The 50mm prime lens and today's digital SLR cameras ...
You may wonder- what is a prime lens, what does 50mm actually mean, and why would I ever want or need such a lens. Back in the ancient days when I was a photo student ALL 35mm film based cameras came with a 50mm -prime- lens- in other words this lens did not zoom. 50mm is a fairy normal focal length- simply holding the camera up to your eye to view through it and then looking at the scene with your eyes there would not appear to be much of a difference- the camera that sported the 50mm lens was neither telephoto - making things appear closer- nor wide angle- meaning you could see wider than with your eyes-like looking through a front door peep hole. As cameras developed in the 1980s the wide angle to mild telephoto zoom lens became a standard item to come with a new camera body. The 50mm prime lens was all but forgotten and Santa Claus himself limited production to only one of his highly skilled elves that made 50mm lenses for Nikon, Canon ,Olympus and Leica. In the current digital world the 50mm prime lens has made a big comeback- WHY? you may ask.The 50mm prime lens is about the sharpest lens you may ever own- not having to make a lens that zooms is a big advantage in making these lenses very very sharp , and even though today's zoom lenses are sharper than ever before; the 50mm lens is much sharper. And another big reason for their new popularity- these new 50mm lenses now autofocus and are priced in the range of around only $150USD. Perhaps you are not into the cult of sharpness- the 50mm has some other big "skillz". Most moderately priced 50mm lenses are about ƒ2- this is called the ƒ-stop and the number 2 is an indication of how much light the lens lets in. ƒ-2 means that the diameter of the front of the lens if multiplied by 2 would touch the sensor chip. Lower numbered ƒ-stops such as ƒ2 actually let in MORE light. The lower the number- the more light the lens is letting in. Most zoom lenses today have an aperture (ƒ stop "hole") of ƒ4- so this means a typical prime ƒ-2 50mm lens actually lets about 4x (times) more light into the camera at the full open aperture of ƒ2 than your typical zoom lens of today. Any lens that is ƒ-2 or has even a larger aperture is known to be a "FAST" lens in photographer parlance. Canon and Nikon also have slightly faster 50mm prime lenses of ƒ1.4 or thereabouts- but note the price on these Faster Fast lenses is going to be at least 2x that of the standard 50mm ƒ2 lens. Leica- the German camera and lens maker also has their famous Noctilux series of 50mm prime lenses. The Noctilux puts the same amount of light on the sensor chip as falls on the front of the lens- to do this it actually gathers light-so therefore it gets a ƒ-stop rated at ƒ1 - wow. Lenses that gather light and are very fast were in the past referred to as "Cat's Eyes" a term that is all but forgotten today in a world of much "slower" ƒ4 zoom lenses. The Noctilux has an incredibly limited depth of focus at ƒ1 and also a look to the areas rendered out of focus like almost no other lens. Needless to say the Leica Noctilux lens is priced over $10,000USD - so I doubt I'll be picking up one soon. This ability to let in a lot of light makes the affordable ƒ2 50mm prime lens excellent for taking night time street scenes without a tripod and also indoor portraits by window light. Also- the 50mm is physically shorter (only about 2 inches in length) than a typical modern zoom lens- meaning that with slow shutter speeds in dark nighttime places ever so slightly shaking the camera leads to less blur in the images as a short lens is not waving around as much as a lens that sticks out 6 inches in front of the camera. Most of todays' digital SLR camera have an APS sized sensor- which is a bit smaller than the actual film size being exposed in 35mm film cameras of the past- so this means that used with your newer SLR camera the 50mm is a slight bit telephoto- which makes it excellent as a portrait lens. However- there is a bit of confusion- portraits made with the 50mm prime lens need to be half or full length view of the human body portraits- the 50mm lens is not telephoto enough to make extreme close ups of adult facial portraits. Portraits made close up with this lens with adults will give them bulby noses- so the answer here is - you will need a nice lens that has a zoom capability over 100mm to take close ups ( shoulders neck and head) for adult faces. I recommend for close ups of faces you will need a lens that zooms to at least 135mm. Notice I said not to use the 50mm lens for close ups of -adult faces- however,close ups of babies and young children may benefit from the 50mm lens as it will make their facial features project ( less flat and more three dimensional ) giving them a slightly more mature look in some cases. Another advantage of the 50mm lens is that used at ƒ2 the lens has a very limited depth of field- this is good for photographing flowers up close to make the background fall our of focus, sure this can easily be done also with a telephoto lens used at ƒ4- but if you like the look of limited focus without the typical telephoto perspective- the 50mm is the way to go. Last but not least- the 50mm prime lens is a favorite of those making HD videos with their SLR cameras. Since most SLR cameras currently do not offer autofocus , the bright image seen through the viewfinder with the -fast-ƒ2 50mm lens makes it really easy to focus. Not only does ƒ2 allow focus t be made quickly - it also allows the cinematographer to know exactly where the focus has been placed. This means that if the lens is then stopped down ( set to a smaller ƒ-stop) to get more depth in the focus you still know where the sharpest point of focus was set. Focus was not so critical with low rez video of the past- but with 1080 HD video - high def.- with more definition comes the ability of the end viewer to see what is sharp and what is not in focus. Budding cinematographers also like making movies with limited depth of focus- and ƒ2 delivers a sharp scene of lovers enjoying a cocktail together while making the little string lights in the distance behind them bloom romantically into circular blobs of light. So - if you do not already own the trusty 50 you may want to think about getting one- and if you bought one on impulse or on recommendation of a pro or enthusiast friend but did not fully grasp why - well now you have a better understanding of the usefulness of this lens and will have some good reasons to employ it.
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