Biggest reverse porro?

[keithdrengen]

That is my question, the biggest I have seen is 8x30:

http://outdoor-optics.com/verrekijkers/waterproof-verrekijker/orion-weather-worthy-8x30-compact-waterproof-binoculars.html

CJ

[dustyview]

I guess it depends on what you mean by "biggest." Bushnell makes the Natureview Plus in 8x30, like the Orion you posted, but also a 4x30 wide angle that gives a 900 ft. FOV and therefore a "bigger" view with the same 30mm objective.

I would like to see an RP design w/ a 32mm objective made with the same quality as the Custom Compact Elite E2......

[ceasar]

I believe that Bushnell made a really big one that many people, like me, mistook for a Roof Prism. It was an 8 x 50 or so, if I recall correctly. Some one should come up with it, bye and bye, I'm sure.
Bob

[Kevin Purcell]

I believe that Bushnell made a really big one that many people, like me, mistook for a Roof Prism. It was an 8 x 50 or so, if I recall correctly. Some one should come up with it, bye and bye, I'm sure.
Bob

Though that's not really a reverse porro but an over/under porro.

See the Funky Bin thread for links and photos of those! I've still not seen one of these second hand.

http://www.birdforum.net/showthread.php?t=140154

In fact you can characterize porros by the angle the L-shaped porro cluster makes to the vertical or horizontal. An over/under porro has the L is tilted at 45 degrees straight (with the point of the L at the outside of the bins). See the picture of the Rollei or L11A1 British Army bins to see this. You can rotate the porro cluster one way or the other that you can make "reverse porros" or "normal" (forward?) porros.

So I guess the case for the biggest "reverse porros" is just before they become "over/under" porros.

The biggest you can make an over/under porro is when

IPD = 2*(objective radius + housing thickness)

or

objective radius = IPD/2 - housing thickness

or for a rough approximation (which I could just have stated)

objective diameter ~ minimum IPD

The minimum IPD is usually 55mm. So 50mm for an over/under porro is perhaps a reasonable maximum.

I leave the case for the true reverse porro which just needs a bit of trig and the cluster angle to be included. But it will always be smaller than this.

And as you become more and more reverse the "offset" (the length of the side of the L) of the porro cluster becomes more important.

The other issue as you get to larger reverse porro objectives is you need bigger prisms (to deal with a bigger light cone) so you might have a problem with those mechanically interfering with each other.

I suspect this is why you don't see reverse porros larger than 30mm to meet all of these requirements.

[ceasar]

Thanks Kevin,
Now my memory is refreshed. The ones I was thinking of were the Bausch and Lomb Elite 8 x 50 shown in Thread 7 of your link.

Back in the70's or early 80's I had the opportunity to use, briefly, a rather compact Swift 9 x 36 Reverse Porro at the Hawk Mountain Migration Watch Site. It had Individual Focusing. The IF was OK for the long distance vistas there. The guy who was using them kept his fingers and thumbs real busy focusing them. I recall them as being very bright and sharp but at that time, I was used to using binoculars that could best be described as "pedestrian;" cheap Sears copies of Zeiss's or Nikon E's. The gentleman using them was from Boston, as I recall. Now that I think about it, I wonder if he might have been with the Swift Company.
Bob

[Renze de Vries]

Möller & Wedel 8x32 Marox, Germany, 1950's

Great build quality, very expensive at the time and some peculiar features like the two 'diopter controls' and the adjustable stem to be placed against the forehead.

renze

[falcondude]

Möller & Wedel 8x32 Marox, Germany, 1950's

Great build quality, very expensive at the time and some peculiar features like the two 'diopter controls' and the adjustable stem to be placed against the forehead.

renze

two diopter controls? Another phrase for individual focusing?

[Renze de Vries]

two diopter controls? Another phrase for individual focusing?

No, no, it's exactly that: diopter controls. The controls don't have enough travel to be used as focus controls (the focus wheel proper is located halfway the hinge pin, see photo) so I guess their function is to adjust close focussing distance and/or infinity for users in need of strong eye compensation.

Renze

[elkcub]

Renze,

What are the dimensions and weight of the binocular?

