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 How to Take Sharp Pictures

Sharpness is the holy grail of photographers. I don't mean that everything in the shot has to be crystal clear - there are lots of reasons for a background to be blurred, but almost without exception you want the central subject matter to be tack sharp. In a portrait, that may only be the eyes, but something needs to be sharp.

There are a number of factors which contribute to sharpness, and they fall into three categories:

Movement
Depth of field.
Equipment

One other factor which is beyond this scope is the general softness that characterizes the digital files taken by today's digicams. This relates to specific engineering and technological constraints (ie the existence of an anti aliasing filter which deliberately softens the image to reduce the "jaggies") and is easily addressed in post processing through a capture sharpening process.

Motion.

Motion that contributes to blur can happen at 2 points: either at the camera or with the subject (or both). Rules of thumb: 1: the faster the subject is moving the higher shutter seed you need. A range between 1/200 and 1/400 is a starting point for action shots. 2: the longer the focal length of the lens, the higher the shutter speed needs to be to eliminate camera shake.

As a general guide for hand held shots you need 1/focal length as your shutter speed. So a 400mm focal length would need a shutter speed of 1/400 of a second. Note that this should probably be based on the "effective" focal length. My Canon 1DMK2 has a multiplier (more correctly a "cropping factor") of 1.3 so my 400mm is effectively 520mm - implying a shutter speed of 1/520. Note that my comments on "equipment quality" can modify this rule somewhat. If you're an experienced biathlete, you can probably hand hold at lower speeds.

Depth of field.  Updated June 11, 2006

At a very high level the starting point is that  (everything else being the same) f/22 will place more of your shot within the range that's acceptably "sharp" than f/2.8. The calculation of DOF depends on 4 variables:

    the f stop (smaller apertures, larger DOF),

    distance (farther gives larger DOF),

    focal length (higher fl = less DOF) and

    Circle of Confusion (your subjective tolerance for blur - the smaller the circle radius, the less DOF).

As an example (using a circle of confusion appropriate for a 1.6 sensor) a subject at 50 feet, f/22, 200mm FL will have everything from 43 feet to 60 within the depth of field, a DOF of 17 feet. While at f/2.8 the DOF is from 49 to 51 feet, a DOF of only 2 feet. At close distances, longer lenses and large apertures the DOF can be incredibly tiny - for 200mm, f/2.8, 5 feet the DOF is only 1/4 of an inch!  Remember though, what you gain in depth of field by using higher F stops is achieved at the cost of slower shutter speeds.

The original text of the above referred to anything within the depth of field as "in focus".  In fact this isn't technically correct.  The only things that are "in focus" are things that are exactly on the plane of focus.  Anything in front or behind that plane may be still perceived as acceptably sharp, as long as it's in the depth of field, but it's not "in focus".  

Here's a good link to a DOF calculator: http://www.dofmaster.com/dofjs.html

There are 2 points of confusion, which both centre around the infamous "circle of confusion".  It's important to realize that depth of field isn't binary.  It's important to remember that softness starts to creep in as soon as an object is not exactly on the plane of focus.  The COC is simply a measure of your subjective tolerance for blur.  In the 35mm film world a typical COC was .03mm.  This means that any point that had a radius of .03mm or less wasn't perceived as a disk, but as a point.  In the digital world, to the degree that the sensor size is smaller than a 35mm film frame, the COC is smaller, so the Canon's with a 1.6 sensor have a COC that's .019mm.  The second point is that the .03 figure is based on "normal" viewing distance (basically arms length) for an 8x10 print, so as you print larger and view closer you need to use a smaller COC to retain the same "impression" of sharpness. 

Diffraction limitation.

Here's a good link with an explanation and demonstration of the effect of diffraction: http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm   The essence of this issue is that the smaller the aperture (usually used to get a larger depth of field) the more the light is scattered as it goes through the aperture, which increases the fuzziness of the image as projected onto the sensor.  If the pixels are large enough this fuzziness isn't particularly relevant but as the pixel size diminishes (based on sensor design characteristics) and the aperture gets smaller, the effect of diffraction starts to become the limiting factor.  For example on the Canon 1D2 diffraction starts to kick in at about f/11 but on the Canon PowerShot G6 the sweet spot is around f/4. (The real world difference isn't as extreme as implied by the difference between f/11 and f/4 since the G6 sensor is significantly smaller than the 1D2 so the "effective" focal lengths are not that different).  In the DSLR world this means that there's a tradeoff in overall sharpness as you stop down beyond the f/8 - f/11 range even though the depth of field is increasing.

So if f/8 is the limit at which point diffraction starts to kick in, what about apertures less than f/8.  The problem there is that the inherent compromises in lens design (exacerbated by zoom) cause edge distortion and other nasty stuff that diminish as the lens is stopped down.  That's why f/8 is often referred to as the "sweet spot."

