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Focal length is the distance (measured in mm) between the surface of a lens and the focal point. Smaller focal lengths indicate wide-angle lenses, larger focal lengths indicate a telephoto lens.

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3
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3answers
454 views

Is the kit lens focal length specified for APS-C or FF?

I have the 18-55mm kit lens for my Canon 50D and was wondering if they're still specified against full frame 1:1 crop? Would my 18mm actually be 1.6x? I ask because I doubt anyone with a full frame ...
38
votes
6answers
2k views

Is crop-factor a bad thing?

It seems to me that there is a preference for full-frame sensors rather than cropped sensors, and I'm curious as to why. It seems to me, that the cropped sensor means that I get more bang for my buck ...
13
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5answers
1k views

Why do we talk about focal-length when frame sizes are different?

I keep seeing people talking about focal-length of lenses without saying how large the frame is. Is there a more sensible way to talk about how much a lens “zooms”? (I have seen so many adverts ...
16
votes
5answers
4k views

What focal length gives a “normal” field-of-view on APS-C cameras?

I wish to purchase a "standard angle-of-view" prime lens for my Canon Rebel, which has an APS-C sized sensor. Various articles note that the popular "nifty 50mm" lenses are a little too much of a ...
31
votes
10answers
7k views

Which focal-length lens is usually used for portrait photography, and why?

What focal length or range of focal lengths are usually used for portraits? What is used by professionals? Why would one select a certain focal length? What are the advantages and disadvantages of ...
12
votes
4answers
4k views

How can a lens like a 18-55mm have more than one focal length?

How can a lens have a range of focal lengths? Shouldn't it be a single number? Isn't focal length supposed to be fixed for a lens of a particular shape and geometry? What am I missing? How many ...
35
votes
10answers
3k views

What is crop factor and how does it relate to focal length?

I'm reading that a 50mm lens is recommended as a first prime lens for DSLR owners as it's supposed to give a 'natural' perspective, but when used on (most) DSLRs, the view is cropped, as if you were ...
20
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4answers
2k views

What is focal length and how does it affect my photos?

What is focal-length? Are focal-length and zoom synonymous? How does the focal length of a photo affect it?
13
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4answers
3k views

How does changing focal length affect depth of field?

I'm curious about how my "area of acceptable focus" changes when the focal length of the lens I'm using changes as I zoom (or switch lenses). In particular, I'd like to know how the front & back ...