Photography Chat

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Euri Pinhollow

3:59 PM

chat.stackexchange.com/rooms/47379 - how quickly do rooms expire?

3 hours later…

mattdm

7:20 PM

We could do a with a decent question about lens distortions (barrel, pincushion, mustache)...

There's this one

Michael Clark

@EuriPinhollow Your example was closed after between 7 and 8 days of inactivity. As long as the discussion is active it will be left open. The threshold is likely 7 days, but the cleanup routines probably only run once per day. So it will be 7 days plus the time until the next time the cleanup routine runs.

mattdm

Q: What are Barrel and Pincushion distortion and how are they corrected?

I have some questions regarding barrel distortion and pincushion distortion. Since they are related I have put them in single post. I am aware that barrel distortion occurs more in wide-angle lenses, wherein straight lines near edges of the frame curve outwards. Is it pincushion distortion whe...

except it's an old, messy question which a) combines another question that's not really what I care about for a canonical question, b) doesn't mention other types like mustache distortion, and c) doesn't encourage answers to explain how this differs from perspective distortion, which is what we really need.

Trying to decide whether to heavily edit that question or just ask a new one

@MichaelClark Any opinion?

I'm leaning towards a new one (and closing that one as too broad, for good measure).

Michael Clark

I'd say new one that specifically asks, "What is the difference between perspective distortion and geometric distortion." Maybe include a sub-question about how geometric distortion relates to different types of projection (fisheye vs. rectilinear).

mattdm

7:35 PM

Q: What is the difference between perspective distortion and barrel or pincushion distortion?

I've heard of: perspective distortion barrel distortion pincushion distortion mustache distortion What are these different types of distortion, and how do they relate? What causes them, and can they be corrected in the field, or in software post-production? What about "fisheye projection" — ...

lens terminology optics distortion

This is actually a genuine question of mine when it comes to the "geometric distortion" part. Online things I find quickly either use it as a catch-all for barrel/pincushion, or as a wider term which does also include perspective ("geometric distortion" discussion having to do with aerial photography)

I looked in The Focal Encyclopedia of Photography, and it mentions geometric distortions twice, the first I think actually referring to distortions in geometry due to perspective, and the second about Petzval curvature.

The technical parts about barrel and pincushion distortion call them "curvilinear distortion", which is new to me.

mustache (or moustache) distortion aren't mentioned at all

Michael Clark

7:51 PM

@mattdm Moustache distortion is just what happens when you have partially corrected barrel distortion that leaves a little pincushion in the middle and barrel on the edges (or vice versa).

mattdm

@MichaelClark I know; just found it a bit interesting that the encyclopedia doesn't mention it. Book is from 2007; possibly a modern/internet term

Doesn't show up in Google Ngrams either

I'd post a link but it's too long for stack exchange chat to accept

Michael Clark

@mattdm Have you been doing some HDR today? It looks like you've got some technicolored vomit rainbows going on.

mattdm

@MichaelClark That is my winter reward for answering a question within 30 minutes that got at least three upvotes.

Michael Clark

@mattdm Yeah, I've got the snaphat hat too but I ain't wearing it.

mattdm

Heh. I'm not wearing it on this site; I dunno how chat chooses which hat to share