The importance of shot discipline


_7035186 copy

Miss it, and the moment is gone. Procession, Nepal. Nikon D700, 24/1.4

Repost: I’ve been referencing this particular early article so often in posts and emails that I think it’s high time we had a reminder. I’ve dusted it off, refreshed it a little. We’ll start by defining shot discipline. There are two main aspects: timing and technique.

[Read more...]

Clearing up the myth of higher resolution, shot discipline and image quality once and for all

Empirical observation #1: Cameras with higher resolutions, for a given sensor size, are harder to hand-hold and get a good result than those with a lower resolution.

And I define a good result as one which the image is critically sharp at 100% actual-pixels view, with no motion blurring or other artefacts such as slightly missed focus (we’ll get to this later). Motion blur is when the camera moves by a greater amount than a pixel during the time when the shutter is open; if it’s less than this, then you see either hard edges on your subject as a perfect sharp edge, or with slightly lower contrast than expected due to the image projected by the lens on the sensor plane ‘spilling over’ into the next adjacent pixel slightly when the camera moves.

The simple reason why higher resolution cameras are less forgiving is that for a given angle of view, the camera with the high resolution will put the greater number of pixels per degree of field of view on the subject. This means, that less angular movement is needed before it becomes visible as blur on the image – i.e. you need to be more static than with a lower resolution camera to avoid seeing the effects of motion blur at the pixel level.

But what about the image when viewed as a whole at the same reproduction size? If we started out with a huge number of pixels with both – say 24MP and 36MP and resized both them down to say, 4MP or so – we would not see any difference between two cameras assuming one assuming both were equally downsized. This is because the downsampling process has enough information for each pixel to accurately determine its color and luminance value and therefore appears as true detail. If we downsize 36MP to 24MP, it might or might not look better: a lot of the outcome depends on the interpolation process. It isn’t a ‘clean’ situation where each new, downsized pixel has multiple pieces of information (the original pixels) to form an average that would be the same whether you used 8 or 12 pixels originally. Since 36 doesn’t divide cleanly into 24 – you get 1.5 old pixels per new one – there’s always going to be some guesswork as to precisely how that half pixel is allocated. And depending on the algorithm, any one of the following might happen – blur edges; stairstep artefacts; haloes or abrupt transitions; odd discontinuities in diagonal lines.

Let’s take an example: if you have a scene shot with 12 (8.45um pixel pitch) and 36 MP (4.88um pixel pitch) cameras, and both are equally motion-blurred. The degree of camera shake may be less than a pixel on the 12MP camera – let’s say 5um for argument’s sake, which will still produce a critically sharp image. However, the 36MP camera is now blurred by more than one pixel, which definitely will not look critically sharp at 100%. Yes, we can downsize – but you are downsizing not to 1/2 of the original linear dimension (which would yield 8MP, and bin the two blurred pixels into one sharp one that looks perceptually okay), but to 1.7x of it – and once again, we run into potential issues in trying to fit discrete, nonlinear data into a linear continuum.

This is one of the reasons why less pixels might actually produce a perceptually sharper/ crisper image for a given reproduction size, providing that this size is reasonable for the amount of resolution you’ve got in the smaller image.

The upshot of all of this in practical shooting is that you’ll need to use a higher shutter speed than you expect, which lowers your shooting envelope by a corresponding number of stops as noise increases as you ramp up the sensitivity to keep shutter speeds high. Perceptually, if you’re going to be shooting under already borderline conditions to get a critically sharp image with a 12MP camera, you’re not going to get one with a 36MP one – even if you print them at the same size.

Empirical observation #2: Cameras with higher resolution require more precise autofocus.

Comparatively, this one is very simple to explain: if the camera misses focus, the resolving power of the lens is diminished. You need to have the ability to resolve slightly smaller structures than the pixel pitch of the camera in order to create a perfectly sharp image at the sensor plane. If you miss focus by an arbitrary amount – let’s say 1% of your subject to camera distance – this may result in a loss of resolution corresponding to the inability to resolve structures below 5um in size. For our 36MP, 4.88um pitch camera, this will appear to be a blurry shot. For our 12MP, 8.45um one, things still look critically sharp.

A lot of what we’re seeing isn’t necessarily worse autofocus; what’s happening is that we are now visibly reaching the limits of tolerances and precision since sensor quality is now high enough to resolve at or close to the previously acceptable tolerances.

