Blue filters and fog

[Q.G.]

Actually, I'm trying to show that a magenta does exist. And that R + G = Y.

Which is not correct.

R + G can give the impression of Y.

But Yellow exists independently of both R and G.

And that's how it differs from magenta: magenta does not exist independently, but only as the impression left by B + R.

But a wide blue filter with low absorption could pass green light, but I would not call it a blue filter. As you noted above, we might agree on another color.

Phew! Back on track! Thanks!

 

[Photo Engineer]

If you look here: http://en.wikipedia.org/wiki/RGB_color_model you will clearly see the position of Magenta on the CIE chart.

If you read what I posted, there are real, identifiable pigments and dyes that are called magenta.

And, if you look further, you will see that the blue filter that can allow passage of green light is called Cyan!

By your definition, white does not exist, as it requires the combination of all 3 primaries. But it does indeed exist even though it fails your test for a "real" color.

PE

 

[Q.G.]

PE,

I don't need Wikis. The chart is 'old hat' to me.

And no, i don't claim that white light doesn't exist (quite the contrary: you appear to claim that yellow does not exit).

Not that it wouldn't because "it requires the combination of all three primaries" (when will you stop talking about colours as if only three and the combinations of these three exist?! Have a look at the chart, and see what it actually shows. Answer the question about sodium light.).

Not that it wouldn't, full stop.


It's time to give up again, i guess.

So a summation:
Films, B&W emulsions are not tri-colour affairs, but respond to single wavelengths out of a broad spectrum.
If such an emulsion records pure yellow light, that is not the result of a combination of red and green light.
Which is painfully obvious as soon as you understand that pure yellow light exists (as the CIE chart also shows) even when there is no red and green present. (Contrary to magenta and white light, which are compound thingies, the result of combinations).
If one emulsion (pan) responds to a wider spectrum than another film (ortho) the pan film can be made to respond the same as the ortho film by simply removing the extra bit of the spectrum.

 

[Photo Engineer]

Well, one thing is clear. I am not disagreeing with you, you are disagreeing with me!

More than anyone else here perhaps, I know that films are sensitive to each wavelength of light according to their sensitivities.

However, you misstate my case. I say magenta exists and yellow exists. They are combinations of two spectral regions just as cyan is! You contend that magenta does not exist! So, you have misquoted me and you are missing the fact that subtractive systems consist of two portions of the additive system (in simple terms). Conversely, you may say that an additive system is one part of each two part subtractive system. Each refers to either density or absorption spectra.

And, you miss the point (or disagree with the fact) that a filter that makes an ortho film from a pan film, although possible, is not blue by the definition agreed to by anyone. It would be a composite of blue and green called cyan!

I applied the things I was taught in Ektacolor 37 paper, where we used a new green sensitizing dye and a new magenta imaging dye, in Kodacolor Gold 400 with a new green sensitizing dye, and in Ektaflex R and C which were built from the ground up with all new dyes. I might add that the green sensitizing dyes were a non-existant magenta in color.

Bob Hunt was our guru for color: http://www.sid.org/pressroom/040818.html and http://www.photomemorabilia.co.uk/Colour_Darkroom/Kodak_S1.html

You see, I learned this from the perspective of a subtractive system engineer for photo systems. IDK your background, but that is where I come from and how I explain things, using the texts that I mentioned earlier. I am truly sorry that we cannot meet somewhere in the middle, but as I see it, I can hand you a bottle of non-existent magenta dye. That is the bottom line!

PE

 

[Q.G.]

Well, one thing is clear. I am not disagreeing with you, you are disagreeing with me!

More than anyone else here perhaps, I know that films are sensitive to each wavelength of light according to their sensitivities.

However, you misstate my case. I say magenta exists and yellow exists. They are combinations of two spectral regions just as cyan is! You contend that magenta does not exist! So, you have misquoted me and you are missing the fact that subtractive systems consist of two portions of the additive system (in simple terms). Conversely, you may say that an additive system is one part of each two part subtractive system. Each refers to either density or absorption spectra.

No, no.

I do not claim magenta does not exist. I do not know where and how you got that idea.
I have said, and will say, that it exists as the combination of two spectral regions.
Because that's how it is.

