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Maximize Image Quality with Shot Discipline, Overview with Key Tips

This discussion is a condensed version of the series found in Medium Format Magazine.  The tips that follow are discussed and may be somewhat simplified here.

Anyone moving to medium format surely wants the best possible results, since medium format is a great expense and more of a hassle than smaller formats. Why bother with the bother if you are not getting the best results?

In this overview, I share key tips for making a technically optimal image, which among other practices I term “shot discipline,” a term I credit to Ming Thein and which he touches upon in his essay in the debut issue of the Medium Format Magazine. Shot discipline includes composition and lighting, but this overview will cover only the technical aspects. The related term “shot execution” refers to the full process of the capture. Shot discipline means consistently doing all the things that ought to be done for optimal results.

The three key elements of image quality are: dynamic range (subsumes noise), color fidelity and tonal gradation, and sharpness (more than just resolving power). Those qualities all have a maximum potential in any given camera system. Shot discipline is a systems approach in how to bump up against the limits in order to extract the full potential of the system as often as possible.

Executing for those three aspects of image quality fall roughly into three buckets: exposure, mechanical/physical settings, and shooting choices (an implicit fourth aspect is the camera system chosen to shoot with).

After a decade of photography in the field, often under difficult conditions, I’ve made just about every execution error that can be made and, with rare exception, never made those mistakes again after consciously committing to shot discipline that eliminated or minimized making the same mistake twice.   Shot discipline is thus about developing best practices and making them habitual.

A medium format large sensor along with “small” execution mistakes is a self-defeating approach.    The goal should be to developing shot discipline in a systematic way so that the hit rate for optimal or near-optimal image quality approaches 100%. Once the habits are encoded and subside into the background, most of them take little or not conscious effort, and what is left are the creative and artistic decisions.

Optimal results are more challenging than ever

Autofocus accuracy and dynamic range keep improving, but truly optimal results on high resolution cameras that approach the full image quality potential of the system_that is not so easy. I see it regularly when even highly skilled photographers send me images in raw format with execution errors (exposure, focus, etc).

Assuming a 44 x 33mm sensor and a high-grade lens: the optical quality is unlikely to improve after f/5.6 or so. However, field curvature and focus shift and focus errors and depth-of-field requirements all mean that on medium format, the use of f/8 is a good way to hedge your bets, for various reasons having to do with the zone of focus. 

Autofocus accuracy has been a major problem on all camera systems, but is greatly improved on modern mirrorless systems. Still autofocus makes errors, and shot discipline requires manual focus with many subjects.   Even if autofocus is spot-on, other issues can degrade sharpness, such as field curvature and focus shift and real depth of field being far less than theoretical.

Thus, maximal sharpness where desired is often a challenge and it’s about to get even more challenging. The medium format market is now moving to 100 megapixels on the same size sensor, making the photosites 1.4 times smaller linearly (half the area per pixel) and thus 1.4X as demanding for per-pixel sharpness. Focus accuracy and the placement of the zone of focus have to be incredibly precise, and lens and camera tolerances have to be held to extremely strict values. So-called “good samples” of lenses are going to be hard to come by at 100 megapixels since the slightest deviations will stand out with optimal shot execution. I have seen too many quality control issues already on 50-megapixel medium format; those same assembly errors are a disaster at 100 megapixels.

The irony is that 100MP is not really twice 50MP in practice because, in terms of per-pixel sharpness, 1.4 times less depth of field is available at the same aperture. Thus, more stopping down is needed for depth of field (in terms of maximizing per-pixel detail), but at the same time diffraction degrades the image sooner since the pixels are smaller. Pick your poison. Diffraction and depth of field are covered in my detailed articles in Medium Format Magazine.

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1. Focusing accuracy

 

Focusing accuracy is not just about what is in focus, but what is out of focus, together contributing the lion’s share of “visual impact”.  The zone of sharp focus is thus a key ingredient to visual impact. Even when stopping down fully masks a focusing error, there may be loss of visual impact because juxtaposing sharp versus unsharp is a key aspect of visual impact, e.g. a background that is too sharp and thus merges with the subject.  Hence the need for accurate focus, even shooting at f/11.

Sometimes focus has to be absolutely spot-on and even f/8 isn’t much help.   Consider a slightly out-of-focus iris of the eye in a close-range portrait. Recording 50 megapixels of full sharpness in a close-range portrait means focusing within a millimeter or so even at f/8. Now consider a sharp iris of the eye at f/2.8—very difficult to obtain reliably, since the photographer or subject need only move a few millimeters. And yet a blurry iris with sharp nose or sharp ears is a throw-away. This is why Eye AF is a “killer” feature.   To date, medium format mirrorless is a ‘fail’ in this regard, as compared to Sony mirrorless.

