Lenses are best described by their focal lengths, so that is where we will get started. The focal length is the distance in mm from the lens focal center to the camera sensor, at a focus of infinity. The optical center is point where all light rays intersect in lens.
Focal length relates to what you see in that it determines the angle of view or the field of view. It determines how the subject will be magnified or diminished in the shot. Short focal length gives wide field of view, while long focal length gives narrow field of view.
Zoom lens are variable focal length lens, while prime are fixed focal length.
Sensor size
You may have hear of cropped sensors. Digital photo camera have photosensitive sensors, which are not all zise. the standard is full frame, witch is 35 mm. There are 3 major categories:
- Full frame – Crop factor of 1
- APS-C – Crop factor of 1.6 for Canon, 1.5 for Nikon
- Micro 4/3 – Crop factor of 2
Camera makers have their own terminology for describing their crop. The crop factor informs how the image will look at a given distance. A 50mm lens in a full frame camera offers close to the perspective of the human eye. My Nikon D3300 DSLR, an APS-C with a crop factor of 1.6, would use that same lense but the perspective would be more like 80mm.
The lens is a projector, projecting the light from in front of the lens to the focal point, where it is forcused and sent to the image sensor. On full frame camera, your sensor sees more of the scene, whearas on a smaller, crooped sensor, you get relatively less of the scene, giving the feel of the longer focal length. This is called Equivalent Field of View or Equivalent Focal Length.
Photo isn’t smaller, as cropped sesnor cameras have as many if not more pixels than full frame, but the amount of the scene that is captured is smaller. It’s cropped around the center of the scene, removing information around he edges.
In order to compensate, we must either move back or use a different, shorter lens. Think of it like this: within given constraints, you can get the saem picture with any camera or lens. Relatively, a cropped sensor camera will feel tigher in it’s compositions and any ultra wide angle images will have distortion on the edges.
Aperture
Aperture is a hole through which something travels, in this case light. Cameras are rated by fNumber, woith lower number being larger and letting more light in. The higher the number, the smaller the aperture and less light gets in, with a larger depth of field.
There is a maximum (lowest) fNumber that a given lens can use, called its Maximus Perture. More expeive lenses have a larger maximum aperture. Prime lenses have a larger maximum aperture than zoom lenses. At most basic, it control the amount of light.
Speed is a relative term used when discussing the shutter speed that you can capture an image at. It is not always possible to use slower shutter speeds, for example, when a subject is moving and you can’t allow motion blur. A lens that has a maximum aperture of f3.5, at the same shutter speed, would let in half the amount of light as a lens with a maximum aperture of f2.8, so the 2nd lens would be faster, allowing for more light at the same shutter speed. This also means we could get the same amount of light with a faster shutter speed, because we are getting more light from teh aperture.
Faster lenses are important when the light is low (inside or outside in the night, without flash). Because there is a maximum to how much noise you can allow, and how much motion you can allow, the aperture becomes your primary means of controlling the light in your scene. More aperture values gives you more possibilities!
Depth of Field
The distance between the nearest and further object in scene that appear acceptaly sharp. In other words, area in front or behind point of focus that appears to be acceptably focued.
Think of DOF as part of scene that is in focus. Aperture affects DOF:
Larger number has longer DOF – Good for landscapes
Smaller number has shorter DOF – Good for portraits. For short depth of field, you need faster lens. Zoom lenses are usually slower, and some have variable maximum apertures. As you zoom in, the aperture closes as well, giving you less control as you move to higher focal lengths
Difraction
The bending of light rays at smaller apertures (higher fNumber), making the image less sharp. Usually images become sharper as aperture becomes smaller, but this trend inverts at the point of diffration. Diffration is also dependent on sensor size:
Full Frame camera can use down to f22
APS-C can use down to f11
Micro 4/3 can use up to f8
If you shoot past the point of diffration, you will get blurry images. Another option is to use ND filters. If I am at f11, the shutter speed I want, at the lowest ISO, but I still need less light, pop on an ND4 for 1 stop reduction to get the shot you want with the settings you like!
What Does a Bad Lens Look Like?
Blurring can occur from crappy lenses. This will occur most commonly in the corners, especially when zoomed in to the pixel level.
Crappy lenses also have lower contrast. The colors will be deeper, especially in the shadow areas. Look for a great quality in the shaded color tones.
Chromatic Abberation is a distortion where there is a failure of the lens to focus all colors to the convergence point. It looks like a smearing of colors on the edges of objects. Happens mostly between high contrast points. It is subtle.
Higher end lenses use low dispersion glass, that results in less chromatic abberation.
Vinettging is a reduction in brightness or saturation at corners, compared to image center. Many lenses have vignetting at max aperture. It often gets better as you stop downt he aperture.
It can be difficult to determine ignetting because of the natural drop off of lgith. You will always see more vignetting on the sides rathen than the top. Cropped sensor cameras will have less problems with vignetting, especially when used with lenses designed for full frame cameras.
When using cropped sensor with digital lens, you willl see more vignetting.