I do (and must) say that you are wrong saying that yellow (and cyan) also exist as the combination of two spectral regions.
They most certainly do not. They are two spectral regions in their own right!


This talk about additive or subtractive really makes no sense here.

If the part of the spectrum in which we find yellow was a combination of the red and geen parts of the spectrum, we would have to say that red extends into the region we would also call green, and green into the region that we would also call red.
So that there would be a region that would be both red and green, which we then call also yellow.
Which is, of course, nonsense.

If we would say they combine without such a confusion of what colour a band of the spectrum would be (both red, green and yellow, all at the same time), without overlap, it could only be that when we have light consisting of both a bit of red (long wavelengths) and a bit of green (shorter wavelengths) the result would be the cancellation of these wavelengths and the creation of light of wavelength in between the two.
That, of course, also does not, cannot happen.

The simple fact is that neither yellow nor cyan light is a combination. They both exist independently of the things you claim they are combinations of.

And, you miss the point (or disagree with the fact) that a filter that makes an ortho film from a pan film, although possible, is not blue by the definition agreed to by anyone. It would be a composite of blue and green called cyan!

If you think so, you misunderstand me.
I don't.

We were talking about whether there are filters that could perform that feat, and while you appeared to say it couldn't be done, i think we have established before that it could. I don't know the number of the post, but i also distinctly remember that i wrote something about it being questionable that blue would be the proper name for such a filter. So agreement about that too.

I applied the things I was taught in Ektacolor 37 paper, where we used a new green sensitizing dye and a new magenta imaging dye, in Kodacolor Gold 400 with a new green sensitizing dye, and in Ektaflex R and C which were built from the ground up with all new dyes. I might add that the green sensitizing dyes were a non-existant magenta in color.

Bob Hunt was our guru for color: http://www.sid.org/pressroom/040818.html and http://www.photomemorabilia.co.uk/Colour_Darkroom/Kodak_S1.html

You see, I learned this from the perspective of a subtractive system engineer for photo systems. IDK your background, but that is where I come from and how I explain things, using the texts that I mentioned earlier. I am truly sorry that we cannot meet somewhere in the middle, but as I see it, I can hand you a bottle of non-existent magenta dye. That is the bottom line!

And that will be what's at the root of the problem.
I have been telling you all along

You are using a tri-colour thingy as your frame of reference.
I have been going on and on (you have noticed ) about the errors that leads to.
Like saying that a blue filter passes magenta. And the still repeated error that yellow is a combination colour.

When we are discussing what filters can and cannot do to the spectrum, when discussing what part of the spectrum emulsions respond to, we are not talking about the colours of pigments, how the 6 tri-colour colous combine to create a visual impression.
Ask yourself why that pigment looked magenta, and you will be heading in the right direction (i.e. the one that will make you see that it is absolutely wrong to believe that yellow and cyan are combination colours) again. You posted the CIE chart. Do have a look at it, and see what that tells you.

 

[Sirius Glass]

:munch::munch::munch::munch::munch:

 

[Lee L]

A Wratten #44 filter (blue-green) is most often suggested for getting orthochromatic response from panchromatic films. The B+W 470 is an equivalent of the Wratten #44, but may not be readily available.

 

[Photo Engineer]

Please note the WR44 description! Light blue green, or cyan.

And, it involves the combination of 2 portions of the spectrum.

And sorry about this guys. I am using a "tricolor" methodology as that is the way the eye works. See the Wikipedia article.

PE

 

[jp498]

Folks, just incase this is not clear, the ability for certain colors to get through fog better than others has zero to do with film's spectral sensitivity or how film works with filters.

 

[Photo Engineer]

Folks, just incase this is not clear, the ability for certain colors to get through fog better than others has zero to do with film's spectral sensitivity or how film works with filters.

Actually, it does if you want to capture the image on film. It also matters to the human eye.

PE

 

[Chazzy]

So do blue filters work to enhance fog or don't they? That's all I need to know.

 

[Ian Grant]

No. Companies make "Fog" filters, these are uncoated very slight diffusers type filters that add very mild flare etc, they are used by the film industry, they cut sharpness.

