Color Meter Weirdness

[Michael Panfeld]

Hi: I recently acquired a Sekonic C-500 color meter. I sent it off to have the sensor replaced and recalibrated (there was a recall of earlier serial #'s). I was excited to test it out against my trusty Milonta Color Meter II (which was also recently calibrated).

The Sekonic has two modes: film and digital. Its supposed to be some fancy new 4-sensor arrangement for use with digital camera sensors.

For the sun, tungsten and HMI light sources, the two meters tracked fairly well together. That is in measuring both color temp and green/magenta shifts. Didn't matter much if I had the Sekonic in film or digital mode for these three light sources.

However, for LED and fluoro sources, there were huge gaps when using the Sekonic's digital mode. I have an LED panel that measured 5600K and no green shift on the Sekonic in digital mode, but mesured huge green shifts and around 8,400K in the Sekonic film mode. This large discrepancy was pretty much confirmed with the Minolta, although the latter had slightly different readings.

1) So my first question is can someone explain a bit more about the "digital" mode on the Sekonic meter? I am looking for something beyond the company's literature and marketing materials (which are usually what is copied and pasted into blog reviews, etc).

2) Is this meter's digital mode (or some similarly-configured meter) how light manufacturers are getting away with claiming 5600K color temps and minimal green that turns out to not be true when you get the products? I'll note that I have returned LED fixtures and CFL & 55 watt fluoro lamps becuase they registered 8,000K and very green on the Minolta meter (which was before I got the Sekonic).

3) Finally, what do these readings, and the meters two modes mean for a cinematographer, a colorist, and someone just trying to buy and use lighting gear in today's fast-changing marketplace?

Thanks

[Mikael Couderc]

Hi,
I'm also very much interested in hearing comments about Michael's questions...

[Godfrey Kirby]

There is that terrible theory that 'Ah, so you have two meters, and so which one do you believe?' Having just bought the Sekonic and having a real strange bunch of lights,350W theatrical Fresnels (on dimmers), via Redheads, to a 575W & 1.2 HMI PAR, plus a Kino with 5600K tubes, I venture forth with half CTO in one hand & the Sekonic in the other, muttering 'Mixed lighting is the way forward!'
If anyone can chip in with this thread, please do......
I really do like my theatre lights - very 'Chimes at Midnight' & I got them for free......

[Michael Panfeld]

anybody have some insight that they want to share? I thought the guy from Cool Lights regularly followed this forum and posted responsive replies.

?????

[Mikael Couderc]

-You said:

'Is this meter's digital mode (or some similarly-configured meter) how light manufacturers are getting away with claiming 5600K color temps and minimal green that turns out to not be true when you get the products?'

-and you also said:

'I thought the guy from Cool Lights regularly followed this forum and posted responsive replies.'

Could it be that the two facts you mentionned appear, in the eyes of manufacturers, to be mutually exclusive (ie: if you're right about the first fact, then you won't get any confirmation from manufacturers)

I think you might be onto something here...
Keep pushing!

[Richard Andrewski]

Most of the time there are mundane explanations behind mysteries and not conspiracies: like someone just doesn’t know how to use an instrument or doesn’t know its limitations. In this case, someone is reporting differences in readings and… by the way there is this button on the color meter I don’t understand--is this the “getting away” with murder button for lighting manufacturers? I don’t think it was put there specifically for that. Maybe it could be someone just needs to learn the limitations and what such measurement instruments can or can’t do, the limitations of the lighting being read, and what that button means before posting cynical questions or accusations. Cool Lights has been at the forefront of education on these subjects and I have often described the limitations of various technologies like LEDs on these forums and in the blog on our site.

Also, if someone doesn’t answer something it could also be an indication that they are busy or have helped out on this topic before. That’s what forum search is for. See these posts where similar questions were addressed:

