I’ve been meaning to write about camera lenses for a while now.
The single most important thing about a lens is that the pictures you
take with it looks great. If it isn’t perfect in every possible way when
you zoom in, but look great I would say it is a good lens. For example
Leica lenses are not the sharpest in the world, but they look fantastic.
And I would say that look better than most if not all of the “perfectly
sharp” lenses available. This is because if you are making a “perfect”
lens you add more elements or glass to the lens that means more stuff it
has to pass through to correct various optical “problems”. And then you
loose something called micro contrast. Some people want a perfect lens
because of reasons that is beyond me (a fancy way of saying: for reasons
that don’t matter) and some of us just want a lens that produces great
Every lens has a focal length. That is the number you read in mm. It is
a horrible system because how close you would be to a subject with X mm
varies based on how large the film or sensor is. You have something
called the crop factor, that is how large the sensor or film in your
camera is relative to 35mm film. For example my Fuji is around 1.5(same
goes for Sony and Nikon APS-C cameras) and a full frame camera is the
same as a 35mm camera; Canon APS-C is 1.6 and MFT (Sony and Panasonic)
has a crop factor of 2.0.
Let’s take a 50mm lens on all of the systems:
We are stuck with the mm system, but it sucks. The mm number on your
lens is not just about how much you can fit in your frame or how far
away you can stand away from your subject. A beginner would probably
chose a lens or focal length based on that. But more experienced
photographers would often chose them based on the look the different
focal lengths give you.
Longer lenses (larger focal lengths) compresses what you take pictures
of while wider lenses (smaller number) kind of makes everything look
more “dragged out”. This means that a portrait taken with my 8mm lens
makes people look fatter than with my 105mm. A longer lens also means
that you need a shorter shutter speed to avoid a shaky image, this is
because the magnification means all shape is magnified. The rule is
usually that the slowest is the same as the focal length equivalent on a
It will also be a larger separation between subject and background when
you use a longer lens. This means that background blur and “bokeh” is
more visible the longer the lens is. This plus that people look slimmer
with longer lenses are the reason you often want to use a as long as
possible lens when shooting portraits.
The next important technical detail about a lens is the aperture. It’s
that strange number with a f in front of it. It basically tells us how
wide a lens can open up. The smaller the number the larger it can open.
For example f/1.2 is very wide. When you set your lens to a small number
means that less stuff are in focus, While a larger one means that more
stuff are in focus. But there is a limit to how large you should go,
relative to how large your sensor is. This is one of the reasons medium
and large format cameras are popular among landscape photographers.
Some lenses also have optical stabilisation, and some camera bodies have
it. This can make it possible to shoot pictures with much slower shutter
speeds than without it. But you should always disable it when you shoot
with a tripod.
Now. Let’s get back to what I started with.
The smaller the f-stop number is, the bigger the lens would be, and the
more “technically perfect” it is the more elements there are in the
lens, often really big and heavy when it is really small, like f/1.2 or
smaller. This means that the lens can be very unfordable to hold and use
for long periods at a time. But it also means that auto focus will be
slower. The reason for this is that there is small motor inside your
lens that moves the elements forth and back until it’s in focus.
For example Fuji has f/2 and f/1.4 versions of both their 23mm (equal to
35mm) and 35mm (equal to 50mm) lenses. The f/2 version is much lighter
and has much faster auto focus speed. This shows the never ending
problem when you pick a lens: what’s most important to you?
When I talk about “technical perfection” that means that the lens
manufacturer add a lot of extra elements or focus more on the lens being
“perfect” than producing good pictures. They are basically trying to
solve a number of optical anomalies. Like making sure all of the lens
always is “sharp”. Or that the light spots in the out of focus parts of
your pictures have the right shape and a million other things.
Some people (that often are more into the technical specs of the camera)
care a lot about this. I personally don’t care. The thing I care about
is that the pictures look good, and that the colours come out right.