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What's the smallest FOV (or AFOV) you've seen? And... does it have any purpose? (2 Viewers)

yarrellii

Well-known member
Supporter
The other day I came across an ad in the local classifieds. It is an old 7x35 roof prism device that doesn't seem to bear any brand or model name, the form reminds me of classic German roofs from 50 years ago, like the Zeiss Dialyt.

Anyway, what really struck me when reading the specifications on the plate is the incredibly narrow field of view, as small as 3,5º for a 7x35 (by the simple calculation method, 7 x 3,5= 24,5º AFOV!!!, accounting for 61 m at 1000 m (and to think people complain about the 7x42 Habicht :D).

I don't think I'v ever seen any binocular with such a narrow AFOV. There are many 7x35 Porro binoculars that easily reach 9º, 11º or even more, although many others make do with less than that. In fact, 3,5º seems more appropiate for something like a 18x56, not a 7x35. In this case, the FOV seems to be such a distinctive feature of this particular device that I wonder whether the information on the label is simply a typo or such a narrow FOV was intentionally created to serve some special purpose (I don't know, maybe by with such tiny AFOV you gain in some area that can be useful for some application that escapes me).

Does anybody have an idea what might be happening here? Typo? Specialised bino?

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henry link

Well-known member
I think that's a pair of plastic toy Galilean field glasses masquerading as a prismatic binocular. I've seen one just like it. In that design the apparent size of the objective lens as viewed through the eyepiece is what determines the apparent field and it's always very small.

The smallest apparent field among my binoculars is 42º at 8x in a Nikon 8-16x40 zoom. The reason is to keep the zoom eyepieces a reasonable size. Some other zoom binoculars are smaller than that at the lowest magnification.

Henry
 

Binastro

Well-known member
2.2 arcminutes with my 317mm Dall Kirkham at 1100x.
However this was empty magnification.

3.5 arcminutes at 700x.
Yes, fully usable on Jupiter's moons.

William Herschel used magnifications of 1000x with spherical single lens eyepiece.
The AFOV was I think less than 10 degrees,
So FOV around 30 arcseconds.
For examining Jupiter, Mars etc.

My monocentric and Tolles eyepieces have AFOV of about 20 degrees.

The 25x-135x80 binocular has a field of about 22 arcminutes at 135x.
But empty magnification.
At 80, fully usable field of 35 arcminutes.

The binocular in the photo above may have small field stops or the stickers from a 20x binocular put there by mistake.
I recall 61m on 20x binoculars.

On an exceptional night on Pic du Midi, the 1.5m NASA scope was used at 1,500x and 2,000x with superb detail shown on Mars.
Probably 1.5 arcminute field.
Mars probably 20 arcsecond across.

Regards,
B.
 
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peter.jones

Veteran of the Battle of Peppa Pig World (2022)
United Kingdom
Sorry, a scope not binocular.. Smallest fov I've used.. Swarovski atx95 at the wide end.
Did it have a useful purpose? Not really!
 

Tringa45

Well-known member
Europe
Most pocket binoculars or small monoculars have a narrow AFoV because there just isn't enough room for larger prisms.
I just made a few quick measurements:-
Zeiss 3x12 Mono, 37°
Zeiss 6x18 Mono, 40°
Nikon 6x20 Rangefinder, 36°

John
 

Binastro

Well-known member
I looked up William Herschel's eyepieces.

Eight were carefully examined and on a 7ft telescope, 85 inch focal length, the magnifications vary from 1504x to about 6500x.
They are spherical or nearly so.
The fields are as small as 26 arc seconds and half of Saturn and rings is visible.

There is a ninth with a magnification of about 7500x.
This is biconvex.
The focal length measured accurately is 1/90 inch. About 0.011 inches.
It is thought this was not used successfully. The field is 20 arc seconds.

The eyepieces are wood and brass.

William Herschel made oboes and used the same lathe to make the eyepiece housings.

These eyepieces are maybe the smallest made and generally made to high standards.

I used Huyghen eyepieces for ten years with a long focus achromat telescope.
The views were good but the AFOV was about 35 degrees.

Huyghenian eyepieces were used in most of the early discoveries, such as the moons of Mars etc.

Regards,
B.
 

Steve C

Well-known member
Someplace around here I have a 7x50 with I.F and a 5* field. That is the smallest I have seen. The view is mostly OK image wise but it is truly like looking through two paper tubes. Basically unusable.
 

John A Roberts

Well-known member
Australia
My two narrowest FOV binoculars are the Leica Ultravid 8x20 and the Swarovski Habicht Porro 7x42:
• the Leica has a FOV of 6.4°/ 113 m at 1000 m, and an AFOV of 51°, and;

• the Swaro has a FOV of 6.5°/ 114 m at 1000 m, but an even smaller AFOV of only 45.5°.


They're similar in that each has a high quality image, with the characteristics associated with their respective line of binoculars.
However, there is one striking difference to the viewing experience.

