[henry link]

It's not at all impossible to do this. 40 years ago Kern made a 42mm Porro with an internal focusing element and a wide true FOV. The Kern 6x42 Focalpin had a TFOV of 8.3*. An 8x42 version using the same size eyepiece fieldstop could have done and would have had the same FOV.

[brocknroller]

Originally Posted by Pinewood

Hello Mr. B. Mustard,

Look at post number 7:

http://www.birdforum.net/showthread.php?t=189732


Happy bird watching,
Arthur

Thank you, Mr. Patum Peperium (aka "Gentleman's Relish").

However, I don't think a sentence starting with "I suspect...." makes me totally confident that Mr. Horseradish, even with his pungent wits, has found the definitive answer.

But at least he has some plausible "speculations" (as someone we know would say, who I'm sure would prefer to hear it from the horse's mouth rather than the radish's - i.e., Leupold's or Minox's engineers).

Mr. Piccalilli

[brocknroller]

Originally Posted by henry link

It's not at all impossible to do this. 40 years ago Kern made a 42mm Porro with an internal focusing element and a wide true FOV. The Kern 6x42 Focalpin had a TFOV of 8.3*. An 8x42 version using the same size eyepiece fieldstop could have done and would have had the same FOV.

Oops! Somehow I missed your post, Henry. Looks like I did have reason to be suspicious about the aforementioned "I suspect..." post.

It's good to hear that internal focus WF porros are possible, but it makes it even more puzzling why optics companies didn't introduce this "evolution" while high quality CF porros still roamed the earth.

If they had, perhaps an internal focus porro wouldn't have been displaced by roofs, and birders wouldn't be paying through the proboscis for a roof that's comparable to what less-expensive-to-make porros could have been with updated coatings/glass and internal focusers.

The Cascades were dirt cheap, and even Minox eventually lowered their price on the 8x and 10x44 BPs after they realized that despite the German name, they couldn't bilk buyers out of $599 for a 6.4* 8x or a 5.1* 10x "Made in Japan" porro).

Were the Kerns expensive to make? Or did they have IF EPs?

There must be some reason why manufacturers didn't pursue this innovation with porros, but instead starting working on perfecting the roof design for the past 30 years.

[henry link]

Brock,

Here's a diagram of the Kern 7x50 Focalpin. The 6x42 just had shorter objective lens barrels. The 7x50 was just as expensive in the US ($700) as Zeiss/Leitz roof prism binoculars in the mid 80's. A complex Porro like it would be pricey today if it came from one of the alpha brands.

BTW, I ran into a NOS pair of 7x50 Focalpins a few years ago for $125. I couldn't resist, but after years of wondering about legendary Focalpin I found out it's not that great.

Henry

[John Dracon]

Brock - following up on your comments and questions for Henry (who always seems to have those "thumbnails", which by the way are most informative) is your question whether the porro was displaced by roofs for among the many reasons not having an internal focusing porros available. The displacement of porros by roofs I believe comes down primarily to compactness and ergonomics. Fellows like you and me with extra large hands handle porros with ease. But I have found over the years that woman with their smaller hands simply prefer roofs. Many times when husband and wives are inspecting my collection of binoculars, the wife goes for the smallest and most compact binocular, and the husband, if he is a backpacker or hunter goes, for the roof, too. If sheer optical quality is being examined, the husband is apt to linger longer with the porros once the good quality view is demonstrated. Until roofs were produced, women had to take pot luck. What is your take on this? John
and that is the roof

[Graham Osborne]

Henry

Looking at that diagram of the Kern Focalpin it appears that the focuser is on the objective end of the central column. Is that correct? And please could you expand on what you found disappointing.

[brocknroller]

Thanks for that info and diagram, Henry. I can see the focuser bridge at the bottom, but in this "x-ray view" I'm not sure where the focuser is located, on top or at the bottom like the Swaro SLs. There seems to be a shaft in the center going from top to bottom but I can't tell from the diagram if that's functional or just infrastructure.

As far as pricing, an internal focus Leica porro made today is going to be as expensive as a Leica roof (although roofs weren't nearly as good optically as porros 40 years ago due to the lack of p-/sliver/dielectric coatings, so I'm surprised you were disappointed at the Kern porro's performance).

If the unthinkable happened, and Leica, Zeiss, and Swaro started making high quality porros with internal focusers, they would no doubt be very pricey even though the "buzz" is that porros are easier to manufacturer (and the examples I gave of the two recent internal focus porros seem to support that as do the low price of porros today).

The more complex, wider FOV EPs would add some cost. Although curiously, you once said that the Zeiss FL didn't have complex EPs, and I meant to ask you about that reference since it contradicts what you wrote in my "Incremental Change$" thread about alpha's complex EPs being one factor in alpha's high cost).

