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10-06-2014, 09:25 AM   #1
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K-2000 Green Hue on left side of images

I have a K2000. The majority of times that I shoot a human model upon a black cloth muslin (6WX9H) using two constant light softboxes at 5500K under a white 10 ft. ceiling I discover upon reviewing the images while in post that I get a green hue on the left side of the image spanning the entire vertical area and varying widths to the middle of the image, sometimes bleeding onto the model if a full body shot or onto their hair if a portrait. I've attempted a manual white balance and it offered no change in the results. Any suggestions would be helpful. Thank you.

10-06-2014, 09:42 AM   #2
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Can you post a couple of examples?

Does it happen always or just under the described conditions?
10-06-2014, 09:53 AM   #3
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Yes, post some sample images. We need to be able to see what you're seeing. Make sure exif data is included. What kind of continuous lights are you using? Are they fluorescent by any chance?
10-07-2014, 04:36 AM   #4
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QuoteOriginally posted by rburgoss Quote
Can you post a couple of examples?

Does it happen always or just under the described conditions?
QuoteQuote:
What kind of continuous lights are you using? Are they fluorescent by any chance?
It only appears with the black background. Yes the bulbs in the softbox are fluorescent.

Here are some examples.

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10-07-2014, 06:36 AM   #5
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That is weird. I don't know what kind of arrangement do you have with both sofboxes, but seems to me that at least one on them has a defective bulb that is out of color temp. You could try switching positions of both lights, then use only one of them at a time. This is to try to pinpoint where is the problem originating.

Also, you haven't told us if your studio gets some amount of external light (next room, window, etc) and if your problem relates to this situation. Last thing would be to check your white balance setting. It should be for 5500K (as your lightboxes) and not to Auto WB.

Btw, are you shooting RAW or JPG directly? The idea is to Isolate one by one every factor involved: box1, box2, white balance, post processing software, external light sources, day or night... hey, even your computer monitor could be out of whack, tricking your eyes into erroneous adjustments.

Let us know your findings.
10-07-2014, 07:02 AM   #6
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QuoteOriginally posted by rburgoss Quote

Also, you haven't told us if your studio gets some amount of external light (next room, window, etc) and if your problem relates to this situation. Last thing would be to check your white balance setting. It should be for 5500K (as your lightboxes) and not to Auto WB.

Btw, are you shooting RAW or JPG directly? The idea is to Isolate one by one every factor involved: box1, box2, white balance, post processing software, external light sources, day or night... hey, even your computer monitor could be out of whack, tricking your eyes into erroneous adjustments.

Let us know your findings.
There is no external light in the studio.
I am shooting JPG, due to the lack of photoshop. The above examples are right off of the SD card.
I've rendered photos on three different monitors (2 different lap tops, and an external monitor) to see if there is a difference. The tint is there.
If you look on the stomach of the second model you'll see a yellowish tint, that tint shows as green on the black muslin of the first model.
10-07-2014, 11:11 AM   #7
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QuoteOriginally posted by KenShutter Quote
There is no external light in the studio.
I am shooting JPG, due to the lack of photoshop. The above examples are right off of the SD card.
I've rendered photos on three different monitors (2 different lap tops, and an external monitor) to see if there is a difference. The tint is there.
If you look on the stomach of the second model you'll see a yellowish tint, that tint shows as green on the black muslin of the first model.
Hmmm.. have you tried a series of "blank" photos. I mean, shooting at straight white backdrop or even a piece of paper. Shoot some frames at different exposure levels as to increase light drop (causing color cast) from whatever light source you are using.

Let us know. In the meantime, I will try to do some measurings on your pictures to see how much color difference is there from the left to the right of each picture.
10-07-2014, 11:21 AM   #8
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May not be anything but maybe fabric is dyed with a black dye that is green based? And the light is reflecting that. black paint and dye can be blue, green, red based.

10-07-2014, 11:42 AM   #9
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Ok, here is a fast analysis of both your pictures:

On the first photo, I blended in all the gray shades of the backdrop on two sports (to take a fair reading of the average dominant color). As you can see, the difference is not much but there is one, throwing a yellowish cast to the left of the frame. On the second picture, the green cast is very evident so I just did a little brightness and contrast adjustments. The backdrop reads almost 99% black (RGB-5-5-6) on both sides, so there is no color cast difference in the backdrop, but the model's skin is another story.

It seems as there is some kind of light contamination in your study. Is there something green/yellow big enough and close to the backdrop, as it can reflect its own color into the frames? (like a carpet, drawer, etc).

Anther suggestion. Do the white paper tests using the camera horizontally and vertically. We also have to rule out the camera sensor as being defective. You can use standard letter size papers, clipped to the black backdrop at several positions. Don't forget to include the whole backdrop in a single frame (as shooting portraits as the examples uploaded)

Last edited by rburgoss; 11-06-2014 at 08:03 AM.
10-07-2014, 01:08 PM   #10
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@rburgoss That's really cool. Thanks. The floor is all black canvas. But to the left I have a short cowboy studio black muslin, tripod and horizontal member kit that's not as tall as the back drop, it's 6ft. not eight foot. 30" beyond that is a wall that is a dark beige. Perhaps that's coming through? But wouldn't the tint only concentrate at the 6 to 8 ft level of the photo? I'll do the white paper tests and post the results. Thank you.
10-07-2014, 02:29 PM   #11
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The only idea I have is a light leak through the viewfinder. You'd have to have a pretty terrible setup to induce that, like a spotlight shining directly into the eyecup.

