DSLR digitizing project

[grat]

So I'm working a project to wring as much resolution out of a negative as is feasible, with as little pain and suffering as possible.

It's nothing revolutionary-- I picked up one of the inexpensive Chinese CNC kits, because it's a pre-built platform with X, Y and Z movement, and I intend to replace the connection to the spindle with a relay plugged into the remote cable port of my camera. A couple of 3D printed replacement parts to mount the camera, and I should be off to the races.

The (current) question I have is about lighting-- Elsewhere, MattKing pointed out that high CRI and full-spectrum aren't necessarily the same thing, and while my panel is CRI 95+, it doesn't say anything about spectrum.

Am I correct that if I take an image of the panel, and all three channels in the histogram (RGB) are identical, then I'm getting something resembling a full spectrum from the light source?

Is there a better way to test?

 

[MattKing]

Electronic flash is a much better option.
It has a continuous spectrum, rather than discontinuous sspectrum.
And old fashioned light panel with a daylight balanced tungsten or halogen source will also work.

 

[grat]

Due to space and size constraints, flash isn't really an option-- even if it was, that's adding an additional layer of complexity I'd like to avoid.

Halogen tends to run hot, bulbs are expensive, and it wouldn't be my first lighting choice.

But the question was, how do I determine if a light source is continuous or not?

 

[MattKing]

Flash, tungsten and halogen are all continuous spectrum sources.
Nothing else comes to mind.
Just look for something like a Metz 45C or 60 C or any other "potato masher" flash, and put the flash head behind the negative or slide.

 

[Helge]

Thing with flash is that it is so powerful it will let you:

A. Stop down all you need and use as fast times as you need, to take any vibration out.
And, make multiple exposures to get all the range of either high Dmax slide, or negative with thin shadow detail that is easily bloomed and veiled away, if you are exposing for the dark highlight areas (one of the main problems of most scanners).

B. Piss away light in diffusion layers to get very even light.

Problem is that you will need a focus light to let you hit focus on the film. But any kind of strong LED will do that.

 

[Lachlan Young]

Something to remember: plenty of high end scanners have done just fine over the last few decades with fluorescent/ cold cathode backlights - but with the caveat that many have a 3x CCD sensor with RGB separation filters. Bayer array filters seem to be closer to Wratten #25/#47/#58 (which have lower exposure differences under daylight), but filtration on scanners may be closer to #29/#47/#61 which are more equal in exposure when used with a tungsten source. And that's before considering the colour of source that is intended to be correct for viewing/ printing the dye image in positives (designed for 5000k illuminant) and colour neg (designed to be printed with 3200k illuminant + appropriate filtration - traditionally 50R).

 

[grat]

As I've said-- flash is impractical. I don't have sufficient space to set up the flash with proper diffusion, and the external sync, while certainly doable, is an extra layer of complexity I'd like to avoid.

Fortunately, I've found other people using the same LED panel as I have, and their DSLR scans have come out very nicely, so it's apparently something in my process.

I think however, that Lachlan may be onto something. I've been using a more neutral temperature (4000k). I'll dial it down to 3200k and see if that eliminates the color cast.

 

[Helge]

As I've said-- flash is impractical. I don't have sufficient space to set up the flash with proper diffusion, and the external sync, while certainly doable, is an extra layer of complexity I'd like to avoid.

Fortunately, I've found other people using the same LED panel as I have, and their DSLR scans have come out very nicely, so it's apparently something in my process.

I think however, that Lachlan may be onto something. I've been using a more neutral temperature (4000k). I'll dial it down to 3200k and see if that eliminates the color cast.

Flash doesn’t take up any more space. Get any cheap one (with a safe trigger sync or a cheap wireless trigger).
Build or find a small box with no lid and with white interior.
Cut a hole in the box for the flash.
Put a piece of frosted Perspex on top.
That’s your setup.
You can even include your LED panel in the box as a pilot light for focus.
Cyan gel in front of flash for orange mask filter is optional.

