Super noob question about what lenses do...

[marie1128]

A lens that is 18-55mm means that it zooms in less than an 18-135mm lens correct? Basically saying that the higher the number the closer you can zoom in? Is that correct, or am I backwards in my thinking?

Thanks!

 

[play18now]

That's correct. 18mm is the focal length for the wide end of the zoom range, and 55mm is the focal length for the narrow end of the zoom range. The higher the number, the closer the image appears. The lower the number, the greater the field of view is. The greater the difference in the two numbers, the greater the zoom range that the lens has. So the 18-55 and 18-135 have the same focal length at the wide end of the zoom range, but the 18-135 has a much greater zoom range than the 18-55, so the 18-135 can zoom in closer to the image subject.

 

[KmH]

18 mm up to about 35 mm is called wide angle and makes things look as if they are farther away than they are.
55 mm is about the same as what our eyes see.
Over 55 mm or so and up is called telephoto and things look closer than they really are.

Camera Lenses

• Understanding Camera Lenses: Focal Length & Aperture
• Using Wide Angle Lenses
• Using Telephoto Lenses

 

[marie1128]

Thank you both! My husband had a much more confusing answer. He knows a bit more about photography than I do, he's just bad at explaining things lol.

 

[Gavjenks]

The lower the number, the wider you can zoom out.
The higher the number, the further you can zoom in.

However, be aware that lenses with larger ranges tend to be somewhat less optically high quality, and they tend to have smaller maximum apertures, due to the various compromises that have to be made to make those things possible.

So something like an 18-250mm lens might be convenient, but will probably have more color fringing, distortions, etc., especially at the extreme ends of the range, compared to a single focal length lens or a short zoom range lens. And it will usually be slow.

Also, the above rule of thumb is really only true of lenses in the same "class." I.e. you have to compare apples to apples (cheaper flimsier plastic lenses of different ranges compared, or high quality luxury end lenses of different ranges compared.) A $1200 24-105L f/4 Canon lens is going to have higher image quality than a $100 18-55mm plastic kit lens, even though the range is broader on the 24-105 (4.3x versus 3x)

 

[marie1128]

The lower the number, the wider you can zoom out.
The higher the number, the further you can zoom in.

However, be aware that lenses with larger ranges tend to be somewhat less optically high quality, and they tend to have smaller maximum apertures, due to the various compromises that have to be made to make those things possible.

So something like an 18-250mm lens might be convenient, but will probably have more color fringing, distortions, etc., especially at the extreme ends of the range, compared to a single focal length lens or a short zoom range lens. And it will usually be slow.

Also, the above rule of thumb is really only true of lenses in the same "class." I.e. you have to compare apples to apples (cheaper flimsier plastic lenses of different ranges compared, or high quality luxury end lenses of different ranges compared.) A $1200 24-105L f/4 Canon lens is going to have higher image quality than a $100 18-55mm plastic kit lens, even though the range is broader on the 24-105 (4.3x versus 3x)

Good point. Thank you.

 

[CaptainNapalm]

Although not really all that useful now, when I first started learning about lenses, it helped me understand them by calculating their zoom range, because this is what I was use to in point and shoot cameras. So you can calculate the zoom range by dividing the largest focal length of the lens by the smallest. Therefore your 18-55mm lens will give you x3 magnification where as your 13-135mm will give you approx. x7 magnification. So without knowing much about lenses, I had no clue what 300mm focal length would give me, but when I knew that it gave me approx. x17 magnification, I knew what to expect. Of course, for this to be an apple to apple comparison, your shortest focal length of both lenses has to be the same. It your case it is, being 18mm.

 

[480sparky41 40]

That's correct. 18mm is the focal length for the wide end of the zoom range, and 55mm is the focal length for the narrow end of the zoom range. The higher the number, the closer the image appears. The lower the number, the greater the field of view is. The greater the difference in the two numbers, the greater the zoom range that the lens has. So the 18-55 and 18-135 have the same focal length at the wide end of the zoom range, but the 18-135 has a much greater zoom range than the 18-55, so the 18-135 can zoom in closer to the image subject.

