Luminous Landscape Forum
Equipment & Techniques => Medium Format / Film / Digital Backs – and Large Sensor Photography => Topic started by: Chris Barrett on December 10, 2015, 05:35:02 pm
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A million years ago, when I was still at Hedrich, my go to accent light was the Arri 150 Fresnel. I carried 9 of 'em, maybe 12, I forget. When I left, I investigated all the heads that were on the market and discovered the Dedolight 150. These were awesome! Sized to match the little Arris and Peppers, only 150 watt draw and they spotted with the intensity of a 300. I bought 7 of those, though they were rather pricey and they have served me well for 8 years.
Recently I started investigating LED Fresnels. Actually, my local rental house offered to let me take home their new Fiilex lights to play with. I dug those, they were pretty cool. You could dim them without color shift, you could dial the color anywhere from 2700k to 6700k and they were pretty bright. They didn't, however, cut like a tungsten fresnel. Using barndoors on them was a joke and forget trying to card the edge of the light. Also, their build quality was just slightly below my preferences.
So, I started investigating again and landed back at Dedo, who have a number of LED heads (varying in power) that use the same Aspheric optics (their own design) that is used in my 150 tungstens. I ordered one (DLED 4.1) and waited anxiously for it to arrive.
(https://scontent.ford1-1.fna.fbcdn.net/hphotos-xlp1/t31.0-8/12314344_10207150194808289_2460048479804365143_o.jpg)
These guys are right spendy at about 1600 for the head and power supply, but being able to dial in the color is a godsend. It seems like I'm always balancing commercial interiors to about 4200k which means gelling all my lights. After the light arrived, I spent a day playing with it at the house. Color and intensity both dial up and down beautifully. The quality of light is identical to the tungsten heads. They spot as tight, but they flood even wider. Barndoor them, card them... they work just like they oughtta! Did I mention that these things only draw 40 watts? By then end of the day I ordered two more and we'll be trying them out on a shoot next weekend. I expect after that, I'll be ordering more.
-CB
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These look great! I had gotten. I love the Fresnel look.
I had some LED panels before and they also shift color as needed and dim down. They are not this concentrated with a fresnel lens, but they were super for $170.00.
I also got a few pieces of the Rosco LitePads. The HO+ which are strong, but no light temp control. They dim also.
For Fresnel I still use a couple different strobes, an 8" and 12" Norman off 2K packs.
The boom for the 12" is a beast as these things are super heavy, and I have the snoot, barn doors, and such for it. It is a great light.
Good to see LED getting creative in usage.
The Rosco's I would look for second hand if you ever need them. They have limited use, but very hand for stills, but really shine for video. But its amazing to me how companies price their products like this. The Rosco has a dail down manual dimmer for $115+. I was able to order a electronic multi step dimmer with other lighting functions for $6, and it is a perfect shape and size unlike the bulk Rosco uses. The manual version also available for $4.
This is the price differences we are dealing with from companies aiming for making a killing. Those rectangular panels I mentioned above, LitePanel sells something like it for about $1200, at least when first released. Then they dropped a bit. But for about $300-400 you can get a top performing model that is as dependable as the old trenched brand name stuff.
Sometimes things like this are just insanely priced. Its supposed to have been for a industry that was thriving...but now that share is so small, the majority is not looking to spend 1600 on a LED lighthead. Maybe its because I use these types of lights as secondary, and not my go to gear. Maybe 4800 on main 3 lights being hot is the way to go for stills these days?
Also partly since I know too much about the MFG of LED lighting. Either way, nice share.
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Let us know how they work, Chris. Earlier this year I almost bought the larger Fiilex Q500 but wasn't entirely convinced the 5" fresnel would work for me. My work is in the studio and I've been shooting with flash adapted 1, 2, and 5k Desisti fresnels from pre-digital days but I don't need the power I once did. Starting to work with motion, I've added a number of Kinos but would like a hard source. Another possibility I've looked at is the Zylight.
