Every time I see a photoshoot video on youtube, the photographers have the biggest lenses I have ever seen in my life to shoot portraits or full-body shots.
For example, the Nikon 70-200 f/2.8 ...or the like, that cost so much money.
Why do they need such big zoom lenses? Isn't a 50mm or a 85mm more than enough with apertures surrounding 1.8-2.8?
Or is it to just look "pro"?
A picture explanation, if necessary, is preferred.
Long lenses are typically used for portraits as the greater working distance they allow flatters the subject. This is due to the effect of foreshortening, the perspective is compressed when shooting further from the subject using a long focal length, making features like noses stick out less.
You can shoot portraits with a wide lens, but you're going to get funky looking shots that aren't always what you want:
You lose the sticky out nose effect by about 80mm or so (when framing tight). So why go longer? There's another plus when shooting with long lenses and that is subject separation. Longer lenses make it easier to get a nice blurry background.
My favourite portrait lens is the Canon 135mm f/2.0L, it's relatively small and light, and wide open it gives very nice backgrounds (better than the 85mm f/1.2 in my opinion):
Regarding aperture, blurring backgrounds is not just about having a really fast aperture like f/1.8 or f/1.4, in fact with some lenses like the Canon 24mm f/1.4L make it pretty hard to get a blurred background even wide open, without focusing very close. In the following shot I completely obliterated the background - at f/5.6!
How? By using an 800mm lens!
Finally, it's definitely not about looking pro - unless there were some advantage to a big lens pro's wouldn't use them and therefore it wouldn't look pro! Something like the 70-200 is a very versatile lens, long enough for flattering perspective, wide enough to use indoors and fast for low light. You don't need all those things at once for portraiture, but why buy an extra lens when the one you have will do great?
I don't worry too much about a large lens intimidating people - it's how you act as a photographer that will make them feel most at ease, not the size of the lens.
The specific lens you mentioned, as well as the Canon counterpart, are particularly high quality lenses. The sharpness, contrast, and control of optical aberrations & flare are extremely good in a high end lens like that...and when it comes to professional work, your customers expect the best quality you can offer.
Regarding why use a zoom lens rather than a prime, I would guess that has to do with personal style and taste, as well as the needs of the moment. A professional grade zoom lens like the 70-200 f/2.8 allows you to achieve 85, 135, and 200mm in a single lens...all common portrait focal lengths. The aperture is nice and wide (a lot of 70-200 lenses that are not pro grade only have an aperture of f/4), so capturing nice, soft background bokeh is within the realm of possibility (especially at the longer focal lengths). Most of the pro-grade 70-200mm lenses also have some form of image stabilization, which is extremely handy and almost essential for sharp hand-held shots at telephoto lengths like 200mm.
Regarding a 50mm or 85mm...most pros would probably not use an f/1.8 or f/2.8 prime lens in those lengths. More common would be the f/1.4 variants, however as a professional, quality for your customer still reigns supreme, and its not uncommon to see professionals using the likes of the Canon EF 50mm f/1.2 L or EF 85mm f/1.2 L lenses. With such wide apertures, capturing portraits, candid or otherwise, in almost any kind of light is pretty easy. The wide apertures also produce rich, creamy bokeh. Both offer the best optics available for those focal lengths, and produce nice soft-focus ideal for portraits.
So, I wouldn't say its just to "look pro"...its to meet the demands of their customers: quality. When your making money off of photography, such items usually become a business expense, and therefor a tax write-off (ultimately depends on locale). So the high cost is really not that much when amortized over a number of years.
You may notice that you might see the photographer moving laterally or up and down in those videos, but rarely moving toward or away from the subject by more than a few inches. I've said it before here: there's no "right focal length" for portraiture (or fashion/glamour), there's a "right distance" for a flattering perspective. The zoom is for getting the correct framing when shooting from the right distance. And you need to keep in mind that photography in this genre is usually framed very tightly and shot from further away than an intimate portrait, since it's really a variation on a product shot -- even when one wants a taste of the environment, it's only a taste.
