What are those numbers on lenses, like 18-55?

I feel silly asking, but those numbers mean nothing to me. What do they mean?

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The numbers - like 18-55mm or 70-300mm - are the focal length of the lens - and, to be honest, I can't explain just what the phrase "focal length" really means in scientific terms. It doesn't matter, just know that the focal length is an indication of how the lens views the world. The longer the focal length, the more the lens magnifies an image.

A "normal" lens is one which sees more or less what your eye sees, neither magnified nor (whatever the opposite of magnified is). If you look through the camera viewfinder when you have a normal lens, you should see exactly what you see when you take your eye away and look directly at the subject.

A "wide angle" lens has a focal length shorter than that of the normal lens, and therefore has a wider angle of view than a normal lens. It's like looking through a telescope backwards.

A "telephoto" lens has a focal length longer than that of a normal lens, and sees a narrower angle of view. In other words, it magnifies the image. To convert the focal length of a telephoto lens on a DSLR to the "2x" notation used by point-and-shoots, just divide the focal length of the telephoto by the focal length of a normal lens.

No need to understand where the numbers, as numbers, come from - it's kind of a historical accident that for 35mm film the focal length of a "normal" lens was about 50mm. So, for 35mm film, any lens with a focal length greater than 50mm is like a telescope ("telephoto"), and any lens shorter than 50mm has a wider view ("wide angle").

In digital cameras the actual focal length number for a "normal" lens isn't usually 50mm, because digital camera sensors aren't the same size as 35mm film (except on some very expensive DSLRs like the Nikon D700 or D3 or the Canon equivalent). Most DSLR's have "APS" sensors which are about 2/3 the size of 35mm film, so the effective focal length of a lens is multiplied by 1.5.

Therefore, the same 50mm lens which would be a normal lens on a film camera is actually about a 1.5x telephoto on a DSLR. For a point-and-shoot with a very small sensor, the same lens might be a 10x or more telephoto. That's why many people refer to "35mm equivalent" when they're evaluating lenses on digital cameras. It allows comparing apples to apples - a normal lens is 50mm equivalent, even if it's actually 35mm or 5mm.

A zoom lens has two focal length numbers, and it is capable of changing focal length ("zooming") continuously from one to the other.

OK, so what does that really mean? Let's look at some examples. For each, I'll give the actual focal length and the equivalent for film. All of these pictures were taken from the same spot, about 50' from the mailbox.

Wide Angles:

This picture was taken with a 10mm-24mm zoom, set at its shortest focal length of 10mm (15mm equivalent). That's a really wide angle, about as wide as you can get before you start getting distortions (think "fisheye"), and lenses shorter than 10mm tend to be very expensive:


(picture taken several years later than the following ones, with a new lens, so it might not have been from exactly the same spot - see my Ultra-Wide Zooms thread for comparisons of this picture with 12mm and 18mm shot at the same time)

This picture was taken with a 12mm-24mm zoom, set at its shortest focal length of 12mm (18mm equivalent):



There's a bunny in that picture - can you see it? Probably not. 12mm is not a good focal length for wildlife.

This picture was taken at 18mm (28mm equivalent), the lower end of most "kit" zooms:



Either of these wide angle lenses would be good for taking landscapes, or pictures of groups without having to back away too far.

Telephoto:

Telephoto lenses are good for bringing the subject closer, to isolate an element or let you get a frame-filling shot of an animal who is too skittish to approach closely.

This picture was taken at 50mm, roughly the upper end of the typical 18-55mm "kit" zoom (70mm equivalent). It would be considered a "mild" telephoto, 1.5x in point-and-shot terms:



Here's 100mm (150mm equivalent), the upper end of the more expensive 18-105mm zoom. It's a reasonably long zoom, about 3x:



At 300mm (450mm equivalent), the upper end of a 70-300mm zoom, you're really pulling wildlife close in - you can think of this as a 9x zoom in point-and-shoot terms. You can find zooms with longer upper ends, but they tend to be very expensive. Also, at much above 300mm you really should be thinking about using a tripod:



Finally, this is a 600mm mirror telephoto (900mm equivalent) - you really need a tripod for this!



The other number you'll see on lenses is the "f" number. The f-stop number is a measure of how much light the lens can gather. The lower the number, the more light it will let in (and hence the lower the light you can take pictures in). A typical "kit" zoom lens might say "f3.5-5.6" or something like that. A good normal fixed lens might be as wide as f1.4. But that's a topic for another time...

The stuffed-bunny pictures show how the various focal lengths work with a fixed subject so you can see the differences. Here are some practical examples of real-life pictures taken at the various focal lengths I show above.

