More Globe Effect, Pincushion & Oculars (1 Viewer)

I'm going to suggest that you guys try a couple of simple tests that may take some of the subjectivity out trying to determine the instrument distortion of binoculars.

First try looking through the binoculars backwards. This will give you a picture of the rectilinear distortion reduced to a manageable circle size subtending about 10º of your eyesight fov, small enough not to engage your own eyesight distortion. Look at vertical lines and move them toward the edges. The sign of the distortion will be reversed, so pincushion will be seen as barrel. The more barrel distortion you see looking backwards, the more pincushion the binocular has when you look through it normally. I've made many photos of grid images viewed this way to compare distortion in different binoculars.

The other test ignores rectilinear distortion and looks instead at angular magnification distortion. Once again you will be using only the undistorted center of your own eyesight. Observe a small circular target that subtends around 5º of apparent field. Move it from the center to the edge of the field at 3:00 and note how its shape changes. If it remains a circle there is just enough pincushion to cancel AMD. If it changes to an oval with the long axis vertical there is positive AMD. The more ovoid the shape the higher the AMD. That is the condition associated with very low or zero pincushion and possible globe effect. If the circle changes to an oval with the long axis horizontal there is negative AMD caused by too much pincushion for exact cancellation of AMD. That could lead to the condition Brock calls "rolling bowl". Do this with enough binoculars and you should get an idea of where your comfort zone for distortion lies.

Thanks Henry!

Viewing through the objective end, using the centre of your vision, is a great way to not only visually determine the starting points of distortion in the field, but also, is much easier to quantify the magnitude, and how that changes through the field. :t:

My bins are pretty close to the circle of condition, so no great optical show to see. Excellent way to test though. :t:


Chosun :gh:

Once again Henry sheds some light allotting optical serfs some delectable crumbs from his vast setting to feast upon. I've been remiss in not previously acknowledging yet another contribution. A tip of the hat and as always a pleasure sir. Perchance even more can gleaned from the great expanse 'tis Henry's field of vision.

I take note that CJ has shared over on the ZR forum a bit 'o wit.

As for "rolling ball" - it's just a 'phenomena', which is merely the result of the sum of 'barrel distortion' in human vision (which varies among individuals) and /or less pincushion in the optical design to correct the AMD, and a whole lot of initial conditions, and situational factors, along with a fair bit of neural plasticity jiggerypoo, that in the end, all only affects 'some' people.

Such elegance I fear I shall ne'er attain so it be me good fortune to 'ave stumbled about finding this nook of optical knowledge.

Now, my current interest, before USPS delivery, is my replaced 8x42 Kruger Caldera. It's predecessor had quite the play in the focus wheel, four acts worth and this one shortened by twain for the almost nearly yet not quite hardly award.

So much for mechanics. Back to the gist of the manner I find w/interest five millimeters of placement having a profound effect. The Caldera has a closed intermediate and fully extended cup setting expressed as 0, 5 & 10 mm. My preferred setting overall/as a rule is fully extended w/cups buried in my eye sockets.

I noticed when I received the replacement how well behaved the limited amount of distortion appeared unto being sedated. After using them and pushing the dust cover on I inadvertently pushed the cups to the middle position. The difference in degree of effect being multiplied several times as if I'd adjusted a potentiometer from mild to wild.

I understand globe effect/RB is a personal interpretation that varies, but I ponder moderation of said effect due to eye placement; in this instance within five millimeters. I only had a few moments, but I cranked the cups down betwixt fully extended and middle position and held them w/thumbs. Certainly no more than/roughly 2 mm of eye placement and see a variable of the two positions.

I suspect the wide fov, 438' at 1000yds, wide oculars, 24mm, and possibly the lack of field flattener lens contributes to this seemingly variable effect of low distortion. I tend to suppose in my mind, in the shorter settings inside of 10mm, my eyes coming to and then passing in front of the focal point, but I'm seeing a clear focus.

That is a common denominator as the focus stays the same. Much as if I'm eyeballing conditional alignment and backing away from the cups to see if the image remains merged or if it splits before arms length.

If the focus indeed remains the same why is the apparent severity of the low distortion effect so variable and noticable? Is it possible that the focus is changing a mite, but is being washed-out/overpowered by my attention to the enhanced movement?

Little doubt I'm over my head and at a loss to explain.

Nix perplexing situation. A couple of questions for you to ponder.

Are you looking on axis or intentionally looking off axis at the edges?

If you are looking on axis, are you aware of the field stop. Are you seeing the same FOV?

