Wide angle lens?

Started Jan 15, 2014 | Discussions thread
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brightcolours Forum Pro • Posts: 12,492
Re: oh dear...

canonagain123 wrote:

brightcolours wrote:

canonagain123 wrote:

the samyang 14/2.8 distortion, including the perspective distortion, can be corrected PERFECTLY, down to the last pixel. this works on JPG and RAW the same.

Nonsense, you lose pixels correcting CA, AND you lose resolution on pixels you have not lost.

CA can be corrected for RAW quite easily, but it can sometimes present a problem. That correction can lead to some lost image information too, if the CA is bad.

Nonsense, you never lose way less "information" correcting CA, you actually gain sharpness and contrast (you restore information).

CA and a little distortion can be more of a hassle to correct than a lot of distortion with the perfect lens profile. If you know you'll never shoot JPG with the lens, then it's not a worry. If there's a chance that you'll want to take even one JPG picture with it, you might be pursuaded by the lack of CA and easy distortion/perspective correction.

It is the same with JPG, one can correct CA in exactly the same manner as in RAW.

You understand that perspective distortion correction means that some objects will be made larger, some smaller, right?

We are not talking about perspective distortion.

In the case of making objects smaller (from 100px to 50px width, for example), they were too big in the first place, so they lose 75% of their pixels. In the case of making them bigger, the new pixels are interpolated (the new algorithms are good) from the original pixels. You win some, you lose some. In the end it's a zero sum game.

Nonsense. With barrel distortion, the width of the central axis is less than the width of the corners. In other words, the corners show a wider view than the central vertical and horizontal axis' do.

Since we can't add the missing part to the central axis, we have to throw away from the corners.

Now, the corners will have less resolution to fill the width/height. We either have to spread the remaining resolution out into the missing parts, or we have to shrink the central axis parts to match the shrunken corner resolution. Either way, one loses quite a lot of resolution.

It's impossible to make a FF 14mm with no distortion. It doesn't matter if it's branded Samyang, Canon, Nikon, or Pentax. It doesn't exist.

Nonsense, it is well possible to make a lens with no barrel distortion. The Canon comes quite close compared to the very heavy distortion of the Samyang. Sigma made a 12mm with virtually no barrel distortion (12-24mm version 1).

Canon 14mm:

Very low barrel distortion

Samyang 14mm:

Very strong barrel distortion with a moustache character

There is only "less distortion", not "no distortion" The distortion even exists in the human visual system, but is ignored/corrected in the brain so you never experience it. It's not a matter of brand X vs brand Y, it's a matter of physics. You can't project a 180 degree hemisphere onto a 2-dimensional rectangular surface and get no distortion. Whatever the distortion is, if you correct it, you "lose" some information, but it may make sense if you think of it this way: if the distortion is not desired, 100% of the original information was useless anyway. The resulting information from a perfect distortion correction is the most you can physically get out of the scene with today's technology, at least out of any sub-$50k technology.

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