Ed

[falcondude]

No, no, it's exactly that: diopter controls. The controls don't have enough travel to be used as focus controls (the focus wheel proper is located halfway the hinge pin, see photo) so I guess their function is to adjust close focussing distance and/or infinity for users in need of strong eye compensation.

Renze

Thanks for clarifying this. It feels good to learn something new each day

[Renze de Vries]

What are the dimensions and weight of the binocular?Ed

Height is 120 mm, width 100-115 mm

Weight is 490 gr, although I should subtract something for the fine layer of dirt inside the prism cluster which should be removed by boiling the cluster apart which I won't do because I'm not yet ready. But it is marring the view.

Renze

[Renze de Vries]

Thanks for clarifying this. It feels good to learn something new each day

Falcondude,
(and Ed, because this may add to your fascination with adjustable eyecup-history)

You're so right. There's another fine example to be found in the central screw in-screw out stem between the oculars of the Marox. As you may know, binoculars eyecups from the 1950's and 1960's can be pretty unfriendly because they're hard and never seem to fit your face nicely. I once bought a big Zeiss West 10x50 porro and after some disappointment to get friendly with the eyecups I decided to modify the eyecups (by applying my all-time favorite, bicycle inner tube) and contemplated to put some provision on the ocular shaft's screw between the oculars to rest my forehead against, and find ideal eye relief. Well, I found a nice rubber foot under my preamp (it had 4, so it wouldn't miss one) and screwed it onto the IPD-scale with no trouble at all (have a look at the picture and you'll know what I mean). It's a pity no-one took pictures of me then, because I definitely looked like the proudest inventor on earth.
Sometime later I bought the Moeller&Wedel Marox, and learned my great invention had already been invented half a century earlier in Germany. And in the UK the idea had been taken up by Ross, where a rubber accessory was used with equal success. In the 1960's if I'm correct.

Renze

[KorHaan]

Is that a piece of bicycle inner tube around the lefthand eyecup, Renze?

Ronald

[Renze de Vries]

Is that a piece of bicycle inner tube around the lefthand eyecup, Renze?

Ronald


Klopt.
See pictures.
After this first try however I decided I liked a more rounded approach better. This cup (see last picture) is built from 4 layers of inner tube.

I also decided I should write an article called The Tyred Binocular (and became awfully tired by the idea).

Renze

[Steve C]

There is nothing handier for the binocular hobbyist than a bicycle innertube of the appropriate diameter, a small sharp scissors, a razor blade or x-acto knife set, and a little patience. ;)

[ScoutMan]

Renze,

a piece of rubber plumbing pipe connector of the correct diameter also works. 1&1/2" works on the Leupold Yosemites for example.

[Renze de Vries]

Correct!

The most useful, i.e. versatile, multi-purpose part I've found and applied, is the Swift eyecup as found on their post-1985 models. They're still readily available. There's a ridge inside which can be removed with a sharp knife so the rubber eyecup will slide nicely over most pre-1970 hard standard eyecups.
A drop of glue and there you are.
Also, this Swift eyecup can be applied with great result to (too) large diameter eyecups as found for instance on Nikon E's and SE's. This time the Swift cup slides INSIDE the standard cup, making it just a bit smaller on the top as well as adding a few millimeters to the height. If you're hampered by blackouts (as a non-spectacle wearer) this is the way to go. In most cases no glue is needed as the Swift eyecups fits in snugly. In case you need more extension, pull up the Swift eyecup and glue in place.

Renze

[Kevin Purcell]

The most useful, i.e. versatile, multi-purpose part I've found and applied, is the Swift eyecup as found on their post-1985 models. They're still readily available. There's a ridge inside which can be removed with a sharp knife so the rubber eyecup will slide nicely over most pre-1970 hard standard eyecups.
A drop of glue and there you are.
Also, this Swift eyecup can be applied with great result to (too) large diameter eyecups as found for instance on Nikon E's and SE's. This time the Swift cup slides INSIDE the standard cup, making it just a bit smaller on the top as well as adding a few millimeters to the height. If you're hampered by blackouts (as a non-spectacle wearer) this is the way to go. In most cases no glue is needed as the Swift eyecups fits in snugly. In case you need more extension, pull up the Swift eyecup and glue in place.

