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Thread started 01 Feb 2018 (Thursday) 16:19
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help, please <3 - I am a Geologist struggling to find the proper camera settings (Canon Rebel XT)

 
Kat9055
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Feb 06, 2018 11:19 |  #76

Archibald wrote in post #18557358 (external link)
To be honest, if I were in charge of this, I would change things a bit. I would accord it some more priority because I think the results might guide decisions and that means it is important.

I would build an enclosure for it to reduce ambient light. The enclosure could be a cardboard box, but preferably something like a collapsible plywood thing. It is open on one side for easy access. It is painted flat white inside. It is big enough to contain the rig.

Wilt wrote in post #18557439 (external link)
This approach is sound in its taking over full control of the 'shooting environment' and eliminating any possibility of the shot being contaminated by variables. While professional photographers can control the variables, expecting a bunch of 'snapshooter' level scientists to do so is more than what we can expect.
The approach which I had espoused earlier also 'takes over control' by making ambient light contribute what is effectively 99.5% of the exposure, but I will admit that it is not as 'fully in control' as what Archibald suggests to be considered.

I agree, that would be ideal, but unfortunately we have to move really fast to keep up with drilling. Sometimes we drill more than 200+ feet a day with one person taking photos every 5 feet, in addition to writing descriptions and keeping detailed notes. We have a lot of other gear to carry as well and usually only one geologist per site, so whatever I can do to simplify, at this point, is my goal. The photos are mainly to track changes in the type of sediment and distribution, so I don't think it will need to be as high-quality as other geologists' photos may need to be. Hopefully knowing this information will assist us with other jobs (we are a consulting firm) that allow a more controlled environment!




  
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Feb 06, 2018 12:02 |  #77

Kat, if you've already identified your sediments and their contents, is it critical to get the colours spot on all the time? Are you expecting a new mineral or rock type to pop up in your samples?

I was going to suggest to use a large piece of black cloth such as flannel (bought cheap at Walmart) to use as a shade to kill ambient light, then it's only your flash illuminating your subject. Then you can simply use a Macbeth colour card to take your WB reference and shoot away. Use the shot of the card in post-processing to correct the WB on all other sample shots.


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Feb 06, 2018 12:07 |  #78

Alveric wrote in post #18557738 (external link)
Kat, if you've already identified your sediments and their contents, is it critical to get the colours spot on all the time? Are you expecting a new mineral or rock type to pop up in your samples?

I was going to suggest to use a large piece of black cloth such as flannel (bought cheap at Walmart) to use as a shade to kill ambient light, then it's only your flash illuminating your subject. Then you can simply use a Macbeth colour card to take your WB reference and shoot away. Use the shot of the card in post-processing to correct the WB on all other sample shots.

...and that is why I earlier specifically mentioned using a 36" - 48" black umbrella, even in direct sun it can reduce light intensity to f/5.6, where the ringflash has more than enough power to overwhelm the ambient 'shade' by 4EV.


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Feb 06, 2018 12:08 |  #79

Sorry, Wilt, I've been just skimming the thread after page 2, the amount of info is just too overwhelming.


'The success of the second-rate is deplorable in itself; but it is more deplorable in that it very often obscures the genuine masterpiece. If the crowd runs after the false, it must neglect the true.' —Arthur Machen
Why 'The Histogram' Sux (external link)

  
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Kat9055
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Feb 06, 2018 12:38 as a reply to  @ Alveric's post |  #80

I actually think that cloth would work well. It gets really windy where I live, which would make and umbrella difficult. Even in the shade, I was having issues with color and WB being off, so I think the flash was way too powerful, but I have created a spread sheet to test my findings over this next week. I will post what I have discovered thanks to all the help given here!




  
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Post edited 6 months ago by Kat9055.
     
Feb 14, 2018 12:00 |  #81

It took a while for the weather to behave, but I ran some tests using the information you all helped me understand. My colleague and I took photos using 2 separate cameras in the sun (using a shade) and in cloudy conditions. We used dirt, with a few large rocks to make sure the depth perception wouldn't cause blurring of the background. We used 1/2, 1/4, and 1/8 flash power settings, with ISO ranging between 100 and 400, and f-stop between F10 and F25, so every photo had one element changing at a time.