10-12mm Wide Angle:
OK, so you can take bunny pictures with a 12mm - but note that anything close to the lens looks really BIG:


So, you'll probably not want to use a focal length this short for portraits, especially if you're shooting from very close to the subject:


Mostly, though, you'd use an extreme wide-angle for landscapes:


Normal Lens:
The wide aperture (f1.4) of a normal lens lets you take pictures in low light and throw the background out of focus.

135mm Telephoto:
This is at the upper end of my "everyday" 18-135mm zoom. Long enough to bring a sheep in close, but probably not long enough for a bird:

300mm Telephoto:
This is the long end of my 70-300mm zoom lens. It's good enough for most bird photography, and bringing other distant subjects close:

Wow that's great, Mike! I learned so much!

Nice pics, btw. That shot of the blue angels, is it? Amazing shot! Did you need a very low fstop lens along with 300mm zoom to get that?

kirbyultra wrote:

Did you need a very low fstop lens along with 300mm zoom to get that?

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No, not really. The 70-300mm zoom is only f5.6 at 300mm. While f5.6 is pretty limiting in low light, that's plenty in full sunlight as at this airshow. This picture was taken at 1/2000 of a second, more than fast enough to freeze the motion of the planes.

One easy rule to remember is that normal exposure in full sunlight is an aperture of f16 and a shutter speed roughly equal to the ISO of the sensor/film. Knowing I would want a high shutter speed, I set the ISO on the camera up one stop to 400, so the normal exposure would be f16@1/500th (the nearest shutter speed to 1/400). That's just a starting point - you can get a faster shutter speed, so long as you open the lens one stop for each step in faster shutter. The same exposure, then, would also be f11@1/1000, f8@1/2000 or f5.6@1/4000.

This is one place where using Shutter priority (where you pick a shutter speed and the camera sets the f-stop) is worthwhile. I chose the 1/2000 speed, and the camera set f8, which left the lens stopped down one stop from wide open. That gave me a bit more depth of field to compensate a bit for autofocus error, and the lens is usually sharper there than wide open.

i do have a question about the lenses , my goal is to get more lenses to add, and i think i really want to get the 100 or 300 mm lens.

so my question is when you put on , say , a 300mm lens can you rake just regular up close pics or is it just for zooming? for example if i put a 300mm zoom is it multi lens that will allow me to take pics of the kids playing in the house but also zoom in on something that is very far away , or is it just for zooming in on things?

Luvmyzoocrew wrote:

so my question is when you put on , say , a 300mm lens can you rake just regular up close pics or is it just for zooming? for example if i put a 300mm zoom is it multi lens that will allow me to take pics of the kids playing in the house but also zoom in on something that is very far away , or is it just for zooming in on things?

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It would probably be unusual to buy just a 300mm lens these days, unless you were going to specialize in bird or sports photography and wanted to lay out really big bucks. Most people would buy a zoom lens which had an upper limit of, say, 200 or 300mm, and zoomed back to a shorter focal length of perhaps 50 or 70mm. The typical "kit" long zoom in the Nikon line is a 55-200mm, and I have their longer 70-300mm zoom.

With that kind of lens you could use it at the shorter end (50-70mm) to take pictures of the kids or bunnies around the house, and zoom out to 300mm for the bird on the feeder outside the window. However, while you could do it, you really wouldn't want to use a 55-200 or 70-300 as an everyday lens. You'd want something with a wider angle of view, which covers the normal focal length of 50mm (film equivalent - that's 35mm for most DSLRs), like an 18-55 or 18-135mm. At 50 or 70mm and indoors you'd often find yourself backing off too far to include all of the kid in the picture. When I'm taking pictures of Scone in my house I do occasionally use something around 70mm, but more often than not I'm using either the 50mm f1.4 or the 12-24 zoom so I can get physically closer to the bunny.

There are "super-zoom" lenses from various manufacturers which cover a huge range like 18-200 (Nikon has one) or even 18-270 (Tamron or Tokina, I think). Those are big, heavy, and expensive, but if you can afford one I bet they're neat.

man i am looking for a lens that is good for bunnies and kids pic, but also for out back when i am outside to be able to zoom in across the yard at the kids or get my wild bunny pics, so what would i want to get exactly

Luvmyzoocrew wrote:

man i am looking for a lens that is good for bunnies and kids pic, but also for out back when i am outside to be able to zoom in across the yard at the kids or get my wild bunny pics, so what would i want to get exactly

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I'm most familiar with Nikon, so the lenses I discuss are specific to that brand. Canon or one of the other lines would have equivalents, but perhaps not exactly the same numbers.

Assuming you wanted to do all that with only one lens, then I'd recommend you get a zoom lens which covers the widest range you can afford - an 18-105mm at a minimum, and if you can afford the 18-200mm (or 18-270) so much the better. However, the wider the zoom range, the more expensive (and heavy) the lens.