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Peter, my local rental house turned me on to the Fiilex and let me take home their P360 kit over Thanksgiving. These came with fresnels, but they just don't cut anything like a real fresnel does. Trying to cut them with a flag, was like cutting a softbox.
The Dedo's totally do the trick and can replace my tungsten Fresnels.
I also recently picked up a used Profoto Multispot Fresnel for a little more punch. I'm anxious to try that out but Profoto is taking their sweet time refreshing it.
More to come,
CB
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Chris, at 3200K what is the color and hue like?
Is it a nice warm color like a tungsten bulb, or is it warm but a little off color and somewhat unpleasing?
I have found that a lot of the newer LED and HMI bulbs used in new construction today are around 3000K but have a magenta hue that does not feel nice. Your thoughts?
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SOmething like these?
http://www.ebay.com/itm/1000w-3200K-5500K-LED-Studio-Fresnel-Tungsten-Light-barndoor-Dichroic-US-S150-/400834045417?hash=item5d539225e9:g:RiIAAOxyLm9TCwXK
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^ Man, that's a cheap looking light!
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This look any better?
http://www.ebay.com/itm/1000W-Fresnel-Tungsten-Light-Spotlight-free-bulb-studio-vedio-photo-lighting/221948458729?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D34492%26meid%3D8e2ac3e8771a4986ad9ace841098825a%26pid%3D100005%26rk%3D1%26rkt%3D6%26sd%3D400834045417
or this
http://www.ebay.com/itm/Nanguang-CN-30F-LED-Studio-Light-LED-Fresnel-Spotlight-High-CRI-Ra-95-for-Video-/321943180412?hash=item4af54f147c:g:xz4AAOSwEetV7-lV
Some are even noted as designed in Germany or Japan to make you feel better.
I don't know what makes them look ugly? But they are Arri design copies, and they are pretty standard looking.
Not that the Dedo's are the same, and they can very well be "better"....
Here is the difference I often see,
http://www.ebay.com/itm/RPS-Studio-CooLED-1500-LED-Light-with-Fresnel-Lens-/191529721634?hash=item2c980f9f22:g:b60AAOSwBahU-gNU
Why they cost more is simply dictated by expected industry/marketing and very little or nothing to do with mfg costs.
Same lights, internationally $195, marketed to the photo industry here with a name on it, $600!
Thats over 50% ADDITION if you don't mind 500 less watts, thats 70%!
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Well, the main differences lie inside these beasts: LEDs, electronics and lens quality.
Looking at the spectral data for Dedo and Fiilex there's a difference, as the Dedo uses higher quality LEDs that produce better colors under any light temperature. We are talking small percentages difference at this level, but it could be enough to show a slight magenta hue around 3000K as lower quality LEDs tend to produce more blue light than higher rated ones.
As for those Arri copies, I'm not sure how well they are sourcing their parts. And not just the LED chips themselves, but also the rest of the electronics. LEDs can be very good and last a long time even if they come from not so reputable manufacturers, but if the internal power supply isn't up to the task or is driving the lights way over spec you will burn those puppies very quickly.
Then we come down to optics (both quality and design) and general contruction. Some are blatant copies so at least they should've gotten some things right, but if the materials used are different, then also the thermal characteristics are going to differ. One can half ass something at a cheap price, but for pieces of kit that cost so much and produce a lot of heat, half assing the cooling is going to cost you way more than buying quality lights in the first place.
There is definitely a price premium on some products which can be outrageous (like the Fiilex costing three times a Dedo and being both very close in quality), but not all the lights are created equal and some are just a waste of money (like those cheap eBay video rigs that will snap and break with normal use but that still cost a few hundred dollars).
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Chris, at 3200K what is the color and hue like?
Is it a nice warm color like a tungsten bulb, or is it warm but a little off color and somewhat unpleasing?
I have found that a lot of the newer LED and HMI bulbs used in new construction today are around 3000K but have a magenta hue that does not feel nice. Your thoughts?
Hi Joe,
Isn't that the general issue with LEDs, that they do not produce a very uniform spectrum of light, and therefore will generally cause some color issues in the overlap between the pass-bands, and maybe in the near UV part (around 470nm) of their output.
