After you've been shooting for a while with your you realize that images made with kit lens lack quality of the professional images. At this point you start to look for better lenses and find that the market is full of various options. It becomes difficult to make a choice because all these lenses are quite expensive. This guide is written to help you out in making the best decision while choosing your new lens.
Understanding Lens Categorization
Most common categorization of lenses is based on fixed or variable focal length. Focal length is the distance between focal point of the 'combined lens elements' from the sensor plane of the camera.
Prime Lenses - These lenses have fixed focal length such as 14mm, 20mm, 24mm, 35mm, 50mm, 85mm, 105mm, 135mm, etc. These lenses produce images that have better sharpness and contrast than zoom lenses. The drawback is that this improved quality comes at the cost of flexibility. To get the right composition one will have to move around quite a bit. Prime lenses are often & lighter than the zoom lenses. Prime lenses perform very well in low light situations due to their wide aperture. Prime lenses also help increase mobility as these are light weight and allow you to be out shooting for long periods without getting tired.
Zoom Lenses - These lenses have variable focal length such as 14-24mm, 24-70mm, 70-200mm, etc. These lenses are loved by everyone because of more flexibility. Most of the time you can carry a 24-70mm and it will be enough. It's easy to carry one lens on your travel compared to multiple lenses. However, zooms come with weight penalty. Zoom lenses also tend to have softer (low sharpness) corners and vignette (lower brightness) around corners.
Next categorization is based on the focal length which governs angle of view. Different genres require different focal lengths with some creative overlap.
Wide angle - (14mm - 24mm)
This range is not very rigid and is mentioned only to give an idea. These lenses are used for landscapes, group shots, advertising, architecture, etc. A peculiar characteristic of wide angle lenses is perspective distortion, i.e. these tend to make the object closer to the lens appear bigger and things farther away smaller producing a very dramatic image.
Normal View - (24mm - 70mm)
Human eye has an angle of view of about 50 degrees. Focal length in this range produces images that look normal to the viewer. This range is ideal for portrait photography & fashion photography.
Telephoto - (70mm -200mm)
This range is used for various purposes. Telephoto lenses produce an effect called tele-compression. It means that it reduced the appearance of the distances between the subject and the background. This range is used for outdoor portraits, fashion, sports, etc.
Fish Eye - Focal lengths less than 14mm with distortion are called fish eye lenses and produce a lot of distortion. Focal lengths more than 200mm are used for wild life and sports photography. Ultra-wide lenses that do not cause distortion and try to maintain the vertical lines and the horizontal lines are called rectilinear.
Macro lenses (or Micro) - These are lenses can focus very close to the subject and have a magnification factor (1:1 or more). These are used for images of bugs, insects or products.
Perspective control lenses - These lenses can alter the focal plane of lens elements with respect to sensor plane. This flexibility helps maintain the flat perspective while taking pictures of tall buildings and architectural photography. If such structures are photographed with normal wide angle lenses then buildings appear to be falling backward.
Next categorization is based on maximum aperture of the lenses.
Fast Lenses - Lenses with wider apertures are known as fast lenses because these allow camera to use faster shutter speeds as they let more light to get in. Zooms are available with maximum aperture of f/2.8. Zoom lenses with constant aperture throughout the focal length range are heavy and expensive. Prime lenses are available with much wider apertures of f/1.4 or even f/1.2. prime lenses with very wide aperture are very expensive. However, primes with maximum aperture of f/1.8 are affordable and produce very good quality. Zooms with variable aperture have limited maximum aperture which reduces as one zooms towards the longer end of the focal length range. For example an 18-105mm lens f/3.5-f/5.6 has aperture opening up to f/3.5 at 18mm but as one zooms up to 105mm aperture opening is available only up to f/5.6. NOTE: Larger the aperture number smaller the lens opening will be.
Quality of Lens
Picture quality of a lens depends on resolution & acutance, chromatic aberration, distortion and vignetting.
- Resolution & Acutance: These are the two characteristics that result in sharpness of the image. Ability to produce two very closely spaced thick lines (black on white background for testing) is called resolution. Ability to maintain boundaries / edges of that line sharp is called acutance. Resolution of the lens must be more than that of the camera sensor to make a sharp image.
- Chromatic aberration: This is a defect caused due to characteristic of white light. Natural white light is made up of seven colours (VIBGYOR). Each of these colors has different wavelength and hence is focused at a slightly different point generally causing a purple fringe along the edges. Lens manufacturers use coatings and Low dispersion elements to minimize chromatic aberrations. Some camera bodies also remove CA.
