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Photovision Calibration Target Review/Test
Old 06-20-2006, 01:48 PM   #1 (permalink)
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While I was at HTL I has the opportunity to work with Bill Ingalls, who is an outstanding portrait photographer. He showed us the setup that he uses for headshots, and let us work with it for a while. The other photographer that was working with Bill at that time was Eric Aschen, who had a Photovision calibration target. I've seen folks advocate this before, but I had never used one, and wasn't willing to drop $60-100 just to try it out. Fortunately, Eric had one of the targets and let me take a turn with it. Here's what I learned.

In short: it's cool, and I want one

Before I played with the target, I took this shot. I metered the light with my handheld incident light meter, and grabbed the exposure on the left. In post-processing, I adjusted the levels to get what you see on the right. As you can see, the original shot was a bit flat, but a "quick" levels adjustment brought the image to life. I'm pretty happy with the final exposure, but I basically had to "play" with the levels adjustment till I was happy. There was no clear way to make sure I had it right.




Now onto the target... The first thing you do is put the calibration target in front of the subject's face; in this case, the charming Julianna.

On the left, you see my original exposure. This is the "proper" exposure because the histogram is centered, not truncating either the highlights or shadows. On the right, you see what the image looks like after I loaded it into my photo editor and adjusted the levels. This levels adjustment was easier, and feels better because you have very clear "spikes" with which to work. I made this levels adjustment as an adjustment layer, to make workflow easier.





Then this is the next exposure I made. You can see that the original image is similarly muddy to the shot I took with the incident light reading. Incidentally (no pun intended), both my light meter and the Photovision target told me to shoot at f/11. I think the very minor difference in the two original exposures is due to the fact that I changed lenses, but I suppose it could also be small differences in strobe output or subject positioning. But I digress... So I simply coppied the adjustment layer from the calibration target over to this layer, and you see the results on the right. I think this is every bit as good as the result I got by "playing" with the levels on the first shot...maybe even better...and it was much simpler.



So in the end, I was pretty impressed with the target. I know you're supposed to be able to use it for white balancing, but I didn't test that feature...as I didn't know I was going to be able to do this till after I had already set my white balance, and honestly it didn't occur to me to fix what weren't broke.

I'm going to put this target on my photo wish list, and will likely pick one up soon. They come in sizes ranging from 6" to 32" (Eric had a 14"), and are probably a good investment for any studio photographer.

Thanks for letting me play with your target, Eric!

-Brian

PS There are some propaganda videos on their website, but I haven't had a chance to watch them yet.
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Re: Photovision Calibration Target Review/Test
Old 06-21-2006, 02:35 PM   #2 (permalink)
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Very informative post Brian.

Can you share any information about the lighting setup for the headshots?
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Re: Photovision Calibration Target Review/Test
Old 06-21-2006, 03:50 PM   #3 (permalink)
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Great post but let me see if I understand fully. Is the benefit of the target - not having to "eye" the levels adjustment by using the copy of the adjustment layer to correct exposure?

Cheers,
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Re: Photovision Calibration Target Review/Test
Old 06-21-2006, 04:02 PM   #4 (permalink)
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LSC, the target allows you to be sure that your exposure is "right" (read: blacks/whites not clipped) as well as easily adjust the levels.

Dman, there was a shoot-thru umbrella right at my left shoulder. There was a small softbox as a hairlight opposite the main. A background light behind the model. Then there were silver reflectors on both sides of the model, as well as below her (just out of the frame in the first pics).
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Re: Photovision Calibration Target Review/Test
Old 06-21-2006, 04:52 PM   #5 (permalink)
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Good post Brian. Very interesting.
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Re: Photovision Calibration Target Review/Test
Old 06-21-2006, 05:03 PM   #6 (permalink)
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Brian,

What is the target made of? I have tried this before with a cardboard card that came in a Photoshop Digital Photography book I have. It says basically what you said. Take a picture of the card under the lights once the lights are set the way you want, then use that picture to create your curves or levels (whichever you prefer). You then use that curves/levels for all the pictures taken under that setup.

Am I missing something here? Despite my best efforts, I have NEVER gotten that to work. The grey point always blows the picture out in some weird way (too blue, too green, etc.) I am hoping/thinking it has to do with the quality of the card that came in the back of a book (duhhhh!). Had you ever tried this using other test cards? Do others use this method with studio lights with good success?

Thanks in advance!

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Re: Photovision Calibration Target Review/Test
Old 06-21-2006, 08:36 PM   #7 (permalink)
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I'm not sure why you would get a color cast, unless you're using it to set the white balance and A) your camera doesn't like doing it that way, or B) the color of the card is off. I think I'm going to try making a card with a piece of black construction paper and an 18% gray card glued to a piece of white foam core. I'll post an update after I've had a chance to do that.

The Photivision unit is made of cloth, just like any collapsible reflector.
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Re: Photovision Calibration Target Review/Test
Old 06-21-2006, 09:15 PM   #8 (permalink)
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Out of curiosity...how do you copy-paste the levels adjustment in cs2? I have my photovision on order...
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Re: Photovision Calibration Target Review/Test
Old 06-21-2006, 09:56 PM   #9 (permalink)
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Brian,

Thanks for sharing the info with us, it's greatly appreciated!

Alan B.
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Re: Photovision Calibration Target Review/Test
Old 06-21-2006, 11:59 PM   #10 (permalink)
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Over the last several years I have posted a number of times on using the Calibration target. It is one of the most helpful tools you can find in digital photography. The 14" seems to be about the ideal size. Here is a photo of Dee holding the target:



When using the target, you must make sure to fill the frame with it during your test shots. Once you make the initial test shot, you then check to see if you have three full spikes in the camera's histogram (see final notes below). If not, you adjust your exposure and shoot again. Once you have three full spikes, then it generally is better to see if you can make micro adjustments to the exposure to move the three spikes as far right as you can without clipping the right spike. By doing this you are allowing MORE shadow data to be collected. Once you have the calibration done, the last shot of the target you took can be used as the reference photo for Custom White Balance. When I apply these above two steps in studio work, I find that about 90% of my shots need no post processing relative to levels and curves. I do usually adjust WB to go a bit warmer.

Another important thing to keep in mind, is that you must calibrate your camera's histogram with the one you use in Photoshop. They are not always the same and depending on whether you shoot RAW, or JPG, you may need to be aware of two calibrations (one for RAW and one for JPG).

Essentially, get a shot of your target perfectly exposed with three spikes as far to the right as possible without clipping. Now bring the shot into Photoshop and look at the histogram. Now set the camera beside the computer and bring up the photo you are testing one the camera's LCD. Compare the histogram and mentally note any differences relative to the right spike's distance from the right in the two histograms. Suppose you find that the spike in the camera's histogram is at the right edge, but about 1/2 stop from the right in Photoshop. That lets you know that you could actually slightly clip the spike shown in the camera. So ultimately you are going to adjust your camera exposure to produce the optimum histogram in Photoshop (since it is more accurate than the camera). You must remember whether to push the histogram right or left depending on what you see in the above test.

Cheers,
rfs
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