http://www.dvinfo.net/forum/photon-m...-lights-6.html

http://www.dvinfo.net/forum/photon-m...ed-lights.html

http://www.dvinfo.net/forum/photon-m...lo-vs-led.html

http://www.dvinfo.net/forum/photon-m...ally-dead.html

What these posts are all saying is that there’s a reason that lighting manufacturers use integrating spheres and not color meters. There is no pocket solution that you can just aim, press and expect consistent and accurate readings every time. I know that’s what people may want or expect but that doesn’t mean it’s possible or practical with the measurement technology available and the popular sources being read by that technology. If nothing else, too many possibilities for contamination with the pocket solution. Paint color on walls, daylight coming in windows, practical fixtures all around, etc. An integrating sphere has a very good and expensive digital sensor in it that’s often calibrated with the tungsten bulb supplied by the sphere manufacturer. It’s a sealed environment with a neutral white and uniform coating on the inside. No light leakage in or out. The “light” equivalent of an anechoic chamber. It’s the only acceptable and repeatable solution for measurement and therefore it’s the standard with lighting manufacturers of all kinds. Then you have the issue of these color meters can’t consistently and accurately read two of the most important sources today: LED and Fluorescent. LED and Fluorescent have a lot in common in how they work so this is to be expected that they both have the same behavior in trying to measure them. It is in fact the spikey, simulated full spectrum behavior of these type sources which makes them harder to read accurately and consistently by a pocket solution out of a predictable environment.

It’s not a big deal for even older meters (as long as they are calibrated) to work correctly with full spectrum sources like real daylight, real tungsten or carbon arc. Even HMI as observed is close enough to full spectrum to show up more consistently in readings, although you can get different readings based on whether an instrument is in flood or spot mode. You still have potential contamination issues between competing sources in an environment, the walls and their color, etc. So again, there’s no reliable 100% “pocket solution” even for HMI.

Film or Digital mode? 99% of the members on this forum should be using the “Digital” mode (which is not the “getting away” button for lighting manufacturers). The first letter in DVinfo.net, “D”, stands for what? We are discussing digital still cameras, digital video cameras and even a couple of “digital film cameras” and all the peripherals used around them including lighting and how they respond to lighting. Some people here have no doubt used or are still using both real film and digital (the other 1% of forum members), but they would hopefully understand already what these buttons are for on a color meter and what the differences are in response between real film and digital to how they react to various kinds of lighting. The lion’s share of the other 99% didn’t even know there was a difference between film and digital however and some will never have used film of any kind.

Digital mode closely mimics the response of digital media and human perception of lighting. Integrating spheres use a digital sensor and model for human perception as well. Why wouldn’t they? Most of the lighting in the world is made for humans and not specifically for cameras. Lighting manufacturers of all kinds use these spheres and again, that is the only serious standard for repeatable light measurement until someone invents something better and gets it adopted by everyone.

Film mode on a color meter mimics the response of real film. Film is more sensitive to green spikes than digital is. This is something people using real film have always had to deal with for as long as fluorescent and more recently LEDs have been around (HMIs too for that matter). People will often report green spikes with even some of the highest CRI flo tubes when using real film. The same tube may show no issues at all in digital. Many report that Kino bulbs seem a trifle too “magenta”. There’s a good reason for that. Kino has been a choice in the film world precisely because they do overcorrect. You may feel it’s too much for digital use however and will seem a bit too pink and a lot of people have said this on forums such as this one. This is not a conspiracy; it’s simply the reality of the differences between the two major competing types of media.

Digital has white balance which can take out a lot of that kind of thing and can decide at the push of a button what white is based on the type of lighting you tell your camera it is experiencing. Not so with film: you have daylight or tungsten balanced film and have to stick pretty close to that and pay attention to the lighting in a far more deliberate sense than most using digital mediums may have to.

Here’s a real pet peeve of mine: used vs. new color meters. So you go shopping for color meters on Ebay and you see the new ones running in the range of $1000 to $1500 and all those used ones for one third to one half the price--what a deal! Why would you get the new one? These “bargains” are mostly there because at some point the owner discovers these older models aren’t that accurate for LEDs or fluorescent, which is what many people are moving to today. He may not even know why but still, there it is and has to be dealt with. The unknown answer may be that it’s an older “RB” (Red/Blue) type that was invented before the digital era and not a newer “RGB” type which has at least some hope or reading newer sources (flo and LED) somewhat. There may also be the issue that they aren’t calibrated and the owner finds out there is no easy way to calibrate his defunct meter. Or both being old and non-calibrated which should hopefully be the best bargain to be found. So these sellers have decided color meters aren’t necessary because they seem to be so inaccurate, or they are going to upgrade to newer RGB models like the Kenko KCM 3100 (which is my meter of choice) and want to pass the meter off to the next “beginner” for him to discover all this later. So until this new owner starts to suspect that it’s the meter and not their lighting that is the issue, it can provide for hours of “perplexity”.

