Photographic Lenses
Written by: Digital PhotographyLENSES
Since optical designs of photographic lenses (wide angle to telephoto) differ so radically we will not go into detail about optics. This lesson will cover a basic discussion of lenses and some good tips on lens use and care. Lenses are designed to refract (bend) light rays. Here is a basic convex lens (crude drawing below). Notice that this bends the light towards the center of the film plane. A magnifying glass is a basic convex lens. 
A concave lens bends the light away from the center. In modern camera lenses, you will find a variety these lenses with some individual elements oddly shaped. 
Below is a cutaway illustration of a typical camera lens. Notice the different shapes of the elements. The science of optical design has become quite sophisticated and, as it has progressed we, the photographers, have benefited with sharper, faster, lenses with greater color purity. 
Depth of field is a term we use in dealing with the sharpness of objects in our field of view. We know the subject we focused on will be sharp, but what about objects in front of, and behind? We control the sharpness of those objects by using THE APERTURE which is built inside each lens. 
The aperture is used primarily for controlling the exposure (the lesson on Exposure follows this page, be patient) but it also controls the depth of field (depth of sharpness would have been a better term). Words cannot explain this as well as visuals so take a look below at how different aperture settings can control the sharpness of objects in front of, and behind, the subject you are focusing on:
Wide open .. f2.8 to f4.5
“Optimum” .. f8 or f11
Stopped down …. f16 to 32
If the lens aperture is “wide open” the depth of field is very shallow… notice how the runner (below) is sharp and the other players are out of focus. However, if you close the aperture all the way down objects in front of, and behind, will appear much sharper (see below). 
By keeping the aperture wide open (left) we give the runner a “3D” look. He stands out among the out-of-focus players and our eye is drawn to him. If we close the aperture down (right) more objects are in focus and the runner gets lost in the crowd. 
Therefore, if you have a camera that offers Manual Control, use “depth of field” to help draw attention to the objects you consider important. Now to some other tips lenses … TIPS ON LENSES: We always use a UV filter in front of the lens (instead of bothering with lens caps). The filter protects the lens and blocks out un-wanted, hazy UV light. The glass used in photo lenses is covered with a coating (to correct some color problems) therefore, you should be very careful when cleaning the lens. We suggest that you not use lens cleaning fluids, rather a gentle blowing (your breath has moisture) followed by a gentle wiping with a clean, soft cloth or lint-free napkin. If the lens is seriously smudged then put a drop of lens cleaning fluid on the cloth and gently wipe. DO NOT apply lens cleaning fluid directly onto the lens… the fluid could get into the edges and destroy the adhesive that keeps the element attached to the barrel. Don’t bring a lens in from extreme cold … the moisture inside will instantly freeze up the whole lens. It is best to carry the camera under your winter coat when not in use. When making photos you should make sure the lens is in the palm of your hand, freeing up the fingers to focus. This takes the pressure of the lens mount AND provides for more steadiness. When using a telephoto lens you should also tuck your elbow into your side … which offers you more camera support (i.e., less shake). 
When carrying the camera on your shoulder (using the strap) the lens should point inward to protect the glass and keep it from banging into other things … like little people. You’ll find that the camera is now positioned in such a way that when you reach for it, it will go into your hand easier and feel more natural. 
FILTERS: There are numerous filters out there, some designed to correct color/light problems … others add special effects. We will discuss three basic filters (which you probably should have). UV/HAZE filter: It cuts out ultra-violet light rays. Although invisible to the naked eye, ultra-violet rays give bluish tint and haziness in color photographs. UV/HAZE filters make the picture clearer. This filter does not block enough light to cause you to make an exposure compensation, therefore it is should be kept on the lens at all times to protect the lens surface. POLARIZING filter: This filter subdues undesired reflections from non-metallic surfaces such as water, windows, etc. When used in color photography it will darken blue sky by blocking atmospheric haze. By eliminating that haze skies will be bluer, red objects will be redder …. in fact all colors will be much more saturated and true. CLOSEUP filters: These are simple lenses that, when attached to the front of your lens, will allow you to focus much closer … allowing you to make full-frame images of very small objects. The more powerful the closeup filter, the more you will have to “open up” the lens, because these filters do “absorb” some of the light rays. The filter should come with instructions that will tell you how much exposure compensation you should make. If not, simply experiment … AND take notes. Next we need to look at EXPOSURE CONTROL.
After all these years of feeling really confused and not understanding what aperture is, I feel very enlightened and confident now!
Thanks!
i agree with Tisha, thanks. ( seem to be saying that every section)The phrase “depth of sharpness” made everything come into focus. Also appreciated the explanation on filters.
Can you put a UV/Haze filter and a polarizing one on the camera at the same time? Would you even want to?
You can stack filters, and use multiple filters at a time. It all depends on the effect your trying to achieve. One reason to stack filters would be to take a picture of a fountain on a sunny day, restricting the light coming into the camera and allowing you to use a slower shutter speed for a more interesting photo.
