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Docter Aspectem 40x80 ED

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#26 JKoelman

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Posted 10 December 2012 - 10:15 AM

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.

#27 Rich V.

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Posted 10 December 2012 - 11:05 AM

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! :question:

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#28 Andresin150

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Posted 10 December 2012 - 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 :confused:

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?

#29 Andresin150

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Posted 10 December 2012 - 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...?

#30 Andresin150

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Posted 10 December 2012 - 01:26 PM

found it..
is was at Nikon's web site
http://www.nikon.com.../basic/basic...

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

#31 Rich V.

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Posted 10 December 2012 - 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°. :shrug:

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

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#32 Andresin150

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Posted 10 December 2012 - 02:14 PM

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

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#33 Rich V.

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Posted 10 December 2012 - 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°

:D

Rich

#34 Andresin150

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Posted 10 December 2012 - 02:36 PM

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

#35 Rich V.

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Posted 10 December 2012 - 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

#36 Tamiji Homma

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Posted 10 December 2012 - 03:34 PM

Hi Rich,

You can find Docter UWA 12.5 spec here.

Docter UWA Eyepiece PDF document

Tammy

#37 Andresin150

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Posted 10 December 2012 - 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....

#38 Rich V.

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Posted 10 December 2012 - 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

#39 Andresin150

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Posted 10 December 2012 - 05:24 PM

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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#40 Andresin150

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Posted 11 December 2012 - 10:02 AM

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

#41 AlbertoJ

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Posted 29 December 2012 - 10:20 AM

Hello again.
I´ve seen a parallelogram mount, Universal Astronomics Unimount Light.
Is this mount big enough to charge steady and without shaking a Docter 40X80 ED binocular? or
Does it need an Universal Astronomics Millennium mount?

#42 Andresin150

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Posted 29 December 2012 - 10:29 AM

The Docters weight near 5 kg, look for the máximum load for each mount

#43 AlbertoJ

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Posted 29 December 2012 - 10:48 AM

Universal Astronomics Unimount Light has a maximum load of 12 Ibs, 5.4 Kg.
But I don´t know how steady Unimount is. I´ve read something about this mount. Look at shaking and dampening times at pages 7, 8 and 9 here:

http://www.cloudynig...bino_mounts.pdf

And besides, Docter is a 40X binocular, not a 16X or 20X.

#44 Rich V.

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Posted 29 December 2012 - 10:57 AM

Alberto, I use an older Unimount Light for with my WO 22x70s which weigh ~4.5kg which is the mount's max. rating. The mount works but I would prefer the Millennium mount with it. Damping times are a bit slow at maximum load. Having to use 6.8kg of counterweight doesn't help matters.

The Docters are 5kg and the newer light Unimount is rated for 5.5kg now. You would still be at the mount's maximum. It may work but you'll have to be careful not to induce oscillations in the mount while viewing, particularly at 40x. That high mag. makes a big difference over 15x or 20x.

The Millennium mount would be well worth it if you've made the investment in the Docters, IMO. It would certainly be my choice. Your binos will be well within the bottom half of its weight rating. You will then have the extra capacity to assure sufficient damping at 40x. Make sure you get the Ultra Swing Hinge option which is necessary for comfortable reclined viewing. No point setting yourself up for disappoinment! ;)

Rich

#45 AlbertoJ

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Posted 02 January 2013 - 08:05 PM

Thanks Rich, I think Millenium mount with Hinge is the best choice to charge a Docter 40x80 ED binocular on.

#46 ngc 9999

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Posted 02 January 2013 - 08:32 PM

Have someone tested the field illuination of the 40x80 ED?

#47 Andresin150

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Posted 07 January 2013 - 08:47 AM

I'm back :)
If someone can indicate me how to measure it I'll give it a try....

#48 ngc 9999

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Posted 07 January 2013 - 10:07 AM

Try to line the edge of the objective with the prism edge or baffle and see how much of the exit pupil is blocked.

#49 Rich V.

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Posted 07 January 2013 - 10:58 AM

Andres, here's a great example of lining up the objective edge with the rest of the optical system as provided by Michael (GamesForOne). In the case of the Porro prism Docters, one angle is probably fine:

Photo from the "General comments on angled binos" from March 2010

Rich

#50 Andresin150

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Posted 07 January 2013 - 10:42 PM

Ok, I'm trying... Taking pictures of the image circle backwards, depending on the distance, makes the circle change its size apparently (the farther it gets bigger, so I took the pictures aproximately at 15 cm from the glass to get a small one). Pictures are from my iPhone, with not too much light and without flash, not too good but good enough... First, an image of the circle just when it starts to clip... I did a rough calculation and found that it has 100% illumination at 50mm of diameter (49.7mm)...

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