How The DX Format Impacts People Photography
http://silverbased.org/dof-vs-format/
The DX sensor crops OFF,and does not utilize, much of the image circle a full-field Nikkor lens projects. Because a DX format SLR does not capture the outside of the image circle of a full-field lens, to gain a wider angle of view with a DX camera, one must compensate by using a lens with a much shorter focal length than if one were using an FX format camera. Example: a 28mm lens on DX has "roughly" the same angular view as a 43mm lens on FX format (figuring the Nikon 1.5x FOV factor as being close to 1.53 actually).
Because a DX sensor does not "catch" or image the outer areas of a lens's image circle, in order to use an 85mm lens to photograph a six foot tall man, one must have the camera at distance of 30 feet,to allow a field of view of 8.47 feet tall,to allow the person to be shown with 2.47 feet of real estate alloted for foot space and head space, as well as for some allowance for cropping to 8x10 or 16x20 aspect ratio. Using an FX format Nikon and the same 85mm lens,one can position the camera at only 20 feet from the subject,and achieve the same 8.47 foot tall field of view when posing a 6 foot tall standing man.
What's the problem with this? In a studio of 25 feet depth, with a DX camera, one can NOT use longer focal length lenses like 85mm,105,135,or 200mm unless the subject area is very small. When indoors and using a DX format camera, to frame something as large as four to eight people, one simply can NOT deploy a lens of much over 50mm in length in most studios or in most rooms, unless the photographer is able to stand 40 feet away from the subjects and to communicate with them via walkie-talkie or via yelling. The problem with this situation? Well, there are several problems. First, the DX format demands a short focal length lens in order to encompass a group of four to eight people in most studio or wedding or social photography situations,and the required short focal length lens will 1) foreshorten objects,making extended limbs look awkward and unnaturally long in seated poses or reclining poses 2)distort the relative size of those close to the camera in relationship to those in the back--ie the closer people are imaged at a large size on the sensor,but those farther from the camera are imaged disturbingly smaller in size 3)distort the shape of objects or people placed anywhere near the corners or edges of the frame
4) cause keystoning on vertical objects,like standing people or upright objects like bottles or glasses,unless the back of the camera is kept absolutely parallel with the back wall--which is very difficult to do many times and limits composition tremendously 5) provide deep depth of field at normal flash apertures like f/5.6 and virtually hyperfocal depth of field at apertures like f/8 to f/11 6) the short focal length lens will be focused fairly close to hyperfocal distance at normal indoor working distances, thus robbing the photographer of the ability to selectively throw a background out of focus and 7) the short focal length necessitated by the small capture format of DX will invariably mean that in order to photograph people, posed indoors or outdoors in groups, the actual,physical width of the background behind said group will need to be physically large, and wide, both in terms of inches, and in subtended viewing angle.
Remember--a typical studio backdrop is 107 inches wide, and two support poles are positioned 3-4 inches on either side of the edges of the background support bar. Using a DX camera for studio photography or location photography of people imposes a lot of limitations on the photographer, because the lenses used are so short,and because short lenses have a whole host of rendering "issues"; keystoning propensity, geometric distortion,unfavorable foreshortening of limbs and noses,and distorted near-to-far spatial rendering (technically known as apparent perspective distortion,but commonly called "the wide-angle effect" by many) that makes anything in the background look small and insignificant. The short focal length lenses needed on DX-format cameras bring with them hyperfocal distances that are very short,and which eliminate the photographer's ability to use selective focusing effects. Short lenses on small capture formats bring with them wide Field Of View angles. When the photographer must use his camera to encompass "people-sized" subject areas inside of real buildings with things like windows and ceilings and cluttered backgrounds, having a camera with a small capture area and a short lens is a drawback in many ways.
One might ask--if one wishes to throw the background out of focus, why not simply move farther away with the DX camera? That strategy doesn't work, since increasing the camera-to-subject distance brings with it greater depth of field. Increasing depth of field is MOST easily done by lengthening camera-to-subject distance; in fact, increasing camera-to-subject distance is the PRIMARY means to quickly increase depth of field. Once the camera-to-subject distance hits around 20 feet, with a small capture format and a moderately small aperture, one is ALREADY at, or sufficiently close to the hyperfocal distance to ensure deep depth of field! That means that in effect, one can NOT throw the background out of focus. Well,why not use a longer lens and also move back? Again...long camera to subject distances like 40,50,60,and 80 feet with a small-format DX camera means very deep depth of field. Long camera to subject distance on DX format, EVEN with a long telephoto lens, means ample depth of field. And at long shooting distances the background's distance behind the subject in ANY indoor situation short of a domed indoor football stadium, means that for all intents and purposes, the main subject will be in good focus AND a background that is anywhere from three to twenty feet behind the main subject will ALSO be rendered in quite acceptable (and often distracting) focus. This in a nutshell, is a summary of some of the depth of field facts encountered when using small capture formats, both film and digital. The smaller the capture format and the shorter the lenses used, the worse this problem becomes. This is one reason I think the 4/3 format is lousy for people photography, but offers truly superb potential for creative,interior architectural photography, or for social-documentary-artistic work where one desires deep depth of field.
The problems encountered in studio work, studio portraiture,location portraiture,and weddings are greatly compounded by using a small, DX-sensored camera. A typical scenario of a family group of four people shot on DX means that one will be very limited by the crop factor of DX; a DX sensor in a camera does not "magnify" the image projected by every lens mounted,it merely crops off the edges of the lens's projected image. So, in order to encompass something larger than a flower, something as large as a family group of four standing people, with a DX camera, one must use a lens that is much shorter in focal length than if one had an FX format camera. That short lens has a wide angle of view,and renders things with backgrounds that appear small, sharp, and wide-view! Because the format is small, hyperfocal distances are very close to normal,indoor portrait shooting distances--this is NOT a good situation. Why? A background is only "so wide", a studio's ceiling is only "so high" and light stands typically are only 13 feet tall at the most,and a "long" muslin is 24 feet. But if a six foot tall man and his wife and two kids are to be posed,standing,in a room with only a 10 foot ceiling, to get them into the picture, the top of the background will likely show in the picture _IF_ one has to use a DX camera, with a short lens, in any room other than a huge, 60 foot deep commercial studio.
The diagonal measurement of the capture medium is what determines the "normal" lens length for each format. The problem,in real-world studio use,is that the DX format CAMERA and its SHORT LENS FOCAL LENGTHS impinge directly on the picture,and how the picture can be made with regard to subjects such as people who are standing, or family groups that have four to 18 people in them. A group of people is a very large thing--much larger than many natural world subjects, and they must be presented to the camera pleasingly,without those in front having huge,fat heads, and without the people at the edges of the frame appearing like alien beings,with distorted eyeglasses,and hunched over backs. And how must they be presented? Often, an entire group wishes to be shown full-figure, posed literally ON a background of paper or muslin. Often the portrait and wedding shooter will photograph people in offices,bedrooms used as dressing rooms,church foyers,city hall judge's chambers, work rooms, hallways, porches, back decks, patios, aboard boats, in motor homes, in restaurant reception rooms,etc. If one wishes to avoid keystoning, geometric distortion,and extreme foreshortening and exaggerated appearances on heads,legs,arms,and noses,one absolutely MUST avoid using short focal length lenses at close distances. But that is exactly the situation the small DX format sensor forces upon the photographer--to compensate for the crop factor,the DX photographer must drop his lens focal length into the range where geometric distortion and foreshortening are huge issues on groups, causing corner positioned people to look horrible,and causing the heads in the front row to look huge, while the people in the back look far-away and pin-headed, and the photographer's control over both angle of view and depth of field is no longer under his control,but more under the control of optics. Simply stated, the CAMERA is driving the photographer when trying to use a DX format camera for serious people photography work! If one deliberately selects a DX format camera for studio portraiture,location portraiture, or wedding use, he is handicapping himself tremendously.