I think it would require significant specific additional filtering to even things out, especially if we want to get closer to a type of color emission that is a good balancing match for a camera, instead of accentuating the deficiency of RGB sensors to match human color sensitivity (Luther Ives condition). The latter by itself can already lead to all sorts of metamerism and Color Constancy issues.
Cheers,
Bart
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Yes, Bart, that is part of the problem with LEDs. However I feel there have been a good deal of advancements recently in the high end of lights, but I have no practical knowledge since these lights are outside of my budget right now.
So I was just wondering if there did have a magenta hue at 3200K, like most LEDs used in place of traditional building lighting.
I am fixated on this because recently I shot a project that have LED lighting that was natively at 2400K with a wicked magenta hue. It was a pain to edit, especially with indirect sunlight flooding in at 7800K and blue.
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One of the most expesive part in LED lighting is the binning, when they sort the light tempretures from each diode.
But even the cheap ones have CRI of 90+ with stable temps. There is cheap and then there is cheap. If you just look for price, chances are you''l get something crappy. But if you research the product you can make an informed purchase.
I have the Rosco LitePads and they are not cheap. They just haven't been copied yet. When they do, it should be just as nice as the originals.
Sure if you're looking for a new set of lights and are new in the business, you'll want that extra boost in confidence and the idea that you're doing "the right thing"..since you budgeted some figure for lighting. I don't see how 3 Fresnels would be useful, specially with such a small diameter. I love the look of the 12" I have and would opt for that over the 8" if it werent so darn heavy and big. Besides, I have yet to start using the LitePanles in any real shoot, as the mounting is not so straight forward, and so I have done some tests, but not so experienced with continuos lights in still shooting.
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Well, here's a quick setup I did at home the day I got the first Dedo. The image on the left is ambient window light, which white balanced to 5800k. I dialed the Dedo to 58 and lit the right side of the mantle. Check the color picker results...
(https://scontent.ford1-1.fna.fbcdn.net/hphotos-xpf1/t31.0-8/12304272_10207108745252076_7751677812223284621_o.jpg)
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Chris,
This is impressive indeed!
Cheers,
Bernard
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Yes, Bart, that is part of the problem with LEDs. However I feel there have been a good deal of advancements recently in the high end of lights, but I have no practical knowledge since these lights are outside of my budget right now.
So I was just wondering if there did have a magenta hue at 3200K, like most LEDs used in place of traditional building lighting.
I am fixated on this because recently I shot a project that have LED lighting that was natively at 2400K with a wicked magenta hue. It was a pain to edit, especially with indirect sunlight flooding in at 7800K and blue.
The rv guys have all moved over to cheap LED lighting and the color is impossible to correct. The shooters who are using tungsten and trying to balance the practicals are going nuts. Since I use strobe I just dial the practicals out, and then, if the image warrants it, I'll layer in some reflected highlights from the led practicals.
The lights they use well and truly suck.
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Yeah, I'm running in to this a lot lately in residential work. On one hand I was thinking I need less lighting with CMOS sensors, but then need more lighting again to make up for the crappy LED lighting. ::)
Blending a frame w/ practicals in luminosity or lighten mode has been working pretty well.
I am fixated on this because recently I shot a project that have LED lighting that was natively at 2400K with a wicked magenta hue. It was a pain to edit, especially with indirect sunlight flooding in at 7800K and blue.
The rv guys have all moved over to cheap LED lighting and the color is impossible to correct. The shooters who are using tungsten and trying to balance the practicals are going nuts. Since I use strobe I just dial the practicals out, and then, if the image warrants it, I'll layer in some reflected highlights from the led practicals.
They lights they use well and truly suck.
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The rv guys have all moved over to cheap LED lighting and the color is impossible to correct. The shooters who are using tungsten and trying to balance the practicals are going nuts. Since I use strobe I just dial the practicals out, and then, if the image warrants it, I'll layer in some reflected highlights from the led practicals.
The lights they use well and truly suck.