As for the speed, well, there are a few reasons for picking the fast glass. One is for visual focus confirmation (faster lenses have a shallower depth of field, and obvious focus errors really are obvious before you press the shutter release). Another is for control of the DoF in the final picture, though (admittedly) the aperture used is often smaller than wide open -- but the photographer has the choice, and is unlikely to purchase more than one lens of the same (or similar) focal length range. The third is just the viewfinder brightness. When you do this stuff for a living, the fatigue from looking down a long, dark tunnel really is trying.
A 70-200/2.8 would be an intimidating bit of ordnance to bring to a portrait session; the size alone gives the subject the feeling that she's under the microscope, so to speak. For portraits, I much prefer dinky little lenses. The 85/1.8, for instance, is no more intimidating than the 18-55mm kit lens. In the film days, I really liked the 250mm/5.6 Rokkor/Minolta reflex lens -- it was about the size of a typical 85mm, and was great for intimacy at a distance, since the sitter was unable to see it as a long, invasive lens. On a crop-sensor body, the Tokina 50-135mm gives about the same field of view as a 70-200mm lens on a full-frame body, but the lens is a very reasonable size (comparable to the larger-range kit lenses) and, importantly, doesn't change its physical size when zoomed. But these lenses are best for "stealing your soul" portraits -- there's something of the inner superstar you want to capture in a fashion or glamour shot, and longer/larger lenses actually help the model perform.
So yeah, I guess you could say that there is something of a psychological aspect in choosing something like the 70-200mm/2.8 for a fashion/beauty shoot, but it's not about the photographer.
You say a "photoshoot video," of portrait shots [I infer this from the title of the post]. There is a vast difference between portraits, fashion, glamour, etc. With portraits, you see far fewer whacky perspectives. That rules out lenses 50mm or shorter on a full-size sensor. So as @jrista said, the 70-200mm really hits the sweet spot of portrait focal lengths for head shot, head and shoulders, and full length.
The reason the lens is so bit is not to look "pro" but to be able to gather enough light at all those focal lengths. f/4 really is too slow.
I'll mildly disagree that pros don't use f/1.8 lenses. The Canon 85mm f/1.8 is one sweet lens and it is relatively light. I love it -- shot for a solid week with just that lens. But when I really want the best results, I use the f/1.2. It's just better glass and gives me a few more options.
I have the 70-200mm Canon L-Series lens and have taken it out for some fashion stuff, but never for portraits. I prefer a more compact camera for portraits, which I believe is a more intimate, slower-moving session. Fashion, and glamour tend to be more active -- different/changing poses, etc. -- and a zoom can be really useful.
One thing to be clear on: No pro I've ever met spends money just to look more "professional." Photography just doesn't pay well enough to throw thousands of dollars at questionable investments designed to make you look like more of a star than you are. Pros tend to buy what they absolutely need, rent what they are missing on a given shoot, and live without the rest. In my experience.
The 70-200mm f/2.8 is a fantastic lens for portraits because it gives so many options, this is why it is a must have for many pro photographers. It is also a basic for photo journalism where the 200mm reach at f/2.8 is very often a god send. One thing you have to bear in mind with lenses like this is that they are extremely heavy so no pro would use one unless there was a good reason. Believe me I've done a couple of hours with a Canon 70-200 f/2.8 and my arms felt like they were about to fall off so it follows that a pro using such a lens all day isn't going to do so just for show.
It's an amazing lens for portraits because it allows you to stand a lot further away from the model meaning they are a lot less affected by the camera even with such an imposing piece of kit attached. At weddings and similar events its fantastic for candid long range shots in low light too and in a studio having faster glass gives much greater flexibility in lighting. In short there are many reasons to own a lens like this, looking flash tends not to be one of them.