Focus Tip #1: validate focus accuracy of your gear regularly and under varying conditions, particularly with new untested gear.
Focus Tip #1: always verify focus using magnified Live View using manual focus if need be.
Focus Tip #3: field curvature may mean that off-center focus points very in focus distance versus the center; understand lens field curvature when choosing a focus point; all focus points are not equivalent.

Below, focus on the iris of the eye is ~2mm or so too deep. The image still works, but with more enlargement the slightly blurred iris would be visible.

L Chambers

1a. Assess camera autofocus

Manual focus (left), autofocus (right)

Camera autofocus is getting better and better, and indeed is quite excellent on the latest mirrorless cameras. However in years of testing I have found that it is sometimes optimal, frequently almost optimal, and sometimes way off. The latest 100-megapixel cameras will be unforgiving of tiny errors when the goal is resolving to the sensor. It’s not clear to me that the mechanical aspects of the lenses are even up to the task. Accuracy might be good with varying precision (scientific sense of both terms) = unreliable results.  Autofocus even in magnified Live View can deliver sub-optimal results.

With any camera + lens combination, shot discipline includes assessing focusing accuracy with every camera body and every lens you use and then applying that knowledge when shooting.

At right, this pair of actual-pixel crops was made on a medium format DSLR, the sharp one being manual focus, with f/8 barely catching up for the AF shot. I saw this type of error frequently with that camera (and with more than one camera body and multiple lenses)—it was inherently a below-consumer-grade AF system.

Tip: Validate the autofocus performance of new gear, particularly on medium and far distance scenes.  In particular, compare autofocus to the results from manual focus in magnified Live View.

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2. Optimize focus for key elements

The old rule of “1/3 in and stop down” is a non-starter for high-grade work on high resolution digital unless the key subject elements are at or near that focusing distance. High average sharpness results in a loss of visual impact when there are key subject elements that are almost but not quite sharp.

Excluding relatively flat, planar subjects (similar distance) and relative to the resolving power of the sensor, depth of field is shallow even at f/11. Maximize the visual impact by optimizing sharpness for the most important elements, which means considering the depth (distance range) over which the image is very sharp, and where that sharpness drops off, and how it affects the image.
Biasing focus at or very near the most important elements is the idea. It makes no sense to shoot a stunning scene of high mountain peaks with the peaks slightly blurry so that some unimportant foreground element is fully sharp—emphasize the key element(s) by making them sharpest.   There is an additional benefit to this approach in some cases: what is de-emphasized by some amount of blur makes the image more powerful by juxtaposition. Surroundings or context are often very important, but that purpose is usually well served by having the context recognizable—sharpness is not required.

Optimizing focus tip #1:  bias focus closer to key subject elements
Optimizing focus tip #2:  become expert at focus stacking.

In the example below, I could not obtain the depth of field I wanted at f/11, but I felt that an out-of-focus boulder or corners or immediate foreground, being prominent, would not be acceptable. But neither would a blurred distance.  I “cheated” using a 2-frame focus stack.

Near-to-far sharpness using focus stacking
f11 @ 1/500 sec, ISO 100; 2017-03-30 16:19:24 [focus stack 2 frames]
GFX 50S + Fujifilm GF 32-64mm f/4 R LM WR @ 25mm equiv (32mm)

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Lichen-Covered Boulder in Beaver Pond Meadow (“Impossible” sharpness near to far)
f11 @ 1/20 sec, ISO 64; 2018-11-16 15:15:48
[location “Lundy Canyon”, altitude 8150 ft / 2484 m, 55°F / 12°C, diffraction mitigating sharpening, USM{0.8,50,0}, focus stack 7 frames]
Hasselblad H6D-100C + HC 120 II @ 79mm equiv (120mm)

[low-res image for bot]

3. Use magnified live view

The newer medium format cameras offer Live View with magnification options.   Zooming in to 50% or 100% to focus  takes time, and that’s where the discipline comes in—pressing an AF button is so quick and easy! But it is poor shot discipline if time allows for verifying optimal focus, especially if a wider aperture is used, where a small error is really a big one.   The difference in focus on this tree can vary by a few feet with autofocus, depending on whether it picks up a leading branch or the tree trunk—don’t take the chance; focus in magnified Live View.

Live View tip #1:  use magnified Live View at full aperture (assuming no focus shift) to manually focus and/or use camera autofocus on that tiny area (when available). Cross-check manually if the image isn’t crispy crunchy sharp using autofocus as per the example above.

Live View tip #2:  check focus across the width of the frame also (because of field curvature).  There may be a slightly tweaked focus that is significantly better across the frame in overall sharpness but slightly less good at the point of focus. Stopped down a little, a substantial difference in total sharpness can accrue without sacrificing peak sharpness on the desired spot.

