I have been contracted to shoot a night tim cityscape in B&W that will be printed on a wall in an office. 30 feet wide by 6 feet high. I am shooting a Canon 5D mkiii with lens options being a range L series. Whats the best tactic to get the resolution high enough for such a large print that will be viewed from a close distance?
I'm going to cut straight to the answer — panoramic stitching — before the analysis.
I assume that you will only want to take a single-row panorama. That is, your final image will consist only of images stitched together horizontally.
When taking a landscape panorama, turn your camera into portrait orientation. This will give you more resolution in the vertical dimension. For your camera, this means you will have at most 5784 vertical pixels on your 30' × 6'. (In reality, you will lose a few pixels due to cropping the top and bottom, even under the best panoramic technique.)
Thus, when your mural is printed, your image will have a maximum print density of 5784 px / 72 in ≈ 80 PPI.
Drfrogsplat's answer to the question, "Is there a general formula for image size vs. print size?", gives us some useful formulae to help us determine the tradeoff between viewing distance and required print resolution.
According to that answer, somewhere between 53 and 100 pixels-per-degree (PPD) is considered "retina resolution", that is, the point at which the human eye can't distinguish individual pixels.
Using the formula
d ≈ PPD / (PPI * 0.01745)
where d is in inches, PPI is 80, then your "retina viewing distance" for a single-row panorama is 38"–72" (for PPD in the range of 53—100).
Now, the single-row panorama, combined with the required print size and the viewing distance, doesn't leave you much room for cropping, possible "de-warping" in software, etc. Your choices to deal with this are:
- Accept a lower spatial resolution (i.e., lower PPI, meaning possibly less-than-retina viewing);
- "Suggest" a farther viewing distance, to maintain retina viewing);
- Reduce the print size;
- Use a camera with higher resolution;
- Take a multi-row panorama.
(Obviously, 3. and 4. are not an option, based on the statements in your question).
As far as taking the panorama images, if you're not familiar with that, I suggest the following questions: