Except power zooming lens , Zooming in/out manually while clicking the photograph in order to give effect is safe .however below is some tips to improve the result .
Here are a few tips to help you improve your results with zoom effect :
Keep the Camera Still – as you will be using a slow shutter speed any movement of the camera will significantly impact your shot. Ultimately you want to capture a zooming movement in these shots so any side to size or up and down shake will impact the smoothness of the lines in your image. Of course camera shake can also add interesting effects to the shot but it can also make the shot too blurry. To eliminate camera shake use a tripod or set your camera on a still surface.
Lower Light Situations might help – one of the problems with using longer shutter speeds is that you let more light into your camera. You can help your camera cope with this extra light by using a larger aperture (the larger the number the smaller the hole that lets light in) but in bright situations you still might not be able to use long shutter speeds without over exposing your image. As a result it can be easier to get well exposed zoom effect shots in lower light situations.
Lights are Fun – taking the last point into consideration one of the most popular subjects for the zoom effect is lights whether they be city lights, Christmas lights, neon signs etc. They are often a good place to practice the technique and can produce pretty spectacular effects.
Move the Camera Manually if you don’t have a zoom lens or your camera won’t let you zoom while the shutter is open (as happens on some point and shoot cameras) the other way to get this effect is to manually move your camera towards or away from your subject. Of course this introduces other camera shake (see above) but it is possible to get a nice shot if you’re good (or lucky).
When choosing a shutter speed – there is no one shutter speed that will work for all situations. Factors to consider will include the levels of light, the speed at which you’ll zoom etc. I generally would shoot at up to a second (or even a little longer) which is usually enough to zoom a lens from one end to another. The key is to experiment with different shutter speeds to see what works best.
Work on Smooth Zooming – to get nice smooth motion lines in your photo you’ll need to work at a ‘smooth zoom’. ie you don’t want to zoom at one speed early on and then speed up and then slow down (see next point for the exception). This will make your lines a little jerky. Getting a nice smooth zoom technique takes practice.
Pause mid-zoom – another technique to experiment is to pause your zooming either at the start, end or during the procedure (while the shutter is still open). This will mean that what your camera sees at the point when you pause your zoom will be stronger and hopefully clearer in your shot.
Fire your Flash – another element that you can add to this technique is light. You can do this with virtually any light but the most common one is obviously the flash. Fire it during your long exposure and you’ll freeze part of the image while still getting movement behind and around it. Some cameras will allow you to do this using ‘night mode’.
Reverse the Zoom – zooming in on a subject can give a different result than zooming out, especially if your subject is moving and depending upon whether you pause at the beginning and or end of the zoom. Experiment with both.
Partial Zoom – some zoom lenses have very wide focal lengths. I have a friend with a 28-200 zoom and he finds that using the zoom effect can be too much if he starts at one end and goes right to the other. For starters he can’t maintain a smooth zoom over that focal length but also it’s just too much motion for one image. Instead it can be more effective to only zoom part of your focal length range. If you have a 28 200mm try zooming from 28-100mm or from 80-200mm or even smaller ranges.
Most of all have fun with the zoom effect and experiment.