Live View tip #3:  choose a camera with a high-res EVF. Otherwise, use a high-quality loupe brand, like Zacuto.

Magnified Live view reduces the guesswork of autofocus on 3D subjects

4. Stop-Down Appropriately to avoid diffraction

There is no free lunch—stopping down to f/16 or guarantees substantial image quality loss in terms of overall contrast, micro contrast and sharpness.  At 50 megapixels it is obvious on a 44X33mm sensor, at 100 megapixels it is a disaster. Diffraction losses depend on pixel density, but as a rule for medium format, diffraction is a subtle factor at f/8 and the decline accelerates from there. It will be more noticeable sooner on a 100-megapixel camera versus 50 megapixels (assuming the same sensor size). Don’t just stop down as a lazy way of “focusing”.

Diffraction Tip #1:  do not stop down more than f/11.
Diffraction Tip #2:  become expert at focus stacking.
Diffraction Tip #3:  use diffraction mitigating sharpening (see Making Sharp Images at diglloyd.com).
Diffraction Tip #4:  use a tilt adapter (if available), however this is of no use on many subjects.

Loss of contrast from diffraction, f/5.6 through f/32

5. Eliminate camera vibration

The physical way the exposure is made has an impact on image sharpness. A fractional pixel movement (a few microns!) will look sharp and motion blur will seem absent, but the image will be oddly low on micro contrast—it will seem dull and not fully sharp. Larger movements create obvious motion blur.

Older medium format DSLRs have big mirrors. When that mirror goes up, the camera’s world is an earthquake. At certain shutter speeds, even fairly fast ones, sharpness is quickly lost. Although results will vary, the dangerous speeds are typically 1/2 second to as much as 1/125 second (or 1/800 with a long telephoto!). If the camera has an option for mirror lockup, use it and your results will improve. Consider two seconds the minimum delay after the mirror goes up to when the shutter opens, and longer for telephoto lenses.

Vibration tip #1:  use mirror lockup with self timer delay.
Vibration tip #2:  use the electronic first curtain (EFC) shutter option.

Medium format mirrorless cameras such as the Hasselblad X1D and Fujifilm GFX-50S solve the mirror-shake issue by having no mirror. The Hasselblad X1D has a leaf shutter in each lens and I have not been able to detect any vibration effects from the leaf shutters. Focal plane shutters can damage sharpness, so it’s important to use the electronic first curtain (EFC) shutter option if there is one. The Fujifilm GFX has several different options for shutter; that’s the one to use. The shutter is already open when exposure starts, finishing the exposure by closing.

Using an all-electronic shutter sounds good, but the sensor scan time is usually quite slow (e.g., a 1/4000 exposure might take 1/4 second to scan the entire sensor aka “transit time”), so it can result in the “jello” effect so disliked by videographers, except that the damage is subtler, like distorted shapes.

Electronic First Curtain (EFC) shutter on Fujifilm GFX-50R
Self timer option on Fujifilm GFX-50R

Below, shape distortion and smearing caused by all-electronic shutter—avoid an all electronic shutter except when subject and camera are guaranteed motionless.

Extreme case of image deformation caused by all-electronic shutter (bottom of frame)
f1.2 @ 1/5400 sec handheld, ISO 100; 2017-04-25 17:26:17
GFX 50S + Olympus Zuiko 50mm f/1.2 Auto-S @ 50mm equiv (41mm)

[low-res image for bot]

6. Camera-Photographer Mass coupling when shooting handheld

Handheld shooting has its own shot discipline: the manner in which the camera is held and the shutter released while exposing, contribute to sharpness. The worst possible technique is holding the camera out in front to view the rear LCD—the iPhone technique. Good shot discipline in handholding means another two or three shutter speeds of shooting envelope.

Shoot handheld using what I term mass coupling. The camera should be pressed firmly against the face or forehead or eye area, thus tying the camera to the head. This technique turns high frequency shaking into relatively slow overall body motion. Sharp images can be made at surprisingly low shutter speeds. For example, with image stabilization on the new Nikon Z7, I had many tack-sharp successes at 1/6 second and some at 1/3 second and I can reliably get tack-sharp images at 1/25 second (35mm focal length). It takes a conscious effort to develop the habit and it can be slightly contortionist, but it works incredibly well. Nearly everyone I see does it badly, having little contact between the eyepiece and the face area.
Below is an older image showing the technique plus a few more points:

  1. Mass coupling—camera firmly against head area.
  2. Both hands grasp the camera.
  3. Also press the camera against the shoulder (can be hard with small cameras).
  4. Pin elbow to side (when feasible).
  5. Take advantage of any nearby object to steady the whole body.
Things that can greatly help sharpness with handheld shooting

7. Nail-Down Optimal Exposure

Why worry about whether a new camera model has another 1/3 or ½ stop of dynamic range when incompetent exposure by camera auto-exposure gives up 1 or 2 or even 3 stops of dynamic range?  That is not an exaggeration, but typical of many cameras.