You're best just shooting as normal without a filter. I shoot a lot in fog

Ian

 

[Photo Engineer]

Chazzy;

Just as yellow filters tend to cut haze and fog, blue filters can tend to enhance it as shown earlier in this thread. There are limits and as pointed out here and there (wheat from chaff kinda thingy ), the filtration can limit spectral sensitivity depending on the filter.

See post #7 for example.

PE

 

[Ian Grant]

One of the interesting things about images made in fog is the way parts of the image stand out others get submerged. As Ron says altering spectral response might have limitations.

My experience shooting in Cornwall (over the past 7-8 years) where the mist rises from the sea and swirls around the cliffs is that unfiltered B&W films capture it perfectly. It's effectively fog often it drifts inland getting worse, fog & clouds forming while it's sunny out at sea and on the immediate coast.

Under exposure and over development need to be avoided when shooting in fog. It's not the opposite of haze, it's very different.

Ian

 

[Ray Rogers]

What we have to get clear is that blue, cyan, yellow, red, green are all pure spectral colours You can assign a single wavelength to them, or a band of wavelengths you will want to call "blue" etc. But magenta is not.

This is understood.

Magenta does not exist except as a mix of blue and red.

Also understood.

A blue (!) filter will block red (and, as PE points out, every other colour too - Now that is a matter of blue or blueish.). So lacking the red component needed to create magenta, there really is no possibility on earth how the light coming through a blue filter will contain magenta.

As I understand it,
Blue is most effecient at blocking Yellow, followed by Red... thus Magenta will be the last to go even though the filter may be quite bluish in appearence.

As far as blocking magenta, Green is the most suited,
as it can block all the components of magenta, while blue can only block half of them.

Any way, do you think that a typical filter that does block red and or blue... does so with 100% efficiency?
Even the good filters are not really perfect or IDEAL.

We really have to stop thinking in terms of tri-colour!
It may be appropriate when discussing how CRTs and such produce colours, but it is completely out of place, wrong, here.

Can you explain how if we stop thinking in terms of tricolor, I will be able to create better photographs?

What ADVANTAGE is there to dropping this attachment to tricolor?

Yes. It is REALLY true.
You can split the entire EM radiation into a spectrum, and nowhere will you encounter magenta.

What happens to white light if you remove the green?


You wrote the following sentences:
1.
magenta is not part of the spectrum,
2.
magenta can only exist as a mix of spectral colours.

These 2 sentences are incongruent!

If magenta exists as a combination of two things which are present, the combination is by definition present!

You are simply saying what is clear... there is no particular wavelength that on it's own appears to us as "magenta".
(Magenta is in this sense is a synthetic color created in the brain.)

that's obviously not more accurate. There's nothing more accurate.

I take it you are referring to the philosophy of degrees of absolutes?
To paraphrase a line from the Big Bang Theory...

It is a little wrong to call a tomato a vegetable,
but it is very wrong to say it's a suspension bridge.

 

[Photo Engineer]

Ray;

There are definitions of magenta. Magenta pigments and dyes exist! See my earlier posts.

PE

 

[Ray Rogers]

So do blue filters work to enhance fog or don't they? That's all I need to know.

Sorry, I did not know the conversation had gone back to normal... I will probably curtail my posting on "color theory" ....

I would have to say "yes"... but the price you pay, in terms of "side effects" may not be acceptable.... it depends.

Ian is correct there are clear "fog filters" that can create a "mist" effect, and simply shooting in fog that exists works pretty well too!

But I don't think you will get an artificial fog effect that you like if there is none there in the first place... by using a blue filter.

I would say you would be more likely to get a "haze" rather than a "fog".

Please try it and let us see what really happens when one actually pick up a camera!

 

[Ray Rogers]

Ray;

There are definitions of magenta. Magenta pigments and dyes exist! See my earlier posts.

PE

Yes, of course.

 

[Sirius Glass]

We really have to stop thinking in terms of tri-colour!

How do we do that? See the attached.

 

[Q.G.]

As I understand it,
Blue is most effecient at blocking Yellow, followed by Red... thus Magenta will be the last to go even though the filter may be quite bluish in appearence.

No.
Magenta goes as soon as red goes.
Magenta only exists as the impression left by a combination of blue and red. The blue filter blocks red. So there is no way to prodyuce magenta.

As far as blocking magenta, Green is the most suited,
as it can block all the components of magenta, while blue can only block half of them.