Then comes the issue of lighting of backgrounds, light falloff to control background color or rendition, and the actual types of lighting that can be used to light locations or backdrops. The short focal lengths, close working distances,and inherently deep depth of field that comes with a DX sensor and its short focal length lenses (at each range-ultra-wide, wide-angle,normal, short telephoto,long telephoto) means that the CAMERA is having a very large impact on what is actually possible to do,within the confines of modern buildings of all types,and on-location, the small DX format changes the behavior of telephoto lenses....they can NOT encompass an entire figure....the sensor is not "catching the image" from the 85mm lens's edges--it is not using that part of the lens. Moving farther back brings one closer and closer to the hyperfocal focusing distance,and cuts down on the ability to throw the background out of focus. It is easier to throw a background out of focus if the subject is close to the lens,and the background is far away from the lens; unfortunately in portraiture and wedding photography,people are often forced to be rather close to the background. Moving far away from the subject is the easiest way to bring huge,expansive depth of field--physically increasing shooting distance builds depth of field faster than stopping the lens down or going to a shorter focal length. By the time a person is far enough away from a DX camera for an 85mm lens to show them full-figure, the ability to throw the background out of focus has pretty well negated by the camera-to-subject distance approaching relative closeness to the hyperfocal distance of an 85mm lens.
A really bad DX camera scenario is this: you're hired to do some location portrait work,and you arrive and the conference room promised is not available,and the work must be done that day, using a small break room area. There is not room enough to set up a full-width background,and the ceiling is a low 9 footer, and the walls are littered with memos and posters on safety, the company newsletter, employee coffee mugs and office junk. You have a 17 foot deep room,and must photograph the five top salesmen, during their lunch break. Hmmm....there's one narrow swath of wall that's clean and uncluttered. You mount a single light on a stand and dial in 200 watt-seconds, position the first guy, and with your D300, you are forced to stand very close to him,and use a 24-70mm from 4 meters away. At 70mm you can get a head to waist composition with a clean,uncluttered background. At 65mm, you get a bit more of him and a LOT more background. If you need a full-length photo of him,in that room, with him 4 meters from the camera and main light, as soon as you set the lens to 35mm on your D300, to get the full length shot you want of him and a tiny bit of extra space for subject breathing room and or an 8x10 crop,and BAMMO! you immediately pick up a HUGE expanse of the ugly office walls which are a mere 7 feet behind the subject. It is at a time like this that it would be HUGELY advantageous to have a larger camera format that was not _FORCING_ you to shoot at 35mm just to include a six foot tall man 4 meters away from your camera. The wasting of the edges of the lens's field by the small sensor is a real drawback when photographing in tight,indoor situations,where you wish to control the photographic result. With FX, you can control the situation much better; with DX,indoors in smaller rooms,or on boats,etc, you are a prisoner to DX's small sensor, short focal length,deep depth of field issues. Not to mention keystoning and geometric distortions. The width of the wall shown behind the man is 7 feet two inches. If you had a 6x6 120 rollfilm slr with a 65mm semi-wide-angle lens, you could photograph the man looking pleasant,and have the background looking nicely out of focus. At times like this, a larger capture area and a commensurately appropriate focal length would produce a more-pleasing out of focus look to the background than using the tiny DX sensor and a very short lens. At times like this, bigger is indeed better.
