Using Yellow Filter

[octo]

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Would you use a blue filter for stage (theatre) shots where most projectors are incandescent and very often dimmed, to get a better balance on faces?

I am not trying to rekindle a semantic scuffle here; it is a genuine question as I am thinking of trying it.

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Someone will recommend putting a yellow filter on a digital camera next...

 

As a matter fact, using a filter in front of the lens and simulating a filter in pp does not yield identical results. For a yellow filter, the difference may not be very marked. It ought to become noticeable for the more dense ones.

[jaapv]

That is certainly true. To get the same optical effect as a color filter in post processing one will need to change the levels of separate color channels, which will influence the dynamic range per channel and the noise level per channel. On a well-exposed low ISO shot the difference will not be visible however.

[StS]

Would you use a blue filter for stage (theatre) shots where most projectors are incandescent and very often dimmed, to get a better balance on faces?

I am not trying to rekindle a semantic scuffle here; it is a genuine question as I am thinking of trying it.

 

I would guess this depends on the nature of the lamp and the filtering. But looking at the options below, the answer is most probably, that a blue filter will have no effect.

 

If the lamp is filament style* (a "lightbulb"), and the dimming is done by reducing the power of the lamp, a blue filter probably does not help, since there should be not much blue light left. If the dimming is done by grey filtering, there might be some blue light left. If the dimming is done by coloured filter foils, the filtering has already happened and the camera can only register the remaining colours. Adding more filters to the camera will only attenuate the remaining light.

 

If the lamp is an arc lamp, the only real way to dim should be by filtering anyhow. Arc lamps are tricky, because their spectrum is not really continuous, some wavelenghts are exaggerated***

 

I suspect the lighting crew is dimming the light to get a "warmer" mood**. In this case, blue light is already attenuated.

 

Stefan

 

 

*The model behind is a "black body", which is heated up to a certain temperature. It is black in the model, to make sure, all light comes from the thermal excitation of it's electrons. Nothing else happens to a lightbulb - the filament gets hot, the electrons of the filament are excited to form a continuos spectrum. The spectral distribution of such a black body for different temperatures can be seen here:

Black body - Wikipedia, the free encyclopedia

The more a lightbulb is dimmed, the more the spectrum shifts to the "left", attenuating blue and ultraviolet, until only infrared is left.

 

** "warmer" in the sense of the psychological perception of the colour, physically speaking, the filament is colder...

 

*** Just for completeness, for theatre illumination it will be most probably continuous wave or CW, pulsed will have a different spectrum, but should only be used for lithography

[01af]

And although our differences are only semantic ...

No, they're not.

 

 

'You want to lighten green, so first you make everything else darker with a green filter and then compensate for this by increasing the exposure'

 

or

 

'You want to darken blue, so you have to make everything else lighter with a yellow filter and compensate for this by increasing the exposure'

 

It may be true ...

The first statement is true; the second in nonsense.

 

 

... but then why would you say it?

Because someone wants to know, or someone (guess who!) is mistaken.

 

 

Nobody should need to know how a filter works to if you want to encourage them to use one, just what it does is enough.

You really believe communication is when people say, 'The proper explanation is too complex for you to understand.'? If you really think that people mustn't know about the details of how a filter works then why do you propagate misconceptions about it? The correct explanations are always the easiest to understand in the long run. It's the misconceptions that make life complicated.

[250swb]

The first statement is true; the second in nonsense.

 

I know it is nonsense, that is what I said , it is semantic garbage

 

But you and AlanG can't have both ways, it is the logical consequence of banging on about a filter making everything else darker than its own colour. If a green filter makes everything except green darker, and by consequence green appear lighter in the print, the alternative has to be also true, when you are using a yellow filter to make a tone like blue sky darker, your logic must therefore say it has to lighten all the other complimentary tones in the print. It doesn't make easy sense as an explanation, but you are advocating it. It is the ying yang of your argument. This is what a novice will be fighting to get their head around, so it is much clearer to say that a filter lightens its own colour and darkens a complimentary colour.

 

Steve

 

 

Steve

[AlanG]

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I know it is nonsense, that is what I said , it is semantic garbage

 

But you and AlanG can't have both ways, it is the logical consequence of banging on about a filter making everything else darker than its own colour. If a green filter makes everything except green darker, and by consequence green appear lighter in the print, the alternative has to be also true, when you are using a yellow filter to make a tone like blue sky darker, your logic must therefore say it has to lighten all the other complimentary tones in the print. It doesn't make easy sense as an explanation, but you are advocating it. It is the ying yang of your argument. This is what a novice will be fighting to get their head around, so it is much clearer to say that a filter lightens its own colour and darkens a complimentary colour.

 

Steve

 

 

Steve

 

Please tell me if you are pulling my leg. How many times do people have to say that you understand the results but fail to accept the process that gets those results? Yes of course it is common to say we use a filter to lighten similar colors.