LED light is notoriously uneven in output. Even so called high CRI bulbs (at some point we are going to figure out how much it fucks with our hormonal balance and cognitive function and try to resurrect halogen manufacturing).
LED panels are especially bad because light quality is not an issue with most uses, only power and evenness.
You can correct your way out of it. But the results will not be optimal, it’s going to take longer than necessary and it will be hard to find a routine.
Dyes used in film, both sensitizing dyes and colour dyes are far purer and peakier than the ones used in a Bayer filter.
That’s why colour film is better at recording colour.
And that’s why LED panels are “not that much of a problem” with digital.

It’s very important to realize that you can not necessarily detect bad light quality with your eyes directly.
Sometimes you can merely sense something is off.
Often you just get used to it as our senses has a way of quickly doing.
Small holes, dips or valleys in the spectrum are rarely detected, while peaks are.
Has to do with how the colour sensors in the retina work together and derive colour.

Film is actually more sensitive to colour difference and is often more neutral than human sight is.

 

[grat]

Flash doesn’t take up any more space. Get any cheap one (with a safe trigger sync or a cheap wireless trigger).
Build or find a small box with no lid and with interior.
Cut a hole in the box for the flash.
Put a piece of frosted Perspex on top.
That’s your setup.

No. It isn't. First, what you're describing would produce a one-sided flash, which isn't acceptable. Lining the box with foil and/or painting the interior white, would help, but most of the flash-based setups have relied on twin flashes.

Secondly, it would require raising either the height of the camera mount, or the entire Y-axis. Or, following the logic that seems to be prevalent here, cutting a hole in the table. The first two would decrease the stability of the entire system, and the third is just daft.

This is another example of a user on this forum asking a question, and getting a totally unrelated answer. Yes, I floss.

LED light is notoriously uneven in output. Even so called high CRI bulbs (at some point we are going to figure out how much it fucks with our hormonal balance and cognitive function and try to resurrect halogen manufacturing).
LED panels are especially bad because light quality is not an issue with most uses, only power and evenness.

First, LED light *CAN* be notoriously uneven. This is known. But it doesn't have to be. Welcome to the 21st century.
A/C driven florescent lights have a much worse light spread, and I hate them with a passion-- but that wasn't the question either. This isn't a room lighting solution, this is a panel specifically designed, and used, for photography fill-lighting.

Given that blue light appears to be relatively important to our circadian rhythm, and that halogen is notoriously poor at that end of the spectrum, I'm not sure it's quite the solution you think it is.

You can correct your way out of it. But the results will not be optimal, it’s going to take longer than necessary and it will be hard to find a routine.

Not the question either, but getting closer.

Dyes used in film, both sensitizing dyes and colour dyes are far purer and peakier than the ones used in a Bayer filter.
That’s why colour film is better at recording colour.

So there's a magic property in these dyes that keeps them from being recorded properly by a Bayer filter? That sounds implausible.

It’s very important to realize that you can not necessarily detect bad light quality with your eyes directly.

Yes! And that's the question. Not "What light source should I use?", but "How do I tell if the light source I'm using is sufficient?".

The light source I'm using appears to generate identical curves in the R, G and B curves of the histogram (actually, "curves" is misleading-- I get a relatively thin vertical bar in the exact middle of the histogram that goes all the way up). This suggests to me that the light is relatively uniform, and probably continuous (otherwise R G and B would have different appearances), but I know the histogram isn't exactly a spectrum analyzer, so I came here for a second opinion.

Film is actually more sensitive to colour difference and is often more neutral than human sight is.

But I'm not trying to collect light with film. I already did that. I'm trying to collect light modified by film, and I'm trying to do it with an LED panel that appears to correspond almost exactly with the digital sensor I'm using.

 

[reddesert]

The (current) question I have is about lighting-- Elsewhere, MattKing pointed out that high CRI and full-spectrum aren't necessarily the same thing, and while my panel is CRI 95+, it doesn't say anything about spectrum.

Am I correct that if I take an image of the panel, and all three channels in the histogram (RGB) are identical, then I'm getting something resembling a full spectrum from the light source?

Is there a better way to test?

If you take an image and the R, G, B channels have similar levels, it doesn't tell you that the light source is continuous. It tells you that the amount of light in each of the R, G, B channels is matched to the sensitivity of the camera (or, the sensitivity of the detector as modified by whatever you set for white balance on the camera). But the light within those channels could be unevenly distributed in ways that will cause color shifts.

