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Old Oct 28, 2010, 1:24 AM   #1
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Default What lense is what? for DSLRs?

I am having difficulty telling how much magnification is offered by which lenses.

For example, I have an Olympus sp500 uz that offers a 10x optical zoom and DPREVIEW.com lists the zoom range as 38-380mm. My question is this.

What kind of lense type would I need for a DSLR that would achieve the same level of zoom capability as the SP500 UZ? I thought it would be a lense with a max of 380mm, but the sony website lists a lense that is 300mm, but lists it as "Long 4X Zoom Capability". This is a lot less than what I was expecting. This is very confusing right now.

Any help and clarification on this matter would be greatly appreciated. Thank You!
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Old Oct 28, 2010, 2:06 AM   #2
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The X factor of a camera zoom lens is simply the longest focal length divided by the shortest. It is only really useful as a marketing tool and conveys little information.

For example a 16-35mm zoom lens is a 2x zoom, and a 200-400mm lens is a 2x zoom. The former is for wide angle shots and the latter is for telephoto shots. The pictures from the two are VERY different.

The 35mm equivalent focal length range is more useful. Because 35mm was the "standard" format of the past, and because there are so many different formats now (sensor sizes in cameras vary enormously) it is useful to have a common standard to convert to.

So your old camera did 38-380mm equivalent. (The actual focal length was probably something like 6mm-60mm).

If you get a DX or APS-C format DSLR they have a "crop factor" of approximately 1.5. What this means is that for any lens you buy you need to multiply by 1.5 to get to the 35mm equivalent.

So for example to get the same range as you had with your olympus you would need: 38-380/1.5 = 25-250mm lens. There are a number of lenses with a similar zoom range and coverage because that is fairly standard for a "superzoom" type of lens. The most common would be something like 18-200 - which is also approximately 10x and is a bit wider and a bit shorter than what you had before.

HOWEVER. You may be used to thinking that a big X factor is a GOOD thing. Actually it's not. The bigger the X factor the more difficult a lens is to design and it gets bigger and heavier. DSLRs can change lenses, so in general you would be much better off from an image quality point of view with two lenses to cover the same range.

Big zoom ranges are convenient, but make for poor optics. Usually the reason you go for a DSLR is to improve optics at the cost of the convenience of a small camera. So mostly the people who buy the 10x zoom lenses for DSLRs are people who have just sold their P&S and think they need a 10x zoom or they will be losing something.

Most entry-level DSLR cameras can be bought with a 2-lens-kit. These usually cover something like 18-55 and 50-200 or 50-300. The two lenses combined give a 35mm equivalent range of 28-450mm. Both wider and longer than you had on your old olympus. If you are just starting out in the DSLR world these 2-lens-kits are an excellent starting point and offer good optics and excellent value for money.
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Last edited by peripatetic; Oct 28, 2010 at 2:10 AM.
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Old Oct 28, 2010, 4:17 AM   #3
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The advantage of a dSLR is that you can change lenses so you can use a lens that's optimized for what you want to shoot. A jack-of-all-trades-and-master-of-none will cover a broad range of focal lengths, but it won't do any of them very well. Multiple lenses of less ambitious zoom ranges will often do a better job, and may even cost less.
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Old Oct 28, 2010, 8:32 AM   #4
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I agree with peripatetic and TCav's comments on the quality of high range zooms. However those lenses do have their uses: I tend to think of them as "parade lenses", very useful when you want to change focal length quickly get a close up of a clown face then the following high school band.

Depending on what you want to do with the pictures, a "parade lens" could be good enough. For the weekly neighborhood paper, snapshots, ...
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Old Oct 28, 2010, 3:39 PM   #5
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A follow-up question:

What is the difference between a lense designed for a full frame DSLR and an APS-C camera? Will a full frame lense not work well on the other kind? Is there an easy way to tell on the lense which camera it is designed for?

Thanks for any help! I am learning much here.
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Old Oct 28, 2010, 4:05 PM   #6
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That relates to the size of the sensor. The full frame will have the largest sensor and obviously the best image quality.

