CFL's and Daylight balanced film making me blue

[Bob Salomon]

As the last two posts mention, you are experiencing the result of "spikes" in the spectral distribution of the light emitted by your lamps. Do a search for the spectral distribution graphs of the particular lamp you are using. You can usually find these on the lamp manufacturer's website. These documents will contain the real answer about your particular lamp's output and will guide you in selecting another lamp that will satisfy your needs. Its not just the CRI, so don't stop there. Get the complete spectral distribution information.

To correct this I suggest you find a lamp that fits your fixtures that gives a smooth distribution of the visible spectrum that most closely resembles natural daylight.

Alternately you can use slight magenta filtration over the lens to improve things, at least to the point that you can correct in Photoshop. If you choose this route, buy a few different value filters and shoot a test of one subject with varying filtration. Please note that filtration is a work-around and won't solve the problem but will get you closer. It won't make up for the absence of a particular wavelength of light nor will it eliminate the overabundance of a particular wavelength.

I suppose you want a transparency as the final reproduction since you mentioned e100vs. That's the last choice of film I'd make. Kodak EPP or maybe Fuji Astia would be the two best choices available for "natural" color rendition.

This is partially true.

Better manufacturers even out the spikes by using special reflective surfaces behind the tube and, if necessary, specially formulated diffusors in front of the tube to reduce the spikes and add the missing colors. That is why it is important that you know the color temperature and the CRI of the system and not the lamp itself.

We have shipped hundreds, if not thousands, of copy light fixtures using high CRI daylight Dulux tubes to libraries, museums, universities, police, FBI, art institutes, etc. ll who use them for accurate color reproduction on film and digital.

And for many of these applications the cool burning under prolonged use is as important as the color temperature when copying many of the items they shoot as they are very delicate and prone to damage from the heat from other light sources.

[Henry Ambrose]

This is partially true.

Better manufacturers even out the spikes by using special reflective surfaces behind the tube and, if necessary, specially formulated diffusors in front of the tube to reduce the spikes and add the missing colors. That is why it is important that you know the color temperature and the CRI of the system and not the lamp itself.

We have shipped hundreds, if not thousands, of copy light fixtures using high CRI daylight Dulux tubes to libraries, museums, universities, police, FBI, art institutes, etc. ll who use them for accurate color reproduction on film and digital.

And for many of these applications the cool burning under prolonged use is as important as the color temperature when copying many of the items they shoot as they are very delicate and prone to damage from the heat from other light sources.

Nope, what I wrote is completely true and based on hard earned experience. I was building color corrected lighting units for digital scanning cameras before your sales organization even knew there was a need for such a thing.

Why not name the fixtures you sell so he can look at the possibility of buying some or deciding that they cost too much? Where are the spectral distribution graphs for your lights? They might be good, so show us - please.

The original poster has choices of filtering, buying new lamps or new fixtures and lamps. Whatever he chooses, depending on CRI rating alone won't get him there.

[Bob Salomon]

Nope, what I wrote is completely true and based on hard earned experience. I was building color corrected lighting units for digital scanning cameras before your sales organization even knew there was a need for such a thing.

Why not name the fixtures you sell so he can look at the possibility of buying some or deciding that they cost too much? Where are the spectral distribution graphs for your lights? They might be good, so show us - please.

The original poster has choices of filtering, buying new lamps or new fixtures and lamps. Whatever he chooses, depending on CRI rating alone won't get him there.

Kaiser makes the lights. You can check the Kaiser web site for info.

http://www.kaiser-fototechnik.com/en...timent.asp?w=3

http://www.kaiser-fototechnik.com/en...ge.asp?nr=3431


We also sold the GO LIghts and we have been selling high CRI daylight lighting for over the 25 years which is longer then digital scanning cameras have been around since we distributed the very first one commercially available - the Rollei ScanPack for the 6006/6008SRC cameras. It predated the first Leaf camera.

[CG]

The OP mentions CFLs with a CRI of 85. I believe I've seen CFLs with much higher Color Rendering Indexes. They seem to be available well into the 90s which presumably would translate into improved rendering.

Even then, test shoots and filtering to improve things, shooting again, till one has a fair set of results, would seem best.

C

[rvhalejr]

A friend of mine (former wedding photographer) told me that there seemed
to be something about the white material used to filter flash and modeling
lights that (for what ever reason) eliminates color drift.

Exhaustive testing and research after this discussion brought me to this
startling conclusion:

One or Two 400 watt CFLs filtered through a quality white umbrella will act
as near perfect CRI modeling light source(s).

This assumes that the CRI color target luminescence has been dialed in by placing
gels (side by side) in front of the light to enhance the temperature
profile as desired .,.

Combine this will carefully calibrated fill flash(s) of the identical temperature
will produce outstanding results.

Using Ambient light that is the same color temperature as the filtered modeling
and flash source(s) is ideal. One light stand, ambient daylight and one flash
seem to work best as to many sources will make the subject appear flat.

This assumes that you are using D50 or D65 light sources (not both)
and are using the appropriate filters (on camera and/or light sources) and
white balance (the DSLR as a simple color sensitive spot meter to check
the lighting setup before exposing that beautiful piece of 4x5 portra nc).

