Please the final word on the effect of Crop factor

[jamiebonline]

For a few years now I have been reading comments on forums on the effect of using, for example, a 50mm prime lens on a crop body and how it makes it like an 80. But with every statement there is at least one person who explains that cropping will not remove the angle of view. It is still a 50mm lens. So If you took a picture with an 80mm lens (if they exist, or even on a zoom lens) on an fx body and a 50mm lens on a dx body, the images would not be the same because one would show wider angle distortion. Is this true??

I thought I had decided about what lens to buy for my new camera as a prime and my only two affordable options now are 19 and 30. The former will give me 28 and the later 45. Which is more useful for street photography and landscapes and shots of architecture with the occasional presence of people? (I like large areas with small people in them. Humanity dwarfed in some way by surroundings. Also in nature) But I am concerned... I think the 19 mm will act as a 19 in terms of distortion even at 28 mm. If people are close to the lens this distortion will be exactly as it would be at 19mm.

I think this might be useful for photographers to have a final word on crop factor and distortion. As I said, I see everywhere people saying that 50 is 80 on a crop sensor camera and that is that.

Thanks for your thoughts

J

 

[dinners]

50mm on a crop is the same 'view' as 50mm on full frame. It's just you only see the middle portion of the image.

If you compare a 50mm lens on a 1.6 crop body to an 80mm lens on a full frame body you will find the depth of field changes.

 

[arad85]

the images would not be the same because one would show wider angle distortion. Is this true??

No.

All that changes is the field of view. Taking a photo with a crop camera with the appropriate lens is equivalent to cropping the FF camera image. Nothing changes, perspective doesn't change, perspective distortion doesn't change (other than is inherent in the lens due to the design).

 

[Brazo]

Sounds like your looking at the sigma primes for sony Nex, they are both great. The 30 is better, both are worth having though!

 

[sk66]

If people are close to the lens this distortion will be exactly as it would be at 19mm.

Not quite, the *lens distortion* will be the same within the smaller (DX/center) section of the lens's FOV. If the lens has most of it's distortion towards the edges (most do) then you will be "cropping" most of the distortions away.
"Perspective distortion" is due to distance and will be the same with any FL lens (it's not really "distortion;" it's just perspective). A wider lens is used "closer" for a given framing so it has a different perspective than a longer lens... the relevant change is distance.