August 2009 Newsletter (Simplify Zone System)

Hello Raw Shooters

The digital era has changed how we store our images. In old days we used archival sleeves and binders to store negatives and slides. Now storing digital files and keeping them safe can be a little challenging for some of us!  Here are some suggestions:

 1. Back up images on an external hard drive or burn to CDs. The cost of external hard drives has come down and is a faster and better option than burning CD/DVDs. The downside of this option is if you need a picture, you need to access and search your external hard drives or CDs. You must be very careful to store them in a safe place, and spend some time to maintain them. But it is very important to have a good back up of your photos!
 2. You can use our safe and secure remote backup service. It is very affordable and you have access to your important file 24/7. Simply log in to your account to upload or download files from/to any computer at any time. The cost is only $6.99 per month for up to 30GB of storage capacity and you don’t need to install any extra software or doing any maintenance.  Contact us at

mailto:info@rawdigitalimageediting.com

to inquire about our easy to use remote backup service and let us set up a storage account for you! 

Now let’s get to our monthly tip:

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Exposure compensation and Zone System
(Part 3)

We all remember the rule of thumb for film photography which says: “Expose for the shadows, develop for the highlights.”
What’s the rule of thumb for the digital era?  That is a very good question!  I’ll try to answer this as simply as possible.

With digital, we can no longer play around with development times. But there are two things that make digital photography very well suited for the Zone System. One of them is that unlike film, we can process each RAW file individually (so in that sense, it is just like sheet film). The other is our ability to move specific tones between zones through RAW digital image processing.

Unlike film, which has great exposure latitude at the highlight end, digital is very unforgiving in the case of over exposure. Detail that is lost through over exposure is clipped and lost forever. For this reason, we never want to overexpose highlights to the point of photon well overflow - not even in a single color channel. That introduces clipped areas with absolutely no detail in the channel.

So why should we not simply place shadow detail in the lowest possible Zone? That should at least do the most to contain our highlights within safe limits.
The problem is that if you do this, you are wasting lots of the pixels that the camera can capture.

Unfortunately, this is not how things work out in practice. The linear capture of the camera's sensors means that if we try to capture a 9 EV range, corresponding to 9 zones, half of the 4096 levels (2048 levels) are devoted to Zone IX, half of the remainder (1024 levels) are devoted to Zone VIII, half of the remainder (512 levels) are devoted to the Zone VII, and so on. Zone V is represented by 128 levels, Zone III by 32 levels, and the extreme shadows in Zone I is represented by only 8 different levels.
This means that if you try to underexpose to avoid clipping the highlights, you are running a significant risk of introducing noise and banding in the mid tones and shadows. When you, as a result of underexposure, try to open up the shadows in the RAW conversion, you have to spread those 8 levels in the darkest stop over a wider tonal range, which exaggerates dark current noise and increases Banding (quantification noise).

So now we can create our digital exposure rule of thumb which says: “Expose for highlights, process for shadows.”

Here is an example of how Visualization works.

    1. First, we survey the scene, and identify the area containing highlight detail             that   we would like to reproduce in the final print.
    2. Spot meter that area. The meter will record a value that translates into                     aperture, shutter time and ISO to place this part of the scene in Zone V.
    3. Visualize the Zone we want highlight detail to appear in, in our print. Let's               say we want it to appear in Zone VII. Moving the area from Zone V to Zone             VII requires an exposure adjustment equal to +2 EV.
    4. Make the adjustment to the camera's setting, and expose the image.


Now we’ll have recorded a RAW file where the highlights should be where we want them. However, our shadows will be too light. And we arrive at the second half of the digital rule of thumb for exposures: process for shadow.

Conclusion:

I encourage you to try the Zone System for those hard lighting situations and send your files to us for professional RAW processing.  I’m sure you’ll see improved results from your DSLR with images you’ll be very proud of. Understanding and using the Zone System in digital photography takes practice and patience, but it’s worth the time and discipline involved.

Have a good month of August.  See you again in September.

Ted and Omnilargess Team

 

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