You also pay for the quality parts and engineering when you buy a German- or Austrian-made roof.

However, a goodly chunk of the costs involved are due to the high cost of labor in those countries and therefore also the high cost of materials. A Swaro rep admitted this to me so this is not my personal "speculation".

And it's no secret revelation, you can easily find references (and I've posted them on BF before) about Germany having the highest wages and highest cost of living in Europe, and Austria being the second in those categories. Those costs get passed on to the consumer.

However, I bet your buttons that if a Japanese or a Chinese bin manufacturer made an internal focuser porro with WF EPs, it wouldn't cost $2K (or at least it wouldn't need to cost $2K).

So cost is not the prohibitive factor in making good quality internal focuser porros with WF EPs. It can be done at competitive prices to alpha roofs.

But as John said above, porros were displaced due to roof's compactness and ergonomics. I would add to that the invention of p-coatings, which enabled roofs to come up to par, or nearly, with good quality porros.

That was the turning point and the beginning of the "heavy bombardment period" for porrosaurs.

Until optics manufacturers started making open bridge roofs, their compactness and ergonomics didn't have any appeal to me, because of my large hands.

I'm sure I'm not the only male birder with large hands, and I can't imagine that women drove the trend toward roofs. There are a lot of couples that bird together, but not nearly as many women hunters, and w/out broaching that subject again 'ere we should get off track with another moral discussion, most bins aimed at hunters are also roofs.

There may have been other factors that drove the Cambrian Roof Explosion besides p-coatings and women's and small handed men's preferences for compact design bin. Roof's superior waterproofness is undoubtedly one of those factors.

But what about the "roof mystique" that Stephen Ingraham and other reviewers have alluded to? How much of role did that factor play in marketing roofs, and where did this "mystique" originate and what exactly is it???

mystique = An aura of heightened value, interest, or meaning surrounding something, arising from attitudes and beliefs that impute special power or mystery to it.

I have some ideas about this, but I probably already lost Henry with my long post, and I know I lost Steve (mooreorless) after the first paragraph! :-)

So e will probe the dark depths of that mystery another time, but I think solving that mystery might be the key to finding how to create a marketing "mystique" for internal focus porros.

[henry link]

Graham,

Yes the focuser is inside the front hinge. The focusing knob is on the front, but it could have been placed anywhere on the central shaft. In spite, or because of the complex design the optical performance is similar to any ordinary 7x50 Porro of that time.

You can see in the photo how petite the 7x50 Focalpin is compared to a 8x50 CZJ Octarem, which is a more typical size for a 50mm Porro.

Henry

[henry link]

Brock,

The FL's use 4 and 5 element, 3 group eyepieces. That's essentially the minimum required for a wide field eyepiece (the Octarem used a 4 element, 3 group EP).

Of course the Chinese could make good inexpensive internal focus Porros, just like the roofs they make now. Most designs could just substitute a Porro for a roof with no other optical change needed. Just don't expect the imaginary Z/L/S Porros to be much cheaper than their real roofs.

Henry

[Kevin Purcell]

Originally Posted by henry link

Graham,

Yes the focuser is inside the front hinge. The focusing knob is on the front, but it could have been placed anywhere on the central shaft. In spite, or because of the complex design the optical performance is similar to any ordinary 7x50 Porro of that time.

You can see in the photo how petite the 7x50 Focalpin is compared to a 8x50 CZJ Octarem, which is a more typical size for a 50mm Porro.

Henry

Very interesting, Henry.

It's almost an open bridge (with a rod in it ... shade of the current Nikon Monarch X).

Are the two prisms cemented together in that porro?

Are they the same size (they seem to be in the diagram but it's difficult to tell)?

[brocknroller]

Henry, Thanks for that clarification on your statement about the FLs, and for the two-shot photo of the Focalpin and Octarem, although I really would like to know if it was "in spite, or because of the complex design" that the optical performance of the Focalpin is similar to any ordinary 7x50.

If the internal focus limits performance, then there's no point in pursing that design with porros, and that could be why it wasn't done?

Kevin, Someone on another thread (Swaro?) was surprised that open bridge designs existed before the EL. Besides the Focalpin, here is a photo gallery by Gary Hawkins that shows a number of early bins with double hinged open bridges.

WARNING: Before clicking on the link, cover your keyboard so it doesn't get short circuited by your drool...

http://www.pbase.com/g_hawkins/binoc...tures&page=all

[Martin Fagg]

Originally Posted by brocknroller

Kevin, Someone on another thread (Swaro?) was surprised that open bridge designs existed before the EL. Besides the Focalpin, here is a photo gallery by Gary Hawkins that shows a number of early bins with double hinged open bridges.