Distortion is also a problem. Barrel distortion means image magnification decreases with distance from center, or optical axis. It looks like the image is mapped around a sphere. In zoom lens, barrel distorion is worst at the wide angle of the range. t begins at the middle of the focal range. The more zoom range you have, the more distortion you will have at the long or short ends of the range.
Pin Custion Distortion
Image magnification increaes as you move from axis. Lines are bowed inward. Usually occurs at longer end of focal range. Center of image looks like it’s being pinched.
Lens Features
Stabilizaion comes from optical image stabilization. Sensors in lens analyze vibration and apply compensation that shift the image parralel to the focal place. This allows you to use slower shutter speeds while still acheiving sharp images.
It has the most effect when working at large ranges with a handheld camera. Rule is 1 over effective focal length, without image stabilization. This rule can be stretched when using image stabilization.
Lens Coatings are treatments applied to the outer surfaces to reduce reflections. Reflctions occur whenever light moves from one medium to another. Without coatings, light would love 4% intensity each time it encountered a new layer of glass.
This is important because lenses are multiple layers of glass, so light is being reduced dramatically upon entering your lens. Complex lenses without coatings would have as much as 70% light absorbed or scatter before it even hits the sensor!
Many layers have multi-coatings and better lenses have nono-coatings. Filters, hoever, some aren’t coated. Cheaper ones have a single layer of coating on each side. Best have nono-coatings on both sides. When using cheap filter, can be throwing away precious light and contrast by using un-coated variety.
Fast Focus Motors
- SSM – Super Snoic motor
- SAM – Smooth autofucus motor
- USD – Ula sonic silent drive
- PZ – Piezo drive
- USM – Ultra Sonic Motor
- SWM – Silent Wave motor
- AF-s – autofocus silent
- SDM – Supersonic drive motor
- HSM – Hypersonic Motor
- IF – Intal Focusing
These technolgies are all compaed to old style focusing lenses, which moved and rotated and mde a bunch of noise. You can still find these, so be sure you knwo what you are buying.
Lenses that focus super fast are very useful when shooting any moving scene.
Standard Zoom Lenses
Stardard zoom lenses are lenses that cover the normal focal distance, plus have wider and more narrow focal distances as well. The normal focal distance is the distance where objects look the same as they do for the human eye. This is a different focal length for different cameras:
- Full Frame – Normal Focal Lengh is 50mm
- APS-C – 28mm – 30mm
- Micro 4/3 – 23mm
- Standard Zooms come in different focal lengths for different cameras, with:
- Full Frame – 24 – 70mm
- APS-C 17 – 50mm or 18 – 55mm
- Micro 4/3 – 12 – 35mm
These standard lenses are most equivalent given the different camera crop factor. They all have roughly the same field of view. These lenses are also interchangeable.
24 – 70 is the standard because they offer a widr range of wide angle and telephoto focal view. Zoom lenses are very versatile and offer a ton pf dofferemt shots!
Mosto standard zoom lenses are kit lenses that come with the camera. They are made at the lowest price but still achieve acceptable performance. When stopped down ,they usually perform better. Certer sharpness is pretty good, but the corners are usually distorted.
Better lenses often use internal focusng, so the actual lens doesn’t change dimensions when moving through teh focal planes. They are better, but they cost more. They genally provid the best value.
Top of the line lenses have metal componeents and lots of great features. They use exotic glass and heavy coating, so they are the best of the best in terms of performance.
There are lots of lens makers, and you can get a great value by using a third party lens, that can be as good but cost much less.
Wide Angle Lens
Wide angles allow substantially more field of view than standard lenses. They also emphasize thedifference in distance betweek forground and bakcgound. Things closre to the camera look very big compared to things further away.
Wide angle is different depending on your camera:
- Full Frame – 12 – 24mm lens
- APS-C – 10 – 20mm ens
- Micro 4/3 – 7 – 14mm lesn
FOr APS-C and Micro 4/3, about he widest field ov view you’ll find is 114 degrees. (with fish eye). Full Frames can go to 142 degrees. We use mostly rectilinear lenses, which have straingh lines. At the furthest angles, however, you’ll get strecthing.
Fish eye lenses are different in that everything si strecthd and distorted. You can get 180 degree or more in the view.
To capture buildings and interiors, you NEED a wide angle lens. Most of the time, there just wont be enough space for you to move for the shot that you want.
Simply correct the distortion when using the wide angle at its largest field of view for amazing images without the artifacts!
Medium Telephoto Zoom
Fills gap between standart zoom and super telephoto. Long lenses are referred to telephoto, but that term actually applies to lots of lenses. Lenses that have a more limitied range are gonna look better.
Medium Telephotos have between 10 – 30 degree field of view. This means:
- Full frame – 70 – 200mm
- APS-C – 50 – 150mm
- Micro 4/3 – 35 – 100mm
You don’t walk around with these because at the wider range, you get a very narrow and close shot. Medium telephotos are good for taking picture of people or watching people in sports / activity. The shots feel a bit tighter. Great for portriats.
Telephoto Zoom Lenses
These are your wildlife lenses. A high quality lens will be one of your most enjoyable to use. They give you less than 10 degrees (super telephoto is around 4 degrees).
