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ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Zeiss uses AK prisms - so why not an open bridge design? (1 Viewer)

henry link said:
Brock,

Just to demonstrate that there's never universal agreement I find that I don't like the wide spacing of Porro objectives. The 3-D effect doesn't charm me enough to make up for the poorer right and left field overlap at close distances. Perhaps that's because much of my birding is in close woodland areas.

Henry
Click to expand...

As an aside, Henry, I've garnered almost the opposite view. As with the unaided eye, retinal disparity works most effectively in the near/mid-range, and has little importance at long distance. What Brock mentioned by way of easier target (i.e., bird) recognition/identification, particularly in a cluttered visual field, is well supported by the 3-D literature. Aesthetically, the sculpting of a 3-D image (which is, indeed, charming ;)) is also much to my liking, particularly if accompanied by narrow-band color enhancements of a few quality Porros, notably the 8x32 SE, 8x30 EII, and 804ED. The often wider FOV of Porros is also a big advantage at the near/mid-range birding distances, primarily due to improved stereopsis and peripheral movement detection.

Just to keep the pot boiling ... I really prefer my Porros. :eek!:

Ed
 
I know only too well from using telescopes between f/4.5 and f/12 how much better any eyepiece works at higher focal ratio. Not even the most large and complex Nagler eyepiece will give a sharp edge at f/3.5, and neither can a small and lightweight binocular eyepiece.

Abbe-Koenig prisms clearly have a much shorter path length than Schmidt-Pechans.

With these two simple facts, I think I can see clearly the progression in size of the sharply focused "sweet spot" in the three "alpha" brands.

At the bottom, with the smallest sweet spot, is the (>32mm) Zeiss FL, which has traded this quality for the added brilliance and perhaps the lighter weight of the AKs.

Next up, the Leica with its SPs, which even though more compact than the Zeiss, has a longer focal length, and a larger sweet spot.

At the top is the Swaro EL, also with SPs, but fully as long as the Zeiss, with the greatest focal length, and the widest sweet spot. The Swarovision is said to be a little better at the edge than the original. Certainly it could only get a little better, which was almost unnecessarily good already. Some of the improvement may result from a compromise related to the new lowered geometrical distortion.

This just makes too much sense. Am I oversimplifying?
Ron
 
Ed,

Perhaps you could quantify "near/mid-range."
Bearing in mind that the values should then be divided by the bins' magnification, there would perhaps be less discrepancy between Henry's and your own views.
BTW, I find that viewing at a distance of 6m with a 10x42 roof requires a reduction in the IPD setting.

John
 
elkcub said:
As an aside, Henry, I've garnered almost the opposite view. As with the unaided eye, retinal disparity works most effectively in the near/mid-range, and has little importance at long distance. What Brock mentioned by way of easier target (i.e., bird) recognition/identification, particularly in a cluttered visual field, is well supported by the 3-D literature. Aesthetically, the sculpting of a 3-D image (which is, indeed, charming ;)) is also much to my liking, particularly if accompanied by narrow-band color enhancements of a few quality Porros, notably the 8x32 SE, 8x30 EII, and 804ED. The often wider FOV of Porros is also a big advantage at the near/mid-range birding distances, primarily due to improved stereopsis and peripheral movement detection.

Just to keep the pot boiling ... I really prefer my Porros. :eek!:

Ed
Click to expand...

Ed,

We agree about long distance, no advantage goes to either. I'm happy enough with the extra 3-D in Porros at mid distances beyond about 20-25'. Things begin to bug me at closer distances. Inside 15' I don't really like any Porro, but especially if the objective spacing is wide, the AFOV is narrow and the magnification is high. I'm sure you'll see what I'm talking about if you give yourself a large dose by looking at an object at the closest focus of your 8x32 SE. No one could tolerate for long such a cross-eyed view, with an object of interest forced toward the edges of two nearly separated fields. The 8x56 FL seems to be a pretty good compromise for me. It has a little extra shot of 3-D compared to straight through for entertainment value and a much more comfortable close focus image compared to a wide Porro.

Henry
 
Hi John,

My main point was to reinforce the behavioral importance of Brock's statement about stereopsis aiding target identification, which is slightly more than simply providing a "charming" view. In any case, Porros provide the advantages of stereopsis at the expense of field overlap at short distances. They also often afford a wider FOV than roofs, which is a net advantage for the brain to construct a more realistic spatial environment.