If you want to know whether the light source is continuous or discrete, you can get a diffraction grating and use it to look at the spectrum of the source. (Educational diffraction gratings in slide mounts are easily available on amazon or wherever.) If you don't have a grating, a CD has about 625 grooves/mm and can be used as a reflection grating. However, for either of these, you really kind of need to mask the light source down to a pinhole, or use an entrance slit and an eyepiece to build a simple spectrograph, to resolve the spectrum you are seeing.

 

[Helge]

No. It isn't. First, what you're describing would produce a one-sided flash, which isn't acceptable. Lining the box with foil and/or painting the interior white, would help, but most of the flash-based setups have relied on twin flashes.

Secondly, it would require raising either the height of the camera mount, or the entire Y-axis. Or, following the logic that seems to be prevalent here, cutting a hole in the table. The first two would decrease the stability of the entire system, and the third is just daft.

This is another example of a user on this forum asking a question, and getting a totally unrelated answer. Yes, I floss.


First, LED light *CAN* be notoriously uneven. This is known. But it doesn't have to be. Welcome to the 21st century.
A/C driven florescent lights have a much worse light spread, and I hate them with a passion-- but that wasn't the question either. This isn't a room lighting solution, this is a panel specifically designed, and used, for photography fill-lighting.

Given that blue light appears to be relatively important to our circadian rhythm, and that halogen is notoriously poor at that end of the spectrum, I'm not sure it's quite the solution you think it is.


Not the question either, but getting closer.



So there's a magic property in these dyes that keeps them from being recorded properly by a Bayer filter? That sounds implausible.



Yes! And that's the question. Not "What light source should I use?", but "How do I tell if the light source I'm using is sufficient?".

The light source I'm using appears to generate identical curves in the R, G and B curves of the histogram (actually, "curves" is misleading-- I get a relatively thin vertical bar in the exact middle of the histogram that goes all the way up). This suggests to me that the light is relatively uniform, and probably continuous (otherwise R G and B would have different appearances), but I know the histogram isn't exactly a spectrum analyzer, so I came here for a second opinion.



But I'm not trying to collect light with film. I already did that. I'm trying to collect light modified by film, and I'm trying to do it with an LED panel that appears to correspond almost exactly with the digital sensor I'm using.

No don’t line the box with foil, for the same reason you wouldn’t use mirrors.
One flash is enough.
You just need a box that is a bit bigger than the flash to create some distance, to let the light “even out”.
Do the experiment.
Until recently LCD screens was lit by a single cold cathode or strip of LEDs on one edge.
On thicker screens this resulted in very even distribution of light, save the corners that was often hotspots.
Two flashes will gain you power if that’s what you need, but otherwise will just complicate things.

The light as you say, is filtered by dyes in the film. These dyes have peaks. If these peaks correspond with a peak of the light of the LEDs or fall in the valley of that spectrum, then it will be very hard to detect was went wrong, where and how to correct it.

A flash-box will add maybe an inch or two to the hight the camera has to sit over the film compared to a LED panel. Not anything that should affect stability in any way, and well within the range of enlargers, copy stands, tripods or whatever you might use.

I think that you are wedded to, or have fallen in love with the idea of the LED panel for irrational reasons. Time to kill your darling perhaps.
Everybody is telling you that flash is better.

All LEDs are uneven in the spectrum they output. That’s a fundamental of the technology.
The manufacturers have gotten better at hiding it to the naked eye, and found clever, creative ways of masking the problem in measurements, with smoothing and their own invented standards (CRI amongst others) based on outdated and strongly simplified notions of how colour vision works.

Considering that we have been in coevolution with fire for the last couple of million years, strong blue is probably the last thing you’d want in everyday room light.
It turns out to be a major problem in recent years with screens disturbing sleep patterns.

Semi-recent research has discovered a new type of light sensitive cell in the eye, only sensitive to light temperature. This cell is quite possibly completely disconnected from what we’d call acute or conscious vision.
Of course lack of blue light in the winter months is large part of what SAD is.
Similarly light with “holes in it” is suspected of having other effects with prolonged exposure.
Light quality in general has a very big influence on almost all regulatory systems.
Which makes great evolutionary sense.