I am amazed how much I have learned already. Easy to understand. Fantastic!
[...] covers things like, A Photography 101, Digital cameras, Lenses, Understanding Light, etc. then, once you’ve got the basics under-your-belt, they also have [...]
i am very impressed with your site,very informative.
I am feeling grateful with what i’m beginning to learn from your website. Thank you!!
Great help, this site is amazing !!!
this lesson really “taught me alot”
these are the strong basics which are badly needed because
if the foundation is strong building never collapse
I very much enjoy all the visual aids you include. They are that much more helpful in understanding the material. I’m a new member and a beginning photographer, but I’m really enjoying the site so far! Best one I’ve found!
these lessons are really informative and seem simple especially with tha visual things….great job…..i am really glad i found this one…thanks!
I just discovered this website and I’m amazed, I’ve been taking some good pictures that my friends find really amazing on facebook (they even ask if I am a pro photographer lol, but honestly I think I was blessed that my pics come out nice without even know what I’m doing, my best teacher was always the try and error thing but now I know what aperture means and I have taken some test photos and I am so happy…….. I am ready for more….. THANK YOU
Learning alot. and everything seems to be making more sense now.
Thank you.
After reading this section I have decided to buy at least a UV/haze filter and maybe a polorized filter, but am overwhelmed with options. can you give some input on size/brand? Will the “cheaper” brand give me the same results and will they work on my canon lens?
Nicole, each lens has a diameter in mm. If it is the right size it will work on your canon. For filters it typically makes littler difference what price you pay. One of the reasons we like Amazon is because they give customer ratings so you know the value of the product you are buying. Just search for the filter you’re looking for with the diameter in mm’s and you’ll find what you’re looking for.
I have a small digital camera. I bought it for like $80 at Walgreens. Does it come with these “lenses” built in? I’m so confused about this. Was I supposed to go out and buy one of the expensive cameras?
You only need lenses for SLR Cameras
Love the courses..for us beginners..it does explain things very easily for us. Thanks so much.
Courses are great… I’ve just bought a digital camera but I don’t think it’s a good one (costs $200), it’s a Samsung with a Samsung lens (18.6mm) My questions are:
How much can I do with that camera?
How important are mm in the lens quality?
Is it possible to use any filter with the camera?
Anyway, my grandmother has an old russian very good camera with a big lens (I will ask for information about it in the future)… But I’d like to know how useful my new cheap camera is.
Thank you!!
Camilo,
We’d have to the model of your camera to tell you more about lenses compatible with it. We can tell you that you can create great photographs with just about any camera. Don’t believe us? Check out our new article on Holga Cameras and Lomography.
So if you were taking a picture of someone outside say at a garden with water falls or fountains you would stack the uv filter and the polarized filter at the same time? What effect would that have on your photo?
UV filters reduce the haze and the fogginess of outdoor light, however their most common use is as a protection for lenses because their effect is undetectable in most situations. By putting a UV filter on your lens, it takes the scratches and little bumps, so if you need to replace it, you are replacing a $10 filter and not a several hundred dollar lens.
The Polarizing filters effects are much more stark. As you know, when you put on a pair of sunglasses that have polarizing lenses, everything becomes clearer and cleaner because the light that is bouncing off the shiny things is removed. Polarizing filters are most useful when photographing snow, water, bright sunlight, etc. Be aware that when you use a polarizing filter you are reducing the light to your sensor/film and increasing the contrast, so you might have to adjust if you don’t have enough light.
So, yes, you can stack a UV filter on a polarizing filter for photographing water. The both have different effects on the image, and both are helpful in reducing the glare and light bounce when you are photographing highly reflective subjects. The result should give you more detail in your image and less “hot” (overexposed) spots. Just leave your UV filter on all the time to protect your lens.
recently i bought a canon powershot g10. i believe extra lenses can be added to it.. if yes then how would it improve the picture quality.. is it needed?
thank u for the great course for beginners. i started today and already feeling enlightened.
Mini, you’ve got a special camera that is not 100% point and shoot and not 100% DSLR. Canon has some accessories and filters that will work specifically with this camera. I wouldn’t say they will prove the picture quality but they will expand the capabilities of the camera by using accessories such as the tele converter or Conversion Lens Adapter. Filters will be just like the one’s described here, only sized for your camera.
WOw this is so helpful. NOw i know what a polorized filter is.. wished i knew about it earlier because i took a picture from my hotel room and all it did was bouce back from the window and i saw my reflection in it.. i even tried it with the flash off and that didnt work either.. Really good to know.. Thanks!
This website is FABULOUS! I finally have a clarity on what aperture is and the purpose of different filters. I started with lesson 1 and will continue until the end. Thanks for such great and FREE information!
It would be good to know what is meant by f2.8 or f8. Right now, I only understand that smaller the number , larger the aperture or the camera opening , which lets in the light.
Also, physically why is it that there is less depth of field when aperture is larger?
Thank you !
Very Good questions, in fact we had to make two new articles just for you to answer them: fnumbers and physics of depth of field