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ErikKaffehr
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« Reply #40 on: February 17, 2009, 11:41:16 PM » |
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Hi, On the last series I shot for Panopeeper I used manual exposure, starting from EV 0 (meter reading) and going down to EV -5. I have some considerations regarding going below say 1/20 s, because illumination varies with alternating current frequency. This flicker may not be noticable with floodlights but was very obvious with my simple flourescent daylight tube arrangement. Gabor suggested that I get an electronic ballast, that would solve the problem. Best regards Erik This should not matter if your printer delivers a smooth, uniform color. Please do not touch the surface with bare fingers if you want to avoid being fingerprinted.
Honestly I have no idea, how auto metering would look like; that's the reason I suggested to make first at least two shows with different underexposure. The darkest patch has to be in the 12th stop; this requires huuuge underexposure. Give it a try with -3 and -4 EV and let's see.
You can pretest it in ACR: pick WB on the white patch, reset everything to 0 (blacks too!), curves linear, then the black patch should show R,G,B in the range 2 to 4.
ADDED
I am an airhead. If you make only one shot (let's say with -4 EV), then I can determine, how much more or less is necessary. |
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marcmccalmont
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« Reply #41 on: February 18, 2009, 01:22:26 AM » |
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I printed the chart A3+ (gloss paper) and was going to shoot it during the day using diffuse sunlight if that's OK? or does it have to be repeatable day to day?
Are 1 stop increments OK (-3 &-4) or are finer increments necessary?
Marc
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Marc McCalmont
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Panopeeper
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« Reply #42 on: February 18, 2009, 01:34:08 AM » |
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I printed the chart A3+ (gloss paper) and was going to shoot it during the day using diffuse sunlight if that's OK? or does it have to be repeatable day to day? 1. Repeatability is not important. 2. Even the shots of the serie you are shooting could be of different setup, light, etc., I would not care. However, for demo purposes it is good if the setup is controlled and the shots are nicely with 1 EV difference as the ISO increases. 3. Sunshine is ok, but pls watch out, that you or the camera do not cause any shadow, not even indirect. I found out, that changing my body posture behind the tripod was enough to change the illumination, even though I was not between the light source and the scenery. Light reflected from the surrounding may change. I hope there won't be moving clouds. Are 1 stop increments OK (-3 &-4) or are finer increments necessary? One stop increment should be fine. Thanks; now I am off to bed. |
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Gabor
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Guillermo Luijk
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« Reply #43 on: February 18, 2009, 06:26:51 AM » |
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Gabor I was planning today to shoot a professional IT8 card I borrowed from a friend to calibrate my camera. Would you be interested in having the RAW files of it for an old fashioned little 350D? I gues I have to shoot all ISOs and at different exposure levels to ensure you have both blown and very deep shadows data.
BR
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Panopeeper
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« Reply #44 on: February 18, 2009, 10:26:06 AM » |
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Would you be interested in having the RAW files of it for an old fashioned little 350D? I don't know if anyone is interested today for the noise characteristics of the 350D, but perhaps for "historical reference" yes (as a documentation of the development). I gues I have to shoot all ISOs and at different exposure levels to ensure you have both blown and very deep shadows data I don't need any highlights, I know the saturation levels, among others from your shots of a computer monitor. The 350D behaves nicely, it always clips at 4095. I don't know if there are intermediate ISO steps and if yes how they behave, but I don't think that is important for anything. |
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Gabor
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Guillermo Luijk
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« Reply #45 on: February 18, 2009, 01:00:06 PM » |
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Not sure if I am happy, proud or offended to have an historical camera. Find here the RAW file at ISO100. However I have to shoot it again because I had a lot of problems with reflections for being this IT8 so glossy. If you prefer to wait till I get a more uniform copy and several ISOs I intend to do that tomorrow. This RAW file provides content for a quite wide range of EV:  |
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Panopeeper
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« Reply #46 on: February 18, 2009, 01:37:19 PM » |
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However I have to shoot it again because I had a lot of problems with reflections for being this IT8 so glossy There is a problem with the card: it's surface appears pearly. Otherwise the gray wedge strip at the bottom would be very suitable, but the texture gets counted as noise. See the attachment. |
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« Last Edit: February 18, 2009, 01:37:59 PM by Panopeeper »
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Gabor
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marcmccalmont
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« Reply #47 on: February 18, 2009, 01:48:00 PM » |
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Marc McCalmont
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Guillermo Luijk
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« Reply #48 on: February 18, 2009, 02:23:39 PM » |
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There is a problem with the card: it's surface appears pearly. Otherwise the gray wedge strip at the bottom would be very suitable, but the texture gets counted as noise. See the attachment. Yes it's because of the reflections. Tomorrow I'll try some darkening strategies (no idea which but I will; indoor rear lighting, defocusing a bit,...). |
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« Last Edit: February 18, 2009, 02:25:14 PM by GLuijk »
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Panopeeper
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« Reply #49 on: February 18, 2009, 02:52:39 PM » |
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Marc and GLuijk,
the exposure of the middle one, #1201 is ok; shutter 1/80. However, the illumination is not even, particularly in the bottom row, and there was some reflection on the last two patches. I see a pearly structure here too; GLuijk thinks that it comes from the reflection, but I am not sure if that is so.
