Bulb Color Temp question (Videography)

12/27/2011 03:00:21 AM · #1

The Pentax K-r I tried using for video has disappointed me for a couple reasons and I am trying to use a pocket camcorder thats giving me acceptable results except for one problem.

I was using 2700K Balanced 200 watt equivalent CFL's and this camera will not let me sample a custom white balance (Nor could I get the K-r to when in video but its presets worked fine). Auto WB at 2700K is as it always is kinda cruddy.

I picked up a pair of 6500K bulbs to test with and Auto WB is working VERY Well. Can I expect similar results with 5000 to 5500 or should I play it safe with 6500 which are usually more expensive in the 105 watt (400 equiv) form I need them in. The 6500 doesnt match the daylight setting in the camera its still a bit yellow and the flourescent setting is not as far off as you would think 5000K might actually match. Matching a setting is preferable since auto self adjusts if the scene changes but atleast it works now.

12/27/2011 05:09:06 AM · #2

Are you using common domestic compact fluorescent lamps? I would of thought the results for any of them would be disappointing for the same reason strip tube fluorescent illumination had always appeared greeny-yellow, no matter what 'color temp' you use. I think it's to do with the 'spectral power distribution' of the CFLs. Traditional tungsten lamps (i.e. 2400 to 4000K) have a very predictable SPD curve shape, with a slope in the visible region according to the C/T. White balance electronics will find that easy to work with, it only needs to measure ratio red/blue to determine the slope. Whereas fluorescent has a very 'peaky' SPD, with emphasis on (photometric?) visual light (green), energy efficiency considered more important to accurate colour rendering. I understand a fluorescent lamp has narrow-band red, green, blue phosphors, and I guess to make a 'daylight' colour appearance to the eye they simply add more blue and maybe remove some red, leaving green unchanged. Bottom line: Is colour temperature applicable at all if using CFLs? Maybe it's all three colours that need to be considered? (not just red/blue ratio)

Message edited by author 2011-12-28 16:52:06.

12/27/2011 09:45:23 AM · #3

I think thats a little beyond the scope. I switched to a Cell Phone camera after getting better results out of it than the Pentax K-r lol. How much more disappointed can you get. The K-r's Tungsten present worked with the 2700K bulbs just a little to the side of blue but it was okay. The noise was cruddy and some of the things I was shooting caused bad moire. Also got some artifacts when wearing a shit with 2 strips on it, looked very much like interlacing artifacts. Very weird.

Pretty bad when a higher resolution, smaller sensor is giving you less noise. Sure I have no focus control among other things but its working for my purpose. I haven't bought a CFL in at least 5 years that gave off a greenish hue. Even these 42W lamps that take forever to warm up mimic incandescent to my eye and camera. Anything that resembles correct is fine with me. I do not want my videos to look yellow.

I pose the question because I am buying the bulbs in a matter of hours. I stand to save 5-10 bucks a bulb and have already waste money buying bulbs that where okay with a one camera but not another due to white balance adjustment. On a pretty tight budget and pretty much ready to say screw this and not do the videos it at all.

So any clue if I might find Auto WB success with 5000-5500K bulbs that I did with 6500K in comparison to 2700K?

This was the K-r in tungsten setting, that wall isnt suppose to be that white but atleast its not yellow - //www.youtube.com/watch?feature=player_detailpage&v=sZsOLp1LAG8 This video does not show the moire problems I had with hour of footage i shot assembling the machine. It was also shot with only 300 watts equiv light (versus the 700 I am working with now) and all indirect I had yet to pick up the clamp lamps at the time.

I dont have anything I am willing to show for the cell yet but heres thumbs. The first one is under 700 watts equiv light, (Key, Fill and ambient) and the second was a quick test under 200 watts of ambient so it looks good for a test but not enough for actually shooting. The second might seem like there is a bit of green color cast but the light is in a floor lamp with a plastic cover and there is not much light. I normally shoot with the bulbs in clamp lamps with 10 inch reflectors.
2700K on preset (auto is worse)

6500K Auto

Another 6500K clip taken from the test video - //i1104.photobucket.com/albums/h337/RainMotorsports/clip.png
Anything out of a cell phone would be "disappointing" to most people. I am just trying to shoot some how to's. I am set on the CFL's question is how much more money do I have to spend I am working with a minimum wage paycheck here lol.

I am happy with the direction of the 6500K test went. I just need to know If i can stand to save some money. Switching to tungsten lamps can be a problem. The amount of power needed and the amount of heat generated. Ive sweated shooting these videos as it is.

Message edited by author 2011-12-27 09:58:47.

12/28/2011 04:27:04 PM · #4

Play safe stick with what you know works? (6500K) OK, it's a sum of money, but they last a long time, they're expected to last several years? If they're going to last 3 years, divide by three for cost per annum. Does it still seem expensive now? If you think so, back in the days of film there was a thing called 'photoflood #1' bulb and the lifetime was just hours!

As for whether success of auto white balance, doesn't look any way of knowing without actually trying it for real. Otherwise, is there any published data for the CFL's Spectral_power_distribution? Knowing that would answer the question. (edit: notice in that hyperlink how very 'peaky' the SPD of a fluorescent lamp is! It's a wonder a CFL works at all properly with cameras! )

You can do a crude approximation of an SPD measurement yourself. You probably want to do this anyway: Illuminate a white card with lamp under test. With the Pentax, shoot with the WB fixed, certainly never use auto on any account, I'd use daylight setting. Take a still of it into photoshop (or similar). Blur the image to eliminate grain/texture. Ideally, the white card would appear grey. With the 'eyedropper' tool, sample the colour and read off the RGB value. That'll tell you in numbers how far off you are from grey. Maybe you could add filters to lamp to compensate RGB balance at source.