Lastly, I don’t think anything called a “color munki” is going to be a defacto standard for measuring lighting, especially since you still have to solve the issues of making a neutral chamber to measure in to be sure of your measurements; and who’s going to rewrite the software to give CRI, accurate color temperature and be sure of the results? And how will you know it’s accurate? I think at that point you aren’t a film or video maker but rather someone interested in going into lighting manufacture of some sort because the time that you would spend on development would be amazing and would never be paid back unless you turn out a real, marketable product of some sort that people can say “yes I trust what this thing is telling me” and “I can afford this”. If you are going to go ahead though, I would rename it and not have “munki” anywhere in the product name.

[Michael Panfeld]

Indeed Mikael: I hope to go to NAB. If I do, I will be bringing my meters and a HV30. I'd love to test the lights on the spot and get the reps reactions if the meter has divergent readings.

If anybody is going to NAB, please do the same.

[Mikael Couderc]

Hi Richard...
...and thanx for taking the time to post your very good points.

I fully agree with your warnings about using color meters to 'rate' new lighting technology, as I do your explanation of using an integrating sphere for more consistent results.
(Trust me, I spend enough time in front of 3D models in Maxwell Render to know the impact of attributes like reflectance, transmitance, IOR, Nd and so on so forth...)
However, (and you seem to be agreeing with me on that point, AFAIU), 'consistent' results don't always mean 'accurate' results.

Indeed, based on my experience (admitedly not as extensive as other members on these fora, nor yours) I j'm convinced that the current way light coming out of these devices is measured is far from being trustworthy, and that color temp and CRI measurements, in their current implementation, are useless for CFLs and Leds.

So, and here's my main point, why do manufacturers of such elements keep using CRI indexing and color temp measurements as strong sales arguments? Why do we still see terms like 'perfect daylight color temp', or 'High 90 CRI for perfectly accurate color reproduction' being used by companies?

That's maybe what Michael was referring to. That's certainly what I've been wondering after investing a lot of money in various Led lighting fixtures and far too many CFL tubes.

One a side note, even though Kino (as you pointed out) and Osram Studioline were designed for film and do exhibit that magenta spike, they're still the best you can get for digital use, even though there are higher CRI tubes on the market. Osram Dulux L 954, for instance, are rated at IRC 96 but have a pretty strong green spike. The CRI of the 5600K version of the Studioline tubes is, I believe, in the high 80's (Osram doesn't publish the CRI index for these tubes anymore, so this is just from memory.). What's clear from this is that CRI isn't an element of comparison, even within the same manufacturers' product range.
FWIW, all this 'high CRI' and this 'number waving' behaviour kind of reminds me of the silly CPU clock speed war in the early 2K years: bigger, better numbers, but performance-wise? Not a lot...

At any rate, please do not consider my remarks as accusations of conspiracies by light manufacturers, but rather as genuine questionning of their commercial practices. All of that in the spirit of constructive cricticism...

Oh, and BTW, I see you've noticed my other post about using a spectrophotometer (yes, a Color Munki! :-) ), as a way to more accurately measure the light quality of CFLs and Leds. I firmly believe that such a device is, given its very nature, perfectly capable of performing such a task. True, Xrite sprovided software is rather poor, but, as I mentionned in my other post, more accurate software solutions to interpret the data are just around the corner. One such solution is HCFR software, which is used to calibrate LCDs (guess what? Fluo or Led backlighting!) and projectors (Yep, incident lighting), but also provides the user with tons of info regarding the light analyzed.
SO the munki might be a viable solution after all...
(oh, and I agree the 'Munki' name doesn't inspire confidence...)

[Richard Andrewski]

Originally Posted by Mikael Couderc

So, and here's my main point, why do manufacturers of such elements keep using CRI indexing and color temp measurements as strong sales arguments? Why do we still see terms like 'perfect daylight color temp', or 'High 90 CRI for perfectly accurate color reproduction' being used by companies?

The problem is there really isn't anything else other than CCT (correlated color temperature) at this point and CRI to describe LEDs and Fluorescent. This is all good enough for the commercial/residential lighting market which is what drives the lighting market in general (the film/video lighting market being infinitesimal in comparison). The needs of the film and video market are much more stringent than for commercial lighting obviously. So lets say 1 company adopts something else. What are you going to compare it to? How will you know its accurate? How would you get all the other companies to adopt it? Etc...

