difference in LED or Dichro filters

srs5694 · Mar 24, 2009

RalphLambrecht said:
Expose a sheet to a mid gray without any filter, then dial in some cyan, and print again. You'll find out how significant the effect of cyan filtration is. Filters have density. C60 has more density than C90. That's why the cyan filter isused by some as a neutral-density filter. No further data required!

As I've stated several times, I can't perform this test because my enlarger is a Philips Tri-Color unit with separate red, green, and blue channels; I have no cyan filter with which to test. Of course, I could go out and buy a whole new enlarger, or at least a cyan filter and enough other equipment to refit my current enlarger, but that's overkill to resolve a question that's unimportant to me personally.

So basically, you're saying that cyan filtration has a significant effect on B&W exposure, but you've provided no details and you haven't even explicitly said that you've performed the experiment you recommend I perform. That leaves a big question in my mind about how significant the effect is. Does 100cc of cyan filtration reduce exposure by 1 stop? 1/3 stop? 1/10 stop? Less? It could also vary from one enlarger to another. Furthermore, there might be green/blue differences in a cyan filter, which could affect contrast -- perhaps not on all enlargers, but maybe in some. For these reasons, I stick to my recommendation to not rely on cyan filtration as neutral density for B&W printing, at least not without performing extensive testing to figure out what the enlarger and filter in question actually do.

RalphLambrecht · Mar 24, 2009

BetterSense

In your opinion, should we use the term UV-light rather than UV radiation?

BetterSense · Mar 24, 2009

I don't see how it matters. Neither is incorrect. Both could be confusing in the wrong context. The fact of the matter is people use both.

RalphLambrecht · Mar 24, 2009

srs5694 said:
As I've stated several times, I can't perform this test because my enlarger is a Philips Tri-Color unit with separate red, green, and blue channels; I have no cyan filter with which to test. Of course, I could go out and buy a whole new enlarger, or at least a cyan filter and enough other equipment to refit my current enlarger, but that's overkill to resolve a question that's unimportant to me personally.

So basically, you're saying that cyan filtration has a significant effect on B&W exposure, but you've provided no details and you haven't even explicitly said that you've performed the experiment you recommend I perform. That leaves a big question in my mind about how significant the effect is. Does 100cc of cyan filtration reduce exposure by 1 stop? 1/3 stop? 1/10 stop? Less? It could also vary from one enlarger to another. Furthermore, there might be green/blue differences in a cyan filter, which could affect contrast -- perhaps not on all enlargers, but maybe in some. For these reasons, I stick to my recommendation to not rely on cyan filtration as neutral density for B&W printing, at least not without performing extensive testing to figure out what the enlarger and filter in question actually do.

According to Lot-Oriel and Opto-Precision (the only manufacturers of Cyan filter, I know about), cyan-filter transmittance in the range of 400-550 nm is 80-90%, then quickly drops below 1%. This means that cyan filters filter up to 20% green and blue light in this range. This amounts to about 1/3 stop, which I call significant. Also, some papers are sensitive up to 660 nm (Forte to name one). A typical cyan filter filters will affect these papers.

Again, 1/3 stop is significant to me, because I fine-tune my highlights to 1/12 stop, but I agree that a cyan filter is only of very limited use as a neutral-density filter.

But since you continue to ask me to provide prove and detail, let me ask you a question. If you can't test for the effect of cyan filters,because you have no such enlarger, how did you prove to yourself that there is no effect? Why are you so certain? How did you verify your claim?

RalphLambrecht · Mar 24, 2009

BetterSense said:
I don't see how it matters. Neither is incorrect. Both could be confusing in the wrong context. The fact of the matter is people use both.

I agree, people use both, but common word usage and scientific correctness are not always the same thing. Maybe you're right, Oxford and Webster should change their definition of light and separate the term from sight to better reflect common usage. Until then, I'll stick to it, and as you said, That isn't wrong either.

srs5694 · Mar 24, 2009

RalphLambrecht said:
According to Lot-Oriel and Opto-Precision (the only manufacturers of Cyan filter, I know about), cyan-filter transmittance in the range of 400-550 nm is 80-90%, then quickly drops below 1%. This means that cyan filters filter up to 20% green and blue light in this range. This amounts to about 1/3 stop, which I call significant. Also, some papers are sensitive up to 660 nm (Forte to name one). A typical cyan filter filters will affect these papers.

