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Explain zoom lens specs please?
January 13, 2014 12:15 PM   Subscribe

Can someone explain these two types of zoom lens specs?

I know nothing about cameras and Google has been surprisingly unhelpful.

What is the difference/relationship between camera zooming claims of 15x or 30x (I understand that part) versus other zooms that don't say anyx but instead say something like "16-50mm Retractable Zoom".

Is there a conversion?
posted by Cosine to Technology (24 answers total) 3 users marked this as a favorite
 
More than you wanted to know: How do I convert lens focal length (mm) to x-times optical zoom?
posted by Nonsteroidal Anti-Inflammatory Drug at 12:17 PM on January 13 [1 favorite]


The key point from that link:

An 18-55mm and a 70-200mm are both about "3x zoom", but a very different range.

For reference, 50mm is a "neutral" focal length on a 35mm film camera (or a full frame DSLR.) Point-and-shoot cameras typically have smaller sensors so a neutral focal length might be something like 10mm. To make things even more confusing, cameras with smaller sensors are often listed with the "35mm equivalent" focal lengths.

For fixed-lens digital cameras, pay close attention to the wide end. You might encounter two lenses with 6x zoom in different ranges:

30-180
40-240

typically the 30-180 is more desirable because it extends further into the wide-angle range. 40mm is not wide enough for, e.g. full room interior shots. That little bit of extra reach on the 240 telephoto is not worth the loss at the wide end.
posted by scose at 12:47 PM on January 13 [3 favorites]


A camera with a zoom of "10x" has a longest focal length 10x longer than it's closest focal length. A lens that can zoom from 20mm-200mm has a 10x zoom.

Conversely, a lens with a 16mm-50mm zoom has a 50/16 = 3.1x zoom.

The actual numbers are more useful because they actually tell you how close and how far the lens can go. A 40-400 and 20-200mm lens are both "10x zoom" but one will get in twice as close and the other will reach out twice as far.

Note that you can't compare mm measurements between lenses for different size cameras. A 500mm lens on a 35mm camera is equivalent to a 25mm lens on a 4/3 camera. Each different size camera sensor will have a correspondingly different sized lens for a "normal" field of view.
posted by tylerkaraszewski at 12:48 PM on January 13


Just so you aren't further confused, I believe tylerkaraszewski has a bit of a typo there - that should read "A 50mm lens on a 35mm camera is equivalent to a 25mm lens on a 4/3 camera."
posted by solotoro at 1:00 PM on January 13 [1 favorite]


Just so you aren't further confused, I believe tylerkaraszewski has a bit of a typo there - that should read "A 50mm lens on a 35mm camera is equivalent to a 25mm lens on a 4/3 camera."

Yes, this.
posted by tylerkaraszewski at 1:02 PM on January 13


Ok, those are fairly clear.

My wife's camera is a Panasonic from a few years back with 10x zoom, 25 - 250 mm. The Sony I would like to replace hers with has a "16-50mm Retractable Zoom Lens".

As someone with no knowledge of these things it certainly seems like you are getting more with the cheaper camera. Even assuming the 16 vs 25mm means a wider angle shot which I understand to be a good thing.

No?
posted by Cosine at 1:03 PM on January 13


It gets even more complicated once you start considering what the aperture range (i.e. how much light it lets in) of the lens is. More zoom might seem/be fun, but if it comes at the cost of being forced to use much smaller apertures, it can kill you ability to shoot in low light for example. Oh, and some lenses create more distortion than others. Basically, the devil is in the details (and there are lots of details).

If it were me, I would favor a lens that gets good reviews for sharpness and has a wide maximum aperture over one with lots of zoom. Unless you only shoot candids and want to be able to get decent portraits from way across the room or something.

YMMV and I'm not an expert or anything.
posted by that's candlepin at 1:10 PM on January 13


...Even assuming the 16 vs 25mm means a wider angle shot...

It does *if the cameras have the same size sensor* (or if those focal lengths are in "35mm equivalent" lengths, which are often published). There is a very good chance that the two cameras have different sized sensors.

To create an extreme example, a Cannon 5D DSLR has a 35mm sensor.

