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When you chose a tripod, first measure your own height as it will need to put the camera at your eye height without being full extended. Secondly consider your needs, do you shoot macros? Do you shoot landscapes? Are you likely to shoot in positions exposed to the weather? What lenses are you going to mount on the camera on the tripod? Is backpacking your thing? All of these type of questions will help you find the features that you will need in the tripod, such as, height raised, lowest height, weight, removable center, weight etc. After working out all the features that you want then study the makers web sites for tripods that match the criteria, set a budget and expect to blow it out a bit, lastly search the web and camera stores for the tripods and price. Lastly come back and ask about the final choices before making the final decision. (With thanks to oldmanemu)
Many photographers recommend leaving a UV or Skylight filter permanently on your lens, to protect the lens from being scratched. It's much cheaper to replace a UV filter than it is to replace a scratched lens. It's worth purchasing higher quality multi coated filters as they will minimize any image degradation from putting another piece of glass infront of the lens. On some professional lenses filters also complete overall weather sealing features. Polarising filters are also popular, and can significantly reduce glare and reflections, darken a bright sky, and enhance colour saturation. They are available as cirularly or linearly polarised. A linearly polarised filter can be rotated, allowing the photographer to adjust the polarisation direction for the best results.
These are hollow sections that you place between the lens and camera body of an SLR style camera. The effect of using these tubes is like that of shining a torch at a wall. If you take a step back then the spot on the wall gets larger. The same thing happens with extension tubes, as you move the lens further away from the film plane or ccd sensor, you are increasing the size of the image appearing in the sensor. Extension tubes are often used in conjunction with teleconvertors to create a Macro stlye effect without needing to buy expensive macro lenses.
Normally sold in 1.4x, 2x and 3x configurations, these glass elements are placed in between your lens and the camera body and have the effect of applying the their modifier to your len's focal length. A 2x teleconvertor would give a 100mm lens and apparent focal length of 200mm, but at the cost of 2 f/stops. So where my 100mm lens may have been an F4, it will now be an F8.