 

[Lachlan Young]

Everybody is telling you that flash is better.

Not necessarily. Colour neg's 'print through' seems designed for a fairly specific illuminant for printing (my own experiments suggest 2700-4000k are about the limits to keep things from wandering way off the straight and narrow - unless you are using a brute force means of colour correction that eliminates inherent/ designed-in negative characteristics in favour of some coder's idea of 'correct') - you can simulate this by a variety of means, but Bayer array sensors complicate this in slightly awkward ways - and more importantly, in ways that RGB filtered 3xCCD's didn't really have to deal with

 

[Helge]

Not necessarily. Colour neg's 'print through' seems designed for a fairly specific illuminant for printing (my own experiments suggest 2700-4000k are about the limits to keep things from wandering way off the straight and narrow - unless you are using a brute force means of colour correction that eliminates inherent/ designed-in negative characteristics in favour of some coder's idea of 'correct') - you can simulate this by a variety of means, but Bayer array sensors complicate this in slightly awkward ways - and more importantly, in ways that RGB filtered 3xCCD's didn't really have to deal with

So what do you suggest/what are you using?

I filter my flash through a couple of Wratten filters to take out some of the orange mask. That also takes out much of the deep blue that might complicated things. And certainly cut down red and eliminate IR.

It would be wonderful if a raw monochrome high resolution sensor with readout electronics and USB plug was available. Of course with the ability to adapt any lens through a lens board.

 

[Lachlan Young]

So what do you suggest/what are you using?

I filter my flash through a couple of Wratten filters to take out some of the orange mask. That also takes out much of the deep blue that might complicated things. And certainly cut down red and eliminate IR.

It would be wonderful if a raw monochrome high resolution sensor with readout electronics and USB plug was available. Of course with the ability to adapt any lens through a lens board.

CTO gel or similar - and if you've got Wratten CC's, I'd certainly try 50R (or a mix of M & Y) on top of the tungsten correction and see how that does. I jumped in mainly to warn people that they can't assume that even nominally 'full spectrum' sources may be correct for what they are doing - and that they need to be aware of the print-through characteristics of the dyes.

A bare-bones monochrome CMOS sensor in a box with a universally adaptable lens-mount would be ideal, but they seem surprisingly hard to get prices on unless you want to buy dozens from an industrial supplier.

 

[grat]

If you take an image and the R, G, B channels have similar levels, it doesn't tell you that the light source is continuous. It tells you that the amount of light in each of the R, G, B channels is matched to the sensitivity of the camera (or, the sensitivity of the detector as modified by whatever you set for white balance on the camera). But the light within those channels could be unevenly distributed in ways that will cause color shifts.

That's fair. However-- if the light source and the sensor are that closely matched, where would the color shift come into the equation?

For all intents and purposes, I'm using the negative as a highly varied filter for the light source. It will block certain frequencies to one degree or another, but it's not going to alter the frequency of light passing through. If the film were blocking frequencies of light that made it incompatible with a Bayer sensor, then DSLR digitizing shouldn't be possible with ANY light source.

If you want to know whether the light source is continuous or discrete, you can get a diffraction grating and use it to look at the spectrum of the source. (Educational diffraction gratings in slide mounts are easily available on amazon or wherever.) If you don't have a grating, a CD has about 625 grooves/mm and can be used as a reflection grating. However, for either of these, you really kind of need to mask the light source down to a pinhole, or use an entrance slit and an eyepiece to build a simple spectrograph, to resolve the spectrum you are seeing.

Now see-- not only is that a helpful response, it makes me feel like an idiot. Well done.

I already have a pinhole, may track down a diffraction grating just for fun-- or possibly an inexpensive spectroscope.

 

[grat]

I think that you are wedded to, or have fallen in love with the idea of the LED panel for irrational reasons. Time to kill your darling perhaps.
Everybody is telling you that flash is better.

No, two people have stated that. Numerous people around the web, however, seem to be using LED's just fine. If someone can tell me how to embed a link to a youtube video without the video itself showing up, I'll be more than happy to link a couple of examples of what I'm up to.

