dichroic filters

[scott]

Hi

 

 

I may be barking up the wrong tree here but heres my idea, dichroic filters let whatever colour of light pass through them by the glass having varying levels of silicon dioxide layered on the surface facing the lamp(only one I can remember), now heres my question is it not possible to tilt/angle the dichroic filter so other colours can be selected using just the one filter?

 

thanks for reading my first post

 

 

scott

[jfitzpat]

Hi

 

 

I may be barking up the wrong tree here but heres my idea, dichroic filters let whatever colour of light pass through them by the glass having varying levels of silicon dioxide layered on the surface facing the lamp(only one I can remember), now heres my question is it not possible to tilt/angle the dichroic filter so other colours can be selected using just the one filter?

 

thanks for reading my first post

 

 

scott

<{POST_SNAPBACK}>

 

Is it your thinking that, because thickness of a dielectric coating impacts wavelength reflection and transmission, altering angle will substantially alter color from a conventional light source? If so, then the practical answer is no. That is why most dichroic color mechanisms in theatrical fixtures either use partial obscuration with fixed density filters (and optical blending) or full obscuration with variable density filters.

 

However, a related physics principle can be used in color for lasers. Acousto-optic modulators use an acoustic wave to create density variations in a small piece of suitable material. Sort of a high speed, variable diffraction grating. In theory, AO could be used for scanning (deflection) as well, but I've only seen in used for color and blanking (a high speed 'shutter').

 

-jjf

[Mush]

Hi

 

 

I may be barking up the wrong tree here but heres my idea, dichroic filters let whatever colour of light pass through them by the glass having varying levels of silicon dioxide layered on the surface facing the lamp(only one I can remember), now heres my question is it not possible to tilt/angle the dichroic filter so other colours can be selected using just the one filter?

 

thanks for reading my first post

 

 

scott

<{POST_SNAPBACK}>

 

Think of dichros as mirrors, gel absorbs light it dont use, dichro reflects it.

 

Couple of lights use that principle,mechanically it ends up complex though,

 

VL5 with twisting vanes

 

http://www.vld.de/home/img/img_gesch/vl5.jpg

 

Color Command with prism and rotating filter changes relative angle

 

http://www.highend.com/products/dichroic_t...olorcommand.asp

[Jamtastic3]

mmm, I've never understood how a fixture like a VL5 works. Using a colour wheel is all fine since the wheel will turn the colour into the lights path, but with a VL5 how is the colour achieved in such a small housing and how do you get nice blends between the colour washes? If it's vanes, how many different colours are on one individual vane

[jamienip]

it works in line with the focal range of lanterns, careful mathematics will determine the best place to situate the "vanes "(VL) or "flags"(Mac600) within this so will saturate the entire beam without an odd coloured pattern (gobo effect) being produced. They are usually placed away from the focal plane (gate) so are not in focus. The Colormerge by High end systems uses 3 glass dichroic filters, which are used to introduce variable saturation of Cyan, Yellow and Magenta into the beam. They are moved into place to create CMY (subtractive) coulour mixing within generic lanterns. These are similar to colour mixing scrollers, but are internal, and although bulky and expensive allow you to alter levels of saturation to create the desired colour more effectively.

 

This is an illustration of "flagged" dichroic filters, similar to those in the mac600.

 

http://www.dichroic.com.tw/img/color_1.gif

[Mush]

mmm, I've never understood how a fixture like a VL5 works. Using a colour wheel is all fine since the wheel will turn the colour into the lights path, but with a VL5 how is the colour achieved in such a small housing and how do you get nice blends between the colour washes? If it's vanes, how many different colours are on one individual vane

<{POST_SNAPBACK}>

 

Jaimie`s illustration is the more conventional colour mixing system used in a lot of lights.

 

VL5 uses Dichro Tune also used in Irideon architectural fixtures.

 

Dichro filters will change transmitted hue depending on angle to the light source, this is the principle used in VL5. Twisting the vanes of glass changes the colour.

 

The catch apart from swiss watch mechanics is narrow beam angle.

 

Sometimes see this with architectural floods with dichro filters, a deep blue at 90 degrees to the lamp will have colour fringing going to magenta at the sides as angle from lamp is less than 90 degrees.Which can be attractive but not always whats wanted, hence still market for traditional `stained` glass filters for architectural uses.

 

Perhaps someone with more direct experience of VL5s can explain a bit better....

[scott]

hi all

 

 

thanks for the feedback, so those dastardly smart vari lite guys have already done it with the VL5 then :-( oh well

 

 

thanks again

[jfitzpat]

mmm, I've never understood how a fixture like a VL5 works. Using a colour wheel is all fine since the wheel will turn the colour into the lights path, but with a VL5 how is the colour achieved in such a small housing and how do you get nice blends between the colour washes? If it's vanes, how many different colours are on one individual vane

<{POST_SNAPBACK}>

 

Jaimie`s illustration is the more conventional colour mixing system used in a lot of lights.

 

VL5 uses Dichro Tune also used in Irideon architectural fixtures.

 

Dichro filters will change transmitted hue depending on angle to the light source, this is the principle used in VL5. Twisting the vanes of glass changes the colour.

 

The catch apart from swiss watch mechanics is narrow beam angle.

 

Sometimes see this with architectural floods with dichro filters, a deep blue at 90 degrees to the lamp will have colour fringing going to magenta at the sides as angle from lamp is less than 90 degrees.Which can be attractive but not always whats wanted, hence still market for traditional `stained` glass filters for architectural uses.

 

Perhaps someone with more direct experience of VL5s can explain a bit better....

<{POST_SNAPBACK}>

 

I believe that part of the key to making Dichro-Tune work in, say, the VL2416 is the use of a short arc lamp. I'll try to dig up some good illustrations which show why I think this is so.

 

Your flood example is a great one for someone to think about if he/she wants to dig deeper. Why the edge is different seems simple enough, the dichroic is basically a selective wavelength mirror that is tuned for an optimum angle of incidence. As light strikes it far from that optimum angle, more is transmitted. But the color shift you describe (deep blue to magenta), and which I've seen myself, is harder to relate back to theory.

 

-jjf

[martinw]

Color Command with prism and rotating filter changes relative angle

http://www.highend.com/products/dichroic_t...olorcommand.asp

Color Command and the VL5 actually use completely different techniques for changing colour, despite appearing to be similar from the front. I attempted to describe how Color Command works here (probably rather badly!). This technique was invented by Brian Richardson (co-founder of Morpheus Lights) and described in this patent.

 

Martin

[jfitzpat]

Color Command with prism and rotating filter changes relative angle

http://www.highend.com/products/dichroic_t...olorcommand.asp

Color Command and the VL5 actually use completely different techniques for changing colour, despite appearing to be similar from the front. I attempted to describe how Color Command works here (probably rather badly!). This technique was invented by Brian Richardson (co-founder of Morpheus Lights) and described in this patent.

 

Martin

<{POST_SNAPBACK}>

 

FWIW, the patent for the Morpheus 'Color Fader' is pretty interesting reading as well.

 

-jjf