MTF Charts

I'm not going into detail here, but here's an excellent explanation: http://www.luminous-landscape.com/tutorials/understanding-series/understanding-mtf.shtml   These charts can be used to get an idea of the performance of a lens - it's ability to capture resolution and contrast.  If you want to see a superb MTF chart here's one from the Canon 300 2.8 IS L:

Basically the flatter and higher the lines, the better the performance.

Equipment Quality - the Camera

Three types of gear have an impact on the sharpness of your pictures. The camera, the lens and the tripod.

The camera impacts sharpness in some direct and indirect ways. Directly, the performance of the auto focus is paramount. The D30 and D60 while having decent image qualities, suffer from dreadful auto focus, particularly in low light. In normal AF mode it can take a "long" time - or, if the subject is of low contrast, "never" to get a focus lock. If the subject is moving you've got a real problem. In AI Servo, the camera tries to track the object and will allow the shutter to release even if not in focus. In low light action scenarios using AI servo and the D30/60 you're going to trash between 60 and 90% of your shots. This compares to a 10% (or less) trash factor with the 1D which has absolutely state of the art auto-focus and focus tracking.

Indirectly the camera (not all cameras have this function) can help improve sharpness (when used with a tripod and timer) by activating the mirror lock up (MLU). This is worthwhile at speeds between 1 second and 1/30 of a second. Normally the timer gives a 10 second delay, but if used in connection with MLU the delay is only 2 seconds. What happens is that at the range of time I mentioned, there is still residual vibration in the camera, both from the act of pressing the shutter, as well as the movement of the mirror as it flips up. Using MLU lets everything stabilize before the shutter is tripped.

Another indirect impact of the camera is its range of ISO speeds. With film if you wanted to change ISO you had to change the film. With digital, it's just the rotation of a dial. I have my D30 set up so that the back dial changes ISO. The D30 goes from ISO 100 to 1600. Each doubling in ISO is one stop so if you need 1 second at ISO 100 (can't hand hold) you would use 1/16th at ISO 1600 and you can push a bit in Photoshop so you could underexpose by one more stop giving you 1/32 and at least have a chance at a shot (at least if the subject isn't moving). The price is noise. The higher the ISO, the more noise in the shot - basically equivalent to film grain. There are reasonable software options for managing noise (and the options are improving all the time). The challenge is to remove the noise but not the detail.

Equipment Quality - the Lens

In general:

primes are sharper than zooms
the cheaper the lens, the softer it will be
the wider the aperture the softer it will be
the closer to the edge of the frame the softer it will be

In the context of the Canon DSLRs (with the exception of the 1Ds which is full frame) the last point is mitigated somewhat by the fact that with a 1.3 or even more with a 1.6 cropping factor a lot of the softness and distortion which is worst at the edges is cropped away. The Sigma 14mm (effectively a 22mm on the D30/60) is useable on the D30, marginal on the 1D (1.3 factor) and unusable on the 1D (full frame).

IS = amazing.

Image Stabilization (IS) uses gyroscope technology to sense movement in the lens and shift the lens arrays to dampen the movement. You can get between 2 and 3 more stops using IS lenses. I have actually gotten a couple of shots at 400mm (640 effectively) at 1/10th of a second - that's really pushing it, but 1/60 is pretty safe for stationary subjects. Relating back to the 1/fl rule: 640 = 1/640 second, one stop improvement = 1/320, 2 stops = 1/160, 3 stops = 1/80. Note that IS doesn't make any sense (and isn't available) on wide angle lenses, although the new Canon 24-105 f/4 L does have IS.

Lens Speed

Finally, all of the issues I mentioned regarding the camera's AF performance are exacerbated by slow lenses. You'll get noticeably better AF performance from a lens with a maximum aperture of 2.8 than you will from a 4.5 lens, but the faster the lens, the more it costs. Note that in this context 2.8 isn't a DOF issue - it's simply a measure of how much light is available to the camera during the AF process. To see this in action, stop down to F22 (or as small as you can) and hit the depth of field preview button (go ahead, check your manual to find it) and see how dark the viewfinder is.

Equipment Quality - the tripod

Actually, the tripod is only one of three links in the support chain. The other two are the head and the manner in which the head is connected to the camera. The purpose of the tripod is to hold the camera still. The heavier the tripod, the "stiller" the camera. The heavier the tripod, the less you'll use it so..... Tripods are a pain. Tripods are necessary (at least for landscape photographers). If you're serious about landscapes you're after the morning and evening light and all the IS in the world isn't going to help you get 1/2, 1, 2 or 3 second shots which is what is often required. If you look at my equipment page, you'll see that I've churned through a number of permutations and combinations. What I've finally settled on is a carbon fibre tripod with a light weight head. It's light enough to carry more often, and in Canada, in the cold, the carbon fibre isn't as miserable to work with as aluminium.