An iPhone 5s has 1/3" sensor.

The (fixed) focal length of the iPhone lens is 4.12mm, but because the sensor os so small, this is equivalent to 31mm on the full-frame Canon DSLR.

This means, that comparing these two cameras, a 28mm lens on the Canon is wider than 4.1mm lens on the iPhone.


Additionally, lens with more variable zooms tend to sacrifice image quality. The "high-end" zoom lenses that professionals use tend to not have zoom factors bigger than 3-4x, because it gets increasingly difficult to build a lens that can do that and maintain sharpness and brightness.

So, with a wider focal length range, you get a wider focal length range. You don't necessarily get a wider angle, a closer angle, or better image quality than whatever you're comparing to, though.
posted by tylerkaraszewski at 1:11 PM on January 13


Some cameras erroneously list "digital zoom" in the total zoom amount. Digital zoom is total BS. Check if this is the case for the Panasonic.

There are other aspects to lens quality besides zoom range. Aperture size is a big one. Basically it describes the diameter of the hole in the middle of the lens that light passes through. If your aperture is 2x bigger, you can use a shutter speed 1/2 as long and let in the same amount of light. This means you can take pictures in low light and they won't be (as) blurry.

Aperture numbers are extremely confusing. Smaller numbers mean bigger holes, and the scale isn't linear. In this list:

1.4, 2, 2.8, 4, 5.6, 8

Each number indicates an aperture half as large (in area) as the previous one.

Cheap zoom lenses often have a really small maximum aperture at the telephoto end. I bet your wife's Panasonic is somewhere in the f/8+ area. This means it's hard to get sharp zoomed-in shots in anything but the brightest hard daylight.
posted by scose at 1:13 PM on January 13


Also, if you're talking about the lens I think you are, you're considering a Sony Alpha NEX somethingorother. If I'm right, read this review from the wirecutter. If I'm wrong, ignore me.
posted by that's candlepin at 1:14 PM on January 13


Yes, the Sony, I've read a bunch of reviews. What none of them can really tell me though is whether the downgrade from 10x zoom to 3x zoom is more than made up for by the increase in quality.
posted by Cosine at 1:18 PM on January 13


Yes, the Sony, I've read a bunch of reviews. What none of them can really tell me though is whether the downgrade from 10x zoom to 3x zoom is more than made up for by the increase in quality.

It depends entirely on how much you need the really long or really close shots. If you're shooting wildlife you'll want a really long lens. If you're shooting architecture, you'll want the really close one. If you're shooting portraits and pictures of your kids in the backyard, you don't need either.
posted by tylerkaraszewski at 1:20 PM on January 13


it certainly seems like you are getting more with the cheaper camera

The cheaper camera had a bigger zoom range, but probably poorer optical clarity and aperture. (And as some above have pointed out its difficult to compare lens angles across cameras with different sensor sizes.)

Zoom range is probably the least important feature in a lens -- you can always stand closer or farther away, but you can't always easily add more light. Max aperture is probably a better measure of a lens's overall quality; it's easy to get a sharp photo even with crappy glass if you're stopped all the way down to f22, but the wider the aperture the better the glass needs to be to perform acceptably.
posted by ook at 1:25 PM on January 13


you can always stand closer or farther away

Not at the zoo.

Not a joke.

Today is a learning day, yay!
posted by Cosine at 1:46 PM on January 13


To join in the fray: the Sony has a much better sensor than any retractable-lens point and shoot camera (though I am rather fond of the ones that Panasonic uses in its LX7). Other things being equal, it will produce better pictures, especially in low light situations, where the better sensor (more sensitive, less noise) will be aided by the wider aperture of the lens.

Whether the different zoom length matters depends on the kind of photography your wife does. Does she like taking pictures of things that are far away--animals, architectural details, etc.? Or is she more inclined to interior shots, portraits, etc.?

But one advantage of the Sony is that you can change lenses. So if the kit (standard) lens turns out to be too short, she can get a separate telephoto lens, or a wide-range zoom.

By the way, the Sony is a deal of the day today at Amazon.com.
posted by brianogilvie at 1:52 PM on January 13


Oh, it gets weirder. Sensor size in P&S digital cameras is expressed 'in the non-standardized "inch" system as approximately 1.5 times the length of the diagonal of the sensor.' [wikipedia]. If you sensor is 1/8", that doesn't necessarily mean 1/8th of an inch on any particular dimension. You have to go look it up somewhere.

Good luck!
posted by chairface at 2:16 PM on January 13


As someone with no knowledge of these things it certainly seems like you are getting more with the cheaper camera. Even assuming the 16 vs 25mm means a wider angle shot which I understand to be a good thing.

No?


No, sorry. :)

Here's the gist of it:

First, sensors. All other things being equal - and bear in mind that all other things are not always equal - a bigger sensor will perform better than a smaller sensor, especially in low light. A bigger sensor will also have, by definition, a larger field of view than a smaller sensor. In practical usage, this will mean that you will have more flexibility with regard to depth of field, i.e. when something is in focus, but things in front of and behind it are out of focus. Also bear in mind that bigger sensors will always require larger lenses than smaller sensors.

That said, many small-sensor devices have very good IQ. Sensor technology has been improving by leaps and bounds. My Olympus XZ-1 compact has a much smaller sensor than that of my Pentax K-5. Up to ISO 200, the XZ-1's IQ is more than acceptable. However, after ISO 400, the XZ-1 starts sweating, whereas the K-5 stays strong through ISO 6400 and probably a bit beyond. Also, at all ISOs, the Pentax has greater dynamic range - in practical terms, this means that I can "rescue" a photo where, say, somebody has been horribly backlit, or where the sky has been blown out. That's one of many nice things about largers-sensor cameras. Also, small-sensor devices will never have the wider FOV of a large-sensor of device, because physics.

Second, lenses.

There are qualities to lenses other than just their focal length, or their range of focal lengths.

Most notably, people often talk about the speed of a lens (how much light it lets in), how sharp a lens is (and how even this sharpness is across the lens), how well the lens renders color and contrast, how much the lens distorts the image, how well a lens renders out of out-of-focus areas ("bokeh"), and how much a lens suffers from chromatic aberrations (ugly fringes of unwanted color). There are other things to think about, including obvious stuff like how big a lens is and how durable it is, but you get the idea.

So, you have this big bundle of qualities that a lens can possess, in varying degrees. So, why isn't every lens a 10mm-300mm f1.8 with perfect sharpness across the frame?

Because lens design always involves compromise. Always. It's like how a bus is physically incapable of being as zippy as a sports car. There are hard-and-fast laws of optics which determine how easy it is to design and produce lenses with certain qualities. There are relatively hard-and-fast laws of economics which determine how much it costs to produce lenses at predictable levels of quality.

This means that a 10x lens will be almost certainly weaker in other categories than less "ambitious" lenses, because when you prioritize focal range, you have to give other attributes short shrift.

Zooms with wide focal ranges tend to be slow (they don't let in much light) and tend to feature heavy distortion. They tend to not be sharp, or if they are sharp, they are only sharp in the center, and/or you have to stop down quite a ways to make the images acceptably sharp. Many superzooms are so "blah" at their long end, that their images are not appreciably better than simply cropping from a photo taken by a better, shorter lens.

Contrast this with how, say, a prime lens will often (BUT NOT ALWAYS) have consistently strong image quality across the frame, even wide open. A 35 f1.4 lens cannot zoom, but on a technical level, it will generally have significantly better image quality than a superzoom - plus, it can shoot in near-darkness.

Having said all that...

On the bright side, all these compromises are manageable in the real world, depending on what you need to do.

If you need a camera to take snapshots on vacation, and to maybe print a few 5x7s for friends and family, then you might very well rather have an all-in-one zoom. This assumes that you are the sort of person who would rather be able to shoot both wide and very long, and it does not faze you that many of your images may have purple fringing, etc. Who cares about some minor optical defects, when you were actually able to get that shot?

On the other hand, if you were a National Geographic photographer, somebody who literally shoots images for print publication, then you would almost certainly not want to shoot with a "superzoom" lens, as you would need much more out of your lens than a superzoom could provide.

Where this gets hinky is if you decide that you would like something which produces nicer images than you'd get out of a small-sensor superzoom camera, but which costs much less, and is much more flexible than, say, a top-of-the-line full frame camera with a top-of-the-line fast prime lens.

The nice thing about the Sony NEX camera (and its competitors from Olympus and Panasonic) is that you could get the kit zoom, and then you could get a separate telephoto zoom. You could also consider replacing the kit zoom with a fast, cheap, wide prime: IMHO, I'd rather do a "sneaker zoom" with a fast prime lens than use a slow kit zoom, but your mileage may vary.

Either way, having two lenses would probably be much better for the zoo, as you could deploy the long zoom for the faraway animals, and then it would take two seconds to switch to the wide lens for when you're in a part of the zoo where the animals are all up in your business.

Contrast that with how a small-sensor superzoom camera may not be able to take nearly as nice photos indoors without a flash.
posted by Sticherbeast at 2:27 PM on January 13 [3 favorites]


Ok, thank you again everyone for all the data, love it.

If the Sony is $280 how can it come with the SELP1650 lens that sells for $370?

Adding a second telephoto lens appears to add ~$1000 to the price, the Sony would have to be staggeringly better than a p&s for $400 to make that work.

I guess we are still in the p&s world, all things considered.
posted by Cosine at 2:33 PM on January 13


Nice interactive demo from Tamron.
posted by Drew Glass at 2:37 PM on January 13 [1 favorite]


Because lens design always involves compromise. Always.

yes this. Particularly when it comes to zoom lenses. As a general rule, the higher the 'x' value (say 10x or 15x vs 3x) the more distorted your pictures will be, especially at the ends of the zoom range. What you tend to see are 'fisheye' and 'pincushion' distortions at either end of the zoom (like looking through a magnifying glass, or, well, a fisheye lens). Usually this is...ok, I guess...but if you have any straight lines in your subject, like buildings or somesuch, it can be pretty noticeable.

If you look at DSLR lenses, you'll see they usually sell them in 18-55mm (~3x), 55-200mm (~4x), and 18-200mm (~10x). The pros will generally use the first 2 (to avoid distortions), swapping them out between near and far subjects, and only resort to the 18-200 when they have to shoot a range of distances quickly...like say, at a car race when they are shooting from one side of the track.

Honestly, what you really need to do is try these cameras out in person at a store to see what works best for you. And 'digital zoom' (done with software in the camera) is just total crap when compared to 'optical zoom' (with lenses). You see this a lot in consumer video video cameas: 30x zoom! (3x optical, 10x digital)
posted by sexyrobot at 3:12 PM on January 13


I hope to explain something about the focal lengths that hasn't been covered in enough detail yet -

First, the focal lengths stated on point and shoot compact cameras are already normalized to match what it would be like on a full frame camera. So if your camera, say, a Nikon Coolpix S6300 says it's 25mm-250mm, that's what you're getting.

The focal lengths stated on a standalone lens, however, are not normalized yet. They're stating what focal length you'll get if you mount that lens on a full-frame sensor. Very few people besides professional photographers buy a camera body with a full-frame sensor. Say if you had the NEX 3 linked above: that uses an APS-C sensor, with a 1.5x crop factor. That means that a 16mm-50mm lens on that APS-C sensor will shoot photos that look like what a 24mm-75mm lens would take on a full frame camera.

In reality, when comparing your old / new camera, you should be comparing 25mm-250mm versus 24mm-75mm.

As a practical note, I wish the lens focal lengths would be expressed in field-of-view instead, as that's much more intuitive for a non photographer. 24mm or 25mm is considered "wide angle" and your picture will encompass an arc of about 84 degrees, so if you stand in the corner of a room you will very nearly capture the entire thing (you need 90 degrees to line up to both walls heading away from you). 75mm is about 33 degrees field of view. 250mm is about 10 degrees field of view.

---

I'd also like to elaborate a bit more about the trade-offs, as already mentioned - building lenses is all about managing the physical constraints and optimizing it for a particular use-case. Focal length is just one consideration, and not only are there measurable specs like Aperture size, but there's also non-measurable ones like color rendition (the way the lens is built can perceptibly affect color rendition in photos, and IMO the most crucial element to taking pictures is how pleasing the colors are, and this is something that you cannot pick up by reading the specs at all)

There's one more trade-off not mentioned - the sensor size - it's a lot easier building high spec lenses if you're only funneling that light into a small sensor. For example the LX-7 camera ($299) looks incredible (24mm-90mm at apertures of f/1.4 to f/2.3) but that's because it's paired to a very small sensor. They couldn't have done a lens like that to a larger sensor, so for example, its competitor the Sony RX100 ($439) is 28mm-100mm at f/1.8 to f/4.9 seems inferior at a more expensive price, but it has a far better sensor, and the companies couldn't have just paired that "better" LX7 lens to the "better" Sony sensor.

That's why your 25mm-250mm camera "looks" like it has better specs even though it's cheaper - it's because it's limited to use on small sensors, which have their own drawbacks (small sensor - more noise and less detail in the photos).
posted by xdvesper at 4:28 PM on January 13


I recently replaced a 12x super-zoom point and shoot with a Sony NEX and I'm very happy with the change. The old camera could definitely zoom in to a longer range, but all zoom lenses lose aperture (a higher f-number is less aperture) when they zoom further and point and shot lenses are particularly bad. So the camera was useless with indoor lighting when using much zoom and took only mediocre indoor shots at its widest setting. The new one can take beautiful indoor shots even zoomed without a flash.

High zoom is not good without a tripod. Even a tiny amount of shake from hands is magnified by the zoom and automatic stabilization isn't enough, causing blurry images. A faster shutter speed can partially compensate for the hand-shake, but when zoomed in you get less aperture, meaning that you have two less-light strikes against you. The camera uses its only remaining tool to compensate by raising the ISO. But the tiny sensors in point and shoot cameras become very grainy at higher ISO, so the zoomed shots become ugly and grainy even in full sunlight.

With the NEX and the stock 16-50 lens I definitely have less zoom than the old camera. But the image clarity is so much better that I can take a shot at 50mm and just crop out the part I want from the middle and it will look as good or better when scaled to the same size as the image at high zoom from the old camera.

There's a good page on dpreview that shows comparison shots with a wide variety of cameras. That's just a guess of the Sony DSC-HX7V as your old camera since it matches your 25-250mm equivalent focal length. Try comparing at even higher ISOs and you can see the real difference between the camera sensors.

You mentioned $1000 for a second lens, but you can get a 55-210mm lens for the Sony for much less than that. That's the real focal length, so the 35mm equivalent range is 83-315mm. Should be excellent for wildlife photography.

The downside of the NEX cameras is that they are very popular and use a newish lens format (the E-mount), so you can't find deals on used lenses and new lenses are comparatively expensive. Lens prices go through the roof very quickly for tiny incremental quality improvements, so don't let the high prices of some of them throw you.
posted by dodecapus at 7:44 PM on January 13 [1 favorite]


I have the Sony, it is amazingly good. One of the appeals is that you can change the lenses. They do zoom lenses, I have the 55-200 for the zoo. They also do a 18-200 which whilst the range means it could be used for all situations, the lens itself is massive. The much larger sensor of the nex compared to a compact means they can't make tiny lenses. None of this mentions aperture - I have a 50mm prime which is fairly zoomed in but is great for portraits and lowlight as is f1.8
posted by JonB at 10:07 PM on January 13


If the Sony is $280 how can it come with the SELP1650 lens that sells for $370?

Adding a second telephoto lens appears to add ~$1000 to the price, the Sony would have to be staggeringly better than a p&s for $400 to make that work.

I guess we are still in the p&s world, all things considered.


When you get the kit, you always get a steep discount on the lens. That's the way they do it.

And you don't have to spend $1,000 to get a big zoom - here are some lens recommendations that includes a $350 tele. Of course, $350 on top of the $280 is nothing to sneeze at.
posted by that's candlepin at 6:34 AM on January 14


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