That's a very interesting tip, Renze.

Where do youget your parts? Do Swift still sell eyecups as parts?

[Renze de Vries]

Do Swift still sell eyecups as parts?

I bought 6 pair with no problem at all, but maybe Holland is heaven. Just try it, there's a good chance they're still available.
For instance, Nicolas Crista should know.

Renze

[elkcub]

I got a pair recently from Swift.

Ed

[Kevin Purcell]

I got a pair recently from Swift.

Ed

Is there a part number or description that they like rather than "post-1985 eyecup".

What are the contact details?

I know if I tried that on a Bushnell parts rep they'd get uppity (!).

[Renze de Vries]

Is there a part number or description that they like rather than "post-1985 eyecup".

What are the contact details?

I know if I tried that on a Bushnell parts rep they'd get uppity (!).


Say for instance Audubon 804 HR/5

Renze

[Kevin Purcell]

Say for instance Audubon 804 HR/5

Renze

Thanks, Renze!

[elkcub]

I must say, Renze, you really are the eyecup expert of the family.
Ed

[Renze de Vries]

I must say, Renze, you really are the eyecup expert of the family.
Ed

That's what history has in store for you when you don't have a driver's license, you don't own a car, you're stuck with a bike and your tyres go flat all the time.

The most important thing I learned from the eyecup experiments is, that the eyecup's size and shape is not only of consequence to how the binocular is 'felt', i.e. more or less comfortable, but that it's also of crucial importance to the binocular's performance. For instance, if an eyecup's diameter is too large the binocular will have a tendency to 'get stuck' in the eyesockets with the result that the Apparent Field of View will be perceived as rather small, closed in. A rigid fit creates a small (perceived) view. Or: apparently there has to be some kind of looseness in the binocular-eye interface which can be quite critical.

Renze

[elkcub]

That's what history has in store for you when you don't have a driver's license, you don't own a car, you're stuck with a bike and your tyres go flat all the time.

The most important thing I learned from the eyecup experiments is, that the eyecup's size and shape is not only of consequence to how the binocular is 'felt', i.e. more or less comfortable, but that it's also of crucial importance to the binocular's performance. For instance, if an eyecup's diameter is too large the binocular will have a tendency to 'get stuck' in the eyesockets with the result that the Apparent Field of View will be perceived as rather small, closed in. A rigid fit creates a small (perceived) view. Or: apparently there has to be some kind of looseness in the binocular-eye interface which can be quite critical.

Renze

Fascinating! And you think that inner tubes reduce eye suction and increase field of view. Good one, Renze. :t:

Seriously, I've noticed something similar. I find that the Zeiss 7x42, Swift HHS Audubon, and to some extent the Nikon 8x32SE, give me a tunnel effect without my glasses. One might attribute this to the binoculars producing a narrow AFOV, — but the perception goes away when using my glasses!!

A probable explanation is that the tunnel percept results strictly from the size of the retinal field that is stimulated by light, rather than the limited content that is determined by the binocular. Otherwise stated, while wearing glasses the whole retinal field is stimulated, as it would be normally, although not necessarily by light coming through the binoculars. Without eyeglasses, however, the eyecups limit the field of stimulation, which produces the tunnel perception.

In this sense, I interpret what you're saying to mean that if side light is allowed in around the eye cups it also alleviates the tunnel perception; because more of the outer retinal field would be stimulated.

This general explanation is supported by the observation that wider apparent field binoculars create a more 'natural' view. The question then becomes: what is the functional (mathematical) relationship between retinal stimulation and tunnel perception, and how independent is the perception from image content?

