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Sharpness from border to border Anonymous
Hello /p/, I'm new here.

I understand basic concepts of exposure, DOF and hyperfocal distance.

But what controls the sharpness from border to border? I've read the article on Wikipedia about field curvature but it got me even more confused.

Do any and all lenses inherently have soft corners/edges/borders or is there a property that makes a lens sharp on the entire plane?
>> Anonymous
Read up about aperture and how it can affect shutter speed.
>> I||ICIT !!mknjFN/v/49
a good design and manufacturing tolerances will help keep the corners in check.

macro's tend to have a near perfectly flat field curvature so they could be good if you need it and theyre also renowned for being sharp across the whole image frame.

other than that, ionno sorry.
>> Anonymous
So stopping down to f/5.6-10 to get a lens' optimum sharpness, the corners will still be softer than the center. Is there anything I can do to get sharp images across the border other than getting a lens with a flat field?
>> Anonymous
>>129381
mostly wrong but has a grain of truth.

Any and all lenses create an image on a spherical plane. Think of it this way: if a lens is focused to a certain distance, then the "plane" that it is focused on will actually be a sphere of radius = focal distance. Understand?

Lenses mostly appear to focus on a plane because (a) the narrow angles of view and long subject-distance:image-distance ratio make the plane you see a small segment of a very large sphere, and (b) lenses are corrected to some extent to try and minimize this.

Fact remains that the plane of focus is more like a bubble of focus. This is the curved field.

Of course, since what the lens is doing is creating a mirrored but identical image of what it sees, the image will also be created on a curved plane. Same reasons as above, a flat plane can approximate this. However, it's not quite true.

As a result, the center of the lens (where the focal plane is parallel to the camera back) is the sharpest part. As the film/sensor picks up the corners of the image, they will be in less ideal focus and so will be a little blurry.

SOME cameras actually do use curved film planes to account for this. The most famous example is the early Minox subminiature cameras (James Bond, CIA, KGB -- the classic open-close wind spy camera). I have one, and the film plane is visibly curved and has a little pressure plate to push the film into that shape for maximum sharpness with such a small negative.

There are also some issues with chromatic aberration that show up because of the higher distortion, but that's more advanced.

If that doesn't explain it well, let me know. I'll try to do better.
>> Anonymous
>>129389

To follow up with some of the other comments: Yes, macro lenses generally have a very flat field. Any lenses designed for microfilming or print work reproduction will as well. But really, there isn't much you can do with a given optical fomula other than stop down or crop off the edges.
>> Anonymous
Nah, I just wanted to know if I was doing it wrong.