A lot of the reasons why an image appears sharp or not has to do with the reproduction medium, as well as how our eyes interpret information: an image with hard edge is seen to be ‘sharper’ than an image without one, even if there is less fine detail or edge definition. The fact that digital capture splits out our images into distinct zones – the pixels – doesn’t help this at all, either. It’s important to remember that a slightly blurred image (depending on the degree of blur, of course) from a higher resolution camera may technically still have more detail, our eyes don’t necessarily pick up on this; it’s a perceptual thing. Bottom line: don’t use more pixels than you are capable of handling properly for a given situation. It’s one of the reasons why I don’t shoot the D800E for casual work…but it’s also the reason it’s my camera of choice when I have full control of the execution. MT

____________

Visit our Teaching Store to up your photographic game – including Photoshop Workflow DVDs and customized Email School of Photography; or go mobile with the Photography Compendium for iPad. You can also get your gear from B&H and Amazon. Prices are the same as normal, however a small portion of your purchase value is referred back to me. Thanks!

Don’t forget to like us on Facebook and join the reader Flickr group!

appstorebadge

Images and content copyright Ming Thein | mingthein.com 2012 onwards. All rights reserved

Achieving ultimate image quality*

*Both with what you own, and what you don’t.

This seeds of this article started to plant themselves in my mind during a recent assignment. It dawned on me that my shooing style had been slowly changing over the last few months; from trying to run and gun handheld with speed and (mostly) precision, I was now bolting everything down to a 5-series Gitzo Systematic, hydrostatic ball head and geared head, shooting at base ISO at optimum apertures and compositing my shots. Oh, and bringing in lighting. I can only suppose this represents the next step in my evolution as a photographer, as my work becomes increasingly skewed towards commercial and less documentary/ ad-hoc/ personal. (I, and my bank balance, can only hope that medium format isn’t next!)

That said, there’s a right and a wrong way to go about the technical aspects of shooting. I want to cover tips on how to obtain the maximum image quality from your equipment under three different scenarios: firstly, handheld with the gear you own; without upgrading or buying any more gear, and finally, a hypothetical what-if scenario if the sky was the limit. Shot discipline basically boils down to two things – support/ stability, and optics. The former resolve as camera shake issues; the latter as softness and a general lack of resolution. I’ll address both here.

Handheld and making do
This scenario assumes you don’t have a tripod, and you’re shooting available light.

1. Watch your shutter speed. Make sure you don’t fall below 1/2x 35mm focal length for critical applications, or 1/35mm focal length if you have no choice. If you have IS or VR, you can safely shoot at twice as long a shutter speed as without; just make sure you give the VR or IS system a second or so to lock in first.

2. Use Auto-ISO, if you can control it. Auto-ISO may be derided as being for amateurs, but the reality is that it helps you to maximize image quality by giving you precisely the sensitivity you need and nothing more; if you increase ISO beyond what you need to get a decent hand-holdable shutter speed, you’re going to also incur unnecessary noise. This of course assumes that your camera allows you to set the minimum shutter speed and maximum ISO; not all of them do. The better ones automatically default to 1/focal length.

3. Check focus. This seems obvious, but relying on your camera to decide what should be in focus is a huge mistake. Pick the AF point, make sure you’re using continuous AF in case you or your subject moves – for very fast lenses, less than a centimeter can make a huge difference to the final result. I typically tap the shutter a few times to confirm focus and even defocus a bit manually and reshoot if I’ve got time. Inevitably, there will be variations in sharpness between frames; sometimes due to camera shake, sometimes due to the focusing system. Especially at the edges; not all lenses are flat-field, and some may have field curvature issues to take into account.

4. Use optimal apertures. Spend some time figuring out at what apertures your lenses perform best, and how this changes if you’re focusing at the borders or edges. Very few lenses deliver optimal performance wide open. Some lenses can also move their point of best focus on stopping down (‘focus shift’); this matters because all AF systems focus with the lens wide open. It’s important to know that even if your depth of field at f8 covers focus shift, it might not extend in the direction you were expecting.

5. Control your breathing. Exhale slowly as you release the shutter; the camera is coupled to your body either via your face (viewfinder) or worse, held at arms’ length; if you’re breathing hard when you take the picture, this motion transfers to the camera, which results in shake and softness.