Oh, another idea: put the lens cap on, viewfinder blind on, a dark room turn off AF, ISO to maximum, mode to bulb, and hold down the shutter button for a few seconds. The image should be dark with a lot of noise. A green tint on one side is bad.
10-07-2014, 05:50 PM   #12
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QuoteOriginally posted by Just1MoreDave Quote
The only idea I have is a light leak through the viewfinder. You'd have to have a pretty terrible setup to induce that, like a spotlight shining directly into the eyecup.

Oh, another idea: put the lens cap on, viewfinder blind on, a dark room turn off AF, ISO to maximum, mode to bulb, and hold down the shutter button for a few seconds. The image should be dark with a lot of noise. A green tint on one side is bad.
Any light leak into viewfinder will only fool the light meter, causing underexposure, but once the mirror is up, no light from viewfinder side can reach the sensor.

This is a matter of first pinpointing where is the problem coming from. In this case it could be one of three things:

1 camera ( this would be very rare. only way to rule out camera is by using another camera under the exact same conditions as when the problem is produced)

2 studio, from light source contamination from windows, colored large objects, etc.
good

3 light sources. those fluorecent light boxes work very nic, but it take onle one tube or coil bulb out of specs to screw up things.

Another thing to think about: It seems this happens only when you use your black (dark) backcloth. Did you know that some fluorescent light souces, also emit "non visible" light waves (ultraviolet), and UV lights make certain chemicals "glow" in the dark?

It wouldn't be strange that the combination of your light boxes and your black backdrop, causes some green low level fluorescence that reflects over light colored nearby objects. Who kows, maybe the cloth manufacturer used some color dyes, starches or whatever chemical they use to promote or avoid certain conditions, for example, something like Scotchgard or a fabric softener.

Flip the backdrop left to right and see what happens!
10-07-2014, 09:08 PM   #13
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QuoteOriginally posted by rburgoss Quote
Any light leak into viewfinder will only fool the light meter, causing underexposure, but once the mirror is up, no light from viewfinder side can reach the sensor.
It can. That's why you get a viewfinder blind (until recently). It's not the most likely problem here, because the light difference has to be extreme - like sunlight shining in the eyecup and an 8 stop ND filter on the lens. Even in that case, you only see it because you're probably not holding the camera up to your eye, shading the VF with your head.
10-07-2014, 10:03 PM   #14
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QuoteOriginally posted by Just1MoreDave Quote
It can. That's why you get a viewfinder blind (until recently). It's not the most likely problem here, because the light difference has to be extreme - like sunlight shining in the eyecup and an 8 stop ND filter on the lens. Even in that case, you only see it because you're probably not holding the camera up to your eye, shading the VF with your head.
The viewfinder blind is used to prevent stray light entering the viewfinder and throwing the light measurement into a false reading. This is very usual when tripods are used in combination with ANY auto exposure mode. Of course, if metering and EV combination chosen is manual, any stray light will make no difference.

As I said before, once the shutter is pressed and the mirror goes up, no light coming from the viewfinder will affect exposure value neither reach the sensor, because the whole viewfinder assembly (focus screen, prism and eyepiece) is blocked from the sensor area by the mirror itself, which during that short moment, is stuck flat against the focus screen.

If light was able to reach sensor from viewfinder DURING the actual exposure (picture taking) then you should be able to see through the viewfinder too. Do the test. Do you know why the viewfinder goes dark guring this instant? Because the mirror is UP doing two things: first, letting the projected image from the lens reach the sensor, and second, blocking any stray light comin in from the viefinder side!f

But don't take my word for granted, instead, do this othe test: Grab any DSLR ( MIRRORLESS NOT USABLE FOR THIS TEST SINCE THE WHOLE PUPOSE IS TO PROVE THAT THE MIRROR BLOCKS THE VIEWFINDER DURIvNG ACTUAL PICTURE EXPOSURE). Remove lens; set amanual shutter speed of 1/2 second or longer. Better set speed to B ( bulb). Now, while staring right into the lens mount, where you can see the mirror and the focus screen, now press the shutter!

Don't panic! The Mirror did did not dissappeared! It just flipped up, OUT OF THE WAY BETWEEN THE LENS (IF MOUNTED) AND SENSOR. AT THE SAME TIME, ARE YOU ABLE TO SEE THE FOCUS SCREEN? I bet not even a hint of it with the mirror up.

BTW, Pentax supplies the viefinder blinds with ALL cameras capable of auto exposure. I still have the one that came with my K2 DMD from 1976 and my ME Super from 1979 (that is 38 and 35 years ago), which can hardly be considered as "just recently". Can't talk about the screwmount era (Spotmatics) even though I had a couple, neither was purchased new and neither had an auto setting.

Last edited by rburgoss; 10-07-2014 at 10:16 PM.
10-09-2014, 05:21 PM   #15
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QuoteOriginally posted by rburgoss Quote
no light from viewfinder side can reach the sensor.
Not so. A simple and alarming test is to flash a strobe (off camera) at the viewfinder in B-mode or using a PC sync cable. The mirror is not light-tight against the focus screen.


Steve

BTW...neither is the non-WR K-mount...
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