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Equipment Discussions >> Binoculars

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Mr. Bill
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Reged: 02/09/05

Loc: Northeastern Cal
Re: Docter Aspectem 40x80 ED new [Re: Andresin150]
      #5560725 - 12/08/12 11:27 AM

Well, anyway you slice it, 80mm no matter how good is still 80mm.

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AlbertoJ
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Reged: 02/20/08

Loc: Madrid (España)
Re: Docter Aspectem 40x80 ED new [Re: Mr. Bill]
      #5563022 - 12/09/12 07:29 PM

Thanks Andres. Now I can imagine how good Docter is.
What´s your preference with it? Astronomy or terrestral.


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Andresin150
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Re: Docter Aspectem 40x80 ED new [Re: AlbertoJ]
      #5563062 - 12/09/12 07:59 PM

Alberto, contrary that some would think, I prefer them for Astronomy.

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Andresin150
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Re: Docter Aspectem 40x80 ED new [Re: Andresin150]
      #5563068 - 12/09/12 08:05 PM Attachment (36 downloads)

Here is something... Just a few minutos ago I confirmed that their TFOV is exactly 2.2 degrees. I used my skysafari iPhone program to confirm it. It frames exactly to the border Aldebaran and star V993. Considering their 40x magnification, should their Afov be 88 degrees instead of 84?

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Andresin150
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Re: Docter Aspectem 40x80 ED new [Re: Andresin150]
      #5563073 - 12/09/12 08:08 PM

The smaller circle is the 1.7 deg of the 40x150 Fujis...

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JKoelman
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Reged: 05/16/11

Loc: Bangalore, India
Re: Docter Aspectem 40x80 ED [Re: Andresin150]
      #5563885 - 12/10/12 10:15 AM

Quote:

their TFOV is exactly 2.2 degrees. [..]. Considering their 40x magnification, should their Afov be 88 degrees instead of 84?




Amazing specs. Scale the magnification down to reach 3.5° TFOV (still a whopping 25x), and give them a 90° angled view. With the optical quality that you describe, that would be my dream bino.


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Rich V.
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Loc: Lake Tahoe area, Nevada, USA
Re: Docter Aspectem 40x80 ED new [Re: Andresin150]
      #5563955 - 12/10/12 11:05 AM

Quote:

Here is something... Just a few minutos ago I confirmed that their TFOV is exactly 2.2 degrees. I used my skysafari iPhone program to confirm it. It frames exactly to the border Aldebaran and star V993. Considering their 40x magnification, should their Afov be 88 degrees instead of 84?




Could be, Andres. But also consider that they could actually be 38x instead of 40x! The only way you'll know for sure is to verify the 80mm aperture with the flashlight test and then carefully measure the exit pupil with a caliper.

Usually in binos, the stated AFOV includes any pincushion distortion that was added to the eyepiece design. This usually causes a smaller TFOV than stated, not the other way around, though.

Knowing the actual magnification is the only way you'll really know!

Rich


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Andresin150
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Re: Docter Aspectem 40x80 ED new [Re: Rich V.]
      #5564116 - 12/10/12 12:55 PM

Hi Rich,
I did that a while ago to make sure they where working at full aperture. They measured exactly 80mm, and the exit pupil measured 2mm. Also, the image scale is identical (by appreciation) to my 40x150's...

Also, this brands are known for giving accurate measures, for example the 30.5x are branded that way, not 30x...., and the other measures help confirm it (Objectives focal length 500mm, and oculars focal length 12.5mm)

Math is not working only in the stated AFOV, in some sites (including Docters) the AFOV is stated as 84deg, and in others they say it is 90deg. Math suggests me that it is 88deg

In fact, I measured it yesterday because I thought its TFOV was 2.1deg (I decided then to believe in the 84deg stated), but when I compared the view (with what was shown by my phone astronomy software) I quickly noticed they showed a bit more fov..., then I measured it as exactly as I could...

I've read but not recall where or how, that Afov has another "later/modern" way to be measured and that the results are slightly different... maybe this is the case?


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Andresin150
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Re: Docter Aspectem 40x80 ED new [Re: Andresin150]
      #5564136 - 12/10/12 01:01 PM

Rich,
I didn't take into account the pincushion distortion, don't know how to measure its influence, but considering that it bends inward, should this cause a larger TFOV than stated instead than a smaller...?


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Andresin150
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Re: Docter Aspectem 40x80 ED new [Re: Andresin150]
      #5564193 - 12/10/12 01:26 PM

found it..
is was at Nikon's web site
http://www.nikon.com/products/sportoptics/how_to/guide/binoculars/basic/basic...

interesting... maybe they used that formula....


