I bought my canon 700D a month ago. Now, I want to do some macro photography, but I do not want to purchase any expensive lens for this at least at this stage. I came to know about some accessories like extension tubes, which are not very expensive but claim to provide the required magnification. Are they really useful? Are there any other accessories( not expensive ), that I can use for macro photography?
Are they really useful?
Yes, extension tubes are useful. What you want is a set of extension tubes that maintain the electrical connections between camera and lens. There are many different brands available at different prices. They all do the same job, and the difference in price is due mainly to build quality. Even cheap ones work fine -- the pricier ones are just built better and are much less likely to break. The main thing to look for is that the tubes have electrical contacts -- the description should clearly indicate that autoexposure and autofocus will work.
Are there any other accessories( not expensive ), that I can use for macro photography?
Another option is to reverse the lens. There have always been adapters that let you mount the lens backward (that is, the front is held by the filter threads and connected to the camera with the "back" of the lens toward the subject), and they can turn a telephoto lens into a macro lens, but that generally meant losing the electrical connections to the lens. There's a new (to me, at least) breed of adapters like this Meike version that use a cord to allow the lens to stay connected electrically. As a bonus, it looks like most of these devices also can also function as an extension tube with the lens mounted normally (that is, not reversed). I haven't tried any of these, but the ones I've seen are pretty reasonably priced.
Macro is generally defined as a type of photography where the size of the subject on the film negative or sensor is the same size as the subject itself.
To take a large picture of a small subject requires a high reproduction ratio. Most 18-55mm lenses don't allow you to focus close enough to get anywhere near a 1:1 reproduction ratio. You can either purchase a Macro lens, or you can use extension tubes to reduce the Minimum Focus Distance (MFD) of your 18-55mm lens. Be aware that using extension tubes to reduce the MFD carries a light loss (effectively they stretch the light in the image circle, thus the part that falls on your sensor is less) and also eliminates the ability to focus on far objects.
Some extension tubes will allow you to use automatic exposure and focus, but many do not. How you can set the aperture with a set of manual extension tubes vary by camera manufacturer. For Canon lenses, you can attach the lens directly to the camera set manual mode, set the aperture you want, and remove the lens while holding the Depth of Field Preview button down. Then attach the extension tube to the camera and the lens to the extension tube. You will then need to focus manually as well. One way to do that is with Live View magnified on your subject.
Your camera has a “mode” dial. You can turn until the symbol of a flower aligns with the index pointer. Now the camera is in “close-up” mode. Your camera now allows super close-up picture taking. This might me all you need however there are other paths.
While the “close-up” mode does a job, you need to know that the kit lens suppled is designed to do many tasks however it is slightly compromised when tasked to do close-up work.
For this task we generally choose a “macro” lens. These lenses are configured to deliver optimum sharpness at super close distances. A true macro lens should be your next purchase if you want to pursue close-up photography.
There are alternative methods: You can purchase a close-up lens or even a set with different powers. These are supplemental lenses that you mount atop your existing lens. They act like reading glasses in that they allow close-up photography. Many will pooh-pooh these but they can actually deliver and certainly they are an entry level way to do close-up work.
These are clear lenses that mount atop your kit lens. They come is various powers, usually labeled +1 or +2 or +3 thru +10. These supplemental lenses are like reading glasses for cameras. I suggest you buy a +3 for starters. These close-up lenses are relatively not too expensive and they will give you an inexpensive entry into the world of close-up photography. The labeling is the same as that used by optometrist. I suggest you take your camera to the drugstore. You can find a display of reading glasses. Take one +3 off the shelf and hold one lens over you camera and play around focusing. Such reading glasses behave just like camera close-ups. Keep in mind that this reading glass experiment is to be used only to introduce you to the concept, you will need to buy camera close-up if you are intrigued by what they do.
There are two other alternatives: You can dismount the camera lens and re-mount it using an extension ring (most often called “rings”. These are relatively inexpensive metal spacers that lengthen the distance lens to sensor (film). Rings do a marvelous job but they are taxing because they disconnect the lens from the automation of camera body forcing you to make manual adjustments. More complex rings are available at a price and these maintain the lens to body connections. A more extreme lens extender is called a “bellows” These work like rings but allow super lens extension.
Super close-up work is enhanced if the lens uses is optimized to work on relatively flat subjects. A macro lens has such a design. When using a standard lens with rings or bellows, we often use a reversing ring. This mounts the standard lens backwards. The rear of the lens is optimized to project an image on the flat surface of the imaging chip (or film). Thus they give slightly improved performance when reversed as the rear of the lens is optimized for flatness.