Full frame / APS-C – 150 – 600mm or 200 – 400mm
Micro 4/3 – 100 – 300mm
These can be very, very expensive. There is large rnge because you can use the same 200mm lens on a cropped sensor to make it much longer (300mm for NIkON).
It’s important to have image stabilization whe using focal distances of these length. These are also used a bunch for sports. At these focal lengths, it is okay to use slower lenses, unless you choose prime lens.
It offers a narrow field of view and great isolation of subject fro teh enviornmant.
When using long lenses, shootings objects that are very far away, will give lots of distortion because of air pressure and temperature changes.
Super Zoom Lenses
If you only have one lens, go with the super zoom. They have a huge range, but they suffer from distortion issues.
Full Frame – 28 – 300mm
APS -C – 18 – 270 mm
Micro 4/3 – 14 – 140mm
Most have variable apertures, but by the time they reach telephoto range, they will be stopped down. At longer photo lengths, distortion will be more apparent. These are okay for hobbiest, but not for pros.
They give lot of variation in the shots tyat you can get. They suffer in low light conditions, so they are great outside. Stopping down on the aperture can improve the carity.
Prime Lenses: Good, Bad, and the Ugly
Prime lenses are great because they have much less glass and less moving parts. This means less lens absorbtion, a lighter weight, faster focus, and a cheaper price. They are also faster than comparable zoom lenses, although zoom technology is improving rapidly.
They also have less distortion than zoom lenses, especially when at open apertures.
Unfortunately, the can’t be applied to as many projects. They also have to be changed often, resulting in dust entering your camera. Zoom lenses are much more flexable, you can change composition and angle quickly and easily.
When beginning, spend money on high quality zooms. If you are using older cameras, use prime lenses for more light. If you have a newer camera, try using zoom lenses with a bit more ISO to get the same amount of light as a prime.
If you are shooting film, use a manual prime lens as they are easier to follow focus with a larger and dampened focus ring.
Fish Eye Lens
Probably the coolest specialty lens, fish eye lenses are ultra wide angle that distort the image to create panaramas. They don’t go for rectilinear images, they go more sperical. They have 180 degree diangonal field of view, while vertical will be smaller.
The fish eye look depends on what you are shooting and where the horizon is. As long as horizon is near cente of lens, you will get less optical distortion. If composed properly, shots can look wide without distortion.
As subjects get closer, they become more distorted, offering cool effect and composition possibilities. Compose creatively and remember that you can correct for distortion with LIghtroom.
They work well for interiors where space is limited. They are also great for captureing the sky and fireworks.
Portrait Photography
You can take andy photo with any lens, but there are some sweet spots you shuld know about. Must understand perspective. Perspective is how the scene looks from a particalar spot in real space.
The human face changes with different focal lengths and different perspectives.
At 18mm – Will have facial distortion as center is barrel distorted, making nose look bigger.
35mm – Less barrel distortion
50mm – Nose reduces and edges of face are refined
80mm – Same as above
100mm –
154mm – When exposing side of face, watch for key or fill being flat against the light. This will make the face look broader and wider bacause the light if fallling on ta broad surface without any shadow runoff. 150mm introduces compression, so anything flat will look even flatter.
200mm – Compression is making objects look closer together, enhancing a flat and wide look. Not the most pleasing for portraits.
Thanks to this experiemnt, we see that between 50 and 100mm (on APS-C) we get good portrais. Less is too wide will more is too compressed and flat. Dramatic lighting can give you more range toward the higher end of the focal distance.
Compose for Compression
Higher focal lengths compress images, which is useful for controlling how large backgournd elements are, and how much background we see.
If you compose a shot at a fairly wide angle (20mm) and then move back from teh subject, you need a longer focal length to get a similar composition. Even though the subject can be composed similairly, the background will be much different.
The subject can be relatively the smae size, but the background will be much closer to the subject. This is known as compression, and occurs as the focal length increases. Object look closer togeteher and the distance between them appears lessended. Background objecs also look larger and more prominent.
Simply moving back and changing focal length can give you a completely differnt perspective, even with similar compositions.
Macro Lenses
Macro lenses offer the ability to focus closer to the lens. Usually, you can’t focus very close to the lens. The size of the subject on the image sensor is greater than life size. Reproduction ratio is comparision of real size to percieved size.
Magnificaion describes the relative size the subject will appear. Several enses have macro features, with amount of magnification depending on lens.
Try to use delay or shutter release (shoot ehered) becuase shifts make beg different. Always manual focus becuase photos will have shallow depth of field.
When lens is close to subject, it can be blocking light from subject. Look into macro flash for this.
Get into macro photography by using extention tube to increase magnification. Cheaper lens extention tubes wont have electonric contacts. If you need to change aperture, press depth of field prview button, then take lens off with aperture locked on lens. Then place extention tube and lens on top, this will give you the magnification with a chosen aperture. Get one with electronics to solve this issue.
Macro photography with a price lens is much sharper, but can be more difficult. Lens tube entenstions are heavier and the force on teh camera increases, so be sure to watch for the weights on the camera.
For lighting, you might have to go with off-camera flash in case the lens must get too close tot he subject.