Do a separate exposure for them, color correct and blend that into the primary exposure?
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Do a separate exposure for them, color correct and blend that into the primary exposure?
That works so long as the the dominating light are not the LEDs, like in residential kitchens where the LEDs are more likely the track lighting under the cabinets.
But in large commercial spaces where the LEDs are the primary light source, it would be impossible to turn them off and recreate that light feel. So you just need to deal with it in post, which is not great.
Chris, thanks for the samples. The light looks very nice and clean.
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Do a separate exposure for them, color correct and blend that into the primary exposure?
That's what I do on occasion, when it makes sense to the scene. The problem is that they just don't really color balance well.
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Working on an image today that is a mix of tungsten, LED and flourescent...inside and outside lighting.
arrrrggghhh
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If you haven't already seen it, Alan Roberts' excellent tests and methodology for LED colour rendition can be found here:
http://www.gtc.org.uk/tlci-results/tlci-results-new-format.aspx
The Dedolight LED's are pretty good but have the usual LED problem: big spike in the blue, gap in the teal/cyan, not much up in the violet or down in the deep reds.
At least these days they're mostly doing OK with skin tones and the grey scales. But if you need to accurately record already-tricky colours like deep blues or violets and purples, they are going to be a headache.
I've been using LED for a while for video work. They're OK but I wouldn't want to be without at least some overall control over green/magenta as well as colour temperature, and ideally full control over all the LED colours independently. I've got Kelvin tiles which offer this, and the newer Arri lights like L7C and Sky Panel allow it too.
Of course as with any "spiky" spectrum it can play havoc with the dyes in the camera RGB filters. If you happen to get a camera whose filter cut-offs are close to one of the LED peaks, the results can be rather unpredictable, producing weird green/magenta shifts which differ with colour. Trying to dial out a blue/green tint on skin tones when the whites have already gone magenta and the blues are looking purple/grey is no fun at all. So as always try for your own use case before you buy.
I've found that my Kelvin Tiles look fine with my RED, pretty horrible on the Hasselblad (massive green tint which you can mostly dial out in Phocus but anything which requires 30+ point adjustments to get back to something approximately neutral hardly inspires confidence) and OK with A7Rii. Testing is the best way to be sure, unless you've got detailed information on your camera's RGB filter passbands.
Cheap LEDs are ghastly. Almost as bad as cheap CFL's, which I simply cannot believe companies get away with selling for photographic use.
Cheers, Hywel
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If you haven't already seen it, Alan Roberts' excellent tests and methodology for LED colour rendition can be found here:
http://www.gtc.org.uk/tlci-results/tlci-results-new-format.aspx
Thanks, that looks like a useful starting place. BTW, those IKEA bulbs look relatively decent ... ;)
The Dedolight LED's are pretty good but have the usual LED problem: big spike in the blue, gap in the teal/cyan, not much up in the violet or down in the deep reds. [/quote]
Yes, the Blue/Violet hump is usually an issue, I assume one could filter that out to get a more well behaved spectral uniformity, except for the dip near Cyan. One or two Lee filters should improve matters and allow more easily correctable color casts.
Cheers,
Bart
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Dedo LEDs have a much lower spike than other types. I've looked at some of the available spec sheets, and their spikes (for tungsten) are smaller than the Fiilex. Daylight seems to be more controlled as well. Chris pretty much showed this in his test.
As usual, it's all up to the dies used inside the diodes. There is a LED maker that has even higher rated diodes available (Yuji http://www.yujiintl.com/high-cri-led-lighting ), but I don't know who's using them in their products.
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A Sekonic C700 spectrometer will be very useful when dealing with LED lights. Just saying. ::)
(http://epcem.org/wp-content/uploads/2015/09/led-light-spectrum-spectral_responses2.png)
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Yes, the Blue/Violet hump is usually an issue, I assume one could filter that out to get a more well behaved spectral uniformity, except for the dip near Cyan. One or two Lee filters should improve matters and allow more easily correctable color casts.
My experience is that filtering LEDs often makes the problem worse rather than better.