The best target for showing the slightest blue (or red) drift is the white wedding
dress material (use a doll or xmas tree angel, they do not complain and
work cheap).

With Daylight it is important to use a colorimeter to find out if it can be used in the
mix or not. If its in the 8500K region (or above) its almost useless except as a
heavily filtered sole source.

Time of day, year and weather can produce 5000-10000K daylight that is not an
ideal CRI light source. Thats why UV, Skylight, ND, Polarizers and gels are very
handy.

Modeling light CFLs followed by a combination of gels (side by side) filtered
through a white umbrella work surprisingly well with temperature matching fill flash(es).

Part of this research included using the highest (and most expensive) rated CRI
CFL made. It's spectrum was also vastly improved with the gel and white umbrella
diffuser technique as evidenced by measured target color image values .,.

With respect to LF, this technique will work for any film (C41, E6 or BW) but the
set of balancing filters and gels will be unique for each sub-type and will most
likely not be interchangeable.

The Temperature of CFLs and Strobes also can vary from one unit to the next and
will change over time (sigh)

[rvhalejr]

You probably already know this already but be sure to scan the film in
16bits (preferably wet, 3200 dpi and tiff).

I'm not sure about the latest photoshop (or scanner) software but picture
window pro is (IMHO) the preferred tool for fine tuning color drift.

Sorry about the previous long winded post (but it is a passion) .,.

All the Best,

Richard

[Jim Cole]

Part of this research included using the highest (and most expensive) rated CRI
CFL made. It's spectrum was also vastly improved with the gel and white umbrella
diffuser technique as evidenced by measured target color image values .,.

Richard,

What CFL bulbs are you referring to in your post?

Thanks,
Jim

[rvhalejr]

Originally Posted by rvhalejr View Post
Part of this research included using the highest (and most expensive) rated CRI
CFL made. It's spectrum was also vastly improved with the gel and white umbrella
diffuser technique as evidenced by measured target color image values .,.

> What CFL bulbs are you referring to in your post?

I'm hesitant to name names for a lot of different reasons. There used to be a
gretag macbeth station (expensive but a great industrial tool) and I happen to
run across a replacement bulb or two (not all that expensive). Something about
full spectrum D50 or D65 and Seven or Nine phosphors if I recall (Its been a
long time).

In theory one could build a couple of arrays of these things to the impress the
curator staff but the roscolux spectural filters and white diffusers (Weston white
umbrella and/or Softboxes) really flatten out the spikes and can saturate colors
as needed.

To validate the setup (beyond targets like gm's) artist paints that are known
to be out of gamut (compared to anything else in the physical world) can be
used (since they are recognized trouble makers). Getting a blank canvas
and painting squares with these colors might be a good idea. Then build a
spectral gel set that equalizes out-of-gamut squares with those on the gm target.

I have to admit my modeling light setup looks "ghastly" by itself (lol).
When combined with a flash (of the same mired value) creates a digital image
(from a ambient daylight white balanced scanned film and/or matching dslr) will
be very precise. When it comes to color the instruments and tests win out
over my eyes ever time.

You can use almost ANY 5000K or 6500K CFL bulb set. It does not even have to
be full spectrum (I like the really big ones). However museums use to not allow
any flash because of UV issues and high luminance burst (the cumulative effect
over time being the same as exposure to direct sunlight). D50 used to be the
closest to the display lighting they use (no daylight) so it or something lower
for modeling lights would be ok as long as the color targets tell us we are golden
OR it matches a look (intentional drift) they want.

I get better results with D65 on paintings as compared to D50 because there always
seems to be some (green building) indirect sunlight around. Then again morning and
evening usually require D50. Who knows, some galleries may use a combination
of yellow (D50) and/or blue (D65) to accentuate the work, and it may vary from
piece to piece (they pay the invoice so .,.).

The calibrated colorimetric standard used are color targets and ambient
daylight temperature values recorded through out the day with 120/220 film
and/or dslr and white balanced mired filters that yield the most closely
matched published values for the color target(s). A gray card, black and white
cloth targets are also used.

Sometimes there are compromises that have to made, but as long as absolute and
relative colorimetric values are well with the 16bit digital color editing working range
of our software tools the setup should all be good to go.

Then we pull out the 4x5 film (same as the 120/220 used in test shots).

[rvhalejr]

Sorry, that last reply was in response to Jim's Question.

One more thing (I'm agnostic about film and digital, both having strong and
weak points), I've seen a transparency that had no grain (way above 3200dpi)
and a digital image that exceeded the nyquist frequency[1] limit by a factor of 2.

These are extremely rare occurrences but do exist. Almost all claims to be able
to achieve these results on a regular basis should be dismissed out of hand (sigh).

That aside, we need to be aware of is the weakness of dslr's and digital backs
since we are using these for calibration tools and are a part of our (or at least
my) daily work flow.

Because of the well known RGBG arrangement slight differences in colors are
the Achilles Heal of the 40Mega-pixel chip.

