In my last post I introduced you to the basic types of DSLR lenses that are on the market as a starting point for answering the question of ‘which DSLR lens to buy?’.
Today I want to turn to a number of other factors that you’ll want to keep in mind when making the decision. Each of the following lens features will differ from lens to lens.
Lens Speed – perhaps one of the first things a lens sales person will tell you when you’re looking at a new lens is it’s ‘speed’. Lens speed, or how fast a lens is, really is describing the maximum aperture of the lens. Aperture is the size of the opening that the lens opens to when the shutter is depressed (or how much light gets through) – it is described as a number with the letter F next to it (an f-stop).
Without going into great detail, the smaller the number the larger the hole and the more light that can get in at a time. This means that the shutter speed can be quicker and means the lens is ‘faster’.
The maximum aperture of a camera will help you work out a number of things.
- A nice fast lens for instance with a maximum aperture of f/1.4 (that’s my fastest one) will be able to take shots in a lot darker places than a lens with a maximum aperture of f/4 or f/5.6. This doesn’t make the slower lens worse – but it’s good to know.
- A faster lens will also allow you to take pictures of moving subjects and freeze them better.
- Faster lenses let you have shallower depth of field. This means that when you’re focussing upon a subject the foreground and background will be blurrier. Of course having a very fast lens means that this can actually make focussing more tricky as your depth of field is very shallow. Of course you can shoot at a smaller aperture with a fast lens to make your depth of field deeper.
- Fast lenses are usually more expensive than slower lenses.
- Faster lenses will help with your flash photography too as they capture more ambient light.
My personal preferences with lens speed are that f/4 is usually good for general purpose shooting in good lighting. F/5.6 will need good lighting or Image stabilization. If you’re shooting indoors without a flash you’ll want to get a lens with at least f/2.8 and if you’re shooting sport indoors you’ll want to go even faster (f/2.0 – an prepare to pay for it).
Focal length – focal length refers to the length of your lens (it’s the ‘mm’ measurements that is associated with a lens). This measurement is the distance between the optical center of your lens to the focal point on the camera’s sensor. We could look at a lot of formulas and graphs at this point – but I’ll keep it simple.
What you need to know is that the focal length of a lens tells you how much it will magnify your subject when photographing it. It will also tell your what kind of angle of view you’ll get (ie a wide angle where you see a large scene, or a more zoomed in and tightly cropped shot).
I’ve talked quite a bit about the different focal lengths that you can expect to find in my previous post on types of DSLR lenses. Ultimately the focal length you’ll need will be determined by the type of photography and subject matter that you have in mind.
Focusing Distance – this is the measurement between the end of your lens and the nearest point that it can focus. It’s particularly useful to know this if you’re going to be doing Macro or close up photography as in these types of photography you need to get in nice and close.
Image Stabilization – more and more DSLR lenses are coming with some form of image stabilization (often referred to as IS). This helps combat Camera Shake.
Camera shake is the movement that happens while your shutter is open. It has a bigger impact when you’re shooting at slow speeds, when you’re not using a tripod and when you’re using a lens with a longer focal length.
There are different types of IS in different types of cameras and lenses but most DSLR lenses that have it contain little gyro sensors which correct any camera shake. I personally don’t understand the mechanics of it all but have found that in my Canon lenses that have it that it allows me to handhold cameras (ie no tripod) at shutter speeds a couple of stops slower than if I didn’t have it on.
Also worth noting is that while IS helps stop camera shake which is very useful in poorly lit situations it doesn’t freeze moving subjects. Basically it allows you to shoot at slower shutter speeds which means your camera is open longer – but if your subject is moving this means it will more blurred.
IS adds cost to your lenses so you’ll need to consider whether you’ll be taking shots that will need it or not – ie will you shoot in poorly lit situations at longer focal lengths without a tripod?
Build and Quality – lenses vary considerably in terms of their quality of construction. You will quite often notice the difference in this simply by picking two lenses up at once and feeling the weight of them. For example I have to 50mm Canon lenses (an f/1.4 and an f/1.8) and there is a significant difference between the two in terms of weight and the materials that are used. The f/1.8 obviously contains a lot more plastic than the f/1.4 – especially noticeable in the mount region, an area that it’s handy to have metal as it is what rubs against your camera.
Most lens manufacturers have a range of different quality lenses. For instance in the Canon range there are a series of lenses called ‘L-series’ lenses. You can spot them by the red ring that they have at their end. These lenses are designated as professional/Luxury quality lenses that use a higher quality of glass and optical elements. They are generally weighty, ruggedly built, are pretty ‘fast’ are fast focussing lenses and take wonderful shots.
This is not to say that all L-Series lenses will be the perfect lens for each person – budget considerations limit the amount of them that a photographer can afford and there are many other lenses that take great shots too – but it is a consideration.
Budget – Speaking of L-Series lenses makes my wife nervous so I should touch on budget here. Lenses cover an incredibly wide spectrum in terms of cost. Most people agree that you usually get what you pay for and my advice to prospective DSLR buyers considering camera models is that if that you can probably improve your shots more by upgrading to a better lens than upgrading to a better camera body (not always the case). Be a little wary of the ‘kit lenses’ that come with camera bodies. In some cases they are good – but it might be in your best interests to buy a camera body alone and get yourself a nicer lens than the kit one if you can afford it.
Brand – Many arguments have been had over whether you should stick to lenses made by the manufacturer of your camera or whether you can achieve just as good results at a lower price with one of the generic brands (like Sigma, Tamron etc). My own opinion is that I first look at Canon lenses and then if I don’t find what I’m looking for I will then take a look at third party lenses. From talking with many DSLR owners I believe that all manufacturers have their good and not so good lenses and it’s worths shopping around. Do plenty of research on lenses before making purchases though. There are many great websites and forums available for making comparisons – make sure you do your research!
Discuss your favorite lenses at our Flickr Group Discussion on Lenses