Instead of spikes interacting with cut-offs in three filter bandpasses, you get them interacting with cut-offs in four filter bandpasses- the camera RGB plus whatever filter you put in front of the LED. Generally speaking the additional filters have been designed to work with continuous spetra, not great big spiky things like LED or (god forbid) CFLs.
The ratio of blue spike to green/yellow/orange tail has already been selected by the manufacturer to "fool" the average sensor into seeing it as equivalent to daylight or tungsten. You can get some totally out-there colour shifts if you aren't careful, and you won't necessarily be able to see them with the naked eye. I've done this for creative effect but the effect is more usually party colour gel than subtle +1/8th magenta, I must say.
Obviously it is never going to be perfect with such a lumpy spectrum. But I've definitely had more practical success with altering the balance of multiple LED colours at source rather than filtering an already malformed spectrum.
Cheers, Hywel
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A Sekonic C700 spectrometer will be very useful when dealing with LED lights. Just saying. ::)
Oh damn you, now I'm going to have to buy one of those, instead of the nice 90 mm Sony Macro lens I'd promised myself for the new year. The urge to know what the light spectrum actually IS will be overwhelming now I know you can get one of those hand-held :(
Cheers, Hywel
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Oh damn you, now I'm going to have to buy one of those, instead of the nice 90 mm Sony Macro lens I'd promised myself for the new year. The urge to know what the light spectrum actually IS will be overwhelming now I know you can get one of those hand-held :(
Cheers, Hywel
Yeah, me too, I've spent the last 20mins reading about the C700….
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Hi,
The suggestion that comes to my mind is that it may be a good way to generate a good colour profile for the illuminant in question.
What is your view on that?
Best regards
Erik
My experience is that filtering LEDs often makes the problem worse rather than better.
Instead of spikes interacting with cut-offs in three filter bandpasses, you get them interacting with cut-offs in four filter bandpasses- the camera RGB plus whatever filter you put in front of the LED. Generally speaking the additional filters have been designed to work with continuous spetra, not great big spiky things like LED or (god forbid) CFLs.
The ratio of blue spike to green/yellow/orange tail has already been selected by the manufacturer to "fool" the average sensor into seeing it as equivalent to daylight or tungsten. You can get some totally out-there colour shifts if you aren't careful, and you won't necessarily be able to see them with the naked eye. I've done this for creative effect but the effect is more usually party colour gel than subtle +1/8th magenta, I must say.
Obviously it is never going to be perfect with such a lumpy spectrum. But I've definitely had more practical success with altering the balance of multiple LED colours at source rather than filtering an already malformed spectrum.
Cheers, Hywel
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Simplistic question: The spectrum is useful obviously in showing spikes and gaps and guiding filtration, but that has issues as has been pointed out, how do you, from that spectrum, then set the single figure white balance the camera allows and which is only in RAW data anyway so has no effect on what is captured, although we are repeatedly told to get it near enough before going to the converter because it does have some effect?
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Simplistic question: The spectrum is useful obviously in showing spikes and gaps and guiding filtration, but that has issues as has been pointed out, how do you, from that spectrum, then set the single figure white balance the camera allows and which is only in RAW data anyway so has no effect on what is captured, although we are repeatedly told to get it near enough before going to the converter because it does have some effect?
Hi Chris,
I don't know what kind of algorithm the Sekonic uses, but one could compare the sampled spectrum with the emission spectrum of a black-body radiator, vary the latter's temperature, and minimize the differences over the full human visible spectrum (maybe add some weighting). Obviously the Blackbody spectrum is smooth like from incandescent lightsources, but by minimizing the differences something usable should emerge. Maybe it also optimizes for a 'tint' in addition to the color temperature.
That temperature is obviously only a tag in the Raw metadata. One would need to actually filter the lightsource, and/or the lens, to really produce better Raw data. That tag can then be used by a camera as a default "as Shot" color temperature/tint.
A spiky/bumpy spectrum will remain an issue for accurate color, even if on-average the differences are minimized, so that still needs fixing before capturing.
