Lens zoom

[benv99]

Im looking to get a digital SLR but I dont know much about lenses. I have a old digital with a 38-115mm lens. It says its a 3x zoom.
Now the SLRs come with 14-45mm , 18-70 etc, is this a smaller zoom than 3x?

 

[Quadophile]

Im looking to get a digital SLR but I dont know much about lenses. I have a old digital with a 38-115mm lens. It says its a 3x zoom.
Now the SLRs come with 14-45mm , 18-70 etc, is this a smaller zoom than 3x?

SLR cameras be they digital or film give the user flexibility of attaching lenses of their choice for different types of photography from extreme wide angle to extreme telephoto. If you think that that is what you want and would be willing to invest in a digital SLR in terms of a number of lenses by all means go for it. However, a high end prosumer digital camera also can be worth looking into but the limitation would be the lens mounted on it since you cannot change it. The possibility of attaching additional lenses is there but with limitations.

Answering your question directly, yes, a 14-45mm lens is in fact a 3.21x lens since the higher figure is to be divided by the lower figure i.e. 45/14=3.21x, applying the same calculation an 18-70mm lens would be termed as 3.88x lens.

The camera you already have has a 38-115 lens, which is not the same as the later two you mentioned, since the later two are quoted in terms of digital and the former in terms of film. You need to understand the “focal length multiplier” when referring to lenses for film and digital. Many digital SLR cameras (such as Nikon and Canon models) take 35mm camera lenses. What actually is needed is to calculate the focal length multiplier. Because the size in area of the CCD or CMOS digital sensor is usually smaller than the 24x36mm size of 35mm film, the effective focal length of a lens increases. The factor ranges from 1.5X (for Canon) to 1.6X (for Nikon), depending on sensor size. A 28-105mm lens for a 35mm film SLR will be the equivalent to a 18-70mm on a digital SLR that has a 1.5X factor. This characteristic increases the power of telephoto lenses, but reduces the effectiveness of wide-angle lenses. Very short focal length wide-angle lenses are needed with digital SLRs to compensate for the conversion factor. There are full frame Digital SLR’s but they are mainly used by professionals due to prohibitive costs for consumers, in time, however this will change as the prices keep coming down.

Just for your information and you may know that the film frame is 24mmx36 mm and in terms of digital if it is to be taken as full frame than anything which is smaller will need the multiplier to calculate the difference. Typically the Nikon dSLR have a sensor size of 23.7mmx15.6mm and Canon typically 22.5x15. An 18 mm focal length lens produces a field of view like a 24 mm lens on a Nikon D70 (18 mm x 1.5 multiplier).

Digital compact cameras are fitted with lenses with short focal lengths to create 35mm equivalent field of views on their small sensor surfaces. Typically the sensor diagonal is 4 times smaller than the diameter of 35mm film. A 7mm lens fitted on such a camera will have the same field of view of a 7mm x 4 or 28mm lens on a 35mm film camera. These lenses are easier to make and cost much less.