If I ask you what kind of lens do you have, what would your response be? Most people’s response would be “the one that came with it the kit. “ Don’t know a long one?” If you’re not sure that is ok. Most beginners don’t have the nomenclature of the large selections of lens out on the market. In this section I will talk first the parts of the lens, cleaning and care of the lens, protective filter or not, filter, and the different types of lens on the market.
The first thing you see on any lens is of course is the glass. In a 50 millimeter lens there are 7 elements (glass) in 6 groups all refining the subject before you into a sharp and clear image on the film or sensor plain in the camera. Typically the better the glass you get the better the images you can capture. Put a great lens on a standard camera and you will get great images despite the lack of technology in the camera. This also holds true in the opposite, putting a poor lens on a professional body will render awful images. It pays to buy good glass.
The second thing you will notice when looking at your lens is the aperture at the back of the lens. These are usually made of thin blades that open and close depending on the setting selected by you.
The definition of aperture for photography is a gap or space in which light passes through an optical or photographic instrument which can vary in size to control the amount hitting the film or sensor plain. This is also known as an F-Stop. On film cameras the F-Stop was controlled by a ring on the lens. Select an F-Stop and if the exposure is correct (or even if it is not) the camera had an arm that pushed the blade’s lever on the lens to the F-Stop selected. On a DSLR, at least mine, I select the F-Stop with a dial on the body and an arm pushes the lever on the lens to the desired setting. For some cameras it is the body talking to the lens and actuators do the work.
So with the combination of the glass and the F-Stop (aperture) will determine how good your lens is. Or you will also hear someone refer to the lens as “glass”. There is good glass and bad glass and depending which one you have will be a big factor on the quality of images you will get. This is not to be confused on whether the photograph is compositionally sound or not. You can have the best lens and camera and still can’t shoot your way out of a paper bag. Good glass or bad is taking in account of the actual glass and the widest F-Stop opening it offers. For example;
A 50 mm lens 1.8 is a good piece of glass. This lens lets a lot of light in a most likely has clean elements or glass are very well crafted. This also means that it will be very expensive. On the opposite side a 50 mm lens at 3.5 is not a good piece of glass. You still can get good photographs from it but it will not allow as much light in therefore you have to use a higher ISO and slower shutter speeds. More noise and more chances of camera shakes caught on the image. This lens will be considerably less expensive. Now don’t get me wrong I don’t want to turn you in to a snotty lens freak and insist you buy only the best lens or your nothing. The whole idea in this explanation is to let you know why some lenses are so high priced and some are so cheap and cheap is not always the way to go. You buy what you can afford and if it means saving just a little more the better glass then you will know your getting a great deal.
Lenses are not only divided up in price but by size. 14 to 35 mm lens are typical wide angle lens, 35mm to 70mm are standard and 70mm to 300 are telephoto lens. These are general measurements and can be broken down in to farther categories so don’t get too tied to these numbers. Lens can also be called prime and zoom. Prime are set numbers like 50mm lens, 300mm, 800mm. Whereas zooms are 24mm to 85mm or 70mm to 210mm. Each type of lens has their pros and cons about each one so which one will work for you will depend on the type of shooting you will do.
Now how is the size of the lens determined? Well the size of the lens is not determined by the length of the front element to the back element, but by the distance from the point of convergence to the film plain or sensor. So where the light is bent to a single point to the place where it falls on the film or sensor is the determination of the lens size. If you have a 300mm lens, it is 300mm from where the point of convergence happens to the film or sensor plain is located. 28mm is 28mm of that same measurement.
To clean your lens;
First you want to blow off any dust and loose grime the front and back element. By blowing off I mean either use canned air or a rocket. This way if you have dirt on the lens when you go to clean it, you will not grind it in to the glass. Next take a lens cloth and start from the inside and wipe out in a circular fashion. Do the same for the back element. Now I don’t use liquid cleaners but if you have to be sure you choose one that will not wreck your coating on the lens. Once the coating has been compromised you may suffer color changes or hazing of the lens and your images. In which case you have to have it recoated it at which point you should just buy a new lens and keep the old one for a paper weight.
To filter or not;
It is up to you whether you should or not but here is my advice. If you have a very expensive piece of glass why would you put a crappy filter in front of it? If you want to protect it place a lens hood on. The only filters I use are a neutral density filter to aid in exposures and nothing more. But again it is up to you on this issue.
The last thing I will say about lenses is now that we are in the digital age there are two types of sensors. One is a cropped or DX sensor and the other is Full Frame or FX sensor. If you are looking for a lens you will have to take into consideration the type of sensor you have. It is a good practice to keep the DX lens with a DX sensor and vice versa but I have heard that is not a hard rule that must be followed.