I then compared the gray card and white card values. Many of the photos came out with similar values, and all look far better than what we were using before. I am still trying to figure out which best represents my "sample". The vote so far is for F16, ISO200, flash at 1/8 power. The depth looks similar to what I saw taking the photos, where some look a little washed out, even with similar gray card and white card values.

Here is the comparison between the best photos, with "sunny day" on top and "cloudy day" beneath with the camera settings and gray and white card values. Let me know if you have any other advice! You all have been super helpful!


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Post edited 6 months ago by Wilt.
     
Feb 14, 2018 12:03 |  #82

Kat9055 wrote in post #18557775 (external link)
I actually think that cloth would work well. It gets really windy where I live, which would make and umbrella difficult. Even in the shade, I was having issues with color and WB being off, so I think the flash was way too powerful, but I have created a spread sheet to test my findings over this next week. I will post what I have discovered thanks to all the help given here!

Somehow there is a means by which the four corners of a black cloth are held outward without ribs to hold it open to shade the specimen area to be photographed, and this is less prone to being caught by a gust of wind (than an umbrella)?


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Feb 14, 2018 12:04 as a reply to  @ Wilt's post |  #83

I guess this would only work if I can convince the drillers to help hold the cloth, but the lid worked fine in trials so far!




  
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Post edited 6 months ago by Wilt. (2 edits in all)
     
Feb 14, 2018 12:16 |  #84

Kat9055 wrote in post #18563682 (external link)
I then compared the gray card and white card values. Many of the photos came out with similar values, and all look far better than what we were using before. I am still trying to figure out which best represents my "sample". The vote so far is for F16, ISO200, flash at 1/8 power. The depth looks similar to what I saw taking the photos, where some look a little washed out, even with similar gray card and white card values.

Here is the comparison between the best photos, with "sunny day" on top and "cloudy day" beneath with the camera settings and gray and white card values. Let me know if you have any other advice! You all have been super helpful!
thumbnail
Hosted photo: posted by Kat9055 in
./showthread.php?p=185​63682&i=i25287644
forum: Canon EOS Digital Cameras

thumbnail
Hosted photo: posted by Kat9055 in
./showthread.php?p=185​63682&i=i63242815
forum: Canon EOS Digital Cameras

Kat,
I brought your posted image into Lightroom and sample with the eyedropper, and what I find is that


  1. as exposed, the shots are a bit brighter than I would expect, if exposed per an incident light meter (or per the Canon in spotmeter mode reading a midtone gray (10% gray) card
  2. as currently White Balanced, the white tends toward bluish and the gray card is similarly bluish...which is not unexpeceted if your camera WB was set to 'sun' and you were shooting shaded or overcast. I suggest that you consider shooting the white or gray card to establish a Custom White Balance setting in camera for the JPG-stored photos to be truly color neutral.


Ordinarily an 18% gray card will have readings of 45-50 when 'properly exposed', whereas your gray cards read about 52-58. Your photos are therefore 'a bit brighter than inherent brightness', which might or might not matter to you...it might actually be preferable for brighter photo for your purposes. Being a dumb non-geologist, I would tend to place greater emphasis on correct White Balance than tonal (brightness) accuracy.

In sampling the white card, I note that typically it is about 80-85 on the scale, where I would ordinarily expect it to be about 90+

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Feb 14, 2018 12:37 as a reply to  @ Wilt's post |  #85

My gray card is an 18% gray card (RGB 119). I have the WB set to flash for both, because we have to all shoot with the same settings with the Canon Macro Ring. The gray card was brighter than I would ideally like and the white card slightly darker, but WAY better than what I was getting last month.

I shot in camera RAW and used Adobe Bridge to load the files into Adobe Photoshop layers. I used the eyedropper tool (averaged 31x31 pixels) over the gray and white card. This was as close I could make it. Then I exported the images as Jpeg and imported them into Adobe InDesign to create a comparison table.

