Alternatives to glass spectrum filters?

[VideoJohn]

I've been experimenting with various materials lately for photography. The journey has taught me dichroic is available on more than glass. This has got me thinking, are there any spectrum filter alternatives to glass?

[Andy Perrin]

Gel filters are available? Tiffen makes some. What do you mean by “spectrum filter”? Are you talking about any filter or just bandpass filters or what?

[Fedia]

I assume you mean color filters. Lee gels are really great, you have more than a hundred different hues. All I use is basically colors gels in asossiation with different kinds of IR cut filters. There also is the Cokin filter system. You can buy whole sets of them used. They are more expensive than gels but also have all kinds of different optical effects.

 

[Doug A]

UVR Optics make the Curb filter that has 2 quartz glass panels with copper sulfate liquid in between. 

Thanks,

Doug A

[VideoJohn]

22 hours ago, Andy Perrin said:

Gel filters are available? Tiffen makes some. What do you mean by “spectrum filter”? Are you talking about any filter or just bandpass filters or what?

 

I'm sorry. I'm still confused about a lot of these terms. A Hoya R72 would be a bandpass filter correct? That's what I'm talking about. Like whatever coating is on that glass, is it available on another transparent surface that could be put in front of lens?

[VideoJohn]

5 hours ago, Fedia said:

I assume you mean color filters. Lee gels are really great, you have more than a hundred different hues. All I use is basically colors gels in asossiation with different kinds of IR cut filters. There also is the Cokin filter system. You can buy whole sets of them used. They are more expensive than gels but also have all kinds of different optical effects.

 

 

I think we've talked about the Lee's before. They don't affect certain wavelenghts of light right, it's just a colored gel.

[ulf]

4 hours ago, VideoJohn said:

I'm sorry. I'm still confused about a lot of these terms. A Hoya R72 would be a bandpass filter correct? That's what I'm talking about. Like whatever coating is on that glass, is it available on another transparent surface that could be put in front of lens?

No, the Hoya R72 is a long pass filter, that cuts away the visible spectrum, passing the very deepest red and longer wavelengths. It is not a bandpass filter.

The filter effect is caused by absorption in a specially formulated glass material.

 

Here is a link to transmission curves of filter glass materials produced by a Hoya company:

http://www.hoyacandeo.de/english/products/eo/color/index.html

 

If there is a coating on the filter it is just to improve the transmission in the filter's passband, by reducing the losses of surface reflections.

Without AR-coating you lose ca 4-5% light for each glass to air passage. 

 

Most coloured filters, including gel-filters work by absorbing parts of the light spectrum.

 

The name gel-filter has historical roots.

I think the very first gel filters was formed by covering a thin carrier foil with a suitably coloured gel producing rather thin sheets.

Modern "gel-filters" are made of thin coloured plastic sheets.

[colinbm]

Roscoe gel filters the colour is in the film.
Lee gel filters the colour is on one surface & can be removed with water or alcohol.

[ulf]

13 minutes ago, colinbm said:

Roscoe gel filters the colour is in the film.
Lee gel filters the colour is on one surface & can be removed with water or alcohol.

Thanks Col for the information. 

 

Then maybe I should have written:

Modern "gel-filters" are made either of thin coloured plastic sheets or of a coated carrier foil.

An interesting addition to this is that colour filters from Tiffen are made from a thin coloured layer sandwiched between two clear glass sheets, like protected gel-filters.

That is why the transition of these filters are less sharp than thicker homogenous glass filters.

 

Gel-filters are almost the only way to add a filter to really wide angle lenses like fisheye lenses.

They often have a holder for such filters on the rear end of the lens.

[Fedia]

The Lee "blood red" gel is comparable to a 720 or 700nm filter. It's not as dark but the result on a full spectrum camera would be too different I suppose.

[Andy Perrin]

20 hours ago, VideoJohn said:

I'm sorry. I'm still confused about a lot of these terms. A Hoya R72 would be a bandpass filter correct? That's what I'm talking about. Like whatever coating is on that glass, is it available on another transparent surface that could be put in front of lens?

The terms bandpass, longpass, and shortpass have nothing to do with the technology used to make the filter, they have to do with which wavelengths are transmitted.

 

longpass = all wavelengths past a particular value will be transmitted (ideally). So R72 is a longpass filter that transmits everything >720nm.

shortpass = all wavelengths shorter than a particular value will be transmitted (ideally). 

bandpass = all wavelengths in a particular range are transmitted, and the rest are blocked (e.g. Baader U transmits roughly 320-390nm and blocks below 320 and past 390).

 

The above terms are all idealizations, which are imperfectly achieved by real filters.

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Filters can also be described by the materials and technology used.

 

dichroic filters are filters that work by interference between microscopic layers. They can be any of longpass, shortpass, or bandpass (or other types not described)

 

gel filters are absorptive and frequently longpass, but they can have very complex transmission.