Alternatively (and much more affordably), get two lenses to cover that range. For example, in the Nikon line there are kits which include an 18-55mm and a 55-200mm lens. The body with the two lenses would be much cheaper than the body with a single 18-200mm lens, and both lenses are smaller and lighter than the super-zoom. Or, get the kit with the regular 18-55mm zoom and add a 70-300mm.

That's what I do - I have separate zooms for everyday use (18-135mm) and for those times I really need to fill the screen with a distant subject (70-300mm). The 18-135mm is nice and light and covers most of what I need or want to do. I find that I only pull out the longer zoom every now and then, but when I want it, it's sure nice to have.

For comparison, a Nikon 55-200 is about $175 ($225 for the version with vibration reduction - at only $50 more, well worth it in my estimation), the 70-300 is $155 ($539 with VR - that's a big jump). You can often get the non-VR 55-200 in a kit for only about $100 over the kit with just an 18-55mm, though. The 18-105 lens with VR is about $300 (it looks like my 18-135mm has been discontinued).

When you get to the wider range lenses, the prices go WAY up. The Nikon 18-200mm VR zoom is $765.

Second-tier lens manufacturers like Tokina or Tamron are worth a look, though - Tamron's 18-200 is about $260 and they have an 18-270 for $520. These are just the prices I found in a quick look - your mileage may vary.

Was that any help?

i believe i have an 18-55 that came with the kit i got so i would have to look into getting a 55-200mm or something like it, i dont want something heavy and dont mind getting another lens to cover the far away stuff, if it is too heavy then i am less likely to take my camera out,lol.

Luvmyzoocrew wrote:

i believe i have an 18-55 that came with the kit i got so i would have to look into getting a 55-200mm or something like it,

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Check out both the 55-200mm and the 70-300mm - if you can get the longer lens for about the same price (Adorama seems to have them priced that way), then the longer the better. If you're not very good at holding the camera steady, though, I'd go for the 55-200 with VR (vibration reduction) rather than the 70-300 without. The VR can make a big difference in picture sharpness.

Mine only goes up to 105. I was reading this thread with my daughter, explaining what you were saying and I could hear my husband sighing behind me. I think he was feeling guilty about no birthday presents for me this year. Maybe I'll find something nice on my desk some time. LOL I really want to go up to 300.

MikeScone wrote:

That's what I do - I have separate zooms for everyday use (18-135mm) and for those times I really need to fill the screen with a distant subject (70-300mm). The 18-135mm is nice and light and covers most of what I need or want to do. I find that I only pull out the longer zoom every now and then, but when I want it, it's sure nice to have.

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Update - this Spring I got the Nikon 18-200 VR zoom lens. To my surprise, it really wasn't much heavier, and only a bit bigger, than the 18-135 - and it added the Vibration Reduction (VR) feature, which the older zoom didn't have. It was expensive - roughly $800 - but, boy, do I like that lens!

When I was in Scotland this summer I took about 2900 pictures - see the "What I did on my summer vacation" thread - and when I'd done editing them all, I still had 1800 or more. When I was done, I looked at the statistics on Adobe Bridge (a useful photo organizer which comes with Photoshop). Roughly 90% of the pictures I took during the three weeks were shot with the 18-200. Just under 5% were wildlife shots with the 70-300 zoom, 5% were landscapes or wide indoor shots with the 12-24, and there were less than two dozen with the 50mm f1.4 (low light shots where I needed the f1.4).

What that tells me is that the 18-200VR could easily become the single lens I carry, unless I intended to concentrate on photography and would want the other four just in case. That would mean a serious reduction in weight and bulk, and no need to change lenses. I know if I go somewhere out of the ordinary, I'll accept the extra weight so as not to miss a shot, but around here, I doubt I'm going to be carrying the bagful very much.

MikeScone wrote:

Update - this Spring I got the Nikon 18-200 VR zoom lens.

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That is a real handy lens to have if you could only take one lens with you. I got my 18-200 VR when I bought my Nikon D200. However, I only use it 10-15%, as I prefer to use my 14-24, 24-70, 70-200zoom lens.

You're threads were really helpful thanks!
your photo's are so beautiful but now I'm not sure
which I'd use more with either needing a macro as half the
time i need to focus in on the tiny things...
but then the other half of the time I'm stuck with not being able to zoom out far enough...

Hmmm... Thanks for all the information you've provided.

Mike, good pics! Just curious, are you strictly a 'digital' guy or did you get into photography during the film days? It took me a long time to not want to pick up my 35mm film camera first!

majorv wrote:

Just curious, are you strictly a 'digital' guy or did you get into photography during the film days?

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I've been into photography since the mid '60's, so definitely film first. I've still got a darkroom in my basement, but I haven't used it in many years.