So I revisited this, this morning at around 9:30 am, in open shade, hazy blue-grey sky, Hanoi, Vietnam., October 19, 2011.
The quality of light could most be describe, in the shade as, “Cool Blue.”
So I set up in my courtyard, which is walled on three sides and semi-walled on the fourth…
…Placed a 18% Grey Card on a laptop, for support only, and the camera on a tripod. Using a normal lens I then filled the frame with the grey card and took a series of shots at f/8 and ISO 100. I repeated this for ISO 400 and ISO 800. At ISO 800 I needed to increase the f-stop to f/16. AWB setting, Manual focus, Av mode for the 18% Grey shot and the Manual mode for the rest. and fired away.
On loading the images into the computer and collating them into a strip, I couldn’t help notice a distinct blue cast to the images.
Even whilst in camera when each image was examined, the histogram showed a distinctly separated blue channel, right shifted well clear of the red and green channels which were more closely aligned. Significantly different from last night’s efforts under artificial light.
Studying online, I don’t really have access to my own Prof. Julius Sumner Miller to prompt me with a, “Why is it so?” So, I have to do the job myself. The issue here is one of white balance and it is clear that the Canon 7D, in this situation is not so good at guessing the correct lighting arrangement.
It took a correction of color temperature in Lightroom, and a minor tint tweak to bring all three channels in line with each other. I then applied this correction to all images taken this morning and this was the result…
I’m sure you’d agree that this is quite a difference. Now, I’m not new to this stuff. I’ve listened to Dean Colins on Lighting; watched Photoshop Cafe‘s “Perfect Exposure for Digital Photography” – The Zone System for metering and Shooting; and read through George Seper’s study notes for The Photography Institute‘s, “Professional Photography Course,” an a myriad other books, online sources etc. but I’ve never really “Got It.”
It wasn’t until I did this experiment, see the results under differing lighting conditions and make the connection with how my camera was actually functioning and why the images, sometimes were not what I wanted. Sure I’d post correct WB as a matter of course, but, it’s always so much better to get it sorted in camera before moving onto post production. the, “Ah ha!” moment has finally hit.
Moving onto ISO 400 and ISO 800 did not reveal any noticeable artifacts due to noise, or appreciable shifts in color, although Zones II and IV seem lighter than at ISO 100 and Zones VI-VIII seem somewhat darker, especially Zone VIII. Here…
This leaves me then with the following thoughts about my camera. The usable dynamic range is 10 stops from black with no detail to white with no detail. The camera favors, detail in shadow, but is fairly unforgiving with the details in the white zone, so highlights an bright detail needs to be carefully considered, whilst the shadows, will pretty much take care of themselves. the other thing that come to mind, is that I need to be mindful of how images might reproduce on paper, especially in print, which means that I may need to shift white with detail into Zone VII as opposed to Zone VIII due to the reduced latitude that paper has compared with camera/screen display.
Lots to think about, lots and lots. But the good thing is that now that I have a better grasp of this, revisiting the above mentioned luminaries means I’ll more fully understand the advice they are giving.
For today, that’s what’s in my
Line of Sight.