WARNING: Before clicking on the link, cover your keyboard so it doesn't get short circuited by your drool...

I particularly like the Kershaw Vanguard 7x50. I bet that looked space age in its day. Still does even, in a black and white sci-fi movie way. As used by Flash Gordon..............

[henry link]

Originally Posted by Kevin Purcell

Very interesting, Henry.

It's almost an open bridge (with a rod in it ... shade of the current Nikon Monarch X).

Are the two prisms cemented together in that porro?

Are they the same size (they seem to be in the diagram but it's difficult to tell)?

Kevin,

It looks to me like the prisms are mounted on opposite sides of a conventional prism shelf, so I think they must be air spaced. The "back" prism looks smaller to me, about 2/3 the height of the front prism, if their centers are at about equal distance in the rendering.

Henry

[BobinKy]

The Swift 8.5x44 ED is nice for sweeping the landscape. The Nikox SE 8x32 is sweet, but not so good for sweeping.

...Bob
Kentucky

[Kevin Purcell]

Originally Posted by henry link

It looks to me like the prisms are mounted on opposite sides of a conventional prism shelf, so I think they must be air spaced. The "back" prism looks smaller to me, about 2/3 the height of the front prism, if their centers are at about equal distance in the rendering.

I wasn't too sure of the rotation of the pair of prisms which would give different projections in that plan (or is it elevation?).

But it really does look like the "occular" prism is smaller. I think that's required to get the focuser and it's optomech in place.

I wonder if the Leupold Cascades porro went with the same size prism (top and bottom) and that restricted the focuser or if they did the same thing and used two different sized prism. It's a rather light bin but it's difficult to tell from the outside. We need a radiograph of that bin

You can see in the photo how petite the 7x50 Focalpin is compared to a 8x50 CZJ Octarem, which is a more typical size for a 50mm Porro.

The Cascades too is a petite 40mm porro. Another feature of the two different prisms sizes? Or just saving from small prisms?

[henry link]

Kevin,

A Porro II, like Canon uses, would be the way to really open up some space in front of the prism. Check out the WWII British 5x40 below. It has large enough prisms for a 10 degree field and still has plenty of room for a Focalpin type internal focuser in front of the Porro II tuna cans.

Henry

[BinoBoy]

Can anyone point me to an explanation of how Porro II is different from regualr porro? It've tried Google and came up empty.

[henry link]

Here's a photo of a Porro II.

It's made by cementing 3 prisms together. In this photo lets say the light rays enter the top back diagonal prism from the left, are reflected down to the bottom prism for two reflections, then up and out of closest top diagonal prism to the right. The space advantage is that less than half as much front to back space is needed compared to Porro I and the prism can be snuggled up close to the eyepiece.

Edit: I see Kevin has provided links with better illustrations. I'll just add that a few current binoculars use Porro II's: Canon IS series, Zeiss 20x60 S and Miyauchi Binon 7x50 and 5x32 (I think Binons are discontinued).

[Kevin Purcell]

Porro II aka Porro-Abbe (is there nothing Prof Abbe didn't do? ).

http://en.wikipedia.org/wiki/Porro%E2%80%93Abbe_prism

Photos

http://www.flickr.com/photos/binocwp...7623234405689/

And one of our threads starting at post 8

http://www.birdforum.net/showthread.php?t=184856

[BinoBoy]

Thanks for the info guys. The Porro-Abbe name is what I was missing.

I found these weird Pulsar binoculars that seem to have a solid body with eyepieces that pivot like the Canon IS. Would that indicate that they have the Porro-Abbe also?

http://www.pulsar-nv.com/product.aspx?prid=4

Another neat feature they have is a set of 3 internal filters (one of which is a polarizer) that can be switched into or out of the light path.

I really like the Canon 15x50, even with IS off. I'm surprised more companies don't use this construction. It works great with a monopod.

[Kevin Purcell]

That Yukon made Pulsar is a Porro II bin. It says in Russlish on the product page: "the 2nd type of porro" and "durable glass-filled body": I should hope so ... but they may mean GRP body. Introduced at the end of last year with a lot of other "tactial" looking stuff. Perhaps they're looking for a new cooler brand.

http://www.yukonopticsglobal.com/

What an odd design choice for a regular bin. I wonder if there is an IS bin in the works?

Or perhaps they just wanted to go down the "moving objectives to focus" route as they say "Exterior flat protective filters, installed in front of the objective lenses, shield the optics from sand, dust and moisture".

They're not expensive at $250

http://www.google.com/products/catal...x40+binoculars

In some ways they're on the route that porros could have gone down. Someone should try them

[ronh]

Thanks for photo and info on Porro II, I always wondered.
Ron