If intentionally looking off axis, remember that the geometry changes, at longer eye relief distances you may have to move the eye further off axis to see the same angles in the AFOV. Generally, eye pieces do not react well off axis.

Next to consider is whether or not you are seeing the correct exit pupil position. Depending on your accommodation the exit pupil will probably only have 0.5 to 1 mm thickness (depth of focus). Since the principle ray from all objects in the AFOV should go through the center of the exit pupil, it would seem that the one furthest from the correct position would be the one causing the most trouble.

All conjecture on my part though.

I'm looking on axis in the pan/scan. I originally noticed no difference in a static view. Howevah, since reading your post I tried both the 5 & 10mm settings w/glass resting on the pane door looking towards the woods. On axis at 10mm my peripheral vision detects a softer view. When I move to 5mm though still looking dead ahead I note a sharper peripheral.

Apparently, only by steadying glass on the pane closing left eye and working the 10/5mm stop back and forth, I'm not seeing the complete field stop at 10mm. I thought I was looking through both eyes. It's so close and uniform. Yet, using one eye I see a bit more/field stop at 5mm and if I look off axis I note at 10mm the edge slightly out of focus, but moving to 5mm it sharpens.

Rotating my head, to the point of looking left eye as far as possible through the inside left barrel to right eye inside right barrel, I detect no discernable difference in fov at 70 yds.

It looks as if I'm not quite seeing the field stop at 10mm and then when I rotate both cups, once again resting glass on the flat plane, looking on axis, to 5mm I note slightly brighter and sharper view w/peripheral. It would appear that by eliminating just a small fraction of the field at 10mm it softens not only the edge but the perception/intensity of the low distortion movement.

The effect is still there at 5mm distance, yet not nearly as intense. To the point that at first I had to look for it as It was so much more subdued.

Thanks.

Moving along from the slack plagued El Caldera dos onward to the Zeiss Conquest 12x45. Interestingly enough the 2011 price list shows MSRP value of $1049.99 whilst 2012 declares $1222.21 to be more in line. I wasn't aware of the escalating dividends of mucho pincushion over merely a year. I should've bought early by the boat load.

Anywho, sold w/all the paperwork as new for $762 to the door. Yeah, it has a blue badge as does the soft case, but as mentioned in the Zeiss forum I'm thinking $625 would represent a more realistic worth panache included.

The distortion isn't overwhelming, yet there's plenty and the closer the view the more intense the ripple. If I train the view on the yard and proceed vertical there's such an upheaval that I can easily imagine two tectonic plates colliding and in due process creating a plateau.

4.6*/240' at 1000yds, 16.4 ft minimum focus, height 6.42", width 4.69" and weighing in at 21.34 oz.

In this application I'm glad there's only 4.6*. As intense as the PC is in the middle/up close it's fairly quiet on the edge and the middle diminishes w/distance. In a vertical the middle will rise/fall, yet I'm not seeing it roll over to the edges in what I deem the fountain effect. I suspect becoming a mite greedy on fov might be a contributing factor, where I've noticed the PC ripple in the middle roll over to the edges, in other bins.

I've read claims that the 12x45 is basically an extended 8x30. From the neck strap lugs to the objective end the 8x30 is 4.25" where the longer 12x45 is 6.5. Yet, the 8x30 is barrel shaped being larger diameter in the center whilst the 12x45 is a slow taper that's thinner where I place me mitts.

I like how it fits my hands, the overall length/taper feel right and I suppose some of the lightweight can be contributed to lack of a tripod adapter. Usually I'd prefer one, but not in this application. This is a bin to throw up quickly and ID a target before it's gone. The ergonomics coupled w/my short fat fingers allow me to grip the barrels and have my thumb tips "locked" on the opposing barrel. A solid and stable platform permitting me to secure the bin w/minimum of effort and unwanted extra movement.

So, again everything is a compromise. The good, the bad & the ugly. I like the shape of this over the Conquest in 8x30 & 10x40. Kind of a mini-Dialyt. The picture is bright though the 3.75 mm EP requires spot on IPD. Especially on setting the diopter. And the colour is accurately rendered. I see no extra tint/pop. Not ED glass and the moon shows a slight yellow fringe on bottom and indigo on the top.

I hadn't planned on spending as much as I did for a 12x bin. I had been hoping to catch these discontinued, somewhere down the road, for around six bills. Still, though I'd enjoy a couple of changes, I'm content and wouldn't wish to pay any more. And as much as I'm fond of this bin I wouldn't give five bills for a new 15x45.