6. Shoot RAW. A no brainer: keep all the image data your camera can produce. Storage is cheap. Near misses are more frustrating than not having the opportunity to shoot something at all.

7. Nail exposure. Getting exposure right, or as close to it as possible in-camera minimizes noise from shadow recovery or posterization and odd colors from highlight recovery afterwards. It gives you the maximum amount of dynamic range to work with. Note that getting it ‘right’ doesn’t mean making it as close to the final desired exposure as possible, it almost always means exposing to the right so that the highlights just clip – this keeps as much of your shadow data out of the lower, noisy, bits of information as possible. You can always reduce the exposure later with no penalty to image quality, but it isn’t the same in reverse.

8. Shoot bursts. Bursts minimize the effects of jerky fingers on the button, as well as giving you a couple of extra shots as insurance. This is especially important under low-light (read: dodgy shutter speed) conditions, as well as fast-moving events where anything could happen.

9. Watch your stabilization system. Stabilizers all involve a moving element of some kind to counter motion – they don’t work well with high frequency motion, simply because there’s a limit to how fast things can reasonably move. If your shutter speed goes above a certain threshold – generally 1/1000s or so – then the moving parts in the camera can create a minor vibration that won’t cause visible shake in the image, but it will trigger the stabilization system to try and compensate for it – and it usually overcompensates, resulting in a double image as it snaps from one place to another. Turn it off if your shutter speed is high enough. At the opposite end of the spectrum, giving the stabilizer a second or two to ‘bed in’ before you shoot can make a huge difference to its effectiveness. Mashing the shutter all the way down simply does not give the stabilizer enough time to lock in.

10. Stand firm. If you can’t bring fixed support, then be your own support. Find something firm to brace the camera on, or at very least, have both feet firmly on the ground. Tiptoeing or holding an awkward angle is almost certainly going to result in camera shake.

11. Don’t jerk around. Be smooth when you release the shutter – roll your finger over it and gently press, don’t stab at it. Use the half press position to lock in or activate focus, then just add a little more pressure to release. You’ll be surprised how much difference this makes to the sharpness of your images.

Under ideal circumstances, but you’re not allowed to buy anything
This is effectively how I approach my current assignments. Note: many of you will be surprised by just how good the image quality from the current generation of compacts can be, if given enough light, careful exposure and used on a tripod. My earlier article on the use of compact cameras for professional work shows some examples of that – and at that point, we didn’t even have such interesting options as the Sony RX100.

1. Support is critical. Although I both of my tripods and heads are rated far beyond the maximum equipment load I have – a light Gitzo 1542 Traveller and a much heavier Gitzo 5562 Systematic, I seem to be using the 5562 all the time. It’s simply as sturdy as a rock: the thinnest leg section is about an inch in diameter, which is much better than metal for damping vibrations. I don’t even use a column; the head – a Manfrotto Hydrostat – is bolted directly to the large platform. This tripod is so sturdy I can sit on it (without the head, of course) and the thing doesn’t move or flex. Simply no comparison to shooting handheld – there’s just no way to obtain this level of stability or precision in framing. I can’t imagine doing commercial work handheld anymore.

2. Use base ISO. Covered above.

3. Use optimum apertures. Covered above. Note that when you’re shooting a high resolution camera on a tripod, diffraction becomes very obvious. Unless you have no choice, don’t stop down farther than you need to – you can actually make the image softer that way.

4. Bracket and composite. For scenes with large dynamic range, or elements so far apart that no depth of field at reasonable apertures will cover them, I find myself using multiple images – one for each distinct exposure or focus zone – and compositing them afterwards in Photoshop. Care has to be taken to make things look natural, too; HDR this is not. And you simply can’t do it without a good tripod.

5. Bring your own light. I’ve always said that without light, there is no photography. With good light, the most banal subject can appear arresting. So why rely on unknown or potentially insufficient or spectrally-odd light? I bring a set of speedlights, umbrellas and softboxes to every job. Not only do I know exactly what I’m getting color- and exposure- wise, bringing your own controllable light also allows you to increase your shutter speeds to further minimize the possibility of camera shake or subject motion. Use the maximum sync speed unless you need to blend in ambient light too.