Again, 1/3 stop is significant to me, because I fine-tune my highlights to 1/12 stop, but I agree that a cyan filter is only of very limited use as a neutral-density filter.

I assume that the 1/3-stop figure refers to placing the filter full-on in the light path, so that no unfiltered light gets past it. If so, then you'd get the equivalent of 10cc of CMY filtration by maxing out the cyan filter's setting on a color enlarger. I agree this is significant if the filter's dial is maxed out, but the difference between 0/30/30 and 30/30/30 C/M/Y filtration would be smaller than that, since then the filter is only partially blocking the light (1/2 way in, I presume). If the 1/3 stop figure you quote is accurate, this might still be noticeable, but it's close enough to the limits that it really needs to be determined empirically.

But since you continue to ask me to provide prove and detail, let me ask you a question. If you can't test for the effect of cyan filters,because you have no such enlarger, how did you prove to yourself that there is no effect? Why are you so certain? How did you verify your claim?

I've made no claim that there is no effect, except in an idealized theoretical way, and those claims were loaded with caveats. You're the one who's been making claims that there definitely is an effect; I've just asked for evidence to back up those claims and to quantify them in some way. Demanding proof of a claim is not the same as making the opposite claim. I'm not trying to play the "I'm right and you're wrong" game; I'm trying to understand (and, hopefully, help others understand) the practical effects, if any, of cyan filtration on B&W printing.

Kirk Keyes · Mar 24, 2009

RalphLambrecht said:
Kirk

Please try that. C/M/Y 0/80/50 vs 30/80/50

You will find that tey are different. The C30 component acts as a neutral density filter and lightens the print.

Ralph - I agree those two filter packs will produce different print densities/exposures. My point is that simply using yellow and magenta can achieve the same exposure and print contrast with VC papers (and it will take slightly more Y and M filtration to equal an exposure made with a CMY filter set).

You can add the Cyan filtration, but I find I usually like the shorter printing times I get simply by using yellow and magenta.

And back to purity of filters, you've seen that a cyan dichroic filter is not "pure" and it does not transmit 100% of the blue and green light. That is why there is a change of exposure when the cyan filter it added to the light path. If it was an ideal cyan filter, one that only filtered out red light, there would be no change in exposure on regular B&W papers. (And let's leave out Forte or even Adox papers which do have some red sensitivity - something that I think is undesireable in a B&W paper, unless you are needed something like the old Kodak Panalure paper which was used for making B&W prints from color negatives.)

It's the non-ideal cyan filter that we have in our enlarger that DOES filter a bit of blue and green, and thus it makes the print lighter, as you've demonstrated.

RalphLambrecht · Mar 24, 2009

srs5694 said:
I'm trying to understand (and, hopefully, help others understand) the practical effects, if any, of cyan filtration on B&W printing.

The only practical use I can see is fine-tuning the print exposure, in case very minute increments are required. In other words, cyan filtration has an effect but of limited practical use. I recommend to dial it out and forget about it.

Thanks for your patience.

RalphLambrecht · Mar 24, 2009

Kirk

I agree with you 100%. If you interested in filter purity (or lack thereof), take a look at.

http://www.opto.com.sg/downloads/filters.pdf

Kirk Keyes · Mar 24, 2009

RalphLambrecht said:
If Einstein could have tested his theories in the darkroom; he would have done so. Some things are easier to try than to talk about.

Well, in a sense, Einstein's theory of general relativity could have been tested in a darkroom. It wasn't Einstein himself, but A. S. Eddington travelled to the island of Príncipe near Africa to watch the solar eclipse of 29 May 1919.

Eddington took pictures of the stars in the region around the Sun during the eclipse. According to the theory of general relativity, the position of stars near the Sun would appear to have been slightly shifted because their light had been curved by the sun's gravitational field. He was able to do this and and he demonstrated that Einstein's Theory did correctly predict the stellar positions.

So there you go - Einstein, photography, and testing theories in the dark.