If someone successfully invents a new and better method that is all encompassing, they get everyone to adopt it, the new testing equipment is provided and everyone makes the investment in it, then you've got a new scale to go by. That's a lot of "ifs" though.

LEDs are in an immature state right now so they will have to follow the path that fluorescent has to getting to higher CRI. We have been experimenting with some higher CRI phosphor for LEDs but the real issue is will people want to pay for it? The LED phosphor is so expensive at this point (as was the phosphor for fluorescent no doubt when higher CRI flos started appearing in the market) that you are talking about a 2 1/2 times difference in price over the typical type LED used today for most of the 5mm LED panels (which seem to be the most popular). There frankly hasn't been a demand for higher CRI LEDs in the general lighting market so we can't benefit from economies of scale yet. The last thing LED companies want to see right now is their lumen per watt figures going down and that's what will happen. Any time you take two sources (flo or LED for that matter), with most things being equal and you make one of them higher CRI, the higher CRI one will be less efficient and loses around 20 to 30 percent of light.

As LEDs follow the same path that Flos have then this will happen and the phosphor prices will be driven down as more competitors for it come into the market.

[Michael Panfeld]

uhh, correct me if I am wrong, but you and other manufacturers state that their fixtures have a certain color temperature. In your case, I believe its 3200K and 5600K. That has to be measured in some way, and one part of my question is what are you using to arrive at the advertised color temp.

Integrating spheres are used for measuring total light output (lumens) of a light source. Spectra radiographic gear measures the breakdown of light amongst the wavelengths (http://www.spectralevolution.com/fil...ter_series.pdf). Neither of these devices measures color temp. Only a color meter does that. So all of that defensive narrative, its mostly gobbledy-gook. IT ALSO SEEMS GEARED TOWARDS SUBTLY DISCREDITING MY OBSERVATIONS AND QUESTIONS, which I do not appreciate.

I am not stupid or inexperienced. Nor do I have some defective cheapo light meter that is uncalibrated, as you imply. Just the opposite. I have one of those $1300 meters, as well as an older model. Both are freshly calibrated. Both are getting consistent readings. So your next to last paragraph is quite offensive.

Also offensive is your suggestion that my observations are haphazard. Again, just the opposite. I performed a controlled experiment by placing both the light source and meter on fixed stands so that their position did not change. I also did this is an enclosed room, covered with duvetyne on all 6 sides. I would actually argue that an integrating sphere with all black is a more accurate way to measure color temp than the white interior of the sphere in your pic, because the white paint will impart a tint to the light it reflects.

You also go on to bash my understanding of the digital mode on my meter. Sekonic has published almost zero information on the digital mode beyond the obvious statements. And yet you suggest that pros should know the difference. How is that possible if Sekonic keeps all the cards to itself?

The fact is that light only has one color temp. So, the digital mode gives a radically different reading, it means that it is simulating how a camera sensor would perceive the light. The problem with that is twofold. First, not all sensors are the same. Second, there are all kinds of assumptions that Sekonic must have made when it programmed its processor to interpret the data. What are those assumptions? How do they relate to the MX sensor (which I saw tonight at Ketch Rossi's demo in DC)? How do they relate to the Canon 5D sensor, Af100 etc... If I have more information, I will be better able to use this tool. That's all I am asking for, Richard.

On the other hand, in spite of all the issues with assumptions, you advertise a certain Kelvin rating for your fixtures. There is no asterisk. There is no caveat. There is no statement of how that was measured. So the consumer must simply take your word for it. And yet, the color meters and simple logic tell me that those advertised Kelvin ratings do not match at least one version of reality.

So yes, some of the light sources that I measured were Coollight LEDs. I really did measure these at about 8500K in film mode. But now that I have read your explanation, I can safely remove all that CTO and minus green gel from the LED lights because the painfully obvious strong blue light that I can plainly see (that would be human perception) when it is placed next to an HMI that is supposedly a slightly cooler Kelvin than your LED's advertised color temp, is just an illusion that will not be captured by the digital sensor.

Except that editors tell me, and I have read posts about all the green casts and color correction that can be seen in footage from digital, not film, cameras when shooting with LEDs or fluoros.

