View Full Version : Optical Zoom on Digital SLRs versus equivalent lens size (mm) on film SLR cameras

01-10-2005, 05:14 PM
If a digital SLR camera has 6X optical zoom, what is the equivalent lens size on regular film SLRs (can we say that it is equivalent to 28 to 300mm?) or is it different?

01-10-2005, 05:37 PM
It depends what the wide angle is...

If it is 70mm(in 35mm conversion), then it means the lense goes from 70-420mm. If its 28mm(in 35mm converstion) then it means the lense goes from 28-168mm. the number x zoom(Nx) just means that the lense goes from a certain number in mm at wide angle and that number multiplied by Nx will give the maximum telephoto power of the lense without adding a converter.

David Metsky
01-10-2005, 07:50 PM
A digital SLR will not have a lens that is typically described as 6X. Since the lenses are changable, it's more important to know what that particular lens has for it's zoom range. It will have a numerical representation, like 28mm to 105mm or something like that. Any lens where the first number times 6 equals the second number is a 6X lens, whether it is 10mm-60mm or 50mm-300mm.

Even with cameras without changable lenses the 3X or 6X doesn't tell you what the equivilent would be for a 35mm film camera. For example, my SD300 is a 3X lens, with a range of 5.8 to 17.4mm. On a film SLR this would be the equivilent of 35mm to 105mm and this is pretty standard for a 3X lens, but it doesn't have to be. It could just as easily be 50mm to 150mm if they wanted to make the camera with that range.

So, you have to look at more than the 6X. You should look at the equivilent range in MM for a 35mm film camera to get an idea. That's usually listed somewhere in the specs.

01-10-2005, 09:09 PM
For cameras without changeable lenses, the 3X or 6X doesn't really tell what the equivalent would be for a 35mm film camera. So, how do I know where the lower mm range starts from. For example, if the range starts at 50mm, then the entire range can be computed by multiplying with 3 or 6 in case of 3X or 6X.

So, the question is for a given digital camera, given the 6X zoom, how do we know what the low end of the range is?

Thanks in advance for your reply.

01-10-2005, 11:01 PM
most often the range is given on the lens, for example, my sony is 7.9mm-23.7mm, when the crop factor is included, it increases it to 38mm-114mm.
with some dslrs, like the 20d, the factor is 1.6x, which is awesome for the sports and wildlife guys, but sucks for landscape and macro shooters, since they loose a lot at the wide end.
the d70 I believe is 1.5x, so you dont lose as much in the wide end.

full frame, ie 35mm size, dslrs have no multiplication factor, since they are already at 35.
when purchasing lenses, be sure to include the crop factor so you know what your actuall range is.

David Metsky
01-11-2005, 06:38 AM
So, the question is for a given digital camera, given the 6X zoom, how do we know what the low end of the range is?
It should be listed in the specs. The actual lens size for a digital camera might be something like my example below 5.8-17.4mm. This translates into an equivilent range of 35-105mm. Different cameras will have different equivilent ranges with the exact same sized lens depending on their geometry, so for comparison you need to use the equivilent.

As TheObiJuan said, for most dSLRs there is a size multiplier that is different for the various manufacturers, but I believe ranges from about 1.4 to 1.6. So my Canon 75-300mm lens becomes an effective 112-450mm lens on a dSLR, great for wildlife but not so good for landscapes.