All LEDs are uneven in the spectrum they output. That’s a fundamental of the technology.

I think you've misspelled "artificial lights".

Considering that we have been in coevolution with fire for the last couple of million years, strong blue is probably the last thing you’d want in everyday room light.

It turns out to be a major problem in recent years with screens disturbing sleep patterns.

Yes. Because of it's influence on the circadian rhythm. You don't want it INDOORS, you want it outdoors to tell you it's day time.

 

[grat]

It would be wonderful if a raw monochrome high resolution sensor with readout electronics and USB plug was available. Of course with the ability to adapt any lens through a lens board.

They're called "astronomical cameras".

 

[Helge]

They're called "astronomical cameras".

Yeah I know, but they tend not to be of very high resolution.

 

[MattKing]

For clarity, if your tungsten and halogen source isn't daylight balanced, it will still have a continuous spectrum (true CRI of 100) but will just need some colour correction to daylight balance.
A halogen light dichroic colour head for an enlarger can make a great light source for digitizing.

 

[grat]

Yeah I know, but they tend not to be of very high resolution.

They exist in 16 and 20mp versions, but they're not cheap. They're equivalent in cost to a mid-range DSLR of a similar resolution. You can even get one with a 5 slot filter wheel controlled via the USB connection.

If I ever decide I'm not burning enough cash on film photography, I may once again pursue digital astrophotography, and then I'd have one camera for two purposes, which would be nice. But I don't see it happening soon.

 

[Helge]

No, two people have stated that. Numerous people around the web, however, seem to be using LED's just fine. If someone can tell me how to embed a link to a youtube video without the video itself showing up, I'll be more than happy to link a couple of examples of what I'm up to.

I think you've misspelled "artificial lights".


Yes. Because of it's influence on the circadian rhythm. You don't want it INDOORS, you want it outdoors to tell you it's day time.

Numerous people “around the web” use flash for this application too.
I strongly suspect the use of, and popularity of light panels is due partly to convenience of focus light, taking light and surface to put film on, all in one manufactured package.
And partly due to superstition, unfamiliarity and an air of old fartism around flash from certain fractions of the self imagined and self perceived “slightly kooky young and hip”.

The physics of LEDs will always lead them to center (and “sputter”) in on certain frequencies, even if they use phosphor.

 

[grat]

For clarity, if your tungsten and halogen source isn't daylight balanced, it will still have a continuous spectrum (true CRI of 100) but will just need some colour correction to daylight balance.
A halogen light dichroic colour head for an enlarger can make a great light source for digitizing.

Color correction, I expect to have to deal with.

So just for fun, I went around my house and took some images of light sources, loaded them up into an image editor, and collected their histograms.

Which of the following would you be most likely to use for DSLR digitizing? The first is actually not so great because I wasn't able to get "just" the diffuse light. The rest, if possible, are cropped down to just the diffuse light output of the source in question.

1.

2.

3.

4.

5.

 

[Helge]

CTO gel or similar - and if you've got Wratten CC's, I'd certainly try 50R (or a mix of M & Y) on top of the tungsten correction and see how that does. I jumped in mainly to warn people that they can't assume that even nominally 'full spectrum' sources may be correct for what they are doing - and that they need to be aware of the print-through characteristics of the dyes.

A bare-bones monochrome CMOS sensor in a box with a universally adaptable lens-mount would be ideal, but they seem surprisingly hard to get prices on unless you want to buy dozens from an industrial supplier.

I know I’m sticking my neck out here, risking sounding stupid:
Are you sure you are not talking about RA4 enlarging, where the 50R would be used to single out two of the channels?

In my experience (which I have had good results with) you want to counter the orange with its opposite Cyan.
I’ve had good luck with two filters. A 50C and a much weaker magenta, I forget how much exactly.
Just to ballpark the negative in.

Adding extra red on top of the already reddish mask would seem completely counterintuitive.
You’d end up with a very blue positive.

 

[grat]

Numerous people “around the web” use flash for this application too.
I strongly suspect the use of, and popularity of light panels is due partly to convenience of focus light, taking light and surface to put film on, all in one manufactured package.
And partly due to superstition, unfamiliarity and an air of old fartism around flash from certain fractions of the self imagined and self perceived “slightly kooky young and hip”.