If this sounds a bit like a sarcastic rant, it is. I asked for some help understanding a complex topic, to which a) you did not directly answer any of my questions and b) you gave misdirection. If there is a conspiracy, I was certainly not implying one. Lighting manufacturers, acting individually and responding to market forces does not constitute a conspiracy. And the marketing forces are this: if you tell people that a color meter will show that a light source is 8500K, and if you shine a "5600" LED next to an HMI or some sunlight, and its obviously bluer than those sources, you are going to have a hard time selling lights. So its actually against your economic interests to bring all of this complexity into your marketing materials. That's why they invented the phrase caveat emptor. My post was imply trying to shed some light on this.

If anybody actually has some answers to my specific questions, I would love to hear it.

[Richard Andrewski]

Integrating spheres and their peripheral devices measure lumens, color temperature and CRI as well as giving a printout of the spectrum, among other things... You can see a printout from one in our blog showing all relevant information about our 55w tubes for example.

[Mikael Couderc]

Hi Richard,
I took a look at your published test reports and I must say I wish all manufacturers were as transparent as you are.
For what it's worth, the data for the 55W daylight tubes reminds me of some old T8 tubes I used to put in my lights a decade ago, before fluorescent lighting became so popular (yes, I proudly consider myself as a precursor :-) ).
Those tubes were the Philips TLD 90 950 if I recall well (edit: confirmed, I just found the graph).
Philips too, at the time, tried to find a balance between lumens output and 'good enough' CRI, and I must say the graphs they published look almost identical to yours. So that's no surprise the resulting light output look similar on camera (which is, honestly speaking, greenish, IMHO...).
What I appreciate is your honesty in saying that you were actually looking for that 'balance'. At least people know what they're buying and it's then up to them to accept or not to trade lumens output for actual color rendition accuracy (which is different than published CRI)

That being said, sometimes later, Philips came up with an improved CRI version of those T8 tubes, called the Graphica, with a CRI of 98, with much better measured data. (see graph). Looking at the 'pro' designation and the published CRI, I was expecting stellar results. Unfortunately, these also had the same green output (again, to my eyes and cameras at the time...).
So, all that taken into consideration, and even though I understand your points about new standards being a pain to come up with and get adopted, I still stand by my point: CRI just isn't accurate enough a value to rate Fluos and leds output quality.
In the meantime, what we need from all manufacturers is graphs, just like the one you provided.
This way, if someone is in the market for, say, a daylight tube, then one can compare the manufacturers graph to the solar spectrum graph and draw conclusions from that.
But what manufacturers shouldn't do is wave terms like 'high CRI' and 'correlated color temperature' at the faces of people who actually work with these products everyday.
Note that I'm only talking about 'pro' products here, destined to color critical applications, like photo or video. Obviously, as you correctly said yourself, CRI is simple enough to understand a value that it still has its uses for consumer orientated fluos or led-based products.

Again, hats off to Cool Lights for actually publishing their test results. This is, IMHO, a step in the right direction and a proof of their seriousness and dedication to make things better in the video world :-)

EDIT: From left to right:
-Philips TL-D 90 950
-Philips TL-D 90 Graphica
-Solar Spectrum

[Richard Andrewski]

Thanks for your comments Mikael. As far as I know, I'm the only lighting manufacturer that takes on these issues and is willing to discuss them.

As far as CCT (correlated color temperature), a flo or LED will always still be measured with that because of the nature of how they produce their light (UV radiating against phosphors). In fact, any light source that isn't close the the theoretical black body that is the model for Color Temperature would be measured in CCT. Carbon arc, tungsten and sunlight are all measured in color temperature and adhere pretty closely to the black body. It shouldn't be a surprise then that sources that are measured in color temperature are more accurately measured with light meters and those using CCT are not as accurate. So you either need improvements in sources measured in CCT so they are more continuous or you need improvements in light meters to include CCT sources better (or both).

Over time the spectrum of flos and LEDs will get better and better and more approximate a full spectrum light. And also over time measuring devices will get better at measuring CCT type sources. But, its also interesting to note that full spectrum lights, while they are better at color rendering, also have many unwanted components of the spectrum as well like UV and Infrared. UV of course causing potential skin cancers and infrared being why many describe full spectrum sources as "hot lights". It wouldn't surprise me to find for example that cutting out these unwanted elements may play some role in diminshing color rendering, particularly the infrared. What if we find out that these parts of the spectrum play some role in CRI? I don't think we're going to want to go back to hot lights and UV filters will always be necessary when there are human subjects under a full spectrum light.