 

I've long since given up trying to follow your logic. But I posted that shot of filters to try to get across the point to you that I have a bit of familiarity of how filters work. Do you think I bought more than a hundred filters to impress people decades later? FWIW I have a degree from RIT in the science of photography. But I don't expect that to mean anything to you either however we learned how filters functioned pretty early in the curriculum. None of my professors would have tolerated your explanation of the process for a second.

 

Since the way something gets "lighter" on film is by more light hitting it, please explain how putting a filter in front of the lens can cause more light to hit the film. And how did your test shots of that green and white wall shot with a green filter turn out? Is the green side lighter? Or did the green side absorb some of the light? (How could it not since the paint and filters are not pure green?)

 

Here is another thought. Let's say you have a deep green filter on you lens. What happens when you put another identical green filter on it too? Can it lighten the green even more?

 

Good luck to you.

[01af]

But you and AlanG can't have both ways ...

Huh!? No-one wants to have it 'both ways' ...

 

 

If a green filter makes everything except green darker, and by consequence green appear lighter in the print ...

Yes—when you also add some exposure.

 

 

... the alternative has to be also true ...

No, of course not.

 

 

... when you are using a yellow filter to make a tone like blue sky darker, your logic must therefore say it has to lighten all the other complimentary tones in the print.

Seems you're having a serious problem with logic.

 

A green filter makes everything darker except green (actually it darkens green, too, but only by a small amount). A yellow filter makes everything darker except yellow, orange, and red (actually it darkens these hues, too, but only by a very small amount). If you don't believe it then just take a look at the filters' transmission curves—Stefan "StS" has posted a few above, for blue, green, and red filters. Some filters come pretty close to 100 % transmission for some parts of the spectrum ... but no filter can possibly go above 100 %. So no lightening of anything, just darkening to varying degrees.

[250swb]

I've long since given up trying to follow your logic......... .

 

It was your logic I was struggling with AlanG. I may have made a mess of describing it because I find it indescribable. It is easy to understand even for a novice the prime method by which filters could be explained when it applies to a green filter making everything darker darker except green foliage (but I wouldn't describe it that way).

 

But there is an obverse side.

 

We know (by your description) for instance that all filters darken all colours except their own (as resolved in the print). So a green filter darkens everything except green.

 

We know (by your statement) that yellow light is not a component of the colour green, because you already told me it isn't when I said a yellow filter will lighten green foliage. This principle is presumably universal for other colours as well?

 

So, a novice comes to you, and says 'Master (for lo, you have a drawer full of filters), I want to make the sky appear darker, and I have a yellow filter, how will that work if I follow your two principles (above), I cannot see any yellow in the landscape in front me?'

 

So it should be easy to answer the question in a clear and simple elegant sentence begining with the words of your prime premise 'A yellow filter darkens everything except yellow............'

 

It would surely clarify the methodology you are using if you could. I am stupid I know, but I take your words as a scientist seriously.

 

Steve

[250swb]

If you don't believe it then just take a look at the filters' transmission curves—Stefan "StS" has posted a few above, for blue, green, and red filters. Some filters come pretty close to 100 % transmission for some parts of the spectrum ...

 

I know what you mean, fully agree, I do believe you. It is the mangled message you are giving to other photographers I do not agree with.

 

Steve

[250swb]

FWIW I have a degree from RIT in the science of photography. But I don't expect that to mean anything to you either however we learned how filters functioned pretty early in the curriculum. None of my professors would have tolerated your explanation of the process for a second.

 

OMG! Not only does he have a filter drawer, but he's done a course!

 

Good communication on the internet is a bit like the members of a good rock band playing together. Even though they each know ten chords it doesn't sound good if they all try to play them all the time. Ditto with communicating to people who just want to know what to do, you can say things easily and in an industry standard way (as do B+W, and I), or you can throw all the things you know at a subject just because you want to show off what knowledge you have. So a Degree makes little practical sense if you can only communicate your knowledge to the real world badly, by playing out all the information you have all the time.

 

As for a Degree in the 'science' of photography, no, that doesn't impress me one little bit. Just like your filter drawer, I think 'yeah, I've got some filters as well, so what, why would I try to impress people with that?'

 

 

Steve

B.A. Hons (Communication Arts Dept) Fine Art Photography 1975-1978

[kanzlr]

It may be true, but then why would you say it?

 

because that's how it works.

Somebody who knows at least a little bit of exposure will get it.

[AlanG]

Have you shot that green and white wall yet or done any other experiment that would prove or disprove what you wrote? I'm not playing in a band. I am explaining to you in very simple terms how this works and the missing part of the communication process is all on your side because you dug your heels in and refused to acknowledge what is obviously fact.

 

Please don't now blame it on our inability to communicate or attack my education and experience.... is that the bet you can come up with now?

 

Instead of going on and on... shoot the white and green paint experiment through a green filter and see that the green wall will be darker.

[andybarton]

I am going to close this thread now to protect the innocent and before one or more members need to call on the emergency services.

It really has run its course now and it's just achieved that nirvana state that is "Oh no it isn't" "Oh yes it is"