Returning to your comment, magnification is a scaling factor and we certainly need to distinguish between real vs apparent distances. My "fuzzy" reference to "near/mid-range" was meant to suggest the physical range at which retinal offset provides meaningful stereo cues in normal vision, i.e., perhaps 15 meters, but which can be extended further out if retinal offset is increased to compensate for magnification. Of course, it would be completely impractical to make the offset proportional to magnification, since an IPD of 65mm would result in 8x65=520mm objective spacing, or 650mm in the case of your 10x42.

At least for my own applications, I have yet to find a roof that satisfies like a top-notch Porro. Still, I own quite a few and use them for other reasons.

Ed
 
Henry,

Yes, we completely agree.:t:

At less than 15' the offset of a Porro gets in the way.

And I really enjoyed your reference to "charming."

"Entertainment value" is even better. :-O

Ed
 
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Just to be totally anal about this you can build a porro to have a huge range of objective separations: from a flat wide porro, through a 45 degree porro (rather like the Nikon ATB series and some of the Nikon compacts), to an over-under porro (L11A1/Aviso and the old Bushnell Elite porro that looked like a roof) with an objective separation the same as the IPD to finally reverse porros with a smaller IPD.

The trade off is 3D effect versus apparent magnification. And perhaps some pointing issues in the over/under design (rather similar to those of the porro 2 bins like the Canon IS designs which can take a little bit of work to get used to so you don't look "high").

I'm surprised there aren't more over/under designs. I guess they just look too weird.
 
These would be entertaining. Your choice of any objective separation from 0-500mm. Your eyes might have to trade places.
 

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elkcub said:
Returning to your comment, magnification is a scaling factor and we certainly need to distinguish between real vs apparent distances. My "fuzzy" reference to "near/mid-range" was meant to suggest the physical range at which retinal offset provides meaningful stereo cues in normal vision, i.e., perhaps 15 meters, but which can be extended further out if retinal offset is increased to compensate for magnification. Of course, it would be completely impractical to make the offset proportional to magnification, since an IPD of 65mm would result in 8x65=520mm objective spacing, or 650mm in the case of your 10x42.
Click to expand...

Ed,

I wasn't suggesting one should increase objective spacing.
Is not the stereo experience of viewing an object at 150m with a 10x roof (assuming objective spacing = IPD) equivalent to viewing with the naked eye(s) at 15m?
The Pentax Papillo, designed for close-up viewing, uses reversed Porros with a small objective spacing to partially compensate for its magnification.
I believe its objectives even "squint" at close focus, which is what we are forced to do with conventional bins at short distances.
The close focus of 1,5m of the new Swarovisions is a mere marketing gag IMO and is only useful for monocular viewing.

Regards, John
 
John Russell said:
Ed,

I wasn't suggesting one should increase objective spacing.
Is not the stereo experience of viewing an object at 150m with a 10x roof (assuming objective spacing = IPD) equivalent to viewing with the naked eye(s) at 15m?
The Pentax Papillo, designed for close-up viewing, uses reversed Porros with a small objective spacing to partially compensate for its magnification.
I believe its objectives even "squint" at close focus, which is what we are forced to do with conventional bins at short distances.
The close focus of 1,5m of the new Swarovisions is a mere marketing gag IMO and is only useful for monocular viewing.

Regards, John
Click to expand...

Yes, ... Is not. Magnification decreases the apparent distance to an object, but the separation of the left/right views must increase for the stereo experience to remain constant. Note that as the separation is increased the apparent object size decreases, which is why the roof's image appears larger than the Porro's. For a given magnification the retinal projection of an image is the same in either case, so visual resolution is identical, — all else being equal.

The reverse Porro design will decrease the stereo experience even beyond that of a roof. But, it does overcome the near-focus field overlap problem, and can often be used for butterflies and such at < 15'. Apparent size is a perceptual experience, of course, and has nothing to do with visual acuity; one quickly habituates to it unless comparisons are constantly made between optical products. As mentioned somewhere above, there is every reason to believe that what people often think is "depth of field" is really stereopsis in disguise.

Ed
 
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Ed: has anyone verified that assertion that the "size illusion" is just an illusion and doesn't affect actual IDs?