It's difficult for some to comprehend, but FX format is a capture size 2.5x larger in area than DX. DX format is fine for many types of photography, but it is a decided and definite hindrance to in-studio photography of anything even remotely large,like a 6'5' tall man who is posed standing, or a family group that wishes to be shown full-body standing or 50-50 standing and seated...the DX format is new,and was brought about for purely economic reasons. As soon as an affordable full frame d-slr, the Canon 5D, was made available affordably, tens of thousands of portrait,wedding,and event photographers worldwide rushed to buy the camera. I myself as a Nikon user,bought a Canon 5D several years ago, simply because it allows me to use 24x36mm capture area, longer lens focal lengths for each angle of view, the resulting shallower depth of field, and the ability to deploy 85-105 and 135mm lenses in places like my back yard, in my living room, in my garage studio, and on-location wherever I find myself. The 2.5x larger area and the longer "normal" lens of FX format means that an entire repertoire of poses are easy to shoot,and look professional,and are easy to light. These days I see otherwise competent people photography shot with DX cameras, and I see the backgrounds are in good,sharp focus--every wrinkle in the paper is visible, every crease in a muslin is in-focus, and all sorts of distracting background elements are rendered in sharp focus. AND, the background's width is wide, due to small capture area,the use of short focal length lenses,and photography done at distances that are at, or reasonably close to the hyperfocal distances which SHORT LENSES HAVE. The shorter a lens, the quicker it gets to hyperfocal distance. The small size of the DX format,with its need for short lenses,and it tendency to make a photographer stand far away with a lens longer than 50mm, is a TRIPLE WHAMMY,with deep depth very common with DX cameras. With larger formats, the norm is more weighted toward SELECTIVE FOCUS, unless extreme effort is made to achieve deep depth of field.
Trust me when I say that the long-lived 24x36mm capture format has been around for a long time because it is very versatile, and it allows a photographer to compose his pictures the way he would like to. Once one gets down into the ultra-miniature formats, there is nothing but deep depth of field,and with a camera with a hyperfocal focusing distance as short as two feet from the lens, one loses basically ALL control over depth of field. This is what I call the "Point and Shoot Digital Look". It looks ghastly. Who would attempt to become a serious portrait or wedding photographer using a Nikon CoolPix camera? Who would suggest that such a camera is a good tool for portraiture and wedding work? I know this has been repetitive, but this is a first draft, written without an outline,and right off the top of my head, but let me summarize by stating this: the 24x36mm capture format is the absolute smallest format one ought to consider if one wishes to photograph people in a world where backgrounds are either 9 or 12 feet wide, and where ceilings and light stands are seldom taller than 13 feet, and where electronic flash systems are needed to light things professionally and repeatably and predictably for clients who are paying for professional results. And for the photographer, 24x36mm is the absolute smallest capture size that will give you FULL use of 85,90,100,105,135,and 180 and 200mm lenses where they produce high image magnification images with extremely shallow, moderately shallow, shallow, to moderate, to moderately deep depth of field effects--depending upon YOUR decisions of shooting distance, aperture, subject to background distances,and focal length. Note the variables the FX format gives: shooting distance, aperture selection, subject to background distance, and focal length; that's a pretty nice set of four parameters that the 35mm or FX format allows the photographer to work with.
