Macro Photography in general term is all about taking photos close to the subject. A real macro photography is working around 1:1 ratio and closer thereby giving an image that is equal in size or larger than the subject being photographed.
Macro Photography is quite addictive. Well, you don’t need to worry about the harsh weather and off course the sandstorm which is been quite as a ritual here. We can choose any subject for macro. In Point & Shoot (PS) camera we have little control on aperture and shutter priority mode but most PS camera have a dedicated mode for macro or close-up photography. In DSLR camera we need to use the Aperture priority mode or still better if we use the Manual mode to achieve sharp focus. To get a shallow DOF (depth of field), it is very important to choose a large aperture (small f number) available. If the subject is moving or is in action, you may need to control the shutter speed to freeze the action. Also depending on the situation you may need to use the Flash. The most important criteria in DSLR camera is the choice of lenses.
Macro photography is at its best with a true macro lens. There are plenty to choose (Nikon, Canon, Sigma, Tamron, Tokina etc.) depending on the camera and its lens mount. If you don’t want to invest on a dedicated macro, there are still options to shoot macro. My friend uses a Nikon 50mm f1.8 lens with reverse ring adapter and using Reverse-Lens technique for his macro shots. You can also use a Close-up lens on a Standard zoom lens for macro. Close-up lens are like filters fitted on the front of the lens and are relatively cheaper than macro lens. I had used a Canon 500D close-up lens on my Nikon AF-S DX VR Zoom – Nikkor 18-200mm lens and the results were fairly good. Macro can also be achieved by using an extension tube and bellows.
Using a tripod to handle the camera still will help to get rid of camera shake. If you have shutter release cable or remote control it is further advised to use to avoid all kinds of camera shake, a cheap alternate to the same is to use the camera built-in timer.
I currently use a Tokina AF 100mm f2.8 on my Nikon D90.
I am interested to buy a macro lens which can also be used for portraits. I have narrowed down to Tamron 90mm f/2.8 SP AF Di Macro , Sigma 105mm f/2.8 EX DG OS HSM Macro or Nikon 105mm f/2.8G AF-S IF-ED VR Micro. Can you suggest which one to buy.
On a Nikon body, there is nothing to beat the beast Nikon 105 f/2.8 VR. However both Sigma and Tamron macro lens produce great images. The re-engineered Sigma with OS (Object Stabilization) and HSM (Hyper-sonic motor) is almost as good to the Nikon both in image quality and sharpness however hunts with Auto focus in low light. The latest version of Tamron with VC (Vibration Compensation) and USD (Ultrasonic silent drive motor) is much better than the Tamron lens you mentioned, however with a short focal length you need to be extremely close to the subject. In terms of the price Nikon is slightly expensive. I would recommend you to go with a Nikon, if budget is a constrain try the Sigma. You can check with Ashraf for the Nikon lens or try the AAB outlet (they do have Nikon, Sigma & Tamron)