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Zoso Aug 5, 2005 8:01 PM

Hello all. My first post as I just found this forum.
I am looking to make the move over from Point and Shoot to DSLR and this is my first major question.

What "power" zoom is it when a lens says it is 100-300mm (most web pages will list that as zoom of 3). My Canon S1-IS is a 10x zoom. When I look up the spec on the Canon site it says it is the 35mm equivalent of 38-380mm (hence the 10x zoom).

I find myself trying to take more and more shots of Wildlife here in Colorado and the zoom seems to be of more use to me than wide angle. So if I was to say buy a Canon RebelXt and a 100-300mm lens.....would the Elk in my picture be larger and clearer on an SLR with 300mm lens vs. the 10x zoom of my point and shoot?

Hope that makes sense and any advice is welcome.

eric s Aug 5, 2005 10:24 PM

I tried to find a previous post about this topic, but I couldn't. I've written about it many times before but it must have been too long ago.

The "X" factor is a meaningless marketing invented number. The faster you forget about it the better. Here is why:

The "X" factor is really just the ratio of the long end of the zoom to the short end of the zoom. You don't care about this, as this example will show you. First fact, the human eye is equivalent to a 50mm lens (basically.) So a picture with a 50mm lens will look the same as if you stood in the same spot and looked in the same direction (you can see more than the lens does, but everything will be the same size... there is no "zoom".) With that knowledge look at this example.

Say you have a 10-100mm lens. At its widest point it is 10mm, which is very wide. This is will produce huge landscape pictures. The long end is 100mm, which isn't that long. About twice the magnification of the human eye. In the X notation, it is a 10x lens (100/10.)

Say you have a 50-500mm lens. At its widest point it is 50mm, which is the same as the human eye. Not wide at all... actually it isn't capable of any type of grand landscape shots at all. At the long end it is 500mm, which is a very powerful telephoto lens. In the X notation, it is a 10x lens (500/50.)

So while both the lenses above at "10x" lenses, they are very different lenses only usable for specific uses (the first is more of a landscape lens, while the second is more for sports wildlife shots where the subject is far away.)

Does that make sense? If not, please ask a question and we'll help.

So your question is actually in reverse (but it is a very good question.) You're used to the Canon S1 camera, so you want to get a similar lens for your DSLR because you understand what that is capable of. Very good thinking. But instead of translating the DSLR lenses into an "X" factor, you should translate the Canon S1 into the DSLR "35mm equivalent" notation. What you list is correct, based on Steves's review of that camera it is a:
"f/2.8-3.1 image stabilized 10x zoom lens (38-380mm equivalent)".

So it has a low fstop (which is very nice) and its a 38-380 lens. There is no lens like that for a DSLR, but the magic of a DSLR is that you can buy more than one lens. For example, two of the lenses that I have would cover than range. The 28-135 IS and the 100-400 IS. Unfortunately your S1 has a larger aperture (smaller fstop) than either of those lenses (a plus for the S1), but the quality of them will probably be better and you'll get the quality advantages of the DSLR.

But there is another factor coming into play here. The DRebel's sensor is smaller than film, and the 100-300 (And all other 35mm lenses) have their focal length measured against film not the smaller digital sensor. What this means to you is that the DRebel crops the center out of the image, making your lens seem like it has more optical focal length (it doesn't really, but it seems that way.) This is calculated by increasing all focal lengths by a factor of 1.6. So if I took an image with a film camera and the DRebel Xt (all Rebels have the same crop factor) using a 300mm lens it would look as if the DRebel was using a 480mm lens (300 x 1.6 = 480mm.)

So the short answer to your question is "yes". you could take the same shot (or make the elk bigger) with the 100-300 as with the S1. They have overlaping (but not the same) focal lengths. But you couldn't take nearly the same wide angle shots and the S1's min f-stop is better so it could stop action better.


rjseeney Aug 5, 2005 10:33 PM

The 100-300 lens would be a 3x zoom. The "x" designation is really a useless marketing designation. A 30mm-90mm focal lenght is also 3x as is a 10mm-30mm...all of which would yield different results. The focal length is means more than the "x" designation.

Your Canon S1 actually has a longer focal lenth 380mm vs. 300 than the lens you mention, thus theoritically allowing you to zoom in tighter.However, taking into account the smaller sensor of a DSLR (1.6x forCanon) you really will have a 160-480mm lens giving you more reach with the DSLR lens.The s1 on the other hand is also image stabilized making it easier to handhold and get sharp results. The rule of thumb for non stabilized lenses is a shutter speed of 1/focal length to prevent blur from camera shake. For the 100-300, that means a shutter speed of at least 1/500 which may not be feasible depending on existing light/DOF considerations.

I would make sure you completely understand basic photography before moving up to DSLR. In order to get the most out of a DSLR, you must know the basic terms and how they affect your images (like focal length). You must also be ready to spend time editing photos in post, as DSLR images generally require more processing (letting the artist make these decisions rather than the camera).

My advice is to practice and do alot of shooting and reading ( already have a solid camera) to make sure you got the basics down, before stepping up to a DSLR..the learning curve is steep (but manageable) and moving up before you're ready is inviting frustration.

Good Luck!!!

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