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# APM 120mm ED APO binoculars

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### #26 MB_PL

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Posted 21 April 2016 - 06:54 AM

Clear aperture on the eyepiece side in the APM 100mm is 23mm and this number should be used in all calculations. Anything else is misleading. To me, APMs data on max fov in the APM 100mm is a clear case of misrepresentation.

### #27 Riccardo_italy

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Posted 21 April 2016 - 07:08 AM

To me, APMs data on max fov in the APM 100mm is a clear case of misrepresentation.

Well, not necessarly because the decrease in illumination is gradual.

You will probably have 2.4Â° fully illuminated, due to the clear aperture on the eyepiece side, and a 2.8Â° field where, at the edges, illumination will be at 50-70%, which is still acceptable.

2x 120mm = 1x 170mm

2 x 120mm ~ 1 x 143mm

Both are right. Same light as from a 170mm refractor with binoviewer or same light as a 143mm refractor without binoviewever. I believe that, since you use two eyes to observe in a binocular, the first example is a more appropriate comparison. BTW, how much for a 7" APO?

Edited by Riccardo_italy, 21 April 2016 - 07:11 AM.

### #28 Mad Matt

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Posted 21 April 2016 - 07:33 AM

Clear aperture on the eyepiece side in the APM 100mm is 23mm and this number should be used in all calculations. Anything else is misleading. To me, APMs data on max fov in the APM 100mm is a clear case of misrepresentation.

The rear baffle is far enough away from the field stop so that it does not limit the field of view. It only causes a drop in brightness towards the edge.

### #29 MB_PL

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Posted 21 April 2016 - 07:39 AM

It was mentioned in one of the threads about the 100mm BT that the diameter of the fully illuminated circle is 6mm.

### #30 GlennLeDrew

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Posted 21 April 2016 - 08:28 AM

As long as full illumination obtains at the field center, one is doing fine. The instrument is operating at full aperture, and an immediate fall-off from the field center will not be detectable. As long as it's gradual, vignetting can have the edge illumination down to 50% or even less and not really detract from the view.

### #31 MB_PL

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Posted 21 April 2016 - 08:56 AM

I am aware of illumination fall-off and of what's generally deemed as acceptable in this regard in binoculars. Owners of the 100mm BT have reported noticeable vignetting when using eyepieces with a 27mm field stop, hence my reservations as to using 27mm for calulating max tfov.
I never use anything other than clear aperture at the eyepiece side for determining max tfov in binoviewers. A 32mm plossle with a 27mm field stop in a BV with a 21mm clear aperture shows very noticeable vignetting. I haven't done the exact maths, but my experience seems to suggest that using clear aperture for determining max tfov is more likely to represent a max tfov that will have satisfactory illumination. After all one could use an eyepiece with a 27mm field stop in a BT or BV with a say 15mm clear aperture at the eyepiece side, but would the result be satisfactory?

### #32 garret

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Posted 21 April 2016 - 12:10 PM

APMs data on max fov in the APM 100mm is a clear case of misrepresentation

Your 100% right.

I have the APM 100mm ED APO and 32 Plossl's for the widest possible true field, I measure almost 2.4 degree between 2 particular stars and the Skyx planetarium software as reference.

You can also use the 3 stars of Orion Belt as reference, they have a separation of 2.45 degree, with the 32mm Plossl's I can see only the glare of the 2 outer stars when I point the APM right in the center, not the 2 stars.

Garret van der Veen

Edited by garret, 21 April 2016 - 12:11 PM.

### #33 StarBucket

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Posted 21 April 2016 - 12:51 PM

APMs data on max fov in the APM 100mm is a clear case of misrepresentation

Your 100% right.

I have the APM 100mm ED APO and 32 Plossl's for the widest possible true field, I measure almost 2.4 degree between 2 particular stars and the Skyx planetarium software as reference.

You can also use the 3 stars of Orion Belt as reference, they have a separation of 2.45 degree, with the 32mm Plossl's I can see only the glare of the 2 outer stars when I point the APM right in the center, not the 2 stars.

Garret van der Veen

So what's the case here?

Theoretical fov versus actual, or outright misrepresentation?

### #34 Skittersqueek

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Posted 21 April 2016 - 12:58 PM

So the real question: Is it worth to sell my current pair of wellenformed 100mm for the upcoming 120mm? Will I notice a big jump?

