APS-C Lens Question

[nigelbond]

I'm new to the world of DSLR cameras so apologies if this is a dumb question. 

I have a Sony Alpha 6000 with the kit lenses. The kit lenses are, I believe, APS-C lenses. 

My question is do you have to apply the Crop Factor ratio to APS-C lenses or just to full frame lenses - ie is a 50mm APS-C lens really a 75mm lens or is it a genuine 50mm lens?

I've tried googling this but I can't find the answer.

Thanks

[Portmixus]

That's not a dumb question, it's a FAQ actually

A 50mm lens (even APS-C designed) is a 50mm lens on FF (full frame). So FF or APS-C lenses have the same focal lenght! 

So the focal length stays the same, but of course, on a APS-C sensor (either APS-C designed or FF designed) the field of view is equivalent to 75mm on FF.

Hope that answers your question. 

In short: 50mm APS-C = 50mm on FF

[nigelbond]

Thanks. I think I understand what you're saying - ie in long form - that if you put a 50mm APS-C lens on a APS-C camera body or a 50mm full frame lens on an APS-C camera body, both will have the equivalent field of view as a 75mm full frame lens on a full frame body (given a crop factor of 1.5). Is that correct?

If that's the case, is there any other difference between an APS-C lens and a full frame lens on an APS-C camera body? Thanks again. 

[Portmixus · Accepted solution]

That is correct!

There is indeed no difference between a APS-C lens or a FF lens on a crop body, at least, concerning field of view.

In practice, things are a bit different. First of all, a FF lens has a larger image circle, therefore it will vignet less on an APS-C body.

FF lenses are generally sharper because you only use the center portion of a FF lens. But they are of course more expensive, larger and heavier compared to APS-C equivalents. It is also more difficult to implement optical image stabilisation (OSS) if the lens is already larger.

But 50mm is a special case: the 50mm F1.8 OSS is a beautiful exception: it's wonderfully sharp and even compared to the 1000 euro Zeiss 55mm F1.8. And although the Zeiss is better, the 50mm is barely worse IMHO. I have both and like both a lot! 

Buying a FF lens for a crop body is therefore not such a smart idea, unless you are planning to upgrade some time in the future or if there are no alternatives available (some lenses will be less likely made voor APS-C, such as the 70-200 F OSS).

[nigelbond]

That's brilliant, thanks. I'm not going to worry too much about other lenses at the moment - I've got to pay for the camera first  But it's useful information to know for future.

Nigel