I do believe it IS about the photographer. Photography is more about personal style. Shooting portraits like all else is about "what" the photographer expects to see and the capabilities of his or her equipment choice that brings them there. As far as equipment the quality of the glass being used is without doubt most important in capable hands. I prefer portraits at 135 up to and including 300mm believe it or not. As previously stated it is about what I want to see and the customers expectations of my ability.
If it is about having just one lens... the 80 – 200 mm ƒ/2.8 can do it. Can it do it "all" for portraiture? No, because lighting reigns supreme.
In my experience, the 24-70 and 70-200 are actually BETTER than the rendering of the cheaper primes like 50 1.8, 85 1.8 etc on canikon. The primes will give you more light, but the final quality in shooting conditions, amount of contrast, etc is better on the trinity zooms. You really need to step into something like the 85 1.2L or 85 1.4G to see something better. And that somewhat makes sense...
Nikon puts more "magic fairy dust" in the 24-70 for example over a 50mm 1.8g. There is the nano coating, 9 blade diaphragm, ED glass, not to mention quicker auto focus, metal construction, etc.
Most of the answers in this thread are at least partial nonsense.
For example, professionals do not typically open lenses up to f/1.2 to shoot headshots with full frame cameras, because depth of field at that aperture and range is so short that you'll have one eye in focus and nothing else! Trust me, I use these sort of lenses! Oh - and image quality is often relatively poor until you close down a couple of stops. And compromises to get large apertures mean that an expensive f/1.2 lens may not get as sharp as a lens with narrower maximum aperture, once closed down; possibly the sharpest standard lens there is the f/2.8 46 mm equivalent on Sigma's Foveon sensor compacts. That f/1.2 85 mm lens that someone above thinks make so very professional has rather poor edge quality until it closed down by 2 to 3 stops (for example, see photozone.de's review of the lens). Now, a real pro would know this — and then either buy the much cheaper and light f/1.8 version, or buy the f/1.2 if he needed the low light focusing boost.
On the other hand, the affect of going from f/1.8 to f/1.2 at headshot distances is provably insane — or at least something you'd very rarely want to do (DoF chart for 85 mm f/1.2). At 2.5 m, it's the difference between a 10 cm sharp zone and 8 cm one. Would any sane person really care about the 2 cm difference? You're more likely to want to narrow the aperture and increase DoF, rather than to double the cost for a lens that can reduce it by 2 cm!
The reason for huge lenses in YouTube videos is because they're often for Guys With Cameras — gullible middle aged men who want to become glamour photographers. The big zooms and huge DSLRs impress them because they're what they see paparazzi using on TV and because of the obvious reason. Real portrait photographers are likely to use something much more compact, like a Fuji X with a 56 mm lens, or a Sony A7 or Nikon whatever with a 50–85 mm.
Possibly the main use of VERY wide aperture lenses by professionals is not to shoot but to focus. Focus systems hate dim light, especially the phase detect systems on DSLRs. Amateurs, on the other hand, often spend hours taking pictures of a tree with just one leaf in focus thanks to that insanely sort depth of field — and if makes them happy, why not?
Another point to understand about lenses like the f/1.2 85 mm Canon is that their DoF is small at f/1.2 and headshot range that they often can't be focused accurately enough for a competent picture. This isn't a problem for mirrorless cameras, which focus much more accurately because they do so from the imaging sensor.
Most of all, the f/1.2 Canon 85 mm isn't sharper than the cheaper and lighter f/1.8, it's LESS sharp. This is almost always the case with very bright lenses on full frame - they're special purpose tools designed to sell either to serious shooters with very unusual needs (20% of the market?) and people who don't actually know what they're buying (80%?)
Again, this doesn't translate to other systems — f/1.2 is the equivalent of f/1.4 or f/1.8 for Fuji and Micro 4/3 systems. f/0.95 is the specialist/insane aperture for standard and short telephoto lenses.