Can you print it semi-glossy/satin, and on thick paper? One of the reasons of the pearliness is, that the paper is thin and its structure becomes visible. Hold the paper (not printed on) towards the light; is the structure visible?
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Gabor
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marcmccalmont
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« Reply #50 on: February 18, 2009, 05:44:51 PM » |
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Marc McCalmont
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Panopeeper
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« Reply #51 on: February 18, 2009, 05:54:08 PM » |
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Satin paper! Excellent! The illumination is very even, the surface is clean (i.e. free of visible texture) and the exposure goes into the 11th stop. Pls make the ISO set with this setup. |
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Gabor
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marcmccalmont
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« Reply #52 on: February 18, 2009, 06:35:25 PM » |
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Excellent! The illumination is very even, the surface is clean (i.e. free of visible texture) and the exposure goes into the 11th stop.
Pls make the ISO set with this setup. OK ISO 50, 100, 200, 400, 800, 1600 & 3200 same aperture same exposure just changing shutter speed. right? Marc |
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Marc McCalmont
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Panopeeper
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« Reply #53 on: February 18, 2009, 07:10:15 PM » |
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OK ISO 50, 100, 200, 400, 800, 1600 & 3200 same aperture same exposure just changing shutter speed. right? Right! |
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Gabor
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ejmartin
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« Reply #54 on: February 18, 2009, 07:19:13 PM » |
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There is a problem with the card: it's surface appears pearly. Otherwise the gray wedge strip at the bottom would be very suitable, but the texture gets counted as noise. See the attachment. Shoot pairs of images at each setting and take the difference image (and don't forget to divide the resulting std dev in the difference image by Sqrt[2]). Surface texture will then be largely irrelevant unless reflectance varies substantially across a patch -- such effects are second order in N/S. If one doesn't use difference images, one is opening the experimental technique to substantial systematic errors -- surface texture, illumination gradients, etc. |
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« Last Edit: February 18, 2009, 07:20:47 PM by ejmartin »
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emil
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Panopeeper
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« Reply #55 on: February 18, 2009, 09:07:17 PM » |
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Shoot pairs of images at each setting and take the difference image This requires a high degree of repeatability, which I do not assume. I take a different route: I carefully check the patches for even illumination, clean surface and close noise levels on parts of the patch. As the quasy same intensity level occurs in different patches and different channels, I can cross-check the results. |
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Gabor
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marcmccalmont
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« Reply #56 on: February 18, 2009, 09:41:48 PM » |
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Marc McCalmont
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Panopeeper
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« Reply #57 on: February 18, 2009, 10:52:16 PM » |
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Marc,
thanks, I got them. It takes some time to evaluate them, I will email you.
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Gabor
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ejmartin
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« Reply #58 on: February 18, 2009, 10:56:45 PM » |
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This requires a high degree of repeatability, which I do not assume. I take a different route: I carefully check the patches for even illumination, clean surface and close noise levels on parts of the patch. As the quasy same intensity level occurs in different patches and different channels, I can cross-check the results. On the contrary, taking difference images does not require a high degree of repeatability between shots, within reason (ie assuming one is using standard good technique -- tripod, manual exposure, manual focus, MLU, etc). As I stated, variations between shots lead to effects that are at most (N/S)^2 in the difference image, while variation within a patch for a single shot is of order N/S, where "N" here denotes the variation in surface reflectivity of the target. Have the person with the "pearly" color chart take a pair of images and see for yourself. As long as you're having people take images to order, it's worth doing it right. |
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« Last Edit: February 18, 2009, 10:58:28 PM by ejmartin »
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emil
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ErikKaffehr
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« Reply #59 on: February 18, 2009, 11:51:46 PM » |
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Hi Marc, Which paper did you use? I used a glossy paper and Gabor still seems to see some structure in my images. I could try to use the same paper as you did. Best regards Erik |
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