Zeiss Commanders glasses

[Gumball]

Just acquired these and am very impressed with the field of view and depth of field.

Can anyone tell me the difference between the "Porro I" and the "Porro II" of the Commanders glasses ??
One is called "tall boy" and the other "fat boy" ? ? ?
How much difference is there ?? Is one superior to the other ??

[Sgt Bilko]

Porro II binoculars were an attempt to maintain as much light as possible - you lose a certain percentage at every air to glass surface (13%?) so, by joining the prisms together, you eliminate some light loss.

Coating has a similar effect and is much lesss expensive which is why coated Porro II binoculars are less common - they're a hybrid really of two differing design philosophies.

Increased focal length gives better resolution which explains why astro telescopes are so long.

So the tall one should give better resolution than the fat and be slighly brighter (all things being equal). Some tall ones have differing oculars giving differing FOV's.

If I've time today, I'll rake some out and compare but I'm sure I've read that the tall one is optically more highly rated - which is not to detract from the fat one which is an awesome glass in itself and more practical for the confines of a submarine and the clattering down from the bridge during an alarm.

[Wpgbinocular]

Optically the blc 8x60 Porro II should be a little superior to the blc 8x60 Porro I Commander’s Glass for the two reasons Sgt Bilko cites: the Porro II’s prisms are cemented giving it a higher level of light transmission and probably its longer objective focal length as well would deliver better resolution (note that the blc 8x60 Porro I has an atypical type objective lens – see Seeger Green book 344 -345 - and I’m not sure what its purpose was or what effect it had on optical performance). Both the later 8x60 Porro II’s and the 8x60 Porro I’s had exceptionally wide 9.1 fields of view and employed highly sophisticated two lens/four element aspheric orthoscopic eyepieces. Note that the earlier CZJ 8x60 Porro II’s were instead H (Helligkeit) models having the eyepiece field lens cemented to the prism assembly, but unless yours has an H marking it is one of the later ones with the orthoscopic eyepieces. A certain amount of light is reflected from every air to glass surface in the binocular reducing light transmission, and the more air to glass surfaces there are the more light is reflected reducing transmission. With single layer coated surfaces about 2% of incoming light is reflected from the surface. Thus the 8x60 Porro I having, I believe, 10 air to glass single layer coated optical surfaces with an approximate 2% light loss per surface would have an 81.7% light transmission whereas the 8x60 Porro II having 8 air to glass single layer coated optical surfaces would have a slightly higher 85.1% light transmission. Whether in actual usage, though, this 3.4% increase in light transmission is noticeable is open for debate.

[Binoswede]

A subject collectors of military binoculars never gets tiered of discussing

My list is as follows (best first):

1. 8x60 Deck mounted. But to big and heavy to be hand held.
2. 8x60 Tall one. Awesome binocular. Specially the latest series.
3. 8x60 Fat one. Heavy, bulky, but the optic is good.
4. 8x60H Rather disappointing . But I only have a straight barrel Swedish issued one without coating.

[Sgt Bilko]

A fair assessment I'd say.

[Wpgbinocular]

To be completely accurate it should be emphasized that the figures of 2% light reflection from single layer coated glass surfaces and the 3.4% difference in light transmissions between the Porro I and Porro II model 8x60's are approximations only. This is because although the number of air to glass surfaces as well as the presence or absence of anti-reflective coatings in a binocular are the primary factors affecting light transmission through the binocular there are other lesser factors which affect transmission as well among them being the refractive indices of the optical glasses in the binocular, the types of single layer coating applied (during WW II there were several different types of materials used to coat optical surfaces, not just MgF2), and the thicknesses of the optical glasses.

[zeissasembi]

Robert
You did miss the 8x60 BNZA

[Binoswede]

Is not an 8x60 BNZA a Deck mounted with a different arrangement of the levers to move the filters?

[zeissasembi]

Yes but normally not called Deckmounted . The Bnza do also have an extra moveable reticle. Its connected to the zaule

[Gumball]

Thank you all for the clear and informative answers to my questions.

[Stew]

Just acquired these and am very impressed with the field of view and depth of field
Can anyone tell me the difference between the "Porro I" and the "Porro II" of the Commanders glasses ??
One is called "tall boy" and the other "fat boy" ? ? ?
How much difference is there ?? Is one superior to the other ??

Hi Gumball ,
the Forum has dealt very well with the differences between the Porro 1 and Porro II systems that the Fat One and Tall One represent.
A little while back I asked myself the same questions that you have put to the Forum.
A collector friend and I arranged to road test a Tall One and two Fat Ones from our collections.
All 3x binos in the test had been refurbished by the same expert bino workshop in recent years.
The Fat Ones included both cxn and blc examples
We compared the binoculars by putting them all through one simple test - we looked at some tall Norfolk pines on an offshore island approximately 3 kms away. We felt that this was an appropriate and simple test for binoculars designed for the Kriegsmarine. Our road test was not very scientific and pretty limited in scope but it did come up with a clear overall winner.
OUR FINDINGS

We both agreed that the Tall One felt easier to hold and operate.
We found that the overall optical performance of the blc Fat One and the cxn Fat One identical.
We both agreed that in terms of sharpness of image of the distant Norfolk Pines the Tall One and Fat Ones were pretty much on a par. No clear winner.
In terms of overall depth of field performance the Fat Ones were the winners.
The Fat Ones provided a noticeable wider field of view to the Tall One
In terms of light transmission (brightness of image ) the Fat Ones appeared superior to the Tall One.

[Sgt Bilko]

Sounds like a fair and concise test Stew and it tallies with my findings but, on papaer at least, I'd expected the Porro2 to be a little brighter with less glass to air surfaces to lose light.

I wonder why the top plates of the cxn 8x60's differ slightly from the blc versions - they're obviously both made to the same design?

[Mikedenmark]

Just guessing, but how about the cxn top plates were actually grinded down blc parts?
Not that I have any idea why that should be the case.

The blc top plates also comes in two versions, but that is a difference on the edges.

[Sgt Bilko]

The cxn has less sculptured areas around the screws - as though less finished perhaps.

[Mikedenmark]

I just noticed how the panel with the engraved code and serial number looked faced off on the cxn model, and slightly larger than on the blc. As if it was grinded down a bit.