6. Watch your shutter speeds. There are a few critical threshold levels for shutter speeds – some support systems or cameras have a range in which there are inevitably vibrations, no matter how stable the tripod; you can’t go below about 1/60s for a slowly moving person, or 1/500s for sport; other, faster, subjects may require even more shutter speed. Even if in theory you could get away with 1/500s to freeze motion, you will probably see a significant improvement at say 1/1000s.

7. Use manual white balance. Although modern AWB is pretty good, and current sensors have a large dynamic range, what doesn’t change is the fact that once a channel blows, you can’t recover the information. Most of the time, RAW converters are interpolating data from the photosites of non-blown channels and adjacent areas to guess what the color for the overexposed area should be. Shifting white balance too much can actually cause channels to blow, or require blown channels to be brought back under Level 255. If you get the white balance right out of camera, not only does this save you the hassle of having to do major color corrections later, but it also prevents false color and minimizes noise in individual channels.

8. Use live view to focus. Both the resolution and focusing system problems of the D800 have made it clear that for critical applications, live view focusing is the way to go. You can’t get any more accurate than focusing on the actual imaging plane. This also allows you to check depth of field and preview exposure; finally, no modern DSLR seems to have been designed with critical manual focus through the viewfinder in mind – the focusing screens simply lack ‘snap’ and are optimized to deliver a bright image with slow zooms. I have to admit, I initially didn’t see the point of live view, but on a tripod, for precision work, it makes perfect sense. Especially with a good LCD. Now, if only we could get Retina Displays on our DSLRs…

9. Shoot RAW. Covered above.

10. Nail exposure. Covered above.

11. Use a timer or mirror lockup. No point in having the most sturdy support system in the world, and then inducing vibration by moving the camera yourself when you trip the shutter. Either use the self timer, a remote release or mirror lockup (or preferably, all three) – this truly minimizes the amount of camera shake at the point of release, and allows any residual vibrations caused by the mirror cycling to die down before the shutter opens.

12. Limit the amount of optical intermediaries. Teleconverters, adaptors and extension tubes all introduce another set of mounts into the equation, not to mention possibly degrading image quality if there are optical elements involved. The perfect planarity of each mount surface is required to maximize image quality at the sensor plane – there’s no point in having a perfectly flat-field lens if the mount is at an angle!

13. Turn IS off. You just don’t need it if you’re shooting on a solid tripod and making your own light.

14. Limit the tilting and shifting. Even though tilt-shift lenses are designed with a much larger image circle than the format they’re meant to cover, like every other lens, the edges of this image circle are often far from perfect. Limiting your lens movements helps to avoid these areas.

Sky’s the limit…
Here’s what I would have if money were no object.

1. Full movements. If I could place my depth of field and focal plane precisely where I want it, I wouldn’t need to use large lights or very small apertures; Scheimpflug is your friend.

2. A large format back with enormous pixels. Large format for better DOF control; a single shot back (if anybody makes them that large for non-military use) with big pixels for fantastic dynamic range and color accuracy. Forget JPEG, RAW is all I need. And it should have a nice, high-resolution preview screen for critical focusing, too.

3. High CRI LED panels, and lots of them. Bringing my own light – with low weight, low power consumption, no chance of bulbs going pop, and good spectral transmission. Plus, the ability to preview the outcome of a particular lighting setup lets you work a lot faster.

4. Some serious support. I’m very happy with the Gitzo 5562 I’ve got now, but it seems that the combination is let down by the head. Specifically, not so much the rigidity of the head as the lack of precision in positioning; I think I need an Arca-Swiss Cube or D4.

5. Apochromatic lenses with leaf shutters. No loss in resolution due to CA; great color reproduction, and minimal camera shake thanks to a teeny shutter with very low mass.

5. A packhorse and/or a good chiropractor. Either it carries itself, or my spine is going to go…MT

____________

Visit our Teaching Store to up your photographic game – including Photoshop Workflow DVDs and customized Email School of Photography; or go mobile with the Photography Compendium for iPad. You can also get your gear from B&H and Amazon. Prices are the same as normal, however a small portion of your purchase value is referred back to me. Thanks!

Don’t forget to like us on Facebook and join the reader Flickr group!

appstorebadge

Images and content copyright Ming Thein | mingthein.com 2012 onwards. All rights reserved

Follow

Get every new post delivered to your Inbox.

Join 26,151 other followers

%d bloggers like this: