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Old Jul 21, 2009, 1:33 PM   #1
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Default Crop factor, is it the same as cropping yourself?

I am a newbie in photography. Initially, I was amazed by the optical zoom camera and camcorder offer. For example, the highest optical zoom for compact camera is 26X and highest optical zoom for camcorder is 70X.

After reading up and understand crop factor, I realized all these are marketing gimmick. For example, the 26X camera and 70X camcorder all have high crop factor, the 70x camcorder having a crop factor of 20X. With the crop factor, I realized it is equivalent to using a (2000mm/20X=100mm lens).

My question is if I use a DSLR camera and a 100mm lens, can I achieve the same picture as the camcorder by cropping it manually in photoshop?
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Old Jul 21, 2009, 2:21 PM   #2
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I don't think you are using the term crop factor correctly. When referring to "x", typically one is referring to zoom, more specifically the longest focal length divided by the shortest. So 70x means the longest focal length is 70 times longer the shortest. the crop factor when talking about dslr's refers to field of view relative to 35mm. Since DSLR's have a smaller sensor area than 35mm film, the same focal length will have a different field of view. Camcorders (and digital point and shoot cameras) can have larger "x" ratings because of their much smaller sensors. As you mention, "x" is a relatively useless term.

Now that being said, you can always crop your photo's to achieve a different filed of view/perspective. However, extreme cropping like your suggesting will lead to a serious reduction of quality. Which isn't all that different from using the extreme zoom on a camcorder, which usually results in extremely poor quality.
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Old Jul 21, 2009, 2:33 PM   #3
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Thanks for your quick reply. Can I conclude all these high optical products are just marketing gimmick as they are equal to 100mm lens? To achieve better optical zoom, I just have to buy a 200-300mm zoom lens and win them hands down??
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Old Jul 21, 2009, 3:13 PM   #4
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Originally Posted by maisatomai View Post
Thanks for your quick reply. Can I conclude all these high optical products are just marketing gimmick as they are equal to 100mm lens? To achieve better optical zoom, I just have to buy a 200-300mm zoom lens and win them hands down??
Yes they are marketing gimmicks, but they are functional if not high in quality. I'm not sure I understand the relationship you've established by stating you're dealing with a 100mm lens. A 100mm lens by definition has no zoom, as it is only a single focal length. Zoom by definition is a lens with a range of focal lengths, the zoom factor being largest focal length divided by the shortest. So, an 18-55 lens is a 3x lens, as is 100-300 lens. Obviously two different lenses, which is why the 'x' is really useless. Also, you mention buying a 200 or 300mm lens to obtain better quality than a 100mm. Longer focal lengths do not imply higher quality. Longer focal length just means narrower field of view. Also, a 200mm lens is not double zoom (or more appropriately 1/2 the field of view) of a 100mm.
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Old Jul 21, 2009, 4:45 PM   #5
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There are two different concepts at play in your original question:

first, "zoom factor" (26x in your compact digicam as an example). this is the ratio between zoomed in and out (but since you haven't specified what the starting point is, there's no way to know what the "zoomed in" point is)

second, is crop factor. this is typically used as a way to compare cameras with different sensor sizes to a common ground (ie, 35mm film)

so, an example:

First, I stole a few values from here so I wouldn't have to calculate them myself: Angle of View - Wikipedia

A 35mm lens on a 35mm camera will have a diagonal angle of view of 63.4 degrees. A 135mm lens on this same camera will have a diagonal angle of view of 18.2.

The same lenses on a camera with a crop factor of 1.5 will have angles of view of ~47 degrees and ~12.5 degrees respectively.

These narrower angles mean the lens sees further given the same focal length, this is due to the size of the actual sensor. There's a good diagram that helps explain it in the link I provided above.

Now, if you have a 35mm camera with no "crop factor" and you put a 35-135mm zoom lens on it (which by reading the numbers you can see is a ~4x zoom lens) your angle of view will be between 63.4 and 18.2 degrees.
Taking this same lens and putting it on your camera with a 1.5x "crop factor" it will attain the same angle of view as a 50-200mm lens on a 35mm camera. multiply 35mm by 1.5 and you get ~50mm, multiply 135mm by 1.5 and get ~200mm. (the 50-200mm lens has a angle of view of ~47 to ~12.5 degrees)

so, 50mm and 200mm lenses (or the zoom who's limits were defined by these two lenses) would have exactly the same "range" as a 35-135mm on a camera with a crop factor of 1.5.