With the Leica I’m constantly aware - almost irritatingly so - that my eye movement is severely restricted
i.e. the looking down a straw analogy. But that’s the necessary price for the convenience of such a compact 8x binocular *

In contrast with the Habicht, there's no such sensation. It's just like any other 7x42 such as my Ultravid or Zeiss FL
- it just shows less of the landscape at the outer field (and it's the central field that's normally the focus of my attention).

The reason for the marked difference between the viewing experiences is of course the size of the exit pupils;
the 6 mm EP of the Habicht has an area 5 3/4 times that of the 2.5 mm EP of the Leica!


John


* However, even just going from a 2.5 to 3 mm EP - with a 44% increase in area - will make a difference to many. So either:
i) the slightly reduced magnification of the 7x21 Swarovski Curio, or;
ii) the increased size of an 8x25 (with a 56% increase in EP area) such as the Zeiss or the Swarovski.
 

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mwhogue

Well Known Member
Supporter
John,

Nice post and pic. When you have a moment, your UV has a black rather than the typical red Leica badge - is it a limited edition? Looks very sharp!

Mike
 

John A Roberts

Well-known member
Australia
Hi Mike (post #11),

Over the years there’s been lots of limited edition Leica’s, and it’s the rarest of them all.
To Leica cognoscenti it’s a unicorn - a Maltese Falcon if you will - only spoken about in hushed tones.
It’s the fabulous Ultravid 8x20 JR Deluxe Stealth Edition - and it’s No.1 of 1!

The comparable holy grail for Nikonistas is the one-off, left handed F100 that Nikon hand made for Ken Rockwell.
See the only two known images from Ken’s site.

And although some claim that another Ultravid DSE may be had by a careful exploration of the following site,
I for one remain unconvinced: https://www.sharpie.com/markers.html


John
 

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mwhogue

Well Known Member
Supporter
Hi Mike (post #11),

Over the years there’s been lots of limited edition Leica’s, and it’s the rarest of them all.
To Leica cognoscenti it’s a unicorn - a Maltese Falcon if you will - only spoken about in hushed tones.
It’s the fabulous Ultravid 8x20 JR Deluxe Stealth Edition - and it’s No.1 of 1!

The comparable holy grail for Nikonistas is the one-off, left handed F100 that Nikon hand made for Ken Rockwell.
See the only two known images from Ken’s site.

And although some claim that another Ultravid DSE may be had by a careful exploration of the following site,
I for one remain unconvinced: https://www.sharpie.com/markers.html


John

John,

Thanks for this. While reading your post, as luck - dare I say FATE ?!?! - would have it, my wife called from the grocery store asking whether I wanted anything in particular. With a wildly pounding heart and trembling hands I asked her to purchase several black sharpies and set a return course to home at flank speed. I'll be blacking out my Leica badges and will revert with results in due course.

Mike
 

John A Roberts

Well-known member
Australia
For some context, Mike’s original question was a perfectly reasonable one . . .

in Leicaland - and especially on M series cameras - there's long been considerable significance as to whether the ID logo on the front
was the traditional Red Dot, or a Black Dot, or now none at all.

Originally the black dot was meant to make it less obvious that a camera was a very expensive one, when used by working photojournalists.
However, such items were limited editions, and so were fiercely sort out by dedicated collectors because of their rarity and associated seriousness!

. . . but of course for a couple of dollars, anyone owning a Leica could join the club.


John
 
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Gijs van Ginkel

Well-known member
According to Gary Hakins Leitz/Leica study, there are different logos used on the second Trinovid series: -1- a black rectangle, -2- a black disk and -3- a red disk.
Gijs van Ginkel
 

Gijs van Ginkel

Well-known member
Gary Hakins must be Garry Hawkins of course in post 16.
With regard to FOV: the new Swarovski Curio 7x21 has an FOV of 135m/1000m and that is rather good for a compact if I compare it with roughly 20 other compacts, as I did in my finished and to be published test report of the Curio.
Gijs van Ginkel
 

yarrellii

Well-known member
Supporter
Gary Hakins must be Garry Hawkins of course in post 16.
With regard to FOV: the new Swarovski Curio 7x21 has an FOV of 135m/1000m and that is rather good for a compact if I compare it with roughly 20 other compacts, as I did in my finished and to be published test report of the Curio.
Gijs van Ginkel
Really looking forward to reading it! Thanks for all your tests and reports, they're always an invaluable asset.
 

Canip

Well-known member
According to Gary Hakins Leitz/Leica study, there are different logos used on the second Trinovid series: -1- a black rectangle, -2- a black disk and -3- a red disk.
Gijs van Ginkel

By the way:

red dot isn't red dot.

The newest Leica products feature a logo that has enhanced orange brightness.
Knowing form my own corporate times how much fuss marketing people make about slight color variations in well-known branded products, this is hardly an accident, but looks like a deliberate change to a more modern, brighter logo.

Even the iPhone photo shows the difference quite clearly (top left and bottom right are more recent products, top right and bottom left are a few years old.

IMG_9734r.jpg
 

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