15mm/2.8 fish eye as normal wide angle

[paul]

why does a 15 mm fisheye , corrected in ACR,so that the lines are straight,still have a wider angle than a normal 14 mm?
I've made a comparison with 16/35 (II) ,15 mm fisheye, en samyang 14 mm,and I think the fisheye,lens-corrected,is the sharpest.(all shot at 2.8,same white balance)

 

[Plamen]

In case of fisheyes, the FL does not tell you all. The projection is different and the same FL (15mm) can create a wider AOV. See the diagram at the bottom of this page, for example:
http://en.wikipedia.org/wiki/Fisheye_lens

 

[RS2021]

Rectilinear UWA lens designs are fundamentally different from the fisheye designs and include specific glass elements to render the focal plane more flat, reduce CA, and overcome a slew of other nifty optical challanges.

The usual trade-off in super wide rectilinear lenses is "stretching out" especially at the corners and edges which shows up as corner/border "softness".

Some of this falls well beyond post processing fixes.

 

[paul]

thanks for your reaction.So should I sell the Samyang and use the 15 mm fisheye instead(lens corrected)?
It's much smaller and lighter.As far as I can see the quality is quite good,and the only disadvantage is you have to guess how much will loose of the frame after software correction.

By the way,what I would like most is Canon making a small fixed 16 mm/f4 lens...