Kirk Keyes · Mar 24, 2009

RalphLambrecht said:
Kirk

I agree with you 100%. If you interested in filter purity (or lack thereof), take a look at.

http://www.opto.com.sg/downloads/filters.pdf

They state "T > 80% at 400nm to 600nm", but their graph shows that it is more likely T>90% over the stated range. That does help with making a more pure filter.

Kirk Keyes · Mar 24, 2009

RalphLambrecht said:
The only practical use I can see is fine-tuning the print exposure, in case very minute increments are required. In other words, cyan filtration has an effect but of limited practical use. I recommend to dial it out and forget about it.

Or one can get a timer that can be set to tenths of a second.

RalphLambrecht · Mar 24, 2009

Kirk Keyes said:
Or one can get a timer that can be set to tenths of a second.

Is there such a thing above 10 seconds of exposure?

RalphLambrecht · Mar 24, 2009

Kirk

Wonderful! When I read that, the picture where Einstein sticks out his tongue popped up in my mind.

Kirk Keyes · Mar 25, 2009

RalphLambrecht said:
Is there such a thing above 10 seconds of exposure?

Do you mean is there a timer that can be set to 10.1 seconds?

Yes, several. I've a Gralab 900 and it can do up to 59.9 seconds in tenths of a second. And I've a much beloved Omega CT-40, I think the best darkroom enlarging/process timer yet made (and it came out about 1984), and it can do 9 min 59.9 second exposures (actually, it can do 9 min 99.9 seconds).

RalphLambrecht · Mar 25, 2009

Kirk Keyes said:
Do you mean is there a timer that can be set to 10.1 seconds?

Yes, several. I've a Gralab 900 and it can do up to 59.9 seconds in tenths of a second. And I've a much beloved Omega CT-40, I think the best darkroom enlarging/process timer yet made (and it came out about 1984), and it can do 9 min 59.9 second exposures (actually, it can do 9 min 99.9 seconds).

That's useful. Last time I checked into darkroom timers, some did 0.1s intervals but only up to 10s, after that, they switched to 1s steps. 10% increments are too coarse for me. My current timer is from RHDesigns and works in 1/12 stop increments, which is all I need.

RalphLambrecht · Apr 9, 2009

BetterSense said:
I'm a materials scientist and I work with electrical engineers, chemists, and materials scientists on a daily basis, and I read and write technical research papers every day. Regardless of any dictionary definition, I can tell you that in the scientific community, the fact is that it is universally understood that "light" does not necessarily refer to visible light. In technical literature and in person, I hear the word "light" used to refer to radio waves, microwaves, infrared lasers, and xrays and gamma rays, blackbody radiation, and basically any electromagnetic radiation. I opine that the above quoted terminological opinion is quite incorrect and should be abandoned in the interest of understandability. There may be a lay usage of the word 'light' just as there is a lay usage of the word 'work' but in both cases I have to consider the respective definitions currently used uniformly by the scientific community as the ones to be touted about as "most correct".

The quite distinct concept of 'visible light' is arrived at by integrating the luminance ("light") over one of various well-argued-over luminance functions that supposedly simulate the average human eye's sensitivity curve, to arrive at an artificial picture of "visible light". There is as parallel situation with sound. Scientists refer to everything from infrasonic waves in the earth's crust to far, far ultrasonic lattice vibrations in crystals as 'sound', quite apart from any individual's ability to hear it. If you hang around semiconductor scientists much, you will eventually hear of "phonons" which are quantum "particles" of sound which are shed to crystal lattices during energy transitions! I'm sure that won't fit in the groove of an LP.

This is all well and good, and we had this conversation a while back, but I stumbled across this by accident:

The 'SPSE Handbook of Photographic Science and Engineering' published by the Society of Photographic Scientists and Engineers has a different view, which is, however, in line with the Oxford and Webster's Dictionary. On page 4 of my 1973 copy it states:

quote
'The term 'light' describes that part of the electromagnetic spectrum to which the human eye is sensitive. It is normally considered to include wavelengths between 400 and 700 nm, although many observers can see wavelengths as short as 380 nm or as long as 760 nm.'
end quote

I have also attached a copy of the diagram which this excellent book shows on page 5. I believe to be in pretty good company with 'my' definition of light and stick to the statement that the term 'visible light' is tautological and redundant, since there is no such thing as not visible light.

difference in LED or Dichro filters

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