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Rich V.
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Re: Docter Aspectem 40x80 ED new [Re: Andresin150]
      #5564220 - 12/10/12 01:45 PM

Pincushion increases the magnification with distance from the optical axis. This expands the AFOV without increasing the TFOV.

The newer ISO calculation of AFOV produces a smaller number than the simple method of mag. x TFOV. In the linked example an 8x bino with a 7° FOV would have a 52.1° ISO AFOV rather than the simple calculation of 56°.

Some binos do have a wider TFOV than stated but it's much less common, AFAIK. My 10x35EII binos show stars that are 7.3° apart at the field stop; the stated TFOV is 7°.

Edit: I see you found the Nikon ISO formula I linked while I was typing!

Rich

Edited by Rich V. (12/10/12 01:48 PM)


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Andresin150
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Re: Docter Aspectem 40x80 ED new [Re: Rich V.]
      #5564263 - 12/10/12 02:14 PM Attachment (21 downloads)

I did Nikons exercise in Autocad..
It worked with their example, but with the Docters it gives just 75deg AFOV...?


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Rich V.
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Re: Docter Aspectem 40x80 ED new [Re: Andresin150]
      #5564280 - 12/10/12 02:25 PM

Yep. Your Docters at 2.2° and 40x have an ISO AFOV of 75°!

AFOV = 2 x [(inv)tan (40 x tan 1.1°)]
= 2 x [(inv)tan (.768)]
= 2 x [37.526]
= 75.05°



Rich


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Andresin150
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Re: Docter Aspectem 40x80 ED new [Re: Rich V.]
      #5564291 - 12/10/12 02:36 PM

That brought me back to the beggining... With what math are its specs calculated????

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Rich V.
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Re: Docter Aspectem 40x80 ED new [Re: Andresin150]
      #5564358 - 12/10/12 03:16 PM

Looking at the specs posted at Euro Optic they state 38.5m @ 1000m which calculates to 2.2°; that's what Andres measured.

That works out to 88° simple or 75° ISO AFOV. Where did this 84° AFOV number come from anyhow? Don't see any reference to AFOV on the Euro Optic site, just TFOV in m/1000m. Any other reference to Docter specs? Can't find much...

Rich


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Tamiji Homma
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Re: Docter Aspectem 40x80 ED new [Re: Rich V.]
      #5564387 - 12/10/12 03:34 PM

Hi Rich,

You can find Docter UWA 12.5 spec here.

Docter UWA Eyepiece PDF document

Tammy


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Andresin150
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Re: Docter Aspectem 40x80 ED new [Re: Tamiji Homma]
      #5564425 - 12/10/12 04:10 PM

Rich, if you browse in the web, most European vendors state 84 or even 90deg Afov for those binoculars. The individual eyepieces, which are supposed to be the same, even have 84 degrees printed on them....

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Rich V.
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Re: Docter Aspectem 40x80 ED new [Re: Tamiji Homma]
      #5564453 - 12/10/12 04:26 PM

OK, thanks, Tammy! They say 84°.

Oh, well, the simple AFOV calculation is close enough to get the idea. Without knowing the exact angular characteristics of the eyepiece design we don't have enough info to say much else.

It is one really wide field binocular any way we look at it. 2.2° at 40x is remarkable!

Rich


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Andresin150
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Re: Docter Aspectem 40x80 ED new [Re: Rich V.]
      #5564561 - 12/10/12 05:24 PM Attachment (23 downloads)

After doing some experiments, not too precise but to get the idea, I think that Nikon / ISO are right and according to reality....
I went to a park nearby, and marked 25m away from where I stand 2 points separated 38.4m. Then proyected imaginarily those points half way up (aprox 20m..) and recorded mentaly a circle inscribed in those boundaries. Then, with the Docters I observed, not even focused to avoid distractions, and the projected circle was exactly the same (AFOV). I was even easier to see when only using one eye in the Docters (defocused) and the other eye looking without binoculars, both images (eyepiece borders and the mental projection of the 2 points) coincided.
Autocad has never lied to me... I wonder from where the usual way to measure AFOV came if ISO calculation is simple geometry?....


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Andresin150
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Re: Docter Aspectem 40x80 ED new [Re: Andresin150]
      #5565640 - 12/11/12 10:02 AM

using ISO, the 40x150's measure 61.37 degrees (29.67m/1000m), with a TFOV of 1.7deg.

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