Um, let's qualify this a bit. 18mm is 'wide' in the 35mm/full-frame DSLR format. But in smaller camera, it may be a 'telephoto'!

 

[marie1128]

That's correct. 18mm is the focal length for the wide end of the zoom range, and 55mm is the focal length for the narrow end of the zoom range. The higher the number, the closer the image appears. The lower the number, the greater the field of view is. The greater the difference in the two numbers, the greater the zoom range that the lens has. So the 18-55 and 18-135 have the same focal length at the wide end of the zoom range, but the 18-135 has a much greater zoom range than the 18-55, so the 18-135 can zoom in closer to the image subject.

Um, let's qualify this a bit. 18mm is 'wide' in the 35mm/full-frame DSLR format. But in smaller camera, it may be a 'telephoto'!

I'm thinking of a Canon Rebel (t5i), if that helps at all. I don't think its a telephoto with a Rebel....

 

[Gavjenks]

That's correct. 18mm is the focal length for the wide end of the zoom range, and 55mm is the focal length for the narrow end of the zoom range. The higher the number, the closer the image appears. The lower the number, the greater the field of view is. The greater the difference in the two numbers, the greater the zoom range that the lens has. So the 18-55 and 18-135 have the same focal length at the wide end of the zoom range, but the 18-135 has a much greater zoom range than the 18-55, so the 18-135 can zoom in closer to the image subject.

Um, let's qualify this a bit. 18mm is 'wide' in the 35mm/full-frame DSLR format. But in smaller camera, it may be a 'telephoto'!

Telephoto doesn't mean long focal length. It means a specific design that makes the lens have a longer focal length than the actual distance from the front element to the sensor.

Typically, telephoto lenses end up just being ones where the lens would be "inconveniently long" with a normal design. In some cases, "inconvenient" would be "too long to walk around with without looking like an idiot or fitting in your camera bag" I.e. around 200-300mm + Other times, "inconvenient" might mean "won't fit in the body of your cellphone housing."

18mm would likely therefore only ever be a telephoto with extraordinarily small camera bodies with very small sensors. Cell phones, basically. Any DSLR, crop or full frame, or indeed even any mirrorless camera will generally have more than 18mm between the sensor and the rear of the lens, yielding telephoto designs irrelevant anyway.

How wide it looks is a different issue. Traditionally, we would say it is no longer "wide angle" anymore when it falls below the crop factor equivalent of 50mm on 35mm. Which comes out mathematically to any sensor that is smaller than 12.6mm on the long end. Which would be some point and shoots or smaller.

 

[480sparky41 40]

That's correct. 18mm is the focal length for the wide end of the zoom range, and 55mm is the focal length for the narrow end of the zoom range. The higher the number, the closer the image appears. The lower the number, the greater the field of view is. The greater the difference in the two numbers, the greater the zoom range that the lens has. So the 18-55 and 18-135 have the same focal length at the wide end of the zoom range, but the 18-135 has a much greater zoom range than the 18-55, so the 18-135 can zoom in closer to the image subject.

Um, let's qualify this a bit. 18mm is 'wide' in the 35mm/full-frame DSLR format. But in smaller camera, it may be a 'telephoto'!

Telephoto doesn't mean long focal length. It means a specific design that makes the lens have a longer focal length than the actual distance from the front element to the sensor.

Typically, telephoto lenses end up just being ones where the lens would be "inconveniently long" with a normal design. In some cases, "inconvenient" would be "too long to walk around with without looking like an idiot or fitting in your camera bag" I.e. around 200-300mm + Other times, "inconvenient" might mean "won't fit in the body of your cellphone housing."

18mm would likely therefore only ever be a telephoto with extraordinarily small camera bodies with very small sensors. Cell phones, basically. Any DSLR, crop or full frame, or indeed even any mirrorless camera will generally have more than 18mm between the sensor and the rear of the lens, yielding telephoto designs irrelevant anyway.

How wide it looks is a different issue. Traditionally, we would say it is no longer "wide angle" anymore when it falls below the crop factor equivalent of 50mm on 35mm. Which comes out mathematically to any sensor that is smaller than 12.6mm on the long end. Which would be some point and shoots or smaller.

