Lens Question for novice

I'm basically a novice when it comes to SLR photography. I had a SLR many years ago (lost it in a divorce) and somewhat know the basics about shutter speed and aperture size. I've been using a Canon G2 since it came out and am now moving to a Canon XTi.

I'm thinking of zoom a lens for a future purchase for this camera.

My question is about the relationship of the zoom nomenclature of the point & shoot camera ie; 3x, 4x etc to the SLR lens of mm ie; 50mm, 130mm, 200mm etc.

Is there a table where I can see the relationship of the power (2x, 3x, 4x etc.) of the point & shoot lens to the mm of a SLR lens?

I understand that the XTi has a 1.6 something about it's sensor??? Will that need to be factored in to that table?

Thanks in advance,
Crockett

Crockett, I'm no expert either but about the 1.6 question,basically the sensor which in a digital camera acts as the 35mm frame in a film camera, but the sensor in for example, your XTi is smaller than a frame of 35mm film. This difference changes the focal length of a given lens by a factor of (in the XTi case,1.6) take a 50mm lens attach it your XTi and its focal length is now 80mm or 1.6x50mm=80mm
What all this means in the real world is you must do some calculations before you buy a zoom. Example,24-70mm zoom on your RebelXTi will be something like 38-112mm
combination,not as wide but a little further in reach.
I,m sure knowing this bunch ,you will get a better lesson very shortly from someone who is an expert,thats the great thing about this group,they all come in with earnest accurate advise
As to the PS zoom ratios I don't know how they compare or are figured as to SLR lenses.
There are some tables on the net but I don't recall which sites have them,regarding the 1.6 factor difference. Hope this helped a little,if I confused you sorry. Good luck,Steve B.

Yes, this does help and you've made the 1.6 part of the question clear. You've answered part of my question.
Thanks,
Crockett

The 3x 4x etc is calculated by the ratio of the longest focal length by the shortest. For example, the Nikon Coolpix 5400 has 4x optical zoom. It's actual focal lenght range is 28-116mm. 116/28 = 4.14. Hope this helps.

Quote:

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Originally Posted by conbu19

Crockett, I'm no expert either but about the 1.6 question,basically the sensor which in a digital camera acts as the 35mm frame in a film camera, but the sensor in for example, your XTi is smaller than a frame of 35mm film. This difference changes the focal length of a given lens by a factor of (in the XTi case,1.6) take a 50mm lens attach it your XTi and its focal length is now 80mm or 1.6x50mm=80mm
Good luck,Steve B.

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To be more precise, the focal length of the lens doesn't change. The crop factor means that to get a similar angle of view as a 35mm camera you need a lens that is 1.6 times wider than the 35mm lens, as the sensor is cropping the image.

It's the same as if you took a 35mm film image, and cropped out the center.

So the "normal" lens for the smaller sensors is anywhere from 31mm to 28mm, depending on the specific crop factor of the sensor. The portrait lens becomes the 50mm lens, which is the "normal" (nominal) for 35mm film. On a 35mm camera, a 75 to 85mm lens is a basic portrait lens.