High ISO - who needs it

With the release of the Leica M9, I came across some discussion threads debating the performace of the said camera and its nominal weakness in maintaining good image quality when shooting in low light (at least as compared to the Nikon D3/D700 sensor). Someone was making the point that the benefit of low light high IQ is not for everybody. After all, people went a long time shooting comparatively slow film for all these years and still created good images.

My take on this is that everybody needs a camera with the highest low light performance they can afford. Sensor light sensitivity (also know as ISO, after the organization that used to rate film 'speed') is just another lever to pull for a photographer. Everybody will encounter some low light at some point or another. Why? Because that's just the nature of available light. Having good low light performance equipment will make you pull the camera and shoot in situations that you would not have considered suitable for capturing before. Even in 'good' light, long telephoto focal lengths and optimal lens apertures usually require longer exposures, so having the ability to change the ISO to shorten the exposure time with no significant hit to image quality is very desirable.

Digital photography is all about controlling the way the light hits the sensor. The more levers we have at our disposal to accomplish that control, the more artistic freedom we have to do more with our equipment. There are tradeoffs with good low light performance - usually camera bulk, which in itself is a compelling argument for giving up some low light ability. However, with today's technology, a take everywhere, shoot in every light condition camera is not available (pocket cameras just can't gather enough light in less than perfect light). Which side of the tradeoff one takes is a matter of personal preference and shooting habit.

The image attached to this post was shot at ISO 3200 with a Nikon D700 camera. The choice of ISO was part of a decision making process that allowed me to handhold the shot (ultra wide angle of view helped as well). The quality of the image is not perfect (there's some noise, especially in the darker areas), but it is much better than what could have been accomplished by pushing film.

Composition and focal length

This post deals with the use of focal length choice as a compositional tool. I will talk about shooting wide angle (short focal length), normal and shooting in the telephoto range.

The obvious effect of a wide angle lens (short focal length) is that you 'get everything in'. In other words, because the angle of view is wide, more of the environment is going to show up in your image. This helps when framing the element of interest with the surroundings is important. Care should be taken, especially at extreme wide angles, to maintain a satisfactory aspect ratio between your subject of interest and the environment. Often enough, the subject will appear too small as related to the rest of the elements depicted. To correct, get closer to that element of interest. Your perspective is not going to change, but the relative size will be corrected. Another compositional advantage of shooting wide is perspective exaggeration. You want this in a two dimensional depiction of a 3D world (unless of course, depicting is not your goal. I use a telephoto lens for most of my abstract work). At wide angles, near elements will look larger in relation to far objects as compared to 'normal'. This creates the illusion of depth and makes it easier to ompose a complex image, with multiple planes of interest. Another benefit of shooting wide, albeit a subjective one, is that the depth of field is larger (everything else being constant - eg the lens' light gathering abilities and chosen aperture). This is great if your aesthetic allegiance is ligned with the likes of the f64 group. I personally think that out of focus areas are more of an accident or necessary evil rather than something that should be used in composition.

Let's now turn to compositional uses for a 'normal' focal length - that is, 50mm for a 35mm camera or the digital equivalent. At this focal length, perspective is about what the human eye perceives. When would you use a normal angle of view for composition? When you want your viewer to concentrate on something else than perspective or lack thereof. I don't see any distinct advantages, from a composition point of view, for choosing this focal length. The viewer will be easily swayed by other compositional elements There are a lot of technical advantages fo shooting 'normal' - such as the availability of low cost, sharp and fast lenses with no or little distortion.

Moving on to telephoto lenses - the main thing to remember about those is that they have the opposite effect on perspective - they compress it. This comes in handy when your intention is to abstract or subtract. Abstracting means to downplay the representational cues in a scene. Long focal lengths help abstraction by flatening composition and by putting everything in the same plane. Subtracting means excluding spurious elements from the scene. Because the angle of view is so narrow at telephoto focal lengths, subtraction becomes somewhat easier - the clutter goes away. Going back to perspective compression - this is a great compositional tool when the ntention is to 'crowd' the element of interest. Perspective compression is perfect for conceptual portraits where the mood conveyed is negative (pensive, melancholic, entrapped, etc.). It also works great for shooting large but far away objects - such as the moon or sun against smaller (but a lot closer) terrestrial landmarks. Last and for me, least, long focal lengths can be used to isolate the subject of interest through use of selective focus, eg by making your in focus subject stand out against the blurred background. This takes advantage of the shallow depth of field typical for telephoto even when the lens is stopped down.

Part two of this article will present a few examples on how to apply
the information above in practice.

Why go full frame?

