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Author Topic: Chosing the right lens  (Read 446 times)
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« on: April 23, 2018, 04:14:17 PM »

Good basic primer on lenses for those wanting to learn the basics.....

"Effective Focal Length

When choosing a lens based on focal length, you’ll also want to consider the size of the sensor in the camera it will be paired with. Sensors smaller than full frame come with a crop factor that will increase the effective focal length of your lens by as much as two times for MFT sensors.

That means the ROKINON 35mm F1.4 AF Full Frame lens, when paired with an MFT sensor, will have a field of view equivalent to that of a 70mm lens. On a camera with a APS-C sensor with a 1.5-time crop, the same lens will have a field of view approximately equivalent to a 52mm lens. Similarly the Nikon AF-S DX NIKKOR 16-80mm f/2.8-4E ED VR, which works with Nikon’s cropped DX sensor format, has an effective focal length of 24-120mm. Know the crop factor for your camera to be sure you’re getting the lens you need.

Prime vs. Zooms

Prime lenses have one fixed focal length while zooms can be used to cover a range. Zoom lenses are typically more expensive, especially as the zoom range increases, but they can take the place of several prime lenses and are convenient for run-and-gun situations where you’re reframing often. Zoom lenses come in two varieties: internal zooming and external zooming. External zooming lenses are more common and more affordable, but internal zooming lenses are a better choice when accessories such as matte boxes are a factor.

Zoom lenses can have a long or a short throw, covering a wide range of focal lengths or only a very narrow range. For instance, the Fujinon MK18-55mm T2.9, priced at $3,800 dollars, covers a comfortable range of wide to normal focal lengths while the Sony E PZ 18-110mm f/4 G OSS, going for $2,900 dollars, offers more versatility with a longer throw. On top of that, this Sony lens offers servo zoom motor for smoother, more controlled zooming.

On the other hand, prime lenses will often have a faster, or wider, maximum aperture than zooms. Fewer elements in prime lenses also leads to generally sharper images compared to equivalent zoom lenses. That’s why the Sigma 30mm f/1.4 DC DN Contemporary lens, with its super fast maximum aperture, can be sold for a modest $340 dollars. Likewise, the Rokinon 50mm f/1.4 AS IF UMC and Rokinon SP 50mm F1.2 lens are priced around $360 dollars and $1,000 dollars, respectively, depending on the mount selected.

Aperture


The aperture is the opening in the lens that allows light to enter the camera. The size of this opening is controlled by a multi-bladed iris, which also influences the appearance of bokeh — or blur— in your image. More blades lead to a more circular opening, producing smoother, more pleasing bokeh in the defocused areas of the image.

This size of the aperture is a key measurement and is noted with the maximum width to which it can open. You’ll usually see this measured as the F-stop of a lens, for instance f/2.8, f/4 or f/5.6. The smaller the F-stop number, the more open the aperture can become, allowing in more light. Also, the wider the opening of the aperture, the more shallow your depth of field will be. This means the plane of focus will be thinner. Think of a shot where the subject is in focus and the background is very blurry; it was probably done with a wide open aperture, like f/2.8 or wider.

When shopping for a new lens, look for maximum apertures of f/4 or wider. Zoom lenses will often feature a variable maximum aperture depending on the focal length used. For instance, the Panasonic Leica DG Vario-Elmarit 12-60mm f/2.8-4 ASPH. POWER O.I.S., priced at $1,00 dollars, will have a maximum aperture or f/4 at the telephoto end of the lens, but gains a whole stop at the wide end with a max aperture of f/2.8. This means you’ll likely need to adjust your exposure when zooming. Zoom lenses with a constant aperture are easier to work with, but they typically come at a higher cost.

Likewise, lenses with wider maximum apertures will usually be more expensive. However, moving from f/4 to f/2.8 can make a big difference for videographers working in low light situations or who want the cinematic look shallow depth of field can provide.

Sensor size

Another important factor of your lens purchase is the sensor format of your camera.  The main types of sensors to consider here, from largest to smallest, are full frame, Crop Sensor (APS-C and Super35) and Micro Four Thirds. MFT is both a sensor size and a mount type. Since full frame sensors are the largest, lenses made to cover a full frame will provide an image large enough to cover a smaller sensor, meaning they’ll work fine. But, if you use a lens made for a crop sensor on a full frame camera, the image will only cover a portion of the sensor, creating heavy vignetting of your image. Unless you very specifically want this look, avoid using a lens made for a smaller sensor on a larger format camera.

Some manufacturers use different mount subsystems that represent the sensor size as well. For example, the Canon EF mount is a full-frame mount, while the EF-S is for Canon crop sensors. EF mount lenses will work on an EF-S cameras, but EF-S mount lenses will not even attach to an EF mount system. While lenses with full frame coverage are generally more expensive, they are also more versatile and more likely to keep their place in your arsenal over time.

Lens adapters


Adapters can be used to attach a lens made for one mount type to a camera with a different mount. They can be found for almost any combination of mounts. Although they allow you a wider range of the lenses you can use for a specific camera, they also have  drawbacks. You’ll still need to consider sensor size and lens coverage when using an adapter, and few adapters allow for digital communication between the camera and the lens. If you lose digital communication, you lose the ability to autofocus, and on newer lenses, possibly the ability to change your aperture. Adapters also can affect the light that passes through the lens to the sensor, often cutting a full stop from your exposure. They’re a handy tool, but if used, the drawbacks should always be considered.

Cine Lenses

Cine lenses are different from still lenses in a few ways: they often have a more robust build and lower tolerance for variation in their specs. They have longer focus throw for smooth racking and smooth, de-clicked manual apertures. Cine lenses are made for use in bad weather. Because of these demanding specifications, they are often considerably more expensive than similar still lenses.

Cine lenses will also measure aperture in T-stops rather than F-stops. Unlike F-stops, T-stop measurements represent how much light hits the sensor of the camera rather than how wide the aperture is. This difference makes T-stops more consistent for cinematic applications. A certain amount of light that comes into the lens is lost as it moves through the glass elements and other parts of the lens and camera. A lens that has an F-stop of f/1.2 might have a T-stop of t/1.4, which would represent a .2 loss of light. You’ll usually only find T-stops on cine lenses, since filmmakers especially value the consistency in exposure they provide.

Cine primes are much more common and affordable than cine zoom. Since it’s important that cine zooms are parfocal, meaning that they are able to maintain consistent focus across the throw of the lens, cine zoom designs are much more complex and expensive to manufacture. Because cinematographers value consistency, cine primes are often sold in sets, such as the Rokinon 24, 35, 50 and 85mm T1.5 Cine DS Lens Bundle. "

https://www.videomaker.com/article/b02/19393-choosing-the-right-lens-the-ultimate-guide?utm_source=enews&utm_medium=email&utm_content=article1_2018_mon_04_23&utm_campaign=traffic
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