Ed

[Renze de Vries]

Ed,

Interesting theory, could very well be right, i.e. play a role, apart from or in combination with my more humble suggestion: the dynamic eye.
I learned from this forum - probably from you - that the eye is never at rest, it's on the move. Now imagine you're placing a small lens, the exit pupil, in front of the eye, quite rigid. Now the eye starts to move within the exit pupil and will constantly stray, inevitably, outside the optical axis. Where it will encounter all kinds of nasty, non linear phenomenae called distortion. The eye doesn't like that.
Now when we are able to manipulate the lens (binocular) in a less rigid way, so that small movements of the exit pupil are allowed, maybe the eye will start 'learning', that is move along with the optical axis. And will encounter less distortion.
I think it's possible we will interpret this as 'less tunnel effect'.

PS. I find your experiences with the Zeiss 7x42 (the classic B/GAT I suppose) quite remarkable as this is the model par excellence for my eyes to really enjoy the wide view. The AFoV of the 7x42 isn't so ourageous at all (a quite normal 60 deg.) but my eyes say WOW!

Renze

[elkcub]

...The most important thing I learned from the eyecup experiments is, that the eyecup's size and shape is not only of consequence to how the binocular is 'felt', i.e. more or less comfortable, but that it's also of crucial importance to the binocular's performance. For instance, if an eyecup's diameter is too large the binocular will have a tendency to 'get stuck' in the eyesockets with the result that the Apparent Field of View will be perceived as rather small, closed in. A rigid fit creates a small (perceived) view. Or: apparently there has to be some kind of looseness in the binocular-eye interface which can be quite critical.

Renze

Hmmm. Going back to your earlier statement, you may not be strictly referring to tunnel vision, which is generally accepted as resulting from limiting the peripheral view. My only contribution to that, in the case of binocular usage, is the speculation that limited peripheral stimulation, rather than a limited image, may be the trigger for the percept. That could be verified in a psychophysics lab with controlled apparatus. For all I know there could also be large individual differences.

I don't follow how the rigidity/flexibility of the eyecups relates to perceived size of the apparent field, except for possibly allowing more light to enter around the edges; but I may be experiencing tunnel thinking again.

As for myself, at this point I'm going back and forth with eyeglasses. In the process I've become rather aware of perceptual changes, and associated preferences. The Zeiss 7x42, for example, is phenomenal with glasses and less so without. Same with the 8x32SE. The reverse is true of the 804.

Regards,
Ed

[elkcub]

Forgot to mention the moving eye. Right, there is no such thing as a stationary eye that sees. If an image is held stationary on the retina (by a feedback controlled oculometer, for example, http://www.photonics.com/directory/dictionary/lookup.asp?url=lookup&entrynum=3575&letter=o) the retinal sensors will simply saturate and no longer respond. The smallest involuntary physiological motions, the so-called micro-saccades http://en.wikipedia.org/wiki/Microsaccade, are too fast to realign the eyecups, — and they are unconscious anyway.

Voluntary eye movements could require realignment, particularly when prolonged rotation is more than ±20 deg. and vignetting results, or as you suggest, various other aberrations influence clarity. Basically, a rotated eye can never retain a parallel exit pupil, so all manner of off-axis things can happen. But, still, I'm struggling to relate that to eyecup size or flexibility.

Part of my problem, no doubt, is that I haven't experimented with eyecups like you have. As a result I haven't experienced the perceptual differences. My last bicycle hung in the garage so long the leather saddle powered and the tires fell off. And I threw them away. :-C

Ed

[Renze de Vries]

Ed,

For an example of what I mean, take your Nikon SE and a pair of Swift 804 Audubon eyecups. Those Nikon eyecups are oversized (in diameter) and would be absolutely terrible if they were not soft and flexible. However, you can still experience the effect of these eyecups on the view (tendency to feel closed in).
Now take the Swift eyecups and stick 'em in the Nikon's. You will get a smaller eyecup ridge on top. This should feel better, for the view I mean.

(Hope this works for other people too...)

Renze

[elkcub]

I'll give it a try and get back to you, Renze. :t:

Ed

[elkcub]

Renze,

It really is amazing that one can place the entire Swift eyecup inside the Nikon's and still have a small amount of wiggle room. Anyway, for me it adds too much length, so I lose field, but it doesn't effect the SE's miniscule tunnel effect. Due to their oversize eyecups I just find them better suited to use with glasses (although not uniquely so).

Ed