- Distortion: This refers to the ability of a lens to produce an image with vertical lines staying vertical and horizontal lines horizontal in the image. Manufacturers use aspherical lens elements to reduce these distortions. Most of the times these distortions can be corrected in post-production.
- Vignetting: This is the characteristic of light fall off around the corners in an image. This is observed usually while shooting at the wide focal length and widest aperture of a lens. For most photographers it is not a great deal because no photographer places anything important around the corners. But it can be a problem if one is planning to stitch the images in a panorama. It can also be important for jewelry and fashion shoots where chances of using the edge are more.
- Vibration Reduction (VR) : This is a very important feature of modern lenses. This feature allows you to shoot handheld at lower shutter speeds such as 1/20 Sec. It's a must have feature in telephoto lenses but now a days manufacturers are including VR feature even on wide angle lenses which is a warmly welcomed by both professionals and amateurs alike.
Few other important consideration before deciding on a lens:
- Flare & Ghosting: When a bright light source is in the frame it causes flares and ghosting due to internal reflections between the glass elements. Modern lens manufacturers use coatings to minimize these defects. Sometimes photographers use flares to make interesting pictures.
- Weight & dimension: This is a major criterion to decide on a lens. Buying a lens that weighs 1.3 Kgs may sound like a no big deal but carrying it throughout the day or trying to shoot handheld may be a big headache for most photographers. While traveling, flights have an in-cabin weight limitation and if your lenses are too heavy you might have to pay extra money for cabin luggage every time you travel through an airport
- Build Quality: There are lenses built with metal body and others with plastic body. Plastic body lenses are usually cheaper and lighter but after years of use their elements may become shaky. Investing in lenses in a good idea because optics stays great for years and years.
Alright you know all of the terms associated with lenses. Let's see how to select which lens you'd like to buy:
0. Decide Full Frame of Crop Sensor. If you are planning to upgrade to full frame camera sometime in the future then definitely buy full frame lenses even though you may have a crop sensor camera right now. All Full Frame lenses are usually compatible with crop sensor cameras too (check camera mount compatibility).
1. Decide your budget based on if you are going to make money with your photography or you are going to shoot for hobby.
2. Decide the Focal length (or range) that you need. Pay attention to what kind of photography you mostly do. If you are mostly into landscape then look for a wide angle, if you like street then there are two types of street photographers one who like making photographs look personal, so they use wide angle lenses and take environmental portraits or group shots. If you like portrait & fashion photography then look for telephoto range of focal lengths.
3. Decide on Zoom or Prime. It's good to have a prime lens of a focal length that you shoot at most often. Let's say you primarily shoot portraits then you would want to have a dedicated portrait prime lens (like 85mm f/1.4). Sometimes if you like shooting landscape then you may want to have a 14-24mm zoom (or something similar) as an additional focal range for landscapes.
4. Decide on Aperture Wide aperture lenses are expensive, fast, heavy and create great. If you need great bokeh chose a fast prime. If you need bokeh and versatility then chose a zoom with f/2.8 constant aperture. For usual landscape shots one doesn't need fast lenses as these are usually done on tripod.
5. 3rd Party lenses There are many companies that manufacture lenses and are expert in this field. Zeiss, Sigma, Tokina & Tamron are well known lens manufacturers in addition to Nikon & canon which one should consider before finalizing a lens. To compare sharpness and contrast you may use websites such as www.dxomark.com to compare lenses & cameras. Don't forget to compare MTF (Modulus Transfer Function) charts before finalizing your lens.
Recommended Prime Lenses (Full Frame):
Wide Angle - Nikon AF-S NIKKOR 24mm f/1.8G ED
Normal Wide - Tamron SP 35mm F1.8 Di VC USD
Normal Telephoto - Tamron SP 85mm f/1.8 Di VC USD
Recommended Zoom Lenses (Full Frame)
Wide Range - Tamron SP 15-30mm F/2.8 Di VC USD
Normal Range - Tokina AT-X 24-70 F2.8 PRO FX
Telephoto Range - Tamron SP 70-200mm F/2.8 Di VC
Now you may chose the lens that fits your budget. You may look at images by any lens or camera on Pixel-Peeper website before buying a lens. I would like to end this article with an advice that lenses and cameras don't make a great picture, the photographer behind the camera does. All the best!