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This is likely a tedious question for you guys but, as a camera noob, I'm miffed, so please bear with me.

I have a:

  • Sony A6000 (APS-C 1.5x crop sensor).
  • With kit lens: SELP1650 lens (16-50mm)

So, with my A6000, am I getting effective focal lengths of:

  • 16-50mm, as advertised on the lens?
  • Or 24-75mm, taking in to account the crop ratio of 1.5x, from APS-C to full frame 35mm?

As a follow on question: are lenses always labelled with their physical focal lengths, or are kit lenses for smaller-than-full-frame sensors sometimes labelled with 'effective' focal lengths?

marked as duplicate by mattdm, Michael C, Philip Kendall, Hugo, inkista Nov 30 '15 at 20:08

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    Although it's about a different brand, I think Is the kit lens focal length specified for APS-C or FF? is pretty much exactly the same question. J.B., do the answers there clear things up for you? – mattdm Nov 29 '15 at 19:39
  • Cheers @mattdm. You're right, I've committed the heinous crime of duplicate questioning and between your answers and the referenced other Qs, my mind's now very much at ease! – yellow-saint Nov 30 '15 at 19:21
  • @J.B. It's not a criticism.The intent is to have authoritative questions and answers, and direct people to them when we can. It's not always easy to find existing questions if you don't use very similar phrasing, though, which is why there's built-in site functionality to help point you to them. – mattdm Nov 30 '15 at 19:43
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Lenses are specified by their focal-length or focal-range for a zoom with the focus set to infinity (unless it cannot, which is possible). Given your example, a 16-50mm has a 16mm focal-length at its widest position and a 50mm focal-length when most zoomed in. Again, this measurement is taken at infinity, so the focal-length can be slightly different with when focused closer.

A 16-50mm lens is labelled 16-50mm because that is its focal-length. A lens gives a different field-of-view on a full-frame than on a cropped-sensor camera, This is what the Crop-Factor or Focal-Length-Multiplier refers too. With an FLM of 1.5, a 16-50mm lens gives the same field-of-view as a 24-75mm lens on a full-frame. Now if you had a 24-75mm lens compatible with a full-frame camera, it would give the same field-of-view on that camera but if you mounted it on an APS-C camera, it would show the equivalent of 36-112mm lens.

Where you will see lenses labelled as their effective focal-length is on fixed lens cameras since there you have no choice and point-of-reference to determine what field-of-view is obtained. The exception to this rule is the Pentax Q system which originally specified their lenses in terms of effective range but then had start specifying 2 sets of focal-lengths or focal-ranges when they increased the sensor size from 1/2.3" to 1/1.7" starting at the Q7.

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On the Sony A6000 (1.5x crop factor) a 16-50mm lens is a 16-50mm lens. In fact, on any camera it is the same 16-50mm lens. What changes is the field of view that the lens can capture which changes based on the sensor size that it is paired with. When you see noted that the 16-50mm lens is equivilent to a 24-75mm lens, that is when you compare the field of view to a 35mm sized sensor(i.e. 1x crop factor or no crop factor). The comparison to 35mm can be especially handy if you are used to using a certain focal length on another camera and what to compare the two.

This site has covered this many times over, and I would recommend some further reading:

In regards to your follow up question, most lenses that are for crop factor cameras are marketed both with their actual focal lengths and also as 35mm equivalent focal lengths.

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