How to choose a photo lens for your SLR or hybrid? - AmosSalden

Senin, 11 Maret 2019

How to choose a photo lens for your SLR or hybrid?

How to choose a photo lens for your SLR or hybrid?

Whether buying the case, or especially after, it is difficult to navigate when you are interested in buying a goal. What do you mean all the technical characteristics, what is the best considering your budget, what type of objective do you need, what is a fixed focal point, etc? In short, you have thousands of questions, which I will try to answer in this article. Since this article, I also treated this topic in video more recently, if you prefer the format:

Indeed, this is the perfect time for me: two friends asked me for advice on equipment last week, and I myself bought a new lens (which I will probably discuss in detail when I have had leisure to have fun with).

First and foremost, I do not want people to think I'm contradicting myself: I always think that buying equipment should not be your priority. If you have a problem with your photos (lack of sharpness, colors, it does not matter), it is more likely a problem with you than with the material. But sometimes, when we start to know what we prefer to photograph, Whether you have special needs or you feel limited by your equipment, you can look for a new goal. As always, what will determine your purchase are your needs. This article is therefore a complete guide to help you choose, but not to choose for you and whatever the brand of course!

However, given the number of existing objectives, it is a little complicated to navigate in this jungle. Let's start with a small precision that seems obvious but that can be useful: you obviously can not mount a Canon lens on a Nikon camera, or vice versa. On the other hand, there are two third-party brands (Sigma and Tamron) whose objectives are available in one version for almost every existing brand. Let's see one by one the different parameters to take into account:

Focal length
In general, this is the first thing that comes to mind when you read the description of an optic: the focal length is expressed in mm, for example 50 mm or 18-105mm. This number tells you how much your subject will be enlarged (or reduced) compared to your vision when you shoot it. This focal length makes it possible to define categories of objectives:

  1. Standard: This word means that what you see in the lens is about what you see with your eyes. For technical reasons that I will not explain, the focal length corresponding to the human eye is about 50 mm for a film camera or a full-format sensor (two cameras that you probably do not have), and 35 mm for an input or midrange reflector (APS-C sensor). What makes this category include all lenses whose focal length ranges from 35 to 85 mmThis type of focal length is generally ideal for portraits or "a little bit of everything". By the way the lens of the kit is usually a 18-55 mm, which covers this category and even a little bit of the next, so you can photograph your holiday spot or your mom 😀
  2. Wide angle: This category is named because what you see in the lens is wider than what you see with the human eye. Optics are generally 28 mm or less. This type of lens is very useful for landscape photographs where we want to capture as much of the scene as possible. As we generally get closer to his subject at these focal lengths, the impression of depth of the images increases, and the deformations due to the perspective as well. There are also very wide angle lenses which distort the image so called « Fisheye", In reference to the eyes of fish that are all round and see no matter how. But these are very special lenses that are not usually the priority of the photographer.
  3. Telephoto: Regarding anything above 100mm (above 300 we call it super-telephoto), this type of optics is used to have a large subject in the frame although they are far. In other words it is used for sports photos and animal photos or for portraits for small telephoto lenses around 100 mm.

How to choose a photo lens for your SLR or hybrid?
From left to right: a wide-angle (10-22mm)
A standard with a bit of wide-angle (15-85mm)
and a telephoto lens (100-300mm)

I hope that these 3 very simple categories already enlighten you a little. Let's talk about 2 points in close relation with the focal length.

Minimum focus distance
At the same focal length, say 50 mm, an ant will not have the same size on the photo if you are 50 cm from her or 5 cm, it seems obvious. This is where the minimum focusing distance comes in: Only macro lenses allow you to focus at a very short distance , and thus get full frame shots of ants 😛 So a lens is macros' it has this characteristic, which has nothing to do with the focal length: there are macro lenses of 50 or 200 mm.

How to choose a photo lens for your SLR or hybrid?
With a very small focusing distance,
 (here on the Tamron macro lens 90mm f / 2.8),
we can make very close-ups (here on a dandelion).

Zoom or fixed focal?
To put it simply: a zoom has a focal length that can change, a fixed focal length, and well is fixed 😀 You will say to me: "But it is no fixed focal lengths, you must walk instead of zoom!". Strip of idlers! 😛 I'm going to generalize a little bit obviously, because there are good and bad lenses in both categories, but let's see their advantages :

Advantages of fixed focal lengths
  • Quality: The zooms are considerably improved, but at an equivalent budget, a fixed focal length produces sharper and more precise images with more sharpness than zooms. Do not leave this prejudgment systematically, but it is a rule that is true in general.
  • Price: The fixed focal lengths are cheaper in a general way, which seems logical since they are of a simpler construction (they do not zoom in particular). There are obviously extremely expensive fixed focal lengths, but only in the professional ranges. The entry-level 50mm is known to be extremely inexpensive and yet of high optical quality.
  • Weight: Always because they are of a simpler design, fixed focal lengths are lighter. This is not negligible after a day of walking or going on a trip.
  • Maximum aperture: They generally have a larger maximum aperture than zooms, but we'll talk about this further.
  • Creativity: It is probably more personal and a little less objective, but by forcing you to move to fit properly, a fixed focal length requires you to be creative and find other angles.

