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08-24-2010, 10:54 AM   #1
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Red Tinge to Flash Pics

I have some experience with the K-x but very little with it and a Sigma 530 Flash. I took some pics of a baptism Sunday using the K-x, (software 1.0) on AUTO PIC, 18-55 AL lens, UV filter, Sigma 530 flash set at P-TTL and orientated to bounce about 70 deg with a hard plastic diffuser.

The lens is stamped "AL" but the EXIF data says "AL II" in Aperture but not iPhoto.

All of the pics were taken in a 40 minute period inside a church. If the lens was zoomed to >42mm the pics would have a strong red tinge with a few exceptions. All of the pics were from the same angle. An example of the Red Effect was taken at ISO 800, f 5.6,1/40, 55mm. Two examples that were OK for snaps, were at 800/ f 4.0,1/25,28 and 800,f 5.6. 1/30, 47.5.

If I was taking a pic at a different angle (90 deg to the right), all of the shots were satisfactory.

I'm thinking that the UV filter might not have been a good idea; I use it to protect the lens.

Suggestions to resolve this issue would be appreciated. Bill

08-24-2010, 11:13 AM   #2
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Lose the filter.

And any chance you were bouncing your flash off a red wall or something else colored?

Remember that for best and most efficient results, you have to bounce off WHITE.
08-24-2010, 12:45 PM   #3
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Ira, the church had a ceiling over 20 feet and was an off white. The vestments were emerald green (off to the left) and there was a stained glass cross in the wall of the building further off to the left that had deep blue, purple and reds. The puzzle for me is why I could take a pic at about 55mm and get the red effect (almost like I had a red filter on the lens) and a minute later I could get a more acceptable coloration with the lens zoomed to 28mm or so without changing anything else.

Thanks for your suggestion about the filter.
08-24-2010, 01:45 PM   #4
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I'm not seeing any example photos, although you've listed the exif from them above. Any chance of posting them so we can see what you are talking about rather than take wild guesses at a solution.

08-24-2010, 04:27 PM   #5
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If you have the K-x, the lens it came with is called the "DA L 18-55 blah blah blah". It's optically identical to the "II" version of the lens. See the sticky thread at the top of lens forum for more on the different versions of the kit lens.

Meanwhile, as said, toss the filter and try again, then post pictures if you're still having problems.
08-24-2010, 06:14 PM   #6
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Here are two pics shot within a few minutes of each other but may have different EXIF data. I never uploaded before so my fingers are crossed!! I'm using iPhoto to size the pics and had to got the the smallest option for both quality and size.
Attached Images
View Picture EXIF
PENTAX K-x  Photo 
View Picture EXIF
PENTAX K-x  Photo 
08-25-2010, 08:49 AM   #7
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EXIF shows shutter speed of 1/30th second, so I'm betting on fluorescent light interference. If you have a chance to replicate the situation, try some with everything the same except for a shutter speed of 1/60 or higher and see if the problem goes away or gets worse. If it gets worse, or changes the color of the tint, then that is probably the problem.

Last edited by Parallax; 08-25-2010 at 09:08 AM.
08-25-2010, 09:02 AM   #8
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Yes, both are 1/30, f/4.5 but one is ISO 400 and one is ISO 800. Could be pulling the ISO 400 exposure up two stops causes the problem or lowering the ISO 800 down 2 stops or something. The scene looks the same so I'm not sure why the 2 stop difference in exposure.

Have these gone through a RAW developer or the jpegs altered? What program are you using to view/edit the images?

As for the florescent interference, I had thought about that also but at 1/30, the lights should be able to fully cycle in that long amount of time. At faster shutter speeds, they might not and you will start capturing individual cycle colors. I don't think this is the problem.

08-25-2010, 09:11 AM   #9
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I've edited the above post for some clarification, but here is some additional. The color temp of the lights is not constant, it is waveform. Conventional wisdom says 1/30th is slow enough to eliminate color tint by allowing the shutter to be open long enough to capture the entire wave, but sometimes I have had to go even slower. You are using flash, so my reasoning that increasing the speed may eliminate it as well is that as speed increases, ambient light is a smaller portion of the exposure.
08-25-2010, 10:10 AM   #10
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A few things:

From ISO 400 to 800 is not two stops - it's only one.

