therefore not reflected, then the reflected light will be slightly bluer, or of higher colour temperature.

 

If desired this could be corrected by a filter, I would initially try a very light colour correction orange, perhaps one eighth or one quarter CTO. Alternatively if a cooler look is desired, then leave these lanterns open white, and apply a light CTB to the others.

 

 

 

[gareth]

On an unrelated note, watch out for cracked reflectors - in a previous job we had something like 36 SLs and 32 of them had cracked reflectors. Some were OK - Strand said that cracks less than 25mm were "normal and expected" but didn't have an answer when I asked them about the one which had split into three pieces in my hand...

 

This is indeed a major problem with SLs. The majority of our stock has cracked reflectors, and in common with GridGirl's experience Strand weren't interested in replacing them when the problem was discovered (not even the ones that are in two or more pieces, held together by the retaining clamps!).

[vinntec]

Hi everyone - we had our maintenance week which included opening up all the SLs (getting them apart is a challenge that reminds me of a Frog desk!) but all lamp bases fine and all reflectors perfect condition once we figured out how to get them out. Lenses also easy to clean "when you know how". Put one up against a cronky old Prelude zoom and certainly a much "whiter" beam but could easily balance the colour by dimming the SL to about 70%. Less noticeable against an axial Acclaim which has the same lamp so conclusion is that it must be a tiny amount of red lost due to the reflector system which we can easily correct by dimming slightly or using an orange colour correction filter where it matters. So with luck we will get at least 10 years use out of the SLs.

[gareth]

all lamp bases fine and all reflectors perfect condition

Wow! Your SLs must have had a very easy life so far, then.