Instead of using flesh tones test subject (you're using) I would be using nuetral grey test card instead. Or better a test card with graduated grey scale.

Another note: does your Pentax have a feature where you can alter the settings of the 'curves', the response of RGB? At default settings it would be 0=0, 100=100, for each the three colours. Tuning them accordingly would be the equivalent of fitting colour correction filters on the lens or lamps. Then you could use whatever lamp you want, including the cheaper CFL you propose.

Message edited by author 2011-12-28 17:02:04.

12/29/2011 12:34:16 AM · #5

I went ahead and ordered the 5000K, was a pretty short time between question and order. Auto white balance range usually starts at 3000 right? So at 2700K bulb type probably would never have come into the question right? Looking to improve my situation rather than perfect it. Using other than fluorescent bulbs means buying new lamps its not an option.

Given the amount of searching I have done it seems a question thats has never been answered. Given any bulb type does a higher color temperature help Automatic White Balance? I would still be asking this if it was not CFL. I get you that the colors are far from accurate at given points which can cause the AWB to make mistakes. But it already seems I can improve upon the situation that occurs with Incandescent bulbs and Auto WB and CFL's of the same color temp. I mean yellow looking video on auto white balance has haunted home video since before CFL's were common.

The Pentax is out, very bad video with usable white balance (though inaccurate, I dont care white things are not yellow and thats ALL I am aiming for). My Cellphone with its smaller sensor and higher resolution actually has less noise, which almost makes no sense. That combine with no moire problem makes for much better video. But since I cant get the white balance anywhere close to correct its a problem. 6500K CFL's much improved the situation to the point where more power is all I wanted.

I used the youtube thumbnails for the videos i shot. I only had my hand in the video for a matter of seconds. The actual video which was not for showing pans around a room of objects, white black, blue, silver, monitors on, etc. I was not intentionally using flesh tones for anything. The only purposeful thing in the shot is a white piece of paper with a large black circle.

I am just trying to shoot some video for youtube without it looking like complete crap. Lifetime is of little concern I will break them or they will die of defect first if not theyll last much longer than I will be using them. I just had a short amount of time to make a decision and literally will live better from having saved a few bucks.

Message edited by author 2011-12-29 01:08:36.

smardaz

12/29/2011 12:59:31 AM · #6

looks like you two are fine here, i'll keep moving.....

12/29/2011 01:02:21 AM · #7

Originally posted by smardaz:

looks like you two are fine here, i'll keep moving.....

:p Thanks smardaz, havent seen you guys in awhile Ive been gone. Its over with I appreciate marc's input and concern and I already bought the bulbs so its over.

Ill be sure to post my final sample video here to let you know how it goes. Thats actually the first video I am doing. Sample clip from a Samsung Galaxy SII.

Message edited by author 2011-12-29 01:07:04.

12/29/2011 10:14:51 AM · #8

You'll never get a straight answer when asking a CT question with a CFL. Here's why.

Theoretically, "Colour temperature" only applies to blackbody radiators, such as Incandescent lamps or the sun. Using the term ColourTemperature with other light sources such as fluorescent lamps is going to be tricky. Instead you have to consider all three RGB colours together. Modern cameras do allow this if you escape from the 'colour temperature' concept.
If you look at the image below, see the curve? That's the change in colour you see in a incandescent lamp. You can see all the white-balance colours from 1500K up to 10,000K.

Fluorescent lamps work on a totally different principle, they blend R,G,B light in a ratio determined by the amounts of coloured phosphors they coat the tube with. Not only that, the mercury lamp they are based on, shines through that coating, and these lamps have awful colour rendering. The only reason lamp manufacturers quote a colour temperature description of a CFL is for marketing reasons, so help a consumer choose what he thinks is the 'right' lamp.

What is the recorded RGB values via the Pentax when you shoot a neutral grey (or underexposed white) card? (as I described last message) Don't forget to set the WB to 'daylight', because if you'd set to Auto, the reading will be all over the place and you'll never get any repeatability.

Another reason for turning off auto WB is if you're always using the same light source you won't need to calibrate WB.

When you get the new lamps, how about redo a colour rendering test with the Pentax again? Just shoot a piece of white paper illuminated by the lamps. Be better if it's a grey scale. Then post link to a youtube film. Then it's just a case of defining a custom white balance for your choice in CFL. Done right you'll get perfect results.

Message edited by author 2011-12-29 10:29:44.

12/29/2011 02:35:01 PM · #9

Originally posted by m_a_r_c:

You'll never get a straight answer when asking a CT question with a CFL.

Another reason for turning off auto WB is if you're always using the same light source you won't need to calibrate WB.

When you get the new lamps, how about redo a colour rendering test with the Pentax again?

Okay well the point is the question is still a valid one if I switched bulb types. New lamps are out of the budget (Though the bulbs being cheaper might fix that) and using anything well over 100 watt will start a fire. Last I checked Metal Halide is out of the question even in equivalent brightness. Im looking at an incandescent equivalent of 400 watts here.

Once again.... I am not using the Pentax. Its video quality is horrible and the White Balance was not the problem for that camera. There is no manual white balance on the camera I am going to use and the presets don't match anything so far.

The quick test with the Samsung Galaxy SII did have a white peice of paper on the wall (the wall is not actually white). I will PM you links to tests done in the past.

Message edited by author 2011-12-29 14:57:04.