Distortion- anyone want to try this?

[jetstream]

I posted this here because an early recognition and understanding of distortion will help many understand how telescope systems work, and in particular eyepieces. Try this out...

Enjoy.

http://www.holgermerlitz.de/globe/test_distortion.html

[jetstream]

Forgot to add I see pincushion starting in "B".

[Putaendo Patrick]

Very interesting - but I might just get arrested for staring at policemen now!

[YKSE]

I can almost assume that many young girls have too much barell distortion in their eyes, so that they see straight line as barrel shape

Seriously, I see B as almost straight lines(very slight pincushion), pincushion is clear in C to me.

[LukeSkywatcher]

Not sure what pincushion means but i can see distortion from E onwards.

[D4N]

Pincushion is important in optics that are intended for visual use, particularly binoculars as the user will sweep around with them.  If there is no curvature then the effect is quite nauseating.  There is a happy medium with just enough distortions to make viewing comfortable without introducing visible distortion.

For imaging the opposite is true and manufacturers go to great lengths to remove the field curvature produced by the optics as the camera has a flat sensor so requires a flat image.

[Soupy]

I wear glasses, but did the test without them, so not sure if this affects the outcome, but I can't tell any curvature until E for left (EP eye) and D for right.

The rest look straight from the distances advised.

 

[YKSE]

I think distortion and field curvature has different meanings, even though they meight feel meaning the same thing:

Distortion in optics usually means geometrical distortion, i.e. either straight lines become bent (Rectilear distortion), or the spacings between equal-spaced lines changes from center to edge(Angular Magnification distortion). while field curvature means the focus in the center is not the same as in the edge, i.e. a sharp focus line in center will be unsharp in the edge, or vise versa.

Rectilear distortion has two shapes:

1. Pincushion distortion, where straight lines bend towards the center like this  ) | (  , and

2. Barrel distortion, where straight lines bend away from the center like this ( | )

Angular magnification distortion has two shapes too.

1. spacing in the edge is closer than in center, most common ones, just like we looking at teleposts in the open field.

2. spacing in the edge is wider than in center, not so common.

Edit: The illustration of pinchshion and Barrel has been corrected.

[jetstream]

Here is the little chart I borrowed from somewhere. A lot of people think distortion is bad but EP designers use it for purposes. Some followers of a certain brand can't fathom that those EP's could have distortion- they should realize there is a purpose in the selection of the amount and type of distortion used based on the intended useage of the EP.

So far the replies indicate the we see distortion at different thresholds and levels, this must make designing eyepieces a balancing act and difficult.

 

[SonnyE]

On 3/2/2016 at 04:06, LukeSkywatcher said:

Not sure what pincushion means but i can see distortion from E onwards.

Same for me, Paul.

I have to wonder what difference it makes. Really, I'm not going to go shopping based on my distortion levels.

Dear Amazon dot com,

I'm returning this because it's distortion level doesn't meet my seeing needs. Might you have something a bit towards the left?

[jetstream]

I have 2 eyepieces that don't "oval" the moon or sun and I find that they are a great compliment to my other eyepieces and were chosen partially for this reason. Knowledge is a good thing,

[todd8137]

cool 

[michael.h.f.wilkinson]

I could clearly spot pincushion in B, although I did not find it problematic (*but, hey, I have a set of Naglers, and an LVW 42, so I certainly have seen a lot more)

[WobblySkipper]

I can see a slight distortion after 'B' as well, does this mean I have 'average' eyes :-)

[SonnyE]

6 hours ago, WobblySkipper said:

I can see a slight distortion after 'B' as well, does this mean I have 'average' eyes :-)

I donno Mate, from your avatar it appears to me you have very large eyes...