The full color pixel value is 40mp/RGBG (four photo sites) == 10 megapixel color camera

I've been using and selling Charles Sleicher targets (RGB and Black on White)
for awhile. To see the 10 mega pixel effect make red line pair targets
on a red background with a sinusoidally decreasingly small difference in color.
At some point the scanned film image will show up to 2-3 times the resolution
(lp/mm) as compared to the dslr or digital back image (given 2G photosites and
perfect point algorithm mentioned in Note 1 on the bottom of a highly intelligent
and no doubt expensive, stack of software).

This is only being pointed out to show that the digital image will lose some
of its color acutance as it approaches the megapixel/RGBG limit.

Given what I've seen (both good and bad) from film and digital sensors I
would be comfortable estimating that a well exposed color balanced piece of
6x6 or greater mirror like flat piece on film (using the fine focusing loupe lp/mm
kit I sell) behind a good Schneider, Nikon, Zeiss etc. APO lens will out capture
the finest color detail of the large format 40 Mega pixel back (based on a
2800dpi 16bit nikon fluid scanning limit for color film).

I did not account for the less than 16bit per channel color depth of the kodak
KAF-39000-AAA chip (has anj internal 12bit dynamic range but outputs 16) so
just think of that as my four bit margin of safety.

A lot of 4x5 film verses digit test reviews have been popping up which I'm having
trouble with.

My Engineering Test Requirements
The first is I want to see a picture of the reflection of an unexposed
piece of film in the film holder to check for flatness. The reflected image
should be perfectly mirror like, demonstrating no out of the box film curl.
(As far as I know flatness can only be obtained by a specific unexposed
film taping technique in the black bag or dark room).

The second is I want to know is the reviewer used my fine focusing loupe kit (for
precision plenum photography) that will bring the lens image and emulsion plane
into perfect focus simultaneously (across the entire frame inspected on the
side and corner stand). Once observed (validates most of the camera system
and) it guarantees the best possible image resides within the approximately
.001 to .002" emulsion plane.

The reviewers will only need to pay actual postage to them AND back to me
(unless they want to buy it or craft their own from almost 70 pages of
documentation, photographs and drawings that comes with every kit).

I don't like to name names but some of great renown have done that and more
for me, so its time to give back to those who share one of my life's great
passions.

Note [1]
40Mega-pixel the monochromatic value. There also is a airy-disc (perfect-point)
algorithm being used that can make digital pictures "scary". But I digress, I do not
even know if its published (a tightly held trade secret no doubt). Simply put it is
possible (with high speed sampling deterministic algorithms) to achieve reliable sub
pixel accuracy (yes, exceeding the monochromatic 2d nyquist frequency limit in
something resembling a virtual 3d working space).

[rvhalejr]

Part of this research included using the highest (and most expensive) rated CRI
CFL made. It's spectrum was also vastly improved with the gel and white umbrella
diffuser technique as evidenced by measured target color image values .,.

> What CFL bulbs are you referring to in your post?

I'm hesitant to name names for a lot of different reasons. There used to be a
gretag macbeth station (expensive but a great industrial tool) and I happen to
run across a replacement bulb or two (not all that expensive). Something about
full spectrum D50 or D65 and Seven or Nine phosphors if I recall (Its been a
long time).

In theory one could build a couple of arrays of these things to the impress the
curator staff but the roscolux spectural filters and white diffusers (Weston white
umbrella and/or Softboxes) really flatten out the spikes and can saturate colors
as needed.

To validate the setup (beyond targets like gm's) artist paints that are known
to be out of gamut (compared to anything else in the physical world) can be
used (since they are recognized trouble makers). Getting a blank canvas
and painting squares with these colors might be a good idea. Then build a
spectral gel set that equalizes out-of-gamut squares with those on the gm target.

I have to admit my modeling light setup looks "ghastly" by itself (lol).
When combined with a flash (of the same mired value) creates a digital image
(from a ambient daylight white balanced scanned film and/or matching dslr) will
be very precise. When it comes to color the instruments and tests win out
over my eyes ever time.

You can use almost ANY 5000K or 6500K CFL bulb set. It does not even have to
be full spectrum (I like the really big ones). However museums use to not allow
any flash because of UV issues and high luminance burst (the cumulative effect
over time being the same as exposure to direct sunlight). D50 used to be the
closest to the display lighting they use (no daylight) so it or something lower
for modeling lights would be ok as long as the color targets tell us we are golden
OR it matches a look (intentional drift) they want.

I get better results with D65 on paintings as compared to D50 because there always
seems to be some (green building) indirect sunlight around. Then again morning and
evening usually require D50. Who knows, some galleries may use a combination
of yellow (D50) and/or blue (D65) to accentuate the work, and it may vary from
piece to piece (they pay the invoice so .,.).

The calibrated colorimetric standard used are color targets and ambient
daylight temperature values recorded through out the day with 120/220 film
and/or dslr and white balanced mired filters that yield the most closely
matched published values for the color target(s). A gray card, black and white
cloth targets are also used.

Sometimes there are compromises that have to made, but as long as absolute and
relative colorimetric values are well with the 16bit digital color editing working range
of our software tools the setup should all be good to go.

Then we pull out the 4x5 film (same as the 120/220 used in test shots).