I love my current pair but am always a sucker for a good upgrade.

Also so it's confirmed the binoptic fork II will work for it then? =D

Edited by Skittersqueek, 21 April 2016 - 01:02 PM.

### #35 MB_PL

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Posted 21 April 2016 - 01:04 PM

By tfov I mean true field of view

### #36 janapier

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Posted 21 April 2016 - 01:58 PM

If they are really going to use the same undersized prisms with which they compromized the 100 mm version, I don't feel the slightest attraction to these binos.

### #37 trener

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Posted 21 April 2016 - 02:03 PM

If they are really going to use the same undersized prisms with which they compromized the 100 mm version, I don't feel the slightest attraction to these binos.

Yes they are going to use the same prims. Let's hope they will solve all the problems from 100 mm version.

### #38 Mr. Bill

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Posted 21 April 2016 - 02:21 PM

If they are really going to use the same undersized prisms with which they compromized the 100 mm version, I don't feel the slightest attraction to these binos.

Yes they are going to use the same prims. Let's hope they will solve all the problems from 100 mm version.

How's  that going to happen?

### #39 TH1

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Posted 21 April 2016 - 02:47 PM

These are great, but why not get a Lunt E152, AVX and a Binotron? Same cash.

### #40 The Ardent

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Posted 21 April 2016 - 02:52 PM

I don't know if that's intentionally or inadvertently humorous.
???

### #41 janapier

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Posted 21 April 2016 - 05:16 PM

These are great, but why not get a Lunt E152, AVX and a Binotron? Same cash.

But less light gathering... You need 170 mm to equal 2x120 mm. Furthermore the 152 ED gives you much better planetary performance, but no real binocular rich field experience. Your max field with binoviewer will be little more than 1Â° @ 50x mag.

### #42 GlennLeDrew

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Posted 21 April 2016 - 07:11 PM

It bears repeating what was pointed out earlier...

The monoscope equivalent to a bino has its aperture 1.19X larger, not 1.41X. Two eyes improve signal to noise by factor root 2, or 1.41, which is equivalent to an *areal* aperture increase of the same ratio of 1.41, which corresponds to a diametrical increase of  the square root of 1.41, or 1.19.

A BV-equipped scope equivalent to a true bino has its aperture larger by the factor of 1.41. By splitting the light the BV renders image brightness as though delivered by a true bino whose objectives have 1/2 the area, or 0.707 the diameter.

And so a monoscope peered into cyclopically must have an aperture of 120 * 1.19 = 143mm in order to be about equivalent to a 120mm bino--when working at the same magnification. A scope with BV must be larger in aperture by 120 * 1.41 = 169mm.

[Edited to correct a faulty train of thought, brought on by lack of sleep. ]

Edited by GlennLeDrew, 22 April 2016 - 03:22 AM.

### #43 Tamiji Homma

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Posted 21 April 2016 - 07:53 PM

It bears repeating what was pointed out earlier...

The monoscope equivalent to a bino has its aperture 1.19X larger, not 1.41X. Two eyes improve signal to noise by factor root 2, or 1.41, which is equivalent to an *areal* aperture increase of the same ratio of 1.41, which corresponds to a diametrical increase of  the square root of 1.41, or 1.19.

A BV-equipped scope equivalent to a true bino has its aperture larger by the same factor of 1.19. By splitting the light the BV renders image brightness as though delivered by a true bino whose objectives have 1/2 the area, or 0.707 the diameter. Two eyes integrating these half-bright images compensate somewhat by now effecting objectives of aperture 0.707 * 1.19 = 0.84 times that of a same (real) aperture true bino. The reciprocal is 1.19, which is how much larger must be the aperture of a scope fitted with a BV to equal a true bino (when operating at the same magnification.)

And so a monoscope either peered into cyclopically or used with a BV must have an aperture of 120 * 1.19 = 143mm in order to be about equivalent to a 120mm bino--when working at the same magnification.

Hi Glenn,

I think it is also important to point out that the maximum benefit (sqrt(2)) of binoviewing summation gain requires  two eyes perform perfectly equally.

If one eye works better than the other, you won't gain the maximum sqrt(2) benefit, given that beam splitter (or two scopes) is delivering light to each eye equally.