Cheers,
Bart
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Simplistic question: The spectrum is useful obviously in showing spikes and gaps and guiding filtration, but that has issues as has been pointed out, how do you, from that spectrum, then set the single figure white balance the camera allows and which is only in RAW data anyway so has no effect on what is captured, although we are repeatedly told to get it near enough before going to the converter because it does have some effect?
Simplistic answer:
I usually just shoot on daylight or tungsten preset- it seems to get close enough as a starting point for RAW processing and it means I know where I am starting from. I know that I need to dial in some plus green to match daylight or tungsten on the RED, but I do that on the lights rather than on the camera.
If I think it is very tricky I set using grey card in most "representative" bit of the scene, this can help dial out gross green and magenta shifts.
Flash is so much more powerful and just as portable, and has something much more like a true black-body thermal emission spectrum, so I still use flash 90% of the time for stills.
Where I have found the LED panels particularly useful is a little extra warm fill and catchlights in model's eyes when shooting available light; here I definitely rely on daylight or tungsten preset depending on what the main light source is, and consult the back of the camera to get some handle on green/magenta shift, then dial that up on down on the panel.
How does the Sekonic meter chooses its overall "Average" colour for a very lumpy spectrum? I guess only the engineers at Sekonic can answer that. Maybe they just do a one-parameter fit to the spectrum and accept the answer, however poor the fit actually is?
But that's not any help when setting stuff on the camera, as the camera's colour temperature settings aren't for continuous spectra either. They are to mix relative amounts of R, G and B channels, as that's the only thing the camera CAN do. The only data it records are the RGB intensities inside the filter passbands.
This sort of thing is what I mean:
(http://www.samirkharusi.net/1ds_dwb_twb_rgb.jpg)
(from http://www.samirkharusi.net/spectrograph.html it was the best passband graph I could find with a quick Google).
As you can see, the R G and B passbands overlap, and the red filter leaks at the extreme violet end. So the camera's response will be the convolution of each filter response with the input spectrum.
Note that the dip in the cyan in the LED spectrum is pretty much where the blue and green filter passbands cross over. This will make the exact response of the camera highly dependent on exactly where the dip falls relative to those two pass bands.
Ironically this might be why my Hasselblad (which generally seems to have very clean colours and low sensitivity, suggesting they may have used stricter passband filters for the RGB pixels) reacts so much worse to the LED spiky spectrum than something like Canons or REDs, where the dyes are chosen with half an eye on low-light performance rather than going all out for colour purity.
If a camera from a particular manufacturer happens to have the filter cross-over more cleanly up in the blue, whereas another has it more down in the green, you're going to get very different camera responses from the same light. One might register the light as very blue, another camera as very green. As this is an artefact of the camera and the light convolved together, it is impossible to see by eye: you can only see it once you've taken a shot. And in neither case does it say anything about how the intensity of the red channel will vary in parallel with the recorded intensity in the blue vs the green. So in general there will not be a "correct" colour temperature setting anyway- that models the response of RGB channels assuming a continuous thermal spectrum, which isn't what's present.
Note that the leakage in the red passband up into the blue/violet happens to coincide roughly with the peak of the blue emission from the LED, too- so the contamination of red in the blues might give a much stronger red contamination than the RAW processor is expecting, resulting in red or magenta shifts in the blues.
There's also a general lack in the far reds both in filter and light, so objects that appear red to the eye might end up looking very dark on camera.