A couple of other points to consider - these are based more on other folks' comments than my own experience. Three section tripods are (might be) more stable than 4 section. The advantage of my 4 section model is that it will easily fit in my luggage, a three section model wouldn't. The higher the centre post is raised the less stable is the platform. This is probably a truism - but I'm not sure that the reduction in stability results in a discernable difference.

One hint: in high wind a light (even if solid) tripod can vibrate - you can reduce this by hanging some weight (eg your equipment bag) off the bottom of the centre column. My Gitzo actually has a hook to facilitate this.

As for the ballhead - that is not the place to economize. My experience is that the Acratech and Markins provide a good compromise between weight, stability and price. It also comes with a built in panorama plate.

I like the Kirk Quick Release plates. I strongly recommend you at least use a system that has the plate that attaches to the camera built specifically for the camera you use. You can often see the camera move when pressing the shutter using a so called universal QR system. Not good.  Note that this can be mitigated through the use of a cable release. 

Final thoughts:

Of all the shots I trash, the vast majority are due to poor focus. Of all the poor focus shots the greatest contributor is the poor AF of the D30. Here are a couple of tips on how to mitigate some of that difficulty:

One source of help is to use a focus assist lamp. The one in-camera is terrible, but using the 550ex flash gives you some helpful AF assistance. Here's a good tip: (I can't find reference to this in the 550 manual anywhere) If you want to use just the FA from the 550ex, but don't want the flash to fire:
1. Press the LCD lighting button; hold it down for 3 seconds. The CF symbol along with "F1 0" will come up on the LCD screen.
2. Click on SEL/SET once. The "F1 0" function will start blinking.
3. Click on SEL/SET twice more until you see "F3 0" (E-TTL)
4. While the function "F3 0" is blinking, click on the "+" button changing it to "F3 1" (TTL)
5. Click on SEL/SET one more time and then the "mode" button.
6. To reset, same procedure except use the - key to set F3 0.

Practice manual focus. I've had even landscape type scenarios where the AF won't lock and it's difficult to reframe the shot to get sufficient contrast to focus and then reframe for composition (usually due to really awkward angles). The Canon Angle Finder C has the ability to click to "zoom" in to the centre part of the frame making it easier to see what's in focus. I did a number of shots at the 2003 Canadian Indoor Rowing Championships using manual focus. Since the rower always ended up at the same point at the end of the stroke I could take a couple of stokes to get the manual focus right for the end of the stoke and take the picture then.

Update June 11, 2006

Some of the more expensive camera's have interchangeable focus screens and some screens with the old fashioned split micro prism are available eg: the Beattie screens, http://www.adorama.com/BTEOS1SIG.html?searchinfo=Beattie%20Canon&item_no=6

If AF won't lock, reframe on something that will lock then reframe for composition. The point of lock and the point of composition need to be the same distance from the camera. (Know your equipment so you know how to preserve focus lock when you reframe).

Use AF to lock on a certain point where you know the action will be, then switch to manual. Eg focus on a basketball hoop, (may take a second or 2) then go manual and when the next jump is made you'll be able to get an in-focus shot without waiting for the AF or servo.

AF will lock faster if you use just one of the (only 3) focus points.

Really, really understand the impact of changing DOF via f stop and the impact of that on shutter speed.

Summary - 10 ways to take sharper pictures.

1. Buy an expensive camera and expensive Canon "L" series lenses. If that doesn't work see points below. (Taking my tongue out of my cheek I mean - Get a camera with good AF and fast lenses).
2. Use a tripod
3. Think! Understand the relationship between aperture and depth of field and general rules of composition.
4. Use a tripod
5. Think! Understand your equipment - how does the AF behave? What ISO options do you have?  Use MLU and/or a cable release.
6. Use a tripod
7. Think! Analyse your shots after the fact. If you're not happy with the sharpness look at the EXIF data and see what you did.
8. Use a tripod.
9. Practice! Learn how to manually focus.
10. Use a tripod

Update: January 22 2005.

When using a tripod an slower exposures, say between 1/30 and 1 sec use the Mirror Lock Up option and a 2 second delay.  When you press the shutter, you can move the camera slightly, and the mirror flapping up can also cause vibration.  This isn't noticeable at faster shutter speeds, or very slow speeds, but in the "mid range" you can reduce blur using this technique - the 2 second delay gives everything a chance to settle down before the shutter opens.  If you camera doesn't support MLU, then consider getting a remote shutter release so at least you aren't jiggling the the camera when you press the shutter.

Finally - if all else fails, check you equipment. There have been a number of reports of cameras that either front or back focus. Ie - you have focus lock, but the shot ends up out of focus because the actual focus was either in front of or behind the subject. Here is a quick test. Lay out a ruler or tape measure on a table angled 45 degrees from the camera. Using different (longer) focal lengths and (larger) apertures focus on eg. the 2 foot marker (you want a DOF that's inches, not feet). Then download the shots and check that the 2 foot marker is in fact in focus and the points on either side at which the ruler starts to go soft