Canon EF 50mm f / 1.8 focal length lens photo
The Canon EF 50mm f / 1.8,
fixed focal length extremely affordable
and of high optical quality.

Advantages of zooms
  1. Versatility: The zooms cover a larger focal area, they allow to take pictures of several different types. Depending on the goals you bring in your bag, they can even be an advantage in terms of weight and cost.
  2. Flexibility: Depending on the focal range it covers, a zoom can offer you the ability to shoot at wide-angle, standard and telephoto with the same lens! I think for example "transtandards" type 18-200mm.

The article may already seem long, but there are many factors to consider, and we are talking about how you will spend your next Christmas bonus and preparing your purchase could save you money a few deniers. But do not worry, the rest will be shorter!

Maximum opening
First of all, if you do not know yet what it is or if you need a reminder, go read the article on Focal Aperture first. The maximum aperture of the lens is designated by a value in f / number which determines how far the iris of the lens can be opened. In other words, the more maximum aperture is important (and therefore the f is small, remember), plus:

  • You can shoot in low light without slowing down your shutter speed, increasing the ISO speed, or using a flash
  • You will get a reduced depth of field

The depth of field is very interesting from a creative point of view, and I can tell you that as long as you did not take a picture below f / 2, you do not really know what the depth is. But being able to take pictures in low light is a great advantage not to neglect! This is why these optics are called with a large maximum aperture of "bright" (they let in more light) or "fast" optics  (they allow to use larger shutter speeds).

Note that these advantages generally increase the price of the lens, especially for zooms and / or important focal lengths. This maximum aperture is indicated after the focal length. Three examples to understand:

  1. 50mm f / 1.8 means that this fixed focal length of 50mm can open up to f / 1.8
  2. 18-55mm f / 3.5-5.6 means that this zoom can be opened up to f / 3.5 to 18mm and f / 5.6 to 55mm
  3. 28-70mm f / 2.8 means that this zoom from 28 to 70mm can be opened up to f / 2.8, whatever the focal length

The maximum aperture you need depends on the situations in which you shoot:
  1. In interior, especially in low light situations (I think of the concert ), you'll need an opening of f / 2.8 or more.
  2. For the days covered, especially in conditions where you need to use a fast shutter speed, you can settle for f / 3.5 or faster.
  3. Finally in full sun, any opening will be appropriate.

At this level, you have in your hand the two main elements that lead to choose a goal: The focal length and the maximum aperture. Let's see the details now.

Stabilization prevents camera shake (when your camera is not stable), so it is not useful if you use a tripod for example. This is especially useful if you are using a large focal length which is more prone to camera shake. This technology also allows you to reduce your shutter speed a bit by two (or more) clicks without having a blur problem, which can be useful in low light situations.

The stabilization is not trivial, I also recently advised against a friend a purchase because of that: a tempting offer with a 18-55mm whose version without stabilization has a bad reputation, and a 75-300 with which he could have made clear photos in ideal light conditions (which never happen when we need it, obviously).

There are bad brand goals for your device, and good at third-party brands such as Sigmaand Tamron. And conversely. My principle is simple: I am looking for an objective of the brand of my device (Canon in this case). If I do not find my happiness, I look for third-party brands.

For some models, we may prefer to turn to third-party brands as the differences in quality are minimal and those of significant price. It's up to you to see if there is a substantial saving to be made by reading the tests on the internet. I have also released a complete guide on choosing a lens for SLR, which you can find in digital format here, or in paper version for Canon or Nikon.

This is obviously the biggest constraint for many of us. I'm not going to lie to you: in general you get what you pay for and a cheap goal is generally worse than one of the higher range, that makes sense. But what is important is the relative price! Take an example: a 50mm f / 1.8costs a hundred euros, and yet it is an optics with a large maximum aperture and excellent sharpness. It is very affordable because it does not zoom, is of a very simple design, and manufactured in inexpensive materials. And there are two lenses of the same type in the range, both 50mm (fixed focal length), but which open at f / 1.4 and f / 1.2 and cost respectively 4 times and 15 times more expensive.

Let's summarize a little bit. Depending on your needs, you must determine:
  1. The focal length you need: wide-angle, standard, telephoto
  2. If it must be flexible (zoom) or if it is not essential (fixed focal length)
  3. If you need a close focus (for the macro), or not
  4. If you need a large maximum aperture , in other words if you shoot in low light or not

At this point, you can determine 2 or 3 objectives that suit your budget or decide to continue saving (I'm not kidding, it may be an option). Read tests on these goals on specialized sites by doing a Google search, and possibly some user feedback on forums. And normally, you should be able to make a choice! That's it, I did not think to be so long, but the subject is vast, especially covering all the needs and trying to talk about all brands! If you have any questions or comments, please leave a comment below.
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