APS-C are smaller sensors to meet DSLR requirements at a budget. Since they're smaller they crop the image and it looks magnified or zoomed in. The Canon magnifies it by a crop factor of 1.6 while Nikon, Pentax, Sony magnify it by a crop factor of 1.5

This means if you use a 300m lens on a Canon APS-C (300 x 1.6 = 480), it will act as a 480mm lens.
If you use 300mm lens on a Nikon (or Sony/ Pentax/ Olympus) APS-C (300 x 1.5 = 450), it acts as if it is a 450mm lens.
If you use 300mm lens on a full frame camera it acts as a 300m lens.

Last edited by Lilacfire; Oct 28, 2010 at 4:07 PM.
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Old Oct 28, 2010, 4:34 PM   #7
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To add to what Lilacfire said:

You can use a lense designed for FF (Full Frame) camera on an APS-C (Crop Sensor) camera
because the "Image Circle" is bigger than the sensor... If you use a lense designed for a Crop
Sensor camera on a FF camera the "Image Circle" is smaller than the sensor so the corners
will be dark and sort of cut off...

Some FF DSLR's have an "APS-C" mode that will use a smaller part of the sensor to equal the
image circle of a Crop Frame camera but that means it will use less megapixels (MP) and be a
lower MP image...

Also, when using a FF lense on a Crop Sensor camera you get a crop factor of 1.5 (example: Nikon)
or 1.6 (example: Canon)... This means that you multiply the focal length by 1.5 or 1.6 times...

Examples:
Full Frame Camera with 50mm lens = 50mm @ 35mm film equivelent
APS-C Camera with 50mm lens x 1.5 crop factor = 75mm @ 35mm film equivelent
APS-C Camera with 50mm lens x 1.6 crop factor = 80mm @ 35mm film equivelent

How to tell if a lense is for a FF camera or an APS-C camera will usually be in the model number,
which will depend on the manufacturer... For example, with Nikon lenses a "DX" in the model number
designates it is a lens made for APS-C cameras and has a smaller "Image Circle" than a lens made
for FF cameras...

Hope that helps...
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Old Oct 31, 2010, 9:43 AM   #8
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Just a slight correction: A 100mm lens does not "act like" some other focal length if it's put on another camera. 100mm is 100mm and that's it. The image it projects remains the same. But different size frames 'see' more or less of that image. Look at that diagram above, with the different frame sizes. Overlay those frame outlines on a picture you've cut from a magazine. The picture remains the same, but smaller frames see less of it. That's all that "crop factor" or formatfaktor is.

I become irate when I see casual references to equivalent focal lengths. Equivalent in the Angle or Field of View, AOV or FOV, yes. Equivalent in other optical qualities, NO!

Most important is Depth of Field, DOF. This is the range of subject distances in which the image looks acceptably sharp. Short focal lengths have much greater DOF than long focal lengths. Suppose you shoot a P&S whose zoom is 'equivalent' to 20-200mm but is actually 5-50mm. You come to expect the image sharpness. Then you buy a dSLR with an 18-200mm lens, and you're disappointed that everything is out of focus. What's wrong with my lens?!? Do I need to upgrade?!? Sure, buy another lens, keep the stockholders happy. Or just learn how each lens behaves on each camera.
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Old Oct 31, 2010, 1:00 PM   #9
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Your ire is best directed elsewhere I think. :-)

Nobody here thinks there is equivalence in anything other than FOV, but the OP really doesn't need to get into that at this point. One step at a time.

And the first criterion for any lens purchase is its FOV. No-one could seriously suggest otherwise.
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Old Oct 31, 2010, 6:50 PM   #10
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Quote:
Originally Posted by peripatetic View Post
Your ire is best directed elsewhere I think. :-)

Nobody here thinks there is equivalence in anything other than FOV, but the OP really doesn't need to get into that at this point. One step at a time.

And the first criterion for any lens purchase is its FOV. No-one could seriously suggest otherwise.
I agree with the first two points, but not with the last. If you have a "parade lens" the major values of FOV are covered. Then things like speed, distortion, size, weight, contrast, ability to make French toast, ... are things to consider.
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