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Old Jun 17, 2007, 5:46 PM   #1
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I have a Rebel XTi with the 18-55mm kit lens. I have another post regarding a new Sigma 18-200mm lens that's been delayed by Sigma--have had it on order. While I've been waiting I've begun to become concerned that this won't be wide enough for my purposes.

Although I shot 35 mm film many years ago, my digital experience is limited to a Canon A80 [point and shoot].

I checked the Photoshop file info five photos I took with the A80 that I really like. I was startled to see that the focal length for three of them [including the one I've posted here] was 7.8mm; for the other two it was 23.4.

Now I'm completely confused: Am I misinterpreting the file info?

I'm wondering whether I should really be looking for a 10-20 or 12-24mm. Would these be completely impractical walkaround lenses?

Any advice would be appreciated--must make a decision as to whether to cancel the 18-200.

Thanks.

dg
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Old Jun 17, 2007, 10:52 PM   #2
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How wide or telephoto a lens is, is determined not just by the focal length but all so by the size of the censer.

The A80 Has a very small censer the 7.8mm end of it's lens gives about the same angle of view as a 24mm lens will give on most DSLR's or a 35mm lens on a 35mm film camera.

So an 18mm lens on your Rebel XTi is in fact wider than the 7.8mm on the A80
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Old Jun 18, 2007, 3:10 AM   #3
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Taking the info from Steve's review on the A80 the following 35mm equivalent focal lengths are found.

7.8 (W) – 23.4 (T) mm
(35mm film equivalent: 38 (W) – 114 (T) mm)


This means the crop factor (the term now commonly used to describe how much a 35mm frame is cropped down to get the sensor size of the camera is 4.87x. On the XTi the crop is 1.6x so if you wanted to get the exact same 35mm equivalent range you would want a 23.75mm - 71.25mm lens. The Sigma you are waiting for is both wider and longer than this so you will get more range than you are used to. I use the Sigma 10-20mm lens for special work general when I want exaggerated effects such as in extreme sports but don't leave it on as a walk around.

Hope that helps,

Mark
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Old Jun 18, 2007, 3:52 AM   #4
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Thanks, tjsnaps and Mark1616 for clarifyinh this for me. I had a feeling I was misinterpreting the data, but didn't know how.

I guess I'll stick with the 18-200mm, though my wife, who shot strictly film in the past and is more knowledgeable thinks I'll never need anything close to the 200mm end.

dg


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Old Jun 18, 2007, 3:58 AM   #5
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Will you use 200mm??? That will depend on the type of thing you do, however I believe you will use it more than you think. I often put on my 70-200mm and when doing birds or sport then the 120-300mm comes out sometimes with a 1.4x tele converter making it 420mm (that is the same as 672mm on a 35mm camera).
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Old Jun 18, 2007, 4:19 AM   #6
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I believe I will use the tele end occasionally or @ least find it handy to have. I do the bulk of my shooting of buildings and landscapes and will often want to zoom in on a gargoyle or other feature on a building after taking wide shots of the whole thing. And since I generallly do not carry a bag, I'm really looking for the best walkaround. Someone on this forum pointed me to this new Sigma. I would have gone for a Canon, but I don't think any of the better ones have this much range. I would love an L series, but can't afford that. I'm in the US $600 range. If you think I should consider any alternatives, pls suggest. I've read so many my head hurts :O.

Thanks.

dg
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Old Jun 18, 2007, 4:45 AM   #7
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It's always tough to decide on lenses as each one is a compromise. To get around this I have 7 different lenses (4 Sigma, 3 Canon) which I use for different types of work. With you only wanting one lens I think you will be very pleased with the 18-200mm OS as the lens it is based on does not give bad results at all. There is nothing in this sort of range with OS from any other supplier so you have a choice of 1 :-)
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Old Jun 18, 2007, 5:03 AM   #8
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>>There is nothing in this sort of range with OS from any other supplier so you have a choice of 1

That's what I thought--thanks.

dg
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Old Jun 18, 2007, 9:47 PM   #9
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I think the 10-22mmcan bea fantastic walk-around lens. Whenever I go into a new city, I use this lens as you can get everything you see on a picture. With practice you can take great people pictures too. I agree that it wouldn't be good to have just the 10-22mm, but it's a very important addition in my opinion...
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Old Jun 19, 2007, 12:19 PM   #10
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Thanks, Michi. I'm intrigued by the idea and will have investgate more. I think I'll stick with the 18-200 mm as my primary lens and look into this as a "must have" when I can swing it. Any particular brand/model recommendations for use with a Rebel XTi?

dg
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