Show us your "vintage" and classic binos (1 Viewer)

[Paultricounty]

You like the BK7 Prominar better than the Bak-4 version?

I don’t know, I never had them side by side. I’d guess the Bak-4 would probably have better edges. I have a Swift 7x35 Sportking 11° with Bk7 that are excellent , central sharpness as good as any of the vintage high end SWF genre, but edges fall off is abrupt.

 

[ChrisNYPilot]

I don’t know, I never had them side by side. I’d guess the Bak-4 would probably have better edges. I have a Swift 7x35 Sportking 11° with Bk7 that are excellent , central sharpness as good as any of the vintage high end SWF genre, but edges fall off is abrupt.

Someone well known on CloudyNights mentioned they prefer the BK7 version as it seems sharper. So just trying to sort it out. Thanks.

 

[Paultricounty]

Someone well known on CloudyNights mentioned they prefer the BK7 version as it seems sharper. So just trying to sort it out. Thanks.

There’s a lot of discussion about these two prisms on bird forum and cloudy nights, if you want to dig deeper into the differences , properties and performance. Here’s a quick general description. Imo if you have the choice go with the Bak4.

Prism Glass Types in Binoculars: BK7 vs. BAK4 (Compared) - BinocularsDesk

Binoculars are made up of several optical elements, including prisms, which are responsible for aligning the image and making it appear right-side-up. There are two main types of prisms used in binoculars: BK7 and BAK4.

binocularsdesk.com

 

[Tringa45]

There’s a lot of discussion about these two prisms on bird forum and cloudy nights, if you want to dig deeper into the differences , properties and performance. Here’s a quick general description. Imo if you have the choice go with the Bak4.

Prism Glass Types in Binoculars: BK7 vs. BAK4 (Compared) - BinocularsDesk

Binoculars are made up of several optical elements, including prisms, which are responsible for aligning the image and making it appear right-side-up. There are two main types of prisms used in binoculars: BK7 and BAK4.

binocularsdesk.com

There are a few errors in that article.
BK7 has lower dispersion (higher Abbe No.) than BaK4 and also slightly better transmission at the blue end of the spectrum.
However, BK7's refractive index is lower and for many binoculars will not be sufficient to provide total internal reflection over the complete field of view. Hence the squared-off exit pupils seen on many bins with BK7 prisms.
The objective lens focal ratio of many hand-held binoculars is around f/3,5 and, according to Holger Merlitz, the lower limit for BK7 prisms is f/5, whereas BaK4 is good down to f/3,3.

John

 

[Paultricounty]

There are a few errors in that article.
BK7 has lower dispersion (higher Abbe No.) than BaK4 and also slightly better transmission at the blue end of the spectrum.
However, BK7's refractive index is lower and for many binoculars will not be sufficient to provide total internal reflection over the complete field of view. Hence the squared-off exit pupils seen on many bins with BK7 prisms.
The objective lens focal ratio of many hand-held binoculars is around f/3,5 and, according to Holger Merlitz, the lower limit for BK7 prisms is f/5, whereas BaK4 is good down to f/3,3.

John

I agree it wasn’t the best representation of the differences but was a good general start. I didn’t wanna post a link that got too deep into the minutia.

 

[henry link]

The diamond shaped chordal cuts that occur when BK-7 is used for the erecting prisms in a telescope with a focal ratio below about f/5 occur at the edge of the objective lens's light cone, not at the edge of the FOV. The result is an overall reduction in brightness across the entire FOV, not just at the edge. The usual photo illustration of the effect shows a bright axial exit pupil viewed from some distance behind the eyepiece. That central exit pupil may subtend only a few degrees of apparent field and yet the diamond shaped shadow at its edge is already fully developed.

Eliminating the shadow can be accomplished by either reducing the aperture of the objective and thereby increasing the focal ratio until it's above f/5 or by simply using the binocular in bright enough light for the reduced size of the eye's pupil to accomplish the same thing. Reducing the FOV, real or apparent, will have no effect at all on the chordal cuts in the center of the field for a properly centered eye.

 

[tenex]

The usual photo illustration of the effect shows a bright axial exit pupil viewed from some distance behind the eyepiece.

(unfortunately some go on to superimpose an image on this as if that's what one would see)

 

[Gumball]

A few of my favorites . . . . .

 

[Maljunulo]

Okay, I'll bite ..... what are they?

 

[Gumball]

A few of my favorites . . . . .

Left to right:
Zeiss 18x50 (1923) . . . . Barr and Stroud CF42 7x50 (1942) . . . . . Zeiss U-BOAT 7x50 (1943) . . . . Leitz Kreigsmarine 7x50 (1944)

 

[Paultricounty]

Spent some time today with one of my Swift Holiday Mark II’s. This is the last version of their high end Mark II’s with 11.5° FOV (600ft at 1000yrds). These are one of the sharpest binoculars available if you can find one in good condition. The sharpness is superior to anything today in the mid upper level ($1000 range imo) and rival some of the best current alpha level bins. They are as sharp as the Swaro Habicht’s. The color hue is on the neutral side, the edge fall off is very gradual and the sweet spot is 75-80%. The FOV is so large that the field stop is barely noticeable, it’s like a window. The image character, combining a true three dimensionality with a 7X depth of field and the huge field of view, there really is nothing today that compares.

The downside is they need good bright lighting to perform at their best, there is a lot of pin cushion distortion at the edges, and they are heavy, about 950 grams.

Another sleeper , not quite as good as the holidays, but definitely a keeper for those know about these little beauties , the Bausch & Lomb Discoverer in 9x35.

 

[Ignatius]

Left to right:
Zeiss 18x50 (1923) . . . . Barr and Stroud CF42 7x50 (1942) . . . . . Zeiss U-BOAT 7x50 (1943) . . . . Leitz Kreigsmarine 7x50 (1944)

Left to right:
Leitz Kreigsmarine 7x50 (1944) ... Zeiss U-BOAT 7x50 (1943) ... Barr and Stroud CF42 7x50 (1942) ... Zeiss 18x50 (1923)

(Maybe you meant the other left and the other right. Little mnemonic: the left hand is the one with the thumb on the right ... and vice versa)

 

[Gumball]

Left to right:
Leitz Kreigsmarine 7x50 (1944) ... Zeiss U-BOAT 7x50 (1943) ... Barr and Stroud CF42 7x50 (1942) ... Zeiss 18x50 (1923

Yes, I made a mistake, they are reversed.

(and thank you for your usual sarcastic reply🙄)