Kind of reminds me of the debate there has been in sound reproduction over the range of human hearing vs. the sampling frequency used for digital sound mediums. Some have felt that the higher sampling and bit rates and their reproduction above 20Khz (normal upper limit of human hearing) may be essential for perception of better and fuller sound. Why would light be any different? But if we do find this, how will human subjects feel about having to be continually subjected to these parts of the spectrum in the name of better color rendering?

After all, research has been showing that often when CRI is lower, its because of a lack of fullness in the "red" area of the spectrum. And this will also be primarily the reason why these lower CRI lights (which are all considered to be high efficiency sources as well) will be described as "greenish". When you want to counteract a particular color you chose the opposite of that color on the color wheel which in the case of green is magenta (notice though that magenta is high in RED content). Its a constant battle therefore between magenta and green or brightness vs. balance.

Its not a particular coincidence that mercury was chosen for fluorescent lighting. As I've observed in my blog, other types of gas have been experimented with which would produce a different color spike than green. They were never quite as efficient in light output. The Green wavelength area happens to be the area where the human eye is most sensitive to light and will lead to a perception that light is brighter given all other things being equal like wattage and type of light source. Efficiency (output per watt used) in this kind of lighting was the main goal. Lighting on the Earth is made for humans by humans so none of this should be surprising then.

The phosphors used therefore in a mercury tube are chosen to balance out the green spike as much as possible. For whatever reason, adding more red (or particularly magenta) to counteract the green leads to a more balanced light that gives better color rendering but also (all things being equal again) will seem not as bright. So, you'd have to boost the wattage and overdrive the source to get back some of the missing perception of light--an obvious loss of efficiency.

All this being said, there's nothing particularly all that different from our 55w tube spectrum from other competing 55w tubes (or our LEDs for that matter) and I am sure over time that improvements will be made in the phosphors used and we will move beyond the RGB types to include more of the spectrum. It will be interesting to see how people feel about the CRI though when the infrared area is still lacking (because very few will be interested in flo tubes which produce immense amounts of heat) and who knows what role UV plays in the low end of the spectrum as well.

No one at Cool Lights has been saying that there aren't trade offs for using particular technologies of light. I can't speak for other companies. We were after all the first that I know of to include minus green acrylic panels with our LEDs to facilitate the easy and proper correction of them. And we aren't using vague terms like "High CRI" to describe the single color LED products either--I can't control what others do, I can only control what we do. As far as our flos go, the lions share of our customers use our tubes and are very happy with the results. Those that need something else, simply use another tube that they perceive better (for use with real film for example). There's at least one customer we have that posts here regularly that chose Kino tube to use in our fixture because he is often hired on real film projects.

LEDs and Flos have their benefits and points for improvement and will benefit over time from those improvements. Carbon arc, tungsten and real sunlight have their benefits but they also have points for improvement too: all heavy on the UV and infrared as I mentioned earlier. That's why we've offered so many different technologies because 1). You can't make one technology that will satisfy everyone and 2). They all have areas where they are strong and weak and you should use them to benefit in the areas they are strong and find your solutions for areas they are weak. In other words, Cool Lights still offers "hot" lights to those that want them.

[Mikael Couderc]

Indeed you are one of the few manufacturers who agree to share their data, and I must say that you coming here (on these fora) and actually discussing your products and the choices and technology behind them has won your company a lot of trust from mine.
I see we agree on most points anyway.

Still, there's something I don't quite understand when it comes to choices you've made with regards to tubes. In a nutshell, why not try and aim to emulate the output from Osram Studioline, or Kino TrueMatch (which we all know have more red and a slight magenta spike), and instead, go for the green spike (ala Philips TL-D 950 previously mentionned or Osram Dulux or Ge cinema plus)?
I know you were seeking the right luminous efficacy (LE)/Color rendering balance, but it turns out the Kino tubes have a LE about the same as your tubes (about 50/52 lm/W), and the Studioline an impressive 69lm/W.
I mean, IMHO, both these tubes work better with film indeed, but also with digital, whereas, as far as I can tell from your tube design choices and your answers here, you don't seem to share the same opinion.
I'd very much appreciate it if you could develop on this point please.

[Mikael Couderc]

Oups...typical case of 'frenchism'. The last sentance in my previous post should read:

I'd very much appreciate it if you could 'elaborate' on this point please.

'Elaborate' instead on 'develop'...
These two are synonyms in French... Not quite so in english :-)
Apologies for the confusion.