Pincushion (1 Viewer)

The wavy "fun house mirror" effect when you pan left to right seems to be a fact of life that most people accept. My Vortex Viper 10x42s "have a bad case." My Leupold 8x42s (Wind river cascade, if memory serves) have it much less, even though, on balance, they're not quite as nice a binocular. (but the price was right). My Pentax 10x43s (DCF SP) have very little of this effect.

That was what I was expecting from them. In the world of astronomical eyepieces, if you want to get funhouse mirror effects, go try something like a Pan Optic 24mm from televue. But the Pentax XW eyepieces don't have it.

Today I get an email from a person who knows more than I about binoculars and he says that ALL his binoculars have pincushion EXCEPT his Leicas. (He has not tried Pentax) I have been moving around the forums here for a couple of days and I see many aspects of performance discussed but no one seems to mention pin cushion. Seems that it is an accepted fact of life and no one cares that a left right sweep in a Vortex is going to be a rollercoaster.

Anyways, methinks that I like my fields flat. If not perfectly flat, at least flatter than my Vortex, which all in all is a very nice binocular. Really. I'm just saying, it ain't flat. It ain't even close to flat.

But it seems to me from reading these posts that most folks don't care about flat. I never see it come up? I'm too new to bird groups to make much of a generalization but it seems like most of the people who even talk about pincushion are coming from astronomy backgrounds....or do I exaggerate?

thanks
greg n

I think you don't understand why it's added.

It doesn't come up with birders because it's a feature ... adding pincushion (which all binocular makers do as part of the design) reduces the perceived "rolling ball" effect when panning.

Another of those things that differentiates terrestrial binocular use from astro use. Rolling ball effect is very notble in daytime but when panning star fields not so much.

Search the forum for more discussion of the rolling ball or rolling globe effect and why pincushion is added deliberately.

And welcome to the forum ...

Hi Greg,
Sure we care, just some of us care more than others. Holger Merlitz, a well known binophile and math geek to the max, cares perhaps more than anybody else in the whole world as you can see from his very nice paper: http://www.holgermerlitz.de/globe/distortion.html
Even if you don't really dig into the equations, the visual aids and reading explains the situation pretty well.

A more accesible wrapup recently appeared in a discussion here in the Swarovski section. BF optics maven, Henry Link, summed it up in his typical stunningly lucid way, and I hope he won't mind being quoted here, first referring to rolling ball, then to how it can be corrected:
"What you're describing is actually the way a flat field appears to the eye. Imagine that your eye is suspended above a huge flat checker board. The square just below your eye looks nice and undistorted. Now imagine swiveling your gaze toward the edge of the board. The more distant squares will appear increasingly foreshortened and smaller, just as you described. The only way to make those edge squares appear more similar to the central square is to distort the flat checker board into the shape of the interior of a bowl. But then the lines that form the squares will curve. That curvature is pincushion distortion. So, we have to choose our poison: a flat field in which objects appear foreshortened or flattened toward the edge creating a "rolling globe" effect when panning or the bowed lines of pincushion distortion."

It seems odd that your ebuddy claims that Leica does not have pincushion. Of all makers, they are the only ones I know of to acknowledge that they DO put pincushion distortion in to mitigate the rolling globe effect when panning. It works, judging from my 8x42 Trinovid Leica. Zeiss and Swaro do about the same as Leica, by the way, just don't beat the drum about having a "distortion' in their binoculars, dubious marketing strategy one one would think on Leica's part, although honest. In comparison, I have a 7x50 Fujinon porro that gives a great image in many ways, one being a lack of distortion, ie telephone poles at the edge look perfectly straight, a beautiful thing to behold. But try panning, and it is funhouse of a different kind than you describe, but funhouse for sure! Having experienced both, I prefer pincushion.

I agree about the Panoptics, the stars swoop pretty bad as you pan along with those things. I've read that it's a necessary evil in that case, in order to have the stars at the edge appear so sharp. I don't pan my telescopes much, so in my fast Newtonians, Panoptics are the ticket. I have not tried the Pentax eyepieces.

Anyhow, the bottom line is you are obviously annoyed by pincushion, and I sure can't tell you "don't be". You need to find out if you are more, or less, annoyed by a "flat", distortion-free, field. But I promise it isn't perfect either.

You can't have it all, all at once. The best field correction "may" be a very wide field, so you don't notice the edges much anyhow, with enough astigmatism at the edge so it's a bit blurred making you care even less, and a little bit of pincushion, not enough to fully eliminate the rolling globe effect, and not enough that the bending distortion is pronounced, either. I am just totally making this up. Oh, well, if only I was optical director of a binocular company!

Welcome to the forum, and thanks for paying attention to what your binocular is doing.
Ron

The best field correction is application specific!

If you are an astro bin designer I think I'd seriously consider making that exponent in Holger paper equal 0 i.e. no pincushion. Astro guys would be happy. Stars would all be in their right places. If you looked carefully they'd look odd when you pan. But no matter, angular distances would be preserved!

But most bins users aren't astro guys. They look at stuff in the real world. And are prone to throw up when panning in the real world. So most bin users don't want the rolling ball and so do want some amount of pincushion. And as Holger points out how much (i.e. what the value of the exponent is) varies from bin maker to bin maker. It's part of what makes a bin a bin.