Optimal exposure is a Big Deal, yet many cameras use what I term “pre-internet exposure algorithms” based upon making a JPEG (or film) turn out with the right brightness. But in digital capture, the goal is maximal exposure for minimal noise and maximum usable dynamic range. To see that cameras do not work this way when metering, shoot an evenly-lit  uniform surface and observe the histogram won’t have anything much outside the middle. The camera’s goal is not optimal digital exposure but making an image of the “correct” brightness. That’s why I shoot either with manual exposure or with aperture priority together with exposure compensation; either way, it lets me nail the optimal exposure.  With some years of experience, I rarely give away more than ½ stop of dynamic range, versus a typical loss of 1.5 to 2 stops with most camera metering systems—and 2 stops equates to 1.4X the noise.

The optimal approach is to maximize the exposure without blowing out any important highlights. Referring to the histogram, the left side is dark tones and the right side is highlights. Thus ETTR (Expose To The Right), that is, expose as much as possible without blowing highlights. When converting from RAW, the image is pulled (brightness brought down) and things settle into place. If the exposure is one stop greater (2X), then certain types of noise decline by √2, if two stops, half the noise, etc.

On the computer, use RawDigger to validate that the raw file exposure.  It is notable that many test sites purport to evaluate noise but never verify that the actual exposure is optimal—GIGO.

RawDigger histogram: highlights preserved with maximal exposure
RawDigger histogram: highlights preserved with maximal exposure

8. Use the camera RGB histogram

Automatic exposure with most cameras regularly throws away a full stop or more of dynamic range, meaning that the image could take double the exposure without blowing highlights. In my experience, it can be as much as 3  stops. On the flip side, most cameras regularly blow out small but important details which are unrecoverable.

The camera histogram cannot be used in fast-paced shooting situations, but when it can be used, bake-in the habit of using the histogram for optimal exposures.  The camera RGB histogram (NOT luminance histogram) ensures optimal or near-optimal exposures if configured and used properly.   Regrettably there is no true raw histogram, showing exactly what the sensor captured without baking in white balance, contrast, color space, etc. Still, the histogram is the best tool at your disposal.

Best practices when making an image: examine the histogram, adjust the exposure, re-shoot if necessary. Usually I nail the exposure within 1/3 stop of optimal.

Best practices:

  • The RGB histogram shows what was actually captured in all three color channels, assuming an appropriate white balance is set. 
  • Set white balance to Daylight and keep it there, otherwise the histogram may hide a blown-out channel. When set to Daylight, the histogram is closest to what a true raw histogram would be (the foregoing assumes shooting raw format).
  • Assume the camera metering will be off; the histogram is authoritative.
  • Set the camera to the widest color space (e.g., AdobeRGB on most cameras) otherwise the histogram will show some channels as blown prematurely. Even so, AdobeRGB is grossly inadequate and some channels may be intact when shown as blown (e.g., bright saturated reds).
Magnified Live view reduces the guesswork of autofocus on 3D subjects

9. Block non-image-forming light

Veiling flare = loss of usable resolving power and sometimes an unusuable image at all. Some lenses have very high flare resistance and some are less good, but all suffer if sunlight shines on the front element (and the sun is not in the image). Always use the lens shade (usually inadequate) and, even more important, do not allow non-image-forming light to strike the front element.

Always shield the front element from any sunlight striking it (or any other source that is very bright relative to the subject). The difference can be subtle or dramatic, but it is always worth doing.

Keep front lens elements and filters spotless. If sunlight or bright light strikes gunk on the front lens element or filter, it *will* have an effect, often floating “ghosts.” Use only high-grade optical glass filters.

f11 @ 1/60 sec, ISO 64; 2018-11-16 14:33:45
Hasselblad H6D-100C + HC 120 II @ 79mm equiv (120mm)

[low-res image for bot]

 

Conclusion

It’s easy to raise a camera to the eye and press the shutter using autofocus and auto-exposure. But with medium format and especially beyond 50 megapixels, the risks of sub-optimal exposure and sharpness increase quickly.

Lloyd’s photography blog is found at diglloyd.com; it covers many brands, lenses, cameras including diglloyd Medium Format. To get the most out of any format requires perfect execution; see diglloyd Making Sharp Images. By subscription. Other areas Lloyd covers are cycling at WindInMyFace.com and computers at MacPerformanceGuide.com.

Lloyd Chambers, November 2011, White Mountains of California, Patriarch Grove
f8 @ 1/500 sec, ISO 80; 2011-11-07 12:52:56
M9 Digital Camera + Super-Elmar-M 21 mm f/3.4 ASPH

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