The crop factor greater than 1 tells you that it will see further at the same focal length (narrower angle of view) and a crop factor less than 1 tells you that it will see less far (wider angle of view) when compared to the baseline which is 35mm film.

...I've read this 10 times over, I hope I've managed to make it clear... if not, please ask!

Last edited by conor; Jul 21, 2009 at 5:03 PM.
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Old Jul 21, 2009, 4:59 PM   #6
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Quote:
Originally Posted by maisatomai View Post
...
My question is if I use a DSLR camera and a 100mm lens, can I achieve the same picture as the camcorder by cropping it manually in photoshop?
If the lens on the camcorder at full telephoto has a focal length 100mm then "yes, sort of...".

If you:
1. stand in the same place
2. use the same focal length lens
3. shoot at the same f/stop
4. crop all images to have the same framing
then:
1. DOF will be the same
2. Perspective will be the same

What will differ is resolution. Cropping a APS-c format DSLR to get the same FOV, under the above conditions, as the same FL lens yields on a camcorder will result in an image that uses a very very small portion of the sensor and thus very few pixels.
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Old Jul 21, 2009, 5:30 PM   #7
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dwig: I'd imagine that the amount of data being captured by the sensor and how much data the camera's processor is extrapolating would make this even more ambiguous. a 1" wide censor that captures 1000 "dots" across a line will output 1/4 the quality (sharpness-wise) as a 3" wide sensor that captures 2000 dots... which means if you cropped out 1/9 of the frame of the larger sensor (to get the same area as the smaller one), you'd actually have less dots picking up light which should lead to a less clear picture... assuming 4:3 ratios the sensors would be 750,000 vs 3,000,000 at full frame, but 750,000 vs 333,333 after the crop...

i guess the question is, wouldn't you have to factor in the resolution (megapixel rating) of the sensor itself to properly determine if the quality of the outputted image is the same? (and to complicate things further, i would think that the resolution of the sensor is NOT the same as the "megapixel rating" of the camera - I'd ASSUME that the camera is processing the retrieved pixels and extrapolating the data....)

Oh, we could also add point 5 to your original list of "ifs": "If both cameras are set at (capable of) the same ISO"

Last edited by conor; Jul 22, 2009 at 11:49 AM.
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Old Jul 22, 2009, 7:45 AM   #8
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Thanks for all reply. If a poster "STEVE" is located far away which is invisible from the eye such that only one device is able to capture it, do you think it will be a

1) Panasonic SDR 26 max 2695mm? (1/8" sensor) Crop factor more than 20X
2) Canon SX10 max 560mm? (1/2.5" sensor) Crop factor 5X. Crop to the size of the poster after that.
3) Nikon 5000D with 50-150mm lens? Note that the previous two telephoto length are expressed after multiplying by the crop factor. For this one the max is 150mm and it is before cropping. The crop factor is 1.5X. After that crop to the size of the poster.
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Old Jul 22, 2009, 11:45 AM   #9
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Quote:
Originally Posted by maisatomai View Post
Thanks for all reply. If a poster "STEVE" is located far away which is invisible from the eye such that only one device is able to capture it, do you think it will be a

1) Panasonic SDR 26 max 2695mm? (1/8" sensor) Crop factor more than 20X
2) Canon SX10 max 560mm? (1/2.5" sensor) Crop factor 5X. Crop to the size of the poster after that.
3) Nikon 5000D with 50-150mm lens? Note that the previous two telephoto length are expressed after multiplying by the crop factor. For this one the max is 150mm and it is before cropping. The crop factor is 1.5X. After that crop to the size of the poster.
Since you have specified that the focal lengths of the first two are "35mm equivalent focal lengths", and the 35mm equivalent of the last one is 75-225mm, the first would see furthest. In order, their Angles of View are about 1 degree, about 4.5 degrees, and about 12 degrees.
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Old Jul 22, 2009, 12:26 PM   #10
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But I thought the last one should win? Because we can crop it using photoshop repeatedly and be able to see the word "Steve" printed on the poster far far away. Am I right?
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