Adding in extra passbands only makes the situation more complex:
(https://chart.googleapis.com/chart?cht=lc&chs=400x380&chg=17,20,0&chls=4|5|5&chco=FFFFFF,FFFFFF,000000&chxt=x,y&chxs=0N**%20,FFFFFF|1N**%20%,FFFFFF&chdlp=bv&chxr=0,400,700,50|1,0,100,20&chf=bg,s,666666|c,lg,0,ffffff,0,7f5686,0.01,58679f,0.15,67b9c1,0.31,67a77d,0.50,cdd058,0.67,ca8e5d,0.84,a53d3e,1&chd=t:0|70.601,70.336,68.816,68.074,67.731,67.278,66.392,66.085,66.733,67.509,68.085,68.288,68.904,69.899,71.018,71.413,70.92,69.467,67.78,66.105,63.478,59.879,55.433,50.872,47.612,45.682,45.12,44.437,43.072,41.103,38.939,37.523,37.966,40.233,44.786,50.941,58.13,64.478,70.854,76.258,80.846,84.391,86.683,87.701,87.232,86.744,86.588,86.831,87.828,89.432,90.745,91.528,91.794,90.67,89.744,89.002,88.377,88.669,89.088,90.277,91.295&now=1450444850608)
(From http://www.leefilters.com/lighting/colour-details.html#247&filter=tf for regular minus-green).
Look at what CTO does:
(https://chart.googleapis.com/chart?cht=lc&chs=400x380&chg=17,20,0&chls=4|5|5&chco=FFFFFF,FFFFFF,000000&chxt=x,y&chxs=0N**%20,FFFFFF|1N**%20%,FFFFFF&chdlp=bv&chxr=0,400,700,50|1,0,100,20&chf=bg,s,666666|c,lg,0,ffffff,0,7f5686,0.01,58679f,0.15,67b9c1,0.31,67a77d,0.50,cdd058,0.67,ca8e5d,0.84,a53d3e,1&chd=t:0|14.451,16.015,17.015,17.876,18.563,18.744,18.383,17.926,17.726,17.799,17.923,18.199,18.839,19.952,21.836,24.13,26.688,29.209,31.432,33.853,36.252,38.708,41.091,43.116,44.404,45.436,46.214,47.266,48.501,50.198,52.531,54.91,57.003,58.744,60.271,61.968,64.189,66.762,69.963,74.156,77.818,81.338,83.731,85.479,86.923,88.041,88.294,88.467,88.027,87.511,87.178,86.822,86.955,87.381,88.4,89.482,90.933,92.023,92.675,92.869,92.403&now=1450445604512)
To get the response of the camera to a spiky spectrum light filtered with that is beyond my capability to visualise in my head! (I think you multiply the light spectrum by the fiilter response, but then have to convolve with the camera dye passbands to get the R, G, B responses). Whatever you get, it probably won't be what you naively expected, and you'll very likely be throwing away a lot of intensity, too.
This is why I worry when I see manufacturers shipping daylight balanced LED panels with slot in CTO filters. What comes out will likely bear little resemblance to a genuine 3200K black body thermal spectrum!
I note that Lee are now doing a range of filters specifically for LED, which have cleaner passbands than their regular range:
http://www.leefilters.com/lighting/colour-details.html#CL180&filter=ld
but at the moment those are more like party gel colours matching to Tungsten, not the subtle effects of a +1/8th CTO or -1/4 green.
Cheers, Hywel
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Bart,
Thank you for expanding, that quest for colour accuracy was well debated here previously and perhaps the spectrum influence was not fully considered, but accuracy with all the variables is probably a quest too far, unless you invest in that Capture One package.
Hywel,
I knew when I asked the answer was not as simple as the question and you kindly have show how right I was!!
Sometimes the more we know, as with the analyser, the less we feel capable of fixing it.
I was shooting a quick 'product" shot today, a new Photobook with a pure black cover (inset B&W print) in diffuse cloudy sunlight the camera balance (Nikon D3) was shall we say poor to be charitable, only by dialling in manually and by chimping the result could I get it near. I presume the algorithms in camera are similarly obscure, at least to the user, but at least the manufacturer is aware of the dye filtration on the sensor. It is that tint rather than the "pure" temperature that seems to skew the result. The D3 does allow a joystick type adjustment of tint presumably for the jpeg output option.
Your input is appreciated, I know more and probably understand less!
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The suggestion that comes to my mind is that it may be a good way to generate a good colour profile for the illuminant in question.
What is your view on that?
