optical or digital zoom

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craigluscar

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Leslie
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Hi there, I am new to this format and have been an avid photographer since digital cameras have come on the market with Canon compacts & now SonyCybershot.
I notice that digital zooms have increased substantially and one Sony is offering 30 X optical zoom with 60 X digital zoom I had always been led to believe that optical was better but presume now that the increase of larger memory cards has led to this
Is it now at the stage where digital zoom is superior to optical?
I look for guidance before upgrading with Christmas coming up
 
Digital zooms just crop the image, reducing image quality. Whilst this might not be a problem if you print small. It will reduce image quality.
 
Digital zoom has nothing to do with the memory card.

You can generally ignore digital zoom when comparing cameras - unless your just shooting video, that's a slightly different kettle of fish with compact cameras.
 
The smaller you make the camera sensor, so the shorter focal length you need for any given angle of view.

APS or 'Crop' sensor SLR's have a sensor aproximately half the area of a full-frame or 35mm SLR. It's roughly 24mm wide by 16mm tall, instead of 36mm wide by 24mm tall.

We now get into 'similar triangles; and 36mm/24mm or 24/16 = 1.5, the effective 'Crop-Factor'.

So, by this similar triangles crop factor; the angle of view of a 50mm lens on a full frame camera is the same of that of a 33mm lens on a Crop sensor. Ie you need less lens length to get the same 'zoom'.

Now make the sensor even smaller; I have a little Kodak compact to hand; with 3x Zoom that proclaims 35mm-105mm 'equivilent' on the front. Exif data says it has an actual lens length of 5.8mm - 17.4mm.... a zoom range of 3x.

Hmm... this is where it gets a bit, err.. deceptive. That 'Zoom Times' doesn't actually tell you how much magnification the lens gives....its just the ratio of longest lens length to longest!

Make the shortest lens length very short, you don't need to go very long to get a very big zoom-times, do you?

I mean, on a 35mm camera, 10mm is pretty wide, probably a fish-eye.. but if I made a 10-100 zoom, I could claim 10x zoom factor... but, gives no more far subject maginifcation than little digi-compact that has only 3x Zoom, but starting from a less wide angle at the small end.

However; the huge crop factor of a micro-sensor compact means you dont need very long lenses to get big 'zoom'. Just 17.4mm on that Kodak, gives the equivilent of 105mm on a 35mm camera. 17.5 on my Crop Sensor DSLR is still a wide angle lens, equivilent to about 26mm on 35mm.

So a 30x zoom? Doesn't actually tell you much; but lets say that they used some of it to get a wider angle of view than 35mm Full-Frame equivilent... and started at something like; 24mm equivilent... we have a 6x crop factor, so that would need a 4mm lens, on compact sensor. 30x 4mm is 120mm; which isn't all that long, and would only be a mild tele-photo on a 35mm camera but with 6x crop factor, that has the effective magnification of a 720mm super-tele on 35mm.

YET the zoom range in terms of focal length is smaller than that of a 70-210 3x soom on a 35mm camera. That gives 180mm of extension, this 30x zoom is giving only 115...

Its magnification rating is coming fro a HUGE crop factor, curtecy of a tiny tiny sensor.

Digital zoom? Basically doubling that again, by simply only taking data of the central 1/3 or so of the already tiny sensor, increasing the crop factor from 6x to 12 times, and doubling again the 'effective' zoom range and magnification.

Great if you want lots and lots of telescopic reach; but 450mm on a full frame camera is enough to fill the frame with the moon.... how much magnification do you want?

Its 'Cheap' magnification; and its at the expense of image quality.

Digital Zoom is no better now than it was ten years ago, and its still doing the same thing, the same way; halving the utilised sensor size, to double the crop factor, and double the effective lens length; but obviousely, if you have a 10x or 20x or 30x optical zoom, doubling that by digital cropping, is going to give much bigger effective numbers than if you had a 3x or 5x or 7x zoom....

Ah! but more modern cameras probably have twice the Pixel Count of older ones!

Which is why they can 'get away' with it! As many pixels in that cropped 2x zoom on modern camera, as there was on early one using the full frame...

However... the sensor is no bigger... the sensor is getting no more light... theres still the same number of photons falling on the sensor, so each pixel is getting less of them, so more 'amplification' is needed to get a signal from them.... means more noise and lower quality.

All in all, its a BIT of a con.... and when it comes to cameras, the numbers are usually always ratios, not actual values... you have to know what they are doing and how they work and relate to each other to know whether they are any more of less useful.... but the marketing men like the big numbers they can present as 'impressive' on the consumer market... in cameras they make down to an 'Acceptable Quality Level' both for price and performance.

And they can get these big impressive 'specs' very easily just by using a smaller sensor area. THAT is all it is. Inflation by crop-factor. Confusion by Pythagoras!
 
craigluscar said:
Hi there, I am new to this format and have been an avid photographer since digital cameras have come on the market with Canon compacts & now SonyCybershot.
I notice that digital zooms have increased substantially and one Sony is offering 30 X optical zoom with 60 X digital zoom I had always been led to believe that optical was better but presume now that the increase of larger memory cards has led to this
Is it now at the stage where digital zoom is superior to optical?
I look for guidance before upgrading with Christmas coming up
Click to expand...

Optical zoom is always better, digital zoom doesn't zoom at all, all it does is trim the picture down, just like taking the scissors to a print makes the subject fill a much smaller frame.

Also as far as quality goes, less is more, making a good comapct lens is hard enough, add in massive zoom range and it's going to end in very poor pictures. You're not likely to need such stupid zoom lengths anyway in everyday shooting.

Typical SLR users will have a telephoto lens that roughly equates to less than 10x zoom and even that hardly will get used, except unless you're a wedding shooter. Wildlife photographers may have one equivalent to having a 20x zoom, but most of us buy a good quality lens equal to about 3x-4x. :thumbs:
 
Teflon-Mike said:
However... the sensor is no bigger... the sensor is getting no more light... theres still the same number of photons falling on the sensor, so each pixel is getting less of them, so more 'amplification' is needed to get a signal from them.... means more noise and lower quality.
Click to expand...
All very good points, but it leads me to ask one question which I have often wondered the answer to. I've read many times that more pixels introduce noise and your explanation makes perfect sense regarding amplification, but now Canon have introduced the 70D which is supposed to be good at high ISOs, why would it be better at, say ISO 800 than my 450D when my 450D is 12.2 MP and the 70D is 20.2 MP?

Is it solely down to sensor technology advances and, if so, would the 70D sensor at 12.2 MP be so much better? If that is the case, why increase MP in the first place?

Help!
 
Goody13 said:
Is it solely down to sensor technology advances and, if so, would the 70D sensor at 12.2 MP be so much better? If that is the case, why increase MP in the first place?

Help!
Click to expand...

I think the simple answer is yes, sensor technology is improving and it now possible to fit more light sensors in the same area without the noise issues that used to occur.

One reason for having more pixels is that it enables larger prints. I am not sure how many people need to print to the size it allows, but the option is there.
 
Goody13 said:
All very good points, but it leads me to ask one question which I have often wondered the answer to. I've read many times that more pixels introduce noise and your explanation makes perfect sense regarding amplification, but now Canon have introduced the 70D which is supposed to be good at high ISOs, why would it be better at, say ISO 800 than my 450D when my 450D is 12.2 MP and the 70D is 20.2 MP?

Is it solely down to sensor technology advances and, if so, would the 70D sensor at 12.2 MP be so much better? If that is the case, why increase MP in the first place?

Help!
Click to expand...

There are two fundamental reasons why digital zoom can never be as good as optical zoom. It's the same reason that compacts are not as good as DSLRs and full-frame is better than the smaller APS-C format.

Larger formats collect more light, more photons, the basic raw material. So noise is lower, high ISO performance is better etc.

Larger formats also requires less magnification for a given size output, to print or on-screen. Less magnification means the lens doesn't have to work so hard for a given standard or resolution and one of the facts of physics is that when lens resolution demands go down, image contrast goes up (basic lens MTF theory) and it's image contrast that contributes most to what we call sharpness.

Pixel count has very little to do with it, within reason, and having more pixels can only deliver higher resolution if the lens is capable. There is a relationship between pixel size and noise etc, but technology has a habit of continually reducing it. Based on the fact that the same number of photons fall on a sensor of a certain physical size, regardless of pixel count, this trend is likely to continue.
 
Digital zoom is pointless, I wouldn't even consider it as a plus when buying a camera, just crop the picture afterwards for the same effect.
 
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