See what this mix up of tri-colour theory with colour theory produces?

Blocking any component (and there are only two: blue and red) is enough to make magenta disappear.
It can and does only exist as impression left by a combination of blue and red.

Any way, do you think that a typical filter that does block red and or blue... does so with 100% efficiency?
Even the good filters are not really perfect or IDEAL.

Well yes. To all intents and purposes, there certainly are filters without transmission above or below a certain cut off wavelength, with a very narrow transition band.
There of course are many other filters too, with different behaviour.
But that's besides the point.

Can you explain how if we stop thinking in terms of tricolor, I will be able to create better photographs?

No.
But it will help you understand how colour works.
That you can't get magenta behind a blue filter.
And also that it is possible to turn a panchromatic film into an orthochromatic film.

Whether that helps to produce better pictures depends on a lot of other things as well.

What ADVANTAGE is there to dropping this attachment to tricolor?

It removes the false underpinning odf the entire thing about effectiveness of filters, in particular that lay at the foundation of the 'claim' that you can't turn pan films into ortho films.

What happens to white light if you remove the green?

It appears coloured.

You wrote the following sentences:
1.
magenta is not part of the spectrum,

It indeed isn't.

2.
magenta can only exist as a mix of spectral colours.

Which is so. red and blue, the two extremes of the visible spectrum.

These 2 sentences are incongruent!

If magenta exists as a combination of two things which are present, the combination is by definition present!

Absolutely not so.

Ever heard the thing about "and never the twain shall meet"?

You can (as i suggested before) split the entrire EM spectrum into very narrow bands, and go through all of them from short wavelength to long, and never and nowhere in that spectrum will you encounter the colour we call magenta.
It is not a spectral colour, and can only exist as a mix, in magenta's case of the two ends of the visual spectrum.
There's nothing impossible or incongruent in that. It's how it is, how the world works. Law of Nature, and all that jazz.

You are simply saying what is clear... there is no particular wavelength that on it's own appears to us as "magenta".
(Magenta is in this sense is a synthetic color created in the brain.)

Right!

I take it you are referring to the philosophy of degrees of absolutes?
To paraphrase a line from the Big Bang Theory...

It is a little wrong to call a tomato a vegetable,
but it is very wrong to say it's a suspension bridge.

I'm not referring to a philosophy or theory, because the Bleeding Obvious (as John Cleese once called it) doesn't need a philosophy or theory.

 

[Q.G.]

Ray;

There are definitions of magenta. Magenta pigments and dyes exist! See my earlier posts.

PE

Of course they, and the colour, do.
Don't know why that would deserve an exclamation mark.



But do you by now know the difference between magenta, and yellow or cyan?

 

[Photo Engineer]

Yes, about 100 nm!

PE

 

[Q.G.]

Yes, about 100 nm!

PE

How many nm is magenta then?

 

[Lee L]

So do blue filters work to enhance fog or don't they? That's all I need to know.

From B+W filter handbooks:

B+W Light Blue Filter 080

This filter renders blue tones lighter, but yellow, orange and especially red darker. “Aerial perspective” caused by haze and fog is increased, the sky will be rendered lighter. It is favored for tonal separation in object photography (darker reds, lighter blues), and also for the correction of excessively light gray values of orange and red colors under artificial illumination.
Its filter factor is approximately 1.5.

B+W Blue Filter 081

This filter produces the same results as the 080 Blue Filter, only more intensely. Therefore it has the same application. Its stronger effect makes it a mood-creating filter when photographing in fog or when aerial perspective is to be accentuated. Tonal separation in the photography of objects is also increased.
Its filter factor is approximately 2.

B+W Filter 470 (Blue-Green)

The correct filter for landscape photography, when haze will improve the mood of the photograph, but green should not be rendered darker.

The B+W 470 is similar to the Wratten 44A.

 

[Photo Engineer]

How many nm is magenta then?

As a rough estimate, a yellow is centered at about 450 nm, magenta at 550 nm, and cyan at 650 nm. Of course, this varies with product, unwanted absorptions and half band witdth.

But why do you have to ask me? You are an expert too! Aren't you?

You may want to look here: http://www.kodak.com/eknec/documents/bf/0900688a80316bbf/E7014e.pdf

for confirmation though.

PE