Hi Erik,
For a spectrum profile based camera profile (like with Anders Torger's DCamProf utility), we also need the CFA-filter response. So we can only do that by taking an image of the illuminant's spectral light emission. I'm (early stage) experimenting with that, based on a not too expensive line grating (http://www.patonhawksley.co.uk/staranalyser.html). I'm now looking for a method to produce a reliable light slit (something with 2 razor blades or knife edges that can be precisely adjusted for a certain slit width).
Taking an image of the lightsource shining through the slit, I will get, after calibration of the wavelengths, a perfect spectral decomposition of the lightsource+lens+Bayer CFA+sensor transmission, and the effective response or sensitivity of the combo.
Maybe this is better discussed in another thread.
Cheers,
Bart
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(something with 2 razor blades or knife edges that can be precisely adjusted for a certain slit width).
Hi Bart,
Ahhh, fun! I must dig my Star Analyser out, haven't used it in ages.
You can buy variable slits off the shelf if you don't want to faff around with razor blades :)
https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1465
or as fixed width slits:
https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1464
Cheers, Hywel
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Hi Bart,
Ahhh, fun! I must dig my Star Analyser out, haven't used it in ages.
You can buy variable slits off the shelf if you don't want to faff around with razor blades :)
https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1465
or as fixed width slits:
https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1464
Cheers, Hywel
Thanks for the links Hywel. I know they can be bought off the shelf, but I'll also search on eBay first. In the end I'd like to create something more 'industrial' ;)
Cheers,
Bart
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I recall seeing in Costco 3-packs of 60W LED bulbs with packaging stating a CRI either 92 or 94 ($19). Are these any good for photography?
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I recall seeing in Costco 3-packs of 60W LED bulbs with packaging stating a CRI either 92 or 94 ($19). Are these any good for photography?
Not really, considering how cheap they are and the average CRI rating.
Quality LEDs, besides being pricey, usually have a CRI of 96+ as well as other ratings like TLCI. Even better if they state the temperature range (good LEDs are usually +/- 200K from the rated temperature).
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Those had 2700 or 2800K rating. Ok, thanks:)
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That works so long as the the dominating light are not the LEDs, like in residential kitchens where the LEDs are more likely the track lighting under the cabinets.
But in large commercial spaces where the LEDs are the primary light source, it would be impossible to turn them off and recreate that light feel. So you just need to deal with it in post, which is not great.
Chris, thanks for the samples. The light looks very nice and clean.
I think that, as long as you can turn the various "house" and supplementary light sources on and off independently, you have a shot at being able to do separate exposures and to correct separately in post, even when the "house" lighting is the dominant light source. Not always, for sure, but I think it depends upon the particular situation and the nature of the ambient daylight, if there is any. I do understand that, with commercial/institutional situations, you might not have the ability to turn the various types of "house" lighting on and off independently, however; and this can occasionally happen with residential too.
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Hi Bart,
My take was that we can generate a normal, target based profile using the illuminant in question. I would agree that it may be better to use spectral response of the sensor, but it may be helpful to just use a colour checker.
My take is that we essentially just strive for a compromise matrix, optimising the matrix to achieve minimum errors. I am not sure a LUT based approach does a better job here, so I would guess that the 16 standard patches on the ColorChecker may be sufficient. Now days we can easily build profiles for DCP but anyone willing to use the command line can also generate ICC profiles with Torger's tool.
Best regards
Erik
Hi Erik,
For a spectrum profile based camera profile (like with Anders Torger's DCamProf utility), we also need the CFA-filter response. So we can only do that by taking an image of the illuminant's spectral light emission. I'm (early stage) experimenting with that, based on a not too expensive line grating (http://www.patonhawksley.co.uk/staranalyser.html). I'm now looking for a method to produce a reliable light slit (something with 2 razor blades or knife edges that can be precisely adjusted for a certain slit width).
Taking an image of the lightsource shining through the slit, I will get, after calibration of the wavelengths, a perfect spectral decomposition of the lightsource+lens+Bayer CFA+sensor transmission, and the effective response or sensitivity of the combo.
Maybe this is better discussed in another thread.
Cheers,
Bart
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Maybe you should be using remote-phosphor LEDs eg cineo.
Edmund