Changing exposure one stop (or even two) would not have had such a noticeable effect on color.

As I see, there are two possibilities. One is the fluorescent light effect Jim mentioned. Fluorescent light changes color constantly, producing the *illusion* of white light, but a camera will often catch the light when it's in part of its cycle and appears to be strongly colored. 1/30" would normally not do that, but heck, I don't design the fluorescent bulbs, and can't say that's completely out of the question as an explanation. The other explanation is that the camera simply picked a different WB for the shots for whatever. Guessing the color of the light which is what AWB does - is an iffy proposition. the camera analyzes the scene and tries to figure out what color of light would have produced the reflected colors it sees. But dependent on the actual colors in the scene itself, these guesses can differ wildly. Consider, how can a camera kno the different between a red object in white light versus a white object in red light? Both will appear *exactly* the same. Although obviously these two scenes look very similar, the subtle differences that do exist (people with different colored clothing, different amounts of background showing, etc) might have been enough to have caused a bad guess on that second shot. Normally, small differences in a scene don't cause large differences in WB, but again, I can't rule that out. If you could repeat this effect in a controlled test, then shooting RAW and checking the WB after the fact would answer this.
08-25-2010, 10:43 AM   #11
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The one on the left says it is in "standard" mode and the one on the right says it was taken in "landscape" mode. Perhaps the white balance is different between these two functions?
08-25-2010, 11:27 AM   #12
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QuoteOriginally posted by Marc Sabatella Quote
A few things:

From ISO 400 to 800 is not two stops - it's only one.
doh, I knew that...just not thinking.
08-25-2010, 05:17 PM   #13
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From the exif I can see in all the shots, I cannot see any pattern that would lead to the Red Tinge.

I have posted more of the shots I took on https://www.me.com/gallery/#100030/_IGP1522. I cannot figure how to put the exif data on them so I have copied it below for some of the pics:

Format is Time, shutter, aperture, mode, zoom, ISO. Again, all of the pics were taken in the "Green" Auto Picture mode. In all shots, Flash was on, One Chip and Center weighted.

11 from end - 12-03-57, 1/20, 4.0, Normal, 25, 800 (Not Red)
7 from end - 12-04-15, 1/30, 5.6 Landscape, 47.5, 800 (Red)
4 from end - 12-04-27, 1/30, 5.6, Normal, 47.5, 800 (Red)
3 from end - 12-04-44, 1/40, 5.6, Action, 55, 800 (Not Red)
2 from end - 12-04-53, 1/20. 4.0, Landscape, 21.25, 800 (Not Red)

the rest of the shots data was within the ranges above.

I cannot duplicate the event so testing is not possible. I was not able to run any test shots b4 the event. The 3 shots I took before the ceremony started looked fine.

What could I do to avoid this Red Tinge "next" time?

Thanks for all your suggestions and the time it took for the analysis.

Bill
08-26-2010, 02:12 PM   #14
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For anyone that is still following this thread, I have some additional info. I have seen two videos shot with a Panasonic DMZ35 (super zoom) and a Canon T1i. The videos and stills from the Panasonic had good color (all shot full auto). The Canon's video (no stills) had a red tinge but not as pronounced as my K-x pics but none of the video was devoid of the Red Tint. Both the Panasonic and Canon were positioned in such a manner as to shoot in a direction that was perpendicular to my line.

The K-x shot about 100 pics at a reception that followed that had good color - none had a red cast. The reception was in a home, 12 foot ceilings, walls were tending toward a light mustard color between 1PM and 4PM. Some additional pics were taken outdoors and they were very satisfactory. No changes were made to the camera settings used in the Church for the Baptism. The Panasonic camera did not have any filter; I don't know about the Canon but I doubt it did either.

Would a faster shutter in a Shutter Priority mode be better in combination with manually setting the white balance to avoid the Red Tinge next time?

Again, thanks for the help.
08-26-2010, 05:08 PM   #15
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Hard to say without knowing the cause. It's either a random WB issue or the fluorescent light issue, but the solutions are entirely different. Either way, I'd assume it was a fluke of the situation and not worry about it unless it happens again.
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