The DX format camera's inability to utilize the full image circle of so many 35mm-based lenses means that when one buys and uses a DX format body, the CAMERA is determining the kinds of pictures that can be made. This cropping-off of the outer edges of each lens's image circle on a DX camera means it is very difficult to photograph a standing, six foot tall man or object a at focal length longer than around 70mm or so indoors, unless the room is huge and the camera to subject distance is measured at 30 feet or more. With 24x36 and larger formats like 645, the photographer has a lot more control over his depth of field, and his camera-to-subject working distances,and with the range of depth of field options that an be produced. For those who wish to become portrait shooters or wedding shooters, please ask a professional who has actually set up a successful studio,or worked in one how he feels about the DX versus FX issue, and consider that in the "people photography" field, one has to direct people, talk to them nicely,and get them to cooperate, and to make them look their best. One can not do that when one is 30 to 47 feet from the subject (a set of DX-camera minimum shooting distances for 85-105-135mm lenses). It only makes sense that having a wide range of creative options over the final results makes for more-successful,and more-varied photographic results than being hemmed in by a short lens,a small sensor, and near-hyperfocal depth of field under a large percentage of real-world "people photography" situations. If you seek out the advice of another photographer in any type of "people photography" field, you need to make sure that their qualifications are relevant to the type of photography you wish to undertake. Ask about the portable strobe systems they recommend, the light modifiers they suggest, the studio flash they suggest,the light correcting gels they use,what types of grids and reflectors and barn doors and gobos and scrims they suggest, what types of light stands they suggest, and what types of camera equipment they themselves have used personally. In short, do not ask a nature shooter, or a sports shooter or a street shooter to give you sound advice on studio- or location-based portrait or wedding work, because it is a whole different ball game--one in which you will be "given" a subject, a paying client, and be expected to produce the "optimal" image for them, in a place or location where a lot of the physical constraints are out of your immediate control,and where practical considerations like light stands,ceilings, background lights, paper rolls, are ALL pre-determined. In many types of "people photography" creating images with distorted limbs,odd-shaped heads, and ungainly-looking bodies and limbs will kill your sales. Unlike in a lot of types of photography, in people photography one often can not "eliminate parts of the subject" like one can when photographing moss or lichens or ferns. In studio and location people photography,there are often very real limits imposed by the studio or location, the lighting, and the camera.
Today, discussions about camera format size are often polarized,and polarizing. Many 4/3 shooters feel that this subject is an affront to their choice of camera, and many APS-C or DX shooters believe that this discussion is slanted against their preferred choice. There are also many people who have NEVER used a medium format camera, a 4x5 camera, or even a 24x36mm capture camera,either film or digital, and whose understanding of these issues is rather fuzzy, or non-existent. These folks often cite how they can do this or that, but they often have no REAL experience, no ACTUAL basis for their position. To those folks I want to say that the depth of field calculators found on-line are certainly helpful and interesting, but the qualitative differences between a portrait shot with an overall depth of field band of 20 feet versus one shot with a depth of field band of 34 feet might "seem",on paper and in the abstract to be not that different, but when seen in a print or even an on-screen image, the degree to which a background is in focus or out of focus depends greatly on the format of the capture medium. TO me, 35mm or 24x36mm is the absolute-smallest format that can TRULY throw backgrounds out of focus under most people photography situations without resorting to "extreme" measures, extreme lenses, or extreme techniques or unrealistic shooting situations. To my eye, the vast majority of DX format people photography suffers from excessively well-focused backgrounds--muslins that show wrinkles, city backdrops that pull my eye from the subject, restaurant backgrounds where the background is in-focus enough that I can see a waitress taking an order,and determine that the customers both have moustaches and eyeglasses, and so on,ad infinitum. The QUALITATIVE differences between FF and DX format captures shot under the same,exact,identical situations are quite large--much larger than many people actually realize,simply because the smaller DX format cameras have been the most commonly-available ones for going on nine years now,and many people have not shot 35mm film or FF digital,and so they have no basis for comparison. Let me put it this way: I see so-called "professional" photographs done in which every wrinkle, every sponge stroke in a painted muslin backdrop fabric is rendered sharply, and creases in seamless paper show up as well; that is a HUGE problem with DX sensors, and NOT a problem with a FF digital sensor,using the same lights, the same studio, and the same lighting setup and the same flash power levels.
