A little confused (zoom)

hansokl · Jul 19, 2012

Hey everyone!! Good morning..

I've been doing a little research because I am thinking about getting an SLR as I am expected my first child pretty soon. From what I have read about zoom.. a standard SLR lens is 18-55mm which is about 3x zoom. I currently have a Panasonic Lumix (DMC-ZS7) 12x zoom which says 25mm. So if I understand the logic correctly.. the focal length would be around 2.08mm for my point and shoot. I'm just trying to figure out if this is correct. So my point and shoot is 2-25mm which is why its considered 12x zoom which basically the max zoom is 12 times more than without zooming at all?

I'm trying to compare this to a Canon EOS Rebel T3i with 18/55mm..This would mean that the 18/55 lens is a 3x zoom.. Before today, I didn't realize that the x times zoom is pretty much pointless.. or so it seems. So if I understand correctly, the focal point is the first # which would be 18mm for the SLR and for my point and shoot it would be 2.08mm or so. I'm trying to determine what this really means.. I know I would need to get a 75/300mm lens if I wanted better zoom with the SLR but I need some help comparing the zoom on the point and shoot I have to the zoom on the basic lens for the SLR.

I would appreciate any help anyone could offer and sorry for being a newbie

Thanks guys!!

Dao · Jul 19, 2012

You are correct about the zoom. The value "X" do not means too much. It just means the camera or lens is capable of changing the focal length. And the ratio between the shortest and longest focal length represent as X. It really does not tell you much until you know the based value, such as the shortest focal length.

However, as you noticed, 2-25mm and 18-55mm are quite confusing since it doesn't seems to add up because a the 25mm in your DMC-ZS7 has a higher magnification power than the 55mm on the DSLR you mentioned.

Here is the catch, the sensor size of the DMC-ZS7 is much smaller than the Rebel T3i and because of the recording medium size difference, the Angle of View (AoV) or the Field of View (FoV) are different for the same focal length.

If you want to compare, we may need to find a common point. Let's compare it to a regular 35mm film size.

The FoV of the focal range of the DMC-ZS7 which is equivalent to a 35mm film is 25 – 300 mm (look up from dpreview.com) while
The FoV of the focal range of the T3i which is equivalent to a 35mm film is 29mm - 88mm (18 x 1.6= 28.8, 55 x 1.6 = 88)

As you can see, a 300mm focal length should be able to bring a distance object closer than a 88mm.

hansokl · Jul 19, 2012

Thanks for the help.. I guess I still am a little confused about the focal length of my point and shoot.. It says 25mm so is that the max or the min? I was thinking that it was the max so doing the math it would be like 2.08 - 25mm to get around 12x zoom. If I understand what your saying, you are saying that the 25mm is the min and max would be 300mm to get the 12x zoom. So it looks like the zoom is a good bit better on the point and shoot I have now.. anyway I can tell how much better? Sorry If am still confused.

Thanks again!!

fjrabon · Jul 19, 2012

25mm is the minimum. it's a 25-300mm full frame equivalent. (most point and shoots list their focal range in terms of full frame equivalency)

a T3i is a crop frame camera, so on that camera 18-55mm is the equivalent of 29-88mm for a full frame camera.

the zoom on the point and shoot is 12X, the zoom on the 18-55mm is 3X. So you get 4 times as much zoom on a point and shoot than you do with the one single lens on your dSLR.

However, you can buy ultra zoom lenses that have as much or more zoom than the point and shoot.

Dao · Jul 19, 2012

Again, zoom do not mean much as far as how close you can see an object. It is the focal length with reference to a recording medium.

For example, a Canon EF 800mm f/5.6 lens has a focal length of 800mm and it is only 1X while your Panasonic is 12X but it is only a 300mm equivalent when using the 35mm film size as a reference point.

I am sure if there is a little bird up there on the tree top, a 800mm lens is going to be better than using a 300mm lens.