layman's question about Rebel XT kit lens

[staceygathers]

So, I've been looking into getting a Digital Rebel XT in a few weeks. However, I'm a former film/video major, so I'm experiencing a lot of crossed wires when it comes to reading up about lenses when I compare what I know with what I'm learning. Are you still following? ;)

I know that this is probably a layman's question, but if the kit lens (18-55mm) that comes with most Rebel XT kits is a zoom, how much "zoom" will I get out of it, roughly? I hate to boil it down to terms like "3x" because I know about all the factors that can affect it, but I'm just looking for a ballpark number. If anyone could help me, I'd really appreciate it!

[Nicole]

Quick answer: Roughly 2x zoom.

More confusing answer: This estimate comes from looking at some old digital cameras and their 35mm equivalent. At 2x zoom, it is equivalent to 76mm on a 35mm camera. With the Digital Rebel, you have approximately a 1.6 crop factor, so at 55mm, your lens is the equivalent of an 88mm lens on a 35mm camera. So, to sum up, with this lens, on this body, you will get a bit more than a 2x zoom. :p

[staceygathers]

Okay, so by that math, if I buy a 55-200mm, that would be between 3.5x and 4x? Am I sort of catching on or not at all?

[Nicole]

To make it more confusing... 200mm would be approximately 11x magnification (http://www.dpreview.com/news/0511/05110103nikon18-200vr.asp). I can't find any actual conversion between magnification factor and focal length (that would make things a lot easier).

Before I keep going, I'll first point you to some info on how the "crop factor" effects photography (DSLR Magnification (http://www.luminous-landscape.com/tutorials/understanding-series/dslr-mag.shtml)). Simply, the same lens on different cameras, will give you different views because of the sensor inside the camera.

The human eye is the equivalent of a 50mm lens (but only on a 35mm camera body). So the view of a human eye would be closer to a 35mm lens on a dSLR body. In theory, the numbers should be somewhat similar to the magnification, but that doesn't seem to work either. :p

I'm afraid that I can't really give a good answer as to how to convert a magnification factor to a lens' focal length. Hopefully some of those links can point you in the right direction though. Sorry, just didn't want to leave you hanging out for an answer :p

[smc1377]

The multiplication rating is just that, a multiplication factor.

So an 18-55 lens is effectively a 3x zoom. Meaning, 55 divided by 18 roughly equals three.

That's why the other lens that Nicole linked to (18-200) is rated as a 11.1x zoom because 200 divided by 18 = 11.1. Then even more deceiving, a 75-300mm lens is considered only a 4x lens, but it can clearly zoom in much more than the 18-200 lens.

The logic would be that a 4x point and shoot would zoom in tighter than a 3x. That would generally be true, but not necessarily. See the following illustration...

Camera A = 35mm equivalent to 18-72mm (4x zoom)
Camera B = 35mm equivalent to 28-80mm (2.9x zoom)

Even though Camera A has a larger zoom factor, we can clearly see that Camera B can actually zoom in closer than Camera A (80mm vs 72mm). Granted that 80 vs 72 isn't that big of a difference, it is deceiving nonetheless.

So what you really have to look for is the "35mm equivalent" ratings. Most cameras list this and even if it doesn't on the box, sites like www.dpreview.com will list it. The general rule is, the larger the 35mm equivalent rating, the more it can zoom in on the subject.

Now with all that said, you also want to make sure that the camera can also take a wide enough picture that you don't have to always be at least 10 feet away from your subjects.

So in short, the 3x or 4x or even 10x has NOTHING to do with how close you can zoom. It has everything to do with the relationship between the widest zoom and the tightest zoom on any particular lens/camera.

BTW, even if you add in the crop factor, it won't change the multiplication factor. See the following...

Canon XTi with 18-55 lens.
Crop factor of 1.6x makes the lens a 28.8-88mm. 88/28.8 still equals roughly 3x. But then again, multiplication factors (3x, etc) doesn't mean much anyways.

[smc1377]

Well here's a couple REAL examples of how the "x" factor can be misleading.

Fujifilm FinePix S6000fd (http://www.dpreview.com/reviews/fujifilms6000fd/)
Fujifilm FinePix S5200 (http://www.dpreview.com/news/0507/05072802fuji_s5200zs5600z.asp)

The first camera says it has a 10.7x zoom. The second says it has a 10x zoom. Logically, any person would conclude that they could zoom in more on a subject with the first camera.

But not so fast. Click on those two links and you'll see that:

S6000fd = 28 - 300 mm (35 mm equiv)
S5200 = 38 - 380 mm (35 mm equiv)

The SECOND camera actually has a much better zoom than the first camera even though it doesn't seem that way when you see the 10.7x vs 10x. The second camera with its 380mm zoom is MUCH better than the 300mm if you are looking for a camera that can zoom in quite a bit.

I hope I am making sense, even though I feel like I'm still just babbling.

[smc1377]

Ok, so after saying all that, I just remembered you're only talking about lenses for your XT. The same rules still apply.

A 75-300 lens is only a 4x.
A 18-200 lens is 11.1x.
The Canon EF 400mm f/5.6L USM is technically a 1x since it has no zoom functions, but it clearly has the biggest zoom.

Rule is, the bigger the number, the more it zooms in. There's no mathematical formula to figure out what 200mm is when it comes to defining it as a 4x or 10x. But that probably is now obvious after my first couple posts. I should go to bed. :D

[Triglav]

:confused: :eek: :confused:

Totally lost...

I try read this again when I am sitting in a nice hot tub and am totally relaxed..:p

[stuart]

to try to give you a visual rather than trying to explain log on to the net and look for a site called camera labs on one of thier reviews of the 400d they show pictures taken with the 18-55mm one at 18 the other at 55 hope this helps