I agree that the readings are slightly bluish, but I am not sure if I can find one camera setting that would solve all these issues, and it is so much closer than before. Do you know of something I could change to reduce the blue tint? I cannot use custom WB because we all must use the same settings (I know this is less accurate, but unfortunately, it is not my decision). They haven't changed the settings in almost 10 years, so it took some convincing to change them as it is.




  
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Post edited 6 months ago by Wilt.
     
Feb 14, 2018 14:09 |  #86

Kat9055 wrote in post #18563717 (external link)
My gray card is an 18% gray card (RGB 119). I have the WB set to flash for both, because we have to all shoot with the same settings with the Canon Macro Ring. The gray card was brighter than I would ideally like and the white card slightly darker, but WAY better than what I was getting last month.

I shot in camera RAW and used Adobe Bridge to load the files into Adobe Photoshop layers. I used the eyedropper tool (averaged 31x31 pixels) over the gray and white card. This was as close I could make it. Then I exported the images as Jpeg and imported them into Adobe InDesign to create a comparison table.

I agree that the readings are slightly bluish, but I am not sure if I can find one camera setting that would solve all these issues, and it is so much closer than before. Do you know of something I could change to reduce the blue tint? I cannot use custom WB because we all must use the same settings (I know this is less accurate, but unfortunately, it is not my decision). They haven't changed the settings in almost 10 years, so it took some convincing to change them as it is.

Kat,

Perhaps you need to increase your Contrast setting a bit, while lowering the Exposure setting a bit...that reduces the gray card brightness to the 45-50 range, while brightening up the white card to 90+.

The blue tint can be reduced via adjustment in post processing...look at the nnnK value currently reported in Photoshop and make it a bit higher so that white or gray are neutral (about equal in R and G and B channels) and simply set that value automatically when post processing all shots as a standard setting. Do not worry about setting value in camera since you are shooting RAW...it only affects the preview image (embedded in the RAW file), which Photoshop ignores anyway.

Just to verify that I was not talking out of my hat, I ran a quick test...overcast day at 9:25am PST

Gray card exposed per 7DII spotmeter; white card used same setting.
White balance set via eyedropper during postprocessing in Lightroom: 5650K
Gray card value (R-G-B) 52-52-52, white card value (R-G-B) 93-93-93, (with Brightness=0 and Contrast=0)


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Feb 14, 2018 14:10 as a reply to  @ Wilt's post |  #87

Thanks! I will try increasing the contrast and lowering the exposure. How much do you recommend changing them to start with?




  
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Feb 14, 2018 15:43 |  #88

Kat9055 wrote in post #18563775 (external link)
Thanks! I will try increasing the contrast and lowering the exposure. How much do you recommend changing them to start with?

-0.33EV Exposure in Lightroom brings 18% gray card exposure down from eyedrop sample 52-52-52, down to 46-46-46

then increasing Contrast to +50 in Lightroom brings up the white card back to the 92-92-92 values which were present before dropping Exposure by -0.33EV


BTW, it is not always necessary to reduce the indicated exposure to get gray card to record so that the peak on the histogram (for the card) is just to the left of midscale on the histogram. I just shot another test with gray card + white card under different lighting, and I got 46-46-46 for gray card (which is more like I would expect to happen) and 90-90-90 for the white card (the same gray card and white card used for prior test) using zero adjustment to Exposure or Contrast in Lightroom.


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Feb 14, 2018 16:00 as a reply to  @ Wilt's post |  #89

Thank you! I will try this tomorrow.




  
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Feb 14, 2018 16:08 as a reply to  @ Kat9055's post |  #90

Kat,
Your flash exposure is set at a fixed manual fractional output, I am not sure about your model flash, but some Canon flashes permit finer adjustment to manual settings,
such as 1/4 power -0.3EV, to reduce output by 1/3 EV. If not, simply tweaking Exposure in postprocessing allows you to bring back overall brightness to standardized level (so that eyedropper on gray card is alway is the 45-50 range, for exampe)


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help, please <3 - I am a Geologist struggling to find the proper camera settings (Canon Rebel XT)
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