Didn't I just say the same thing? :er:

 

[Gavjenks]

No, you were treating "wide" and "telephoto" as opposites/antonyms. They are not. They are values on two totally different dimensions. One is about angle of view, and the other is about designs that physically shorten the lens no matter what angle it is.

The opposite of wide is just narrow or long.
The opposite of telephoto is retrofocus (physically longer distances than the focal lengths). There are also additional design types that can shorten or lengthen lenses that you wouldn't really call either of these. Mirror lenses, for instance, shorten lenses physically while not being telephoto designs.

Those two dimensions can be intermixed in any way (wide retrofocus, wide telephoto, long retrofocus, long telephoto). An example of why you would ever want something like a long retrofocus design would be if it makes it much simpler to design a wide range zoom lens, if range and cheapness are more important than optical quality.



Here is an example of a 500mm lens that does not look like it is telephoto, for example:
http://i775.photobucket.com/albums/yy38/Rokinon/500P-1.jpg

 

[deeky]

I think I see where this is going - Mine is bigger than yours. I mean longer..... I mean wider..... Don't worry, no need for a telephoto, however you choose to define it.

Good grief.



OP - I think it has helped me to think of focal length not as how much it will zoom in a subject, but rather the angle of view. Shorter lengths = wider angle of view. For example, even though I can walk right up and touch a flower, I am most likely to use my long zoom lens at 300mm vs. my 17-35mm lens to have a very narrow angle of view so that the flower fills the whole frame or more. I have found both lenses to be much more useful when I look at it as a perspective issue rather than simply zooming in on a far away object.

 

[480sparky41 40]

No, you were treating "wide" and "telephoto" as opposites/antonyms. They are not. They are values on two totally different dimensions. One is about angle of view, and the other is about designs that physically shorten the lens no matter what angle it is.

The opposite of wide is just narrow or long.
The opposite of telephoto is retrofocus (physically longer distances than the focal lengths). There are also additional design types that can shorten or lengthen lenses that you wouldn't really call either of these. Mirror lenses, for instance, shorten lenses physically while not being telephoto designs.

Those two dimensions can be intermixed in any way (wide retrofocus, wide telephoto, long retrofocus, long telephoto). An example of why you would ever want something like a long retrofocus design would be if it makes it much simpler to design a wide range zoom lens, if range and cheapness are more important than optical quality.



Here is an example of a 500mm lens that does not look like it is telephoto, for example:
http://i775.photobucket.com/albums/yy38/Rokinon/500P-1.jpg

I didn't say diddly about lens dimensions or what a given focal length is 'supposed' to look like.

 

[Solarflare]

What a focal length means depends upon the sensor size.

The standard 35mm film for example has a "sensor size" of 36x24mm. This is typically called full frame. You need a rectangle of diameter 43.3mm to fit a 36x24mm rectangle into it. Thus your optics need an image circle of at least 43.3mm if you want to use them on a 36x24mm sensor area.

A focal length close to 43.3mm would thus be a "normal lens" for the 35mm film. Thats why, for this sensor size, a focal length of 40-60mm (sources disagree what exactly) is considered a "normal lens", while lower focal lengths are considered "wide" and longer are considered "tele" (or rather small).

Another popular sensor size is APS-C, or ca 24x16mm, and diameter ~28.9mm. Here a lens of 28.9mm would have about the same view as a 43.3mm focal length on full frame.

18 mm up to about 35 mm is called wide angle and makes things look as if they are farther away than they are.
55 mm is about the same as what out eyes see.
Over 55 mm or so and up is called telephoto and things look closer than they really are.

Camera Lenses

• Understanding Camera Lenses: Focal Length & Aperture
• Using Wide Angle Lenses
• Using Telephoto Lenses

Wrong.

A 18-55mm will most likely be for an APS-C sensor, with an image circle too small for full frame. Which means the 18-55mm is actually a 27-82.5mm equivalent.

And a 35mm on APS-C is about 53mm on full frame, thus the 35mm is a normal focal length.