Sorry, I'm cantankerous, middle-aged and not at all hip. Waist, perhaps. But not hip. I don't care how old or new a technology is, as long as it works and there isn't a better option. I own (and use) a wide range of old and new technology. I also build my own PC's and 3D printers. Don't make assumptions.

I want LED because of form-factor, efficiency, low heat output, selectable color temperature, and evenness of output. Am I willing to compromise? Yes. But only if someone can prove I need to.

The physics of LEDs will always lead them to center (and “sputter”) in on certain frequencies, even if they use phosphor.

You seem to be convinced that I don't understand the problem, when in reality, I understand the problem perfectly well-- most LED's have different frequencies they excel at, and frequencies they're not so great at. ALL lighting sources tend to specialize in some frequencies and not others-- including the sun. Otherwise it would be a "white" star instead of a "yellow" one.

LED technology used to be really primitive, and if you look at the red or amber LED on your <insert electronic device here>, then yes, it's terrible. But technology has progressed. One LED in particular I was reading the datasheet on this evening starts out OK at the UV end, dips around the purple/blue range, and starts climbing fairly rapidly until it peaks at around 650nm-- Making it almost as good as halogen, only it's not burning a lot of useless energy in the IR and lower wavelengths.

The light pad (Raleno PLV-S192) I'm using allows me to adjust color temperature-- which means it's not a single LED. It's actually 192 of them, 96 of one type, and 96 of the other. Unfortunately, while I know the dimensions of each LED, and know the system uses 12V DC, I haven't found the model number of the LED's, or I'd look up their spectral response on the datasheets. Regardless, in order for the color temperature to be an option, it's got to be a mix of 3200K and 5600K LED's that are blended to create intermediate color temperatures. I would hope the "holes" in one set of LED's is compensated for by the other type of LED, but I don't know that.

 

[Helge]

Sorry, I'm cantankerous, middle-aged and not at all hip. Waist, perhaps. But not hip. I don't care how old or new a technology is, as long as it works and there isn't a better option. I own (and use) a wide range of old and new technology. I also build my own PC's and 3D printers. Don't make assumptions.

I want LED because of form-factor, efficiency, low heat output, selectable color temperature, and evenness of output. Am I willing to compromise? Yes. But only if someone can prove I need to.


You seem to be convinced that I don't understand the problem, when in reality, I understand the problem perfectly well-- most LED's have different frequencies they excel at, and frequencies they're not so great at. ALL lighting sources tend to specialize in some frequencies and not others-- including the sun. Otherwise it would be a "white" star instead of a "yellow" one.

LED technology used to be really primitive, and if you look at the red or amber LED on your <insert electronic device here>, then yes, it's terrible. But technology has progressed. One LED in particular I was reading the datasheet on this evening starts out OK at the UV end, dips around the purple/blue range, and starts climbing fairly rapidly until it peaks at around 650nm-- Making it almost as good as halogen, only it's not burning a lot of useless energy in the IR and lower wavelengths.

The light pad (Raleno PLV-S192) I'm using allows me to adjust color temperature-- which means it's not a single LED. It's actually 192 of them, 96 of one type, and 96 of the other. Unfortunately, while I know the dimensions of each LED, and know the system uses 12V DC, I haven't found the model number of the LED's, or I'd look up their spectral response on the datasheets. Regardless, in order for the color temperature to be an option, it's got to be a mix of 3200K and 5600K LED's that are blended to create intermediate color temperatures. I would hope the "holes" in one set of LED's is compensated for by the other type of LED, but I don't know that.

I didn’t make any assumptions about you, but about the people who prefer light panels in general.

Matching up spectrums from LEDs perfectly (or even well enough) is practically impossible.
There has been some breakthroughs since the sixties that allow for far more powerful LEDs in more colours. But the fundamentals still remain.

Black body radiators especially and gas discharge lamps to a large degree, have an even spectrum. Not so much in that they look like daylight (though Xenon is close) but in that they have a spectrum you can trust, without nasty surprises hiding inside it.

The sun is yellow because of Rayleigh scattering. In space it’s quite white.
And the accumulative output on a sunny day is white.