Cameras behave very differently,based on their capture size and the lenses used with them. Depth of field is not exactly "linear",and once one approaches within about 60 percent of the hyperfocal distance with a small-format camera, the depth of field "effect" becomes one not of selective focus, but of EVERYTHING being more or less in acceptable enough focus to recognize background objects; unfortunately or fortunately,depending on one's needs, the smaller the capture format, the more this effect is true. Look at this article to see that the APS-C Nikon D2x is a deep depth of field,small-format camera,and the Canon FF camera allows shallow DOF http://www.outbackphoto.com/workshop/phototechnique/essay07/essay.html
On large format cameras like 4x5 sheet film objects outside the "best" plane of depth of field will be "less in focus" than if the photographer is using a 120 roll film camera and 6x7 cm capture, and by the time one gets to 24x36mm, very deep depth of field is achievable when the lens is well-stopped down,even on lenses that have a telephoto or narrow angle of view; by the time one gets to consumer digicams with their itty-bitty little sensors, focusing at as close as 15 inches can put the lens and its entire range at hyperfocal distance. The old 4x5 format sheet film camera has a tendency to be classed as a format that is characterized by SHALLOW depth of field.The various 120 rollfilm formats typically offer moderately shallow DOF. The venerable 24x36mm or FF35mm or FX digital format camera has a lot of flexibility in its depth of field characteristics largely because the lenses available offer either very long focal length, or very large wide aperture sizes like f/1.2 or f/1.4, or BOTH very long length AND very wide apertures like the 400mm f/2.8m as well as wide-angle lenses of shiort length and wide aperture like Canon's 24mm f/1.4, as well as wide angle lenses like 14mm f/2.8's that can be used wide open or stopped down greatly. The DX format cameras offer significantly greater depth of field than FX format camera do, at every focal length and f/stop. Exceedingly deep,almost limitless depth of field is available with hundreds of today's compact sensor digicams. Kodak invented the miniscule Disc Format camera in the 1970's specifically and with intent to create a film format so small that focusing the lens was NEVER needed--ever. They succeeded; compact sensor digicams and cell phone cams utilize this principle to this very day--make the capture format very,very small, and a VERY short lens can capture almost unlimited depth of field when focused at 1.5 to 2 feet. There's no way to say this delicately, but the DX format d-slr is a poor choice for commercial photography situations where the photographer must go out to locations and is confronted by tight working quarters and inadequate space. It seems that on location photo shoots, often times one arrives there,and the place is under construction,or there's "not as much space as we used to have", or "we can't shoot in there", and with a DX camera you run into space constraints where you have a very narrow range of focal lengths that can be used--and that is "it". It can be very frustrating to be caught in a tight space situation and have to shoot a DX format camera with a wide angular field of view on the lenses we actually have, like 20mm or 24mm,etc, and also being rendered UNABLE to deploy anything longer than a 70mm lens much of the time!
Because studios and locations present finite limitations, and lighting equipment has finite limitations, it is imperative that a person who wants to enter into a "people photography" field not be limited unduly by his camera and its fundamental nature. If one selects a DX format camera, one has in doing so, seriously limited his creative potential,and has seriously hampered his ability to deal with the limitations found in modern studios,buildings,and with modern lighting systems. Anybody considering becoming involved in portraiture or wedding photography really needs to understand one thing,and that is that the 24x36mm format camera has been a potent,viable tool since the late 1920's, while DX and 4/3 and the various small-format digital cameras are very new to the scene, and are clearly second-choice tools among those who seek the highest quality images with the most flexibility and the fewest "shooting headaches" from their camera equipment. There are already enough variables to contend with without being forced to deal with a camera that throws away half of a lens's field of view,and which forces you to use short lenses, with deep DOF, and wide angles of view in almost 80% of indoor situations. DX is a handicapped format for people photography. There-I've said it. DX format cameras are handicapped for people photography. Both in the studio,and on-location.
************Here is a very useful on-line Field of View Calculator for those who'd like to compare how restrictive,or expansive, lenses are on bodies of various capture formats, like the EOS 5D and Nikon D700 series, as well as smaller-format cameras with 1.5 or 1.6 FOV factors, or the Olympus brand's 4/3 system with its 2.0x FOV factor.
http://www.bobatkins.com/photography/technical/field_of_view.html?focal_length=85&focal_length_mult=1.5&distance=20&ang_horiz_fov=&ang_vert_fov=&ang_diag_fov=&horiz_fov2=&vert_fov2=&diag_fov2=