I don't think I have perfectly performing two eyes but I do see better with two eyes

Tammy

### #44 whosthebadman

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Posted 21 April 2016 - 08:28 PM

So the real question: Is it worth to sell my current pair of wellenformed 100mm for the upcoming 120mm? Will I notice a big jump?

I love my current pair but am always a sucker for a good upgrade.

I think there could be a purge.

### #45 janapier

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Posted 22 April 2016 - 12:30 AM

It bears repeating what was pointed out earlier...

The monoscope equivalent to a bino has its aperture 1.19X larger, not 1.41X. Two eyes improve signal to noise by factor root 2, or 1.41, which is equivalent to an *areal* aperture increase of the same ratio of 1.41, which corresponds to a diametrical increase of  the square root of 1.41, or 1.19.

A BV-equipped scope equivalent to a true bino has its aperture larger by the same factor of 1.19. By splitting the light the BV renders image brightness as though delivered by a true bino whose objectives have 1/2 the area, or 0.707 the diameter. Two eyes integrating these half-bright images compensate somewhat by now effecting objectives of aperture 0.707 * 1.19 = 0.84 times that of a same (real) aperture true bino. The reciprocal is 1.19, which is how much larger must be the aperture of a scope fitted with a BV to equal a true bino (when operating at the same magnification.)

And so a monoscope either peered into cyclopically or used with a BV must have an aperture of 120 * 1.19 = 143mm in order to be about equivalent to a 120mm bino--when working at the same magnification.

Hi Glenn,

my calculation is somewhat different. Both true binoculars and a BV'ed scope offer the use of both eyes, thus allowing for binocular summation. A BV'ed 170 mm scope supplies one eye with the same amount of light (170*0.707) as does the single bino barrel of 120 mm. Summation applies to both instruments, so the 1.41 factor remains.

Cheers

SteVe

### #46 ArsMachina

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Posted 22 April 2016 - 01:43 AM

There is no single fix gain factor, the factor depends a lot on the observed targets.

For pinpoint objects (stars) it will be, 1.4142 and this will also be the gain in magnitudes.

But for faint and wide area objects like galaxies and nebulae this factor is even higher.

Arie Otte, a well known builder of binoscopes, wrote a long explanation of the binocular summation, you can find it here:

http://arieotte-bino...tion Factor.pdf

After reading this article there should not be any questions left.

Jochen

### #47 janapier

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Posted 22 April 2016 - 03:15 AM

There is no single fix gain factor, the factor depends a lot on the observed targets.

For pinpoint objects (stars) it will be, 1.4142 and this will also be the gain in magnitudes.

But for faint and wide area objects like galaxies and nebulae this factor is even higher.

Arie Otte, a well known builder of binoscopes, wrote a long explanation of the binocular summation, you can find it here:

http://arieotte-bino...tion Factor.pdf

After reading this article there should not be any questions left.

Jochen

The factor of 1.41 in my calculation is no binocular summation factor. It is simply sqr(2) to account for the relationship between area and diameter. The summation factors in BV'ed scope and true binos are either equal or the one for the binos is greater, requiring even more aperture to compensate.

### #48 GlennLeDrew

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Posted 22 April 2016 - 03:15 AM

Steve,

You're quite correct; the equivalent BV'd scope must be 1.41X larger in aperture than a true bino. I was in error in thought train, obviously having somehow substituted a mono scope used 'normally' for the mono scope used with BV. I'll blame my error on having been awake for over 24 hours.

### #49 junomike

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Posted 22 April 2016 - 06:06 AM

Looks like Markus has officially released the specs and info on the 120's.

Mike

Edited by junomike, 22 April 2016 - 06:11 AM.

### #50 edwincjones

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Posted 22 April 2016 - 07:21 AM

the refractor people say/use to say that there is a big difference in going from 4" to 5"

but not so much going from 5" to 6".

Is this true for binoculars also?

good to see a 5" option

edj

just a caution to the excitement

I have a miyauchi 4" binocular which is a good size for portability and observing

I also have a fujinon 25x150 which is a BIG increase in size, weight, lack of portability

---and requires/almost requires a fixed location for the 120# setup

Hopefully the 120mm binoculars is a good compromise between size and portability.

Edited by edwincjones, 22 April 2016 - 07:22 AM.

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