BTW, Zeiss held out against this infringement on binocular purity (Don't mention zee Var oder Pinchusiondistortion) for longer than the other bin makers but eventually they saw sense (I presume after user feedback) in the late 50s or early 60s.

This is one of those examples when usability and design purity collide. You can see which won.

Kevin Purcell said:

I think you don't understand why it's added.

Click to expand...

No-one who isn't completely cross-eyed (or cross-brained) understands why this idiotic abberation ought to be there.

It does not make any sense at all to wail about colour rendition and such things if the image is geometrically inaccurate to a ridiculous degree.

Banana comes in from one side, straightens up in the middle, then bends to the other side bevor it vanishes out of sight. Makes a healthy brain sick!

Give us undistortion!


Unbent and unbroken,
T

Well thinking about it mo' bettuh I realize that pincushion is the opposite of the barrel effect in eyepieces and I may have my terms a bit wrong; I think most of us just say pincushion to mean weird stuff off axis and most of the time we get away with it. But I can see I'm being set straight. Actually one of the reasons I like Pentax is that the field appears flat all the way across. One can say that the Pan 24 has to do what it does to have sharp stars at the edge but the Pentax disproves the theory at about the same price and with somewhat more fov. Nonetheless, Pentax's refusal (so far) to venture beyond 70 degrees probably has something to say about the design philosophy and price point in eyepieces.

I see lots of folks here complaining about bins with fovs that are too small and of course from an astronomer's perspective to see the SP DCF 10x43 criticized for having only a 6 degree field is a bit outlandish. But I have since tried to chase some birds on the hoof and I can see why y'all like 8x30s. You have to turn your head fast putting a premium on low mass and you have to focus fast and you have to get that sucker in there before he decides to leave. So wide field, low mass, good intrinsic color correction (so a very-close-focus is good nuff) all makes for good stuff.

Still I use my binoculars for many things, including scanning a shoreline for birds, for example. And I kid not, I actually DID get some nausea one night panning with my Pan 24. Not so far with the Vortex. Anyhow the Pentax SP DCF 43mm shows a significantly flatter field and it doesnt appear to be much, if at all, narrower than my Vortex Viper 10x42.

One of the issues here is as follows. If you are looking straight ahead in the binocular with the object in the center of the field, and then look to the left or right off axis holding the binocular steady on that object, you get a rather head hurting blinking effect in the eye opposite the direction you are looking to the side.

The edge of the field is not usable in the Vortex. It may be well corrected but it is only corrected for peripheral vision.

In the Pentax the look-to-the-side effect is much less pronounced. Therefore, I get more field that I can use with eyeball look around, binoculars stationary. Furthermore, because the so-called well corrected field is only usable with peripheral vision in the Vortex, that means I have to sweep. Now if I sweep I get the rolling ball.

But I don't get the rolling ball in the Pentax--not nearly as much (and not as much in my Leupold 8x42s)--and I have more usable look-around-field. Yet everywhere I read that the Vortex is better blah blah blah.

Birders seem to me to be out to lunch. Up to your ears in pincushion and apparently loving every minute of it.

I mean, cmon the DCF SP Pentax was selling a few days ago for $385 shipped and I'm reading about how great Vortex Viper is at $525? (Actually when I first got my Vortex Viper I was totally enamored of it--these fancies come and go--I still love its ergonomics). Maybe I'll get Alan French to show me some of his toys. I know Alan, hell we all do, but I actually can drive out to see him.

The only real high end binocular I've used are my Mom's 8x30 Swaros which are SLC Habicht or something like that. There's not much rolling ball in those but the effect may be diminished with lower magnification and smaller aperture. IN ANY CASE, right now, my bias is to prefer a flatter field, thank you.

Y'all out to lunch, y'all humoring me, so I'll roll with that and do another post on "brightness."

thanks
Greg N

Tom,

A wide field will always have some form of distortion; either angular magnification, rectilinear or some compromise combination of both.

There is an easy test to see how close a binocular comes to conforming to the "circle condition" mentioned in Holger Merlitz' paper. Just observe a small circular target that subtends a few degrees of apparent field. In the center of the field it will look circular in every binocular. In a wide field optic with zero pincushion distortion the circle will become distorted into an oval shape at the edge; a vertical oval at 3 o'clock, horizontal at 6 o'clock. If just the right amount of pincushion distortion is applied the shape of the circle will appear virtually undistorted in shape at the edge. If more pincushion is applied the circle will again form an oval at the edge, but this time vertical at 6 o'clock and horizontal at 3 o'clock. TeleVue Panoptics and Naglers apply a huge amount of pincushion, much more than any binocular.

I have a few binoculars which have almost zero pincushion distortion. The Nikon 18x70 appears to have none, the Fujinon 8x30 FMT-SX almost none and the Nikon 8x32 SE just a little more. A circular target at the edge of the Fujinon and especially the very wide 72 degree AFOV 18x70 is squashed into an obvious oval. The distortion is visible but milder in the SE. Among my binoculars the one that come the closest to applying just enough pincushion to maintain an undistorted circle at the edge is the Zeiss 8x56 FL. Some other binoculars with pincushion (like the Nikon EIIs) don't have quite enough and some (like the Zeiss 8x42 FL) have a little too much.

For me it takes only a very little pincushion to tame the rolling globe. The SE seems to have it about right for my eyes, but then I'm also not very susceptible to motion sickness.

Henry