As of Summer 2009, if you step up to digital single reflex lens (DSLR) photography, you have two basic choices: cameras with full frame sensors and cameras with 'cropped' sensors. Full frame sensors are roughly the same size as the 35mm film. The cropped sensors (they come in two sizes APS-C and four thirds) are smaller - by a crop 'factor'. The most popular DSLR cameras (at least by volume sold) are the those equipped with an APS-C sensor. The crop factor varies, but it is generally 1.5 to 1.6. What this means is that an APS-C sensor is 1.5 (or 1.6) times smaller than a full size sensor. Both types can use legacy SLR lenses. So which way should one go? Here are the relative advantages:

APS-C (or in Nikon parlance, DX):

- Increased range at the telephoto end. For example, for a 200mm lens on an APS-C sensor, the angle of view and magnification would be similar to a 300mm lens on a full frame sensor. Not bad if you're a wildlife photographer.

- A new breed of DX only lenses. Since these lenses have to cover a smaller sensor, they can be made smaller and lighter (everything else being equal - and by that I mean mostly their light gathering abilities). Smaller and lighter means you need to haul less equipment and attract less attention from your subjects.

- Cheaper lenses. Smaller and lighter usually means cheaper as well. For example the 12-24mm DX Nikon lens is about $700 and 1 pound in weight, whereas the Nikon 14-24mm full frame lens will set you back $1900 and it weighs a whopping 2.2 pounds.

- Increased depth of field at a given focal length. Lens design at wider focal lenghts usually has the advantage of a deeper depth of field (everything else - particularly aperture, being equal). In other words, if you shoot the same scene with a 35mm prime lens on a DX sensor you usually get more in focus at the same aperture than if you shoot that scene with a 50mm prime on a FX (full frame) sensor. This should appeal to some, but not all situations.

- Everything else being equal, less vignetting (a.k.a. light falloff). Because cropped sensors only use the center portion of a lens, they will likely be less affected by light falloff in the corners.

- Slightly better image quality from full frame lenses. This is a gross generalization, but typically, lenses are designed to be at their sharpest and distortion free in the middle.

- Cheaper cameras. Big sensors are expensive to make - as of now, the premium between the most expensive APS-C camera and the cheapest full frame camera is anywhere between $700 to $1000. The chepest FX cameras available today start around $2000 new.

- Smaller, lighter cameras. Bigger sensors need bigger cameras - and that adds weight to the stuff you have to carry. Add the extra weight from bigger lenses and you go from carrying 2-3 pounds (camera and 2 -3 lenses) to 4-8 if you opt for FX.

Full frame (or in Nikon parlance, FX):

- Increased depth of field as compared to images taken with corresponding lenses on DX. This is very desirable for portraiture, as well as for situations where out of focus backgrounds (bokeh) is used in composition.

- Extreme wide angle lenses stay extreme. 12mm on a FX sensor looks ultra wide angle, while on DX it would look only moderately so (12mm x 1.5 = 18mm). Wacky compositions stay wacky and interior spaces look cavernous.

- Bigger viewfinders. When migrating from point and shoot digital cameras to DSLRs, the first thing one notices is how radically different photographic composition becomes. You go from framing your shot on a nice, bright 2.5 inch screen to looking through a dim, small viewfinder. Nasty surprises - picture ruining details that you just didn't see through the viewfinder, are much easier to avoid using a bigger viewfinder.

- Better image quality (IQ). Everything else being equal - namely megapixels and sensor design, a bigger sensor means proportionally more light hitting it. More light means less noise at the same settings. This really becomes apparent at higher ISOs. State of the art full frame sensors allow the photographer to increase the ISO by 1 or 2 stops without sacrificing the image quality (as compared to cropped sensor sensors). Lower noise is just the beginning - more light also positively affects color depth (you get more vibrant colors that accurately reflect what one sees) and dynamic range (hard to explain in a few words - but basically how large the spectrum of light is between the lightest tones and the darkest tones a sensor can capture). This benefit really only kicks in for low light photography and for high dynamic range scenes (anything with strong light). However, this is more important than you think; if one would shoot in perfect light all the time, one would not need a DSLR period. Any cheap point and shoot can produce comparable results with the most expensive full frame DSLR in perfect light. The catch is - perfect light is hard to get.

So which way should you go? It depends on what and how you shoot. If you shoot a lot of distant subjects, have a tight budget and want to travel light, go for a cropped sensor lens. If you can swallow the price premium, don't mind the extra weight of the equipment, and you often find yourself wanting to explore scenes with less than perfect light, go full frame. For me, going full frame made sense, mostly for the IQ and ease of composition aspects. Looking through a horribly small viewfinder was just too frustrating. I also shoot a lot of low light scenes, so getting acceptable results there was important.