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The Right Tempo A blog by Felipe M. G. Ceotto

I've just bought a new digital camera, a SLR, which is very nice. I used to have a film SLR and I basically bought a similar one, but digital. One of the first questions people make me when they find out that I have a new camera is (after asking how many Megapixels it has) how much optical and digital zoom the camera has. This is a much more difficult subject that people would imagine, so I have decided to write a little article on it.

First, let me start by making a strong statement: there is no such thing as digital zoom. Digital zoom is a simulation of zoom done by cropping the image. Look at the image below to get an idea of how it is done. Image 01 on the left is the actual image without any "digital zoom". Image 02 shows the part where we will zoom in, using digital zoom, and finally image 03 is the final "zoomed" image, which is basically the square selected in image 02 stretched to meet the correct size. This stretching is something that most digital cameras don't even do, they just save the little square from image 02 in that small size, which is a basic cropping. When you print your photo it will be stretched to meet the paper size, and that stretching means loosing quality as it is clear on image 03.

 

Digital Zoom Example

So, I can't call that "zoom", for me that is "cropping". Agreed? I always recommend people not to use it. Take the whole photo and crop it later in your computer using Photoshop or something else, which will crop it much better than your regular point-and-shoot camera. SLR cameras usually don't have "digital zoom", I think. At least mine doesn't.

Now let's talk about the optical zoom. When you buy zoom lenses for a SLR camera, what you get in the specs, among other things, is usually the focal length, i.e. 70-300mm. Usually, when you buy a point-and-shoot camera the optical zoom is referred as an "X" value: 12X, 3X, etc. Now that is a very tricky value, let me explain why.

The "X" value is easy to think about because most of us are used to multiply which is what the X stands for. The problem is that the multiplication is not to what we think it will be. When you read on a camera specs that it has 12X optical zoom you think that it will increase the image you can see 12 times, don't you? That's the thing, it might not, and most of the times it doesn't. It does increase the smaller image that those lenses can take by 12 times, but the smaller image is usually smaller than what you see with the naked eye.

For example, the Canon PowerShot S5 IS (great camera, by the way) says that it has a 12X zoom, which is ok because it does increase its farthest image 12 times, but the farthest image has an approximate zoom of 0.72 times relative to the naked eye in that camera which means that its maximum zoom is of 8.64 times (0.72 x 12), again, when comparing to the naked eye. It is still a great zoom, but the number doesn't mean what most people think it would mean.

The problem with this "X" measure is that the base can be different. We can see above that the Canon PowerShot S5 IS has a "starting point" of 0.72 times relative to the naked eye. The Canon Digital IXUS 860 IS on the other hand is advertised having a 3.8X zoom but its "starting point" is of 0.56 times approximately which means that its "real" zoom is of 2.13 times (to the naked eye, always). So if you set your PowerShot S5 IS to 3.8X it will increase the actual image by 2.74 times but your IXUS 860 IS will increase the actual image by 2.13 times when set to the same 3.8X.

That is why when you buy a SLR you usually don't find the "X" in the lenses specs, only the focal length. The "X" figure is useful though, when related to the naked eye image, because we can relate to it better, so here is how you calculate it from the focal length. On a 35mm camera (the usual film camera) a 50mm focal length gives roughly a 1X image, so all you need to do is divide the focal length of your lenses by 50 to have the "X" number, meaning that a 200mm focal length gives a 4X image. The problem with digital cameras is that the image sensor (CCD) has a different size than the film; it is usually smaller than 35mm, meaning that 50mm will not provide a 1X image anymore, it will be bigger. The smaller the CCD, the bigger the image a 50mm will make. To find out the "X" number for your lenses in your digital camera the equation is: X = (35 / CCD) x (FL / 50), where CCD is the size of the CCD in mm and FL is the focal length of your lenses in mm.

SLRs will usually have a bigger CCD because bigger CCDs will give you a better quality of image. On the other hand, to have a big zoom you will need lenses with bigger focal lengths, meaning these lenses will be more expensive. For example, a Nikon D40 has a CCD size of 23.7mm while the Canon PowerShot S5 IS has a CCD size of approximately 5.83mm. The lenses that come with the PowerShot S5 IS are 06-72mm and those 72mm will give a real zoom of 8.64X ((35 / 5.83) * (72 / 50)) and the 06mm will pull up to 0.72X. If you put the same lenses on the Nikon D40, you will get a real zoom of about 2.13X with the 72mm but your image will have a much better quality. To have the same zoom as a PowerShot S5 IS you would need lenses with a focal length of 292.53mm, that is, a 300mm to round it up, and that is going to cost you much more than that 72mm of the PowerShot.

So everything is a trade off, of course, meaning that if you want top quality combined with a big zoom you will need top lenses and you will pay top money for them. On the other hand, most people will find that the Canon I used as an example here (the PowerShot S5 IS) will give them quality enough and a big zoom. Canon also compensates its smaller CCD with more pixels (8MP) to improve the quality of the photo, while the Nikon D40 will give you a really nice quality for its photos but it has fewer pixels (6.1MP) to keep its price lower, basically. Note that in my opinion 6.1MP is more than enough for people printing photos up to 8x6" which is bigger than most people will usually print.

That's it, I hope I've helped. Keep in mind that the number of Megapixels isn't always the most important thing in a digital camera, especially when you're over 5MP and that digital zoom doesn't exist and finally that if you really want to get into it you should also know what kind of lenses your camera has and what kind of CCD sensor it has. If you don't want to get into it, take the camera for a trial and shoot some photos, some inside, some outside, some of people and some of close objects, to give it a good try and see if that's the camera you want. Print the photos in a shop to see the real quality of them, and then buy your camera. :)

Oh yeah, and my new camera is a Nikon D40. Brilliant!

Posted on Tuesday, November 20, 2007 3:23 PM Photography | Back to top


Comments on this post: Zoom in Digital Cameras

# re: Zoom in Digital Cameras
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Great info... can you give me the X value for Nikon D40X which is same as your model, for a lense 18-200 mm
Left by Musthafa on Feb 20, 2008 10:32 AM

# re: Zoom in Digital Cameras
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Zone-India, New Delhi

Actually I am searching for an camera in which, I can capture image and video as well. But problems is that I love to visit forests. In that case several time I missed beautiful pictures because of distance. I know that I need a higher optical zoom camera but WHICH ONE? Can I get some info. about that. I want the possible optical zoom in that camera. It would be great if I may get the price in indian currency. Waiting for reply

Thanks

Akeshwar
Left by Akeshwar Pd on May 01, 2008 1:42 PM

# re: Zoom in Digital Cameras
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I got a Canon PowerShot S5 - it is a great, high quality camera, the 12X zoom is incredible. Great post, thanks!
Left by online casino list on Nov 09, 2010 8:19 AM

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