CLose up filters are available from from Hoya, Tiffen, Kenko etc, in various diopters The canon ones are overpriced. I own Nikon would buy from Nikon. In filters for close-up photography the depth-of-field is shallow so you will need to very small small apertures. close-ups filters offer a cheap neat way to get cretive closeups pics cheaply as they can also be stacked. Also, a close-up diopter, has more effect on a long lens than on a short focal length lens. A 300mm lens that can focus to 1.5 ms, allows a 1 diopter, close up filter lens will let you focus from 1 m down to 600mm, or a 1:4 repro ratio whereas a 28mm that is able focus to 300 would focus 1 metre down to 230mm.with the same CU filter giving a smaller ratio of 1:8.
Check the following links and also be aware CU flters while they can give quite good results "if" setup right are no sub. for 1:1 macro or an extension tube. http://www.camerastore.com/cat_003_hoya/003closeup.html.
Thanks for you help. But can you explain a little bit more as I don't really understand how it works. Does it only shorten the shortest focal lengths? Does it magnify the photo?..
OK here it goes: Close up filters or diopters are one element, often rated at +1, +2, +3, and even +10,. Used alone the first 3 on a standard 50mm ff length lens give magnifications from: 1/7X to 1/4X. They magify basically becuase they are between lens and body allowing the camera to focus closer. They can be stacked to give mag factors of 1/2X. A +10 magnify by 2/3X. Place the (largest diopter) filter first (next to lens) when stacking more than one.
My first anwser mentioned better ways to do macro work. EXTENSION: TUBES AND BELLOWS Extension tubes are a high quality way to achieve close-up work with lower cost. They are basiclally hollow tubes that copule to a lens and main cam body. Although I don use them much, some friends do and a good recommendattion is using a pair of ext. tubes with the lens ranging from from 24 to 300 Normal fixed lenses will give excellent pics and must be stopped down.
IE: A tube of 50mm with a 100mm lens will give 1/2X mag. Again a 50mm tube with a 50mm lens will giive 1X magnification etc etc. Bellows which are basically what they say (variable tubes) at 200mm extension with a 50mm will achiev mag. equal to 4x. As I mentioned you will to read on the web on close up filters as you need to match them to the lens.
I dont know kind of camera you have. Tamron makes or did make a very nice 70-300 lens with macro capability that mounts on many cameras including Nikon although you need to get an authorized camera tech to make a change in Nikon body mount ring to get around voiding warranty etc. hope this helps...
I would like to ask about the magnification factor you mentioned, for example 1/2X, does it mean adding 1/2 to the original size?.
I am using Sony DSC-F707, which has a focal length 9.7-48.5 (equivalent to 38-190 in 35mm), and it is a fixed lens, I couldn't change, so which one should I use to calculated? 9.7-48.5 or 38-190?..
Please check the following web page which explain betters than I can: It has calculator(s) (I rarely use) diopters but tubes and and rulers which with my math easier to work out and give better results. Kodak has this in the pocket guide somewhere. Magnification = focal Length of lens / focal length of Diopter where the focal length of the diopter = 1000 / diopter strength. For example, a 3 diopter has a focal length of 333mm (1000/3). So the magnification of a 3 diopter on a 55mm lens would be 55/333 = .165. If you look at my first example you will see the above ratio 1/4 or the fractional equivalent. but try this sight: http://imaginatorium.org/stuff/cufilter.htm It even has calculator...