It is a very strong effect e.g. comparing my SE 10x42 with my Canon 10x30 IS in the field the "size illusion" is clearly apparent. And both of these bins having controlled for flat 6.0 degree FOV so AFOV doesn't contribute to the effect.

Another PhD in the making perhaps?
 
Kevin Purcell said:
Ed: has anyone verified that assertion that the "size illusion" is just an illusion and doesn't affect actual IDs?

It is a very strong effect e.g. comparing my SE 10x42 with my Canon 10x30 IS in the field the "size illusion" is clearly apparent. And both of these bins having controlled for flat 6.0 degree FOV so AFOV doesn't contribute to the effect.

Another PhD in the making perhaps?
Click to expand...

Well, acuity is measured monocularly and there is no 'stereo experience' under that condition. Given equal magnification and FOV, images will appear to be the same size, and depth perception (i.e., relative distances) will be determined only by monocular cues, e.g., perspective, shading, relative object sizes, etc.

Being somewhat anal myself, the apparent size difference between a roof and a Porro isn't really an illusion in the true sense, which occurs when things appear to be different from what we know them to be. For example, the globe effect is an illusion because there isn't any globe. In this case things just appear different, rather than being correct or incorrect, and the question is "why?".

In the curious case of the 10x Nikon and Canon, I would think that the first question to ask is whether they have the same objective separation. If they do, you may have selected a great dissertation topic. :t:

Ed
 
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Well, acuity is measured monocularly and there is no 'stereo experience' under that condition. Given equal magnification and FOV, images will appear to be the same size, and depth perception (i.e., relative distances) will be determined only by monocular cues, e.g., perspective, shading, relative object sizes, etc.
Click to expand...

I think you miss my point.

I'm talking about the cognitive task of identification (done with two eyes) not the simple perceptual task of measuring acuity. Does the roof illusion affect it? Has it actually been tested (rather than just dismissed)? Perhaps measured as the speed of ID might be the useful measure (given that it's already known that size affects the speed of recognition of objects -- another reason why 10x bins might more effective for ID even if they don't improve acuity).

In that example I mentioned I believed I was seeing more in the immature Northern Shrike I was seeing with the Canon (IS off) than with the SE because it appeared larger.

My question is this self-deception or is it real deception (so to speak!).
 
Kevin Purcell said:
I think you miss my point.

I'm talking about the cognitive task of identification (done with two eyes) not the simple perceptual task of measuring acuity. Does the roof illusion affect it? Has it actually been tested (rather than just dismissed)? Perhaps measured as the speed of ID might be the useful measure (given that it's already known that size affects the speed of recognition of objects -- another reason why 10x bins might more effective for ID even if they don't improve acuity).

In that example I mentioned I believed I was seeing more in the immature Northern Shrike I was seeing with the Canon (IS off) than with the SE because it appeared larger.

My question is this self-deception or is it real deception (so to speak!).
Click to expand...

By "roof illusion" I assume you mean the observation that roof binoculars yield larger apparent images than Porros, but less stereopsis. (It's not an illusion, as I mentioned; it's a perceptual experience.)

There are two closely related tasks, "acquisition" and "identification." The former has to do with capturing (i.e., becoming aware of) the presence of an object in 3-space, the latter with determining what it is. The literature supports the notion that stereopsis declutters a complex visual environment and improves target acquisition. The extreme comparison would be between a binocular (two different images) vs a biocular (two identical images). It's my educated guess that incrementally improved stereopsis also improves target acquisition incrementally.

As for target identification, which necessarily follows acquisition, I don't know that stereopsis makes much difference. (Note that I have avoided reference to apparent size differences for reasons stated earlier. Apparent size is a transitory perceptual experience subject to rapid habituation.)

Down to particulars, the issue at hand with the Nikon vs Canon is: "I believed I was seeing more...because it appeared larger." I can't argue with causal beliefs, my friend, just suggest there may be less evident factors to consider apart from apparent size. In any case, the challenge is really for you or someone with that belief (i.e., experimental hypothesis) to prove that apparent size enhances target identification, rather than for skeptics to prove that it doesn't (i.e., prove the null hypothesis).

This may lend meaning to: "Don't believe anything you hear and only half of what you see." ;)

Ed
 
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