YAGT: Lenses, what do the numbers mean exactly?

I know, another noob question...

When looking at lenses, how do you determine what the lenses capabilities are?

For a few examples:
17-55IS
70-200 IS2
50 mm
17-40L
24-70L
100-400LIS

Here are my questions about lenses.

What are the benefits of using a 70-200 instead of a 100-400?
Is a 50mm just that, 50mm only? What are the benefits of this lens?
Is a 17-55 better for closeups?
What distinguishes how far a lens can zoom/farthest zoom?

I have so many more questions, but I think that's it for now.

Thanks,

~Ace

Hmm, I'll do my best to address your questions.

Regarding the numbers of the lens' name, this pertains to focal length of the lens.

Basically the higher focal length # the more telephoto the lens offers.

ie a 24mm is a general wide angle focal length, while once you hit around 70mm you are getting into telephoto territory.

Usually on a lens ring you will see 2 sets of numbers. 1 set displays the focal length of the lens. On a zoom lens this will be shown as xx-xxmm ie 70-200mm the next set refers to the aperture abilities of the lens. Using the same lens as an example, 1:2.8 means that the aperture of this lens can be opened up to 2.8 throughout the zoom range.

Usually on cheaper zoom lenses you'll have a variable aperture, such as 3.5-5.6 this means that when you are at the lenses widest point the max aperture is going to be a 3.5 while on the flipside, at its most 'zoomed' point you'll only be able to open up to a 5.6 this is generally not preferred. Ideally having a static aperture throughout the zoom range is nice. This way you are able to zoom quickly between wide and telephoto and not have to change your exposure settings... with a lens with a variable aperture, if you go from 3.5 to a 5.6 you have just drastically changed your exposure, and will have to compensate with either shutter speed, iso, or both.

A 50mm lens is whats considered a 50mm prime. There are those who believe that prime lenses offer the greatest image quality over zooms and will only shoot with primes. While in many cases this is true, depending on what you are shooting a zoom can often be preferred. Zoom allows you, the photographer to be in a static location and zoom to compose your image as you like. If you want a subject to fill up more of your frame, simply zoom in on the subject. WIth a prime you would physically have to move toward or away from your subject.

As far as what makes a good closeup lens, that is somewhat subjective... I say subjective as it all depends on what you are trying to shoot. There are lenses made for extremely closeup images or macro style photography. One other thing to pay attention to is the minimum focusing distance of a lens. This refers to the distance necessary between the end of the lens and the subject. For example the 70-200 requires roughly 1.5 meters minimum focusing distance between lens and subject...

I think that basically covers your questions. I hope this helps.

as always this is only my .02c

Great explanation, especially about the zooms with variable aperture. I still have a question, though. Why would you choose to buy, let's say a 70-200 instead of a 70-300? Or why not a 100-400 instead of a 70-300? If you're looking for zoom, wouldn't you want a 'further' zoom just in case?

It's all about the field of view and maximum aperture available vs what you are trying to shoot.

The reasons for buying one lens over another come down to what it is you need the lens to do. None of the comparisons you make are exactly the same lens.

70-200 lenses: These typically have a fixed, maximum aperture (either f/4 or f/2.8); making them much better for use in lower light and for things like some portrait use because of that. These can be used with their maximum aperture set at all focal lengths throughout their range, meaning they can gather much more light at similar focal lengths than the 70-300 or 100-400 could.

70-300L: This one has more reach than the 70-200s, but sacrifices the fixed aperture for a variable aperture that is fairly small at the long end (f/5.6). It is also slightly more compact than the 70-200 f/2.8 lenses. Would make a good, general telephoto travel lens.

100-400: This one is the one to use if reach is your maximum goal; again, longer range than either the 70-200 or 70-300 and also sacrifices a fixed, large aperture for a variable, small one and a narrower field of view. However, you get much more magnification of your subject with this lens than you can with the 70-200 or 70-300 (ie, you can fill the frame better; which is usually the idea behind focal lengths of 400 and greater.)

Eric, nice explanation and respectfully delivered.

Dwain

When looking at lenses, how do you determine what the lenses capabilities are? When you look at a lens

For a few examples:
17-55IS 17mm to 55mm lens with image stabilization
70-200 IS2 70mm to 200mm lens with image stabilization, version II of that design
50 mm
17-40L 17mm to 40mm lens "luxury"
24-70L 24mm to 70mm lens "luxury"
100-400LIS 1 00mm to 400mm lens with image stabilization

Here are my questions about lenses.

What are the benefits of using a 70-200 instead of a 100-400? You choose between the two based on what you want to capture of the scene in front of you. See, the 70-200 doesn't zoom in as close as the 100-400mm. You can crop out of an image from the other zoom to get what you want, but you have more megapixels of the image to play with if you catch it with the lens with more reach. Conversely, you might not be able "to get back far enough" with the 100-400 on your camera and it would be frustrating/difficult to use in closer spaces.

Is a 50mm just that, 50mm only? What are the benefits of this lens? A 50mm prime usually is much sharper than any zoom because of the engineering trade-offs required to make a zoom lens. People prefer prime lenses because they usually offer a much larger aperture (which lets in more light making it easier to capture images in lower light conditions with a faster shutter speed) as well as sharper image.

Is a 17-55 better for closeups? Not sure if you mean "magnification" here or if you mean "getting closer to the subject." If it's getting closer, then you need to find out what the lens's minimum focus distance is. If it's magnification of the image, usually a macro lens is your best option, because "real macro" is 1:1 subject to sensor.

What distinguishes how far a lens can zoom/farthest zoom? As far as the "zoom" - the larger the number, the more you zoom in. You can also buy teleconverters for some lenses (this is based on aperture and a minimum zoom length; what lenses they are compatible with is usually in the listing for the item) to "multiply" their zoom length, usually by 1.4x or 2x

Hope that helps?

Apologies for only addressing one of the questions there; Wuzzi covered those others pretty well, though.

One addition I'd like to add is that distance to your subject controls the perspective of the shot; which means that you can get a different "look" out of an image by using a longer or shorter focal length to achieve the same framing. This is because you would have to be farther from, or closer to, your subject to get a similar framing with different focal lengths, therefore, changing the perspective.

The best read for more, clear info on that is in this thread (Thanks to SkipD, Wilt and the others that created and filled in that thread)

So, in short, you may also choose a focal length because of the perspective it can give to the framing you want.

Outstanding gentlemen, thank you very much. Lenses (to me) just looked like jarbled numbers, but it actually makes sense to me now. You guys are great (and patient)!! Thanks again!

Welcome to the madhouse, btw!

Since you're just starting out; here is a library of reading that should keep you busy for a while

Canon DSLRs and Lenses 101

-=FAQ=- EF LENS FAQ -READ FIRST- Before asking "What Lens?"

EF Lens Work III

-=FAQ=- EOS FAQ -=READ FIRST=-

Protective Filter FAQ

That ought to be enough to keep you busy for quite some time

Snydremark wrote in post #13897946
Welcome to the madhouse, btw!

Since you're just starting out; here is a library of reading that should keep you busy for a while

Canon DSLRs and Lenses 101

-=FAQ=- EF LENS FAQ -READ FIRST- Before asking "What Lens?"

EF Lens Work III

-=FAQ=- EOS FAQ -=READ FIRST=-

Protective Filter FAQ

That ought to be enough to keep you busy for quite some time

^^^^
Very nice suggestions, Snydremark!

Snydremark wrote in post #13897946
Welcome to the madhouse, btw!

Since you're just starting out; here is a library of reading that should keep you busy for a while

Canon DSLRs and Lenses 101

-=FAQ=- EF LENS FAQ -READ FIRST- Before asking "What Lens?"

EF Lens Work III

-=FAQ=- EOS FAQ -=READ FIRST=-

Protective Filter FAQ
That ought to be enough to keep you busy for quite some time

Thanks! I have been reading the manual, and I picked up "T3i for Dummies", and "Understanding Exposure" by Bryan Peterson just arrived today. I'm not sure if any of those cover what is being discussed here or not, but it's a lot easier when hearing someone 'say' it to you (I just started reading the books).

Understanding Exposure is a great read to get started; it will also dovetail well with a few of those links I posted earlier.

Buying a lens is basically choosing a combination of the following factors:
- zoom range (or fixed focal if you're going for a prime)
- aperture
- price (duh)
- image quality, in all its different meanings
- lens mount (EF vs. EF-S)
- some less obvious factors: autofocus performance, stabilization, weight and size, weather sealing, minimum focusing distance, filter diameter, etc

There's a bunch of specific vocabulary you'll need to learn. L indicates the high-end Canon glass; IS is their stabilisation (but it's called OS by Sigma, VC by Tamron, etc.). HSM and the like are indications of how the AF works, and so on.

An example: the Canon 50mm f/1.8 is a prime lens that shoots only at 50mm. 1.8 is a pretty large aperture, so it can let a lot of light in and give you tremendously blurred backgrounds (but also hair-thin depth of field, so your focus needs to be spot on). The image quality is astounding. It's light, it's dirt-cheap, but it's not weather-sealed and the autofocus is terrible.

The Canon 85 f/1.8 appears to be pretty much the same lens, only a bit longer and more expensive. However, when you look into it, while IQ is in the same range the AF is much better.

In the end, in terms of focal range only, a 18-250 lens is better than any 70-200, 50, 85, 24-70 or whatever lens with a range contained within that 18-250 bracket. However, by picking an 18-250 over, say, a 24-70L, you're going to have to accept a severe hit to aperture (superzooms are slow), image quality and so on. It all comes down to what you want and what you're willing to sacrifice, but there's a whole lot of other stuff you need to look at besides the zoom range.

Hopelessdfilms wrote in post #13897485
One other thing to pay attention to is the minimum focusing distance of a lens. This refers to the distance necessary between the end of the lens and the subject.

The minimum focusing distance is not actually measured from the front of the lens, but from the focal plane. Thats the place where the film or sensor is in the camera body. It's usually marked on the top me the camera by a little circle with a line through it symbol. For many lenses this doesn't really matter as the MFD is quite large anyway. It is though very important for macro lenses working at 1:1 as often the camera and lens may be about say 245mm long and the MFD is only 250mm giving a working distance of only 5mm. When looking at macro lenses for 1:1 work it is important to look at the working distance as well as the MFD. PnS cameras normally mistakenly call MWD MFD.

Alan.

OK, so money is a bit tight right now, but I wanted to pick up a cheap zoom lens just to play around with and learn how to use it. What are the significant differences between these three (other than cost)? Am I wasting my time and money buying one of these right now? Thanks!