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Equipment Discussions >> Binoculars

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BillC
on a new path
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Reged: 06/04/04

Loc: Lake Stevens, WA, USA
Re: Need advice on mechanical quality of zoom binos new [Re: Jon Isaacs]
      #5638887 - 01/23/13 12:58 PM

Quote:

Quote:

yes.




I think a more complete answer is required.

Yes, but....

Jon




A 1.25-inch EP is made to fit a 1.25-inch focuser. Short or long the answer is still "yes." CuriousOne said nothing about vignetting, aberrations or overall quality.

BillC


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CuriousOne
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Reged: 01/22/13

Re: Need advice on mechanical quality of zoom binos new [Re: planetmalc]
      #5638893 - 01/23/13 01:00 PM

Thanks, how size of exit pupil was calculated in that case?

1000mm/10mm/F10 ? but still 10, not 1 ?


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Mark9473
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Reged: 07/21/05

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Re: Need advice on mechanical quality of zoom binos new [Re: CuriousOne]
      #5638897 - 01/23/13 01:01 PM

exit pupil = entrance pupil (lens diameter) divided by magnification.

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CuriousOne
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Reged: 01/22/13

Re: Need advice on mechanical quality of zoom binos new [Re: Mark9473]
      #5638907 - 01/23/13 01:08 PM

Ok, so considering my previous experience with binoculars, where I found exit pupil of 2-3mm quite acceptable for my purposes, this means, that if using that 1000mm lens, I should target 30-50 magnification range, which itself translated to eyepiece mm, means that I need eyepiece with 20-33mm range, right?

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Mark9473
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Re: Need advice on mechanical quality of zoom binos new [Re: CuriousOne]
      #5638962 - 01/23/13 01:41 PM

Exactly! I'm happy you're coming to that conclusion. Not much fun in daytime viewing below an exit pupil of about 2 mm in my experience too.

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CuriousOne
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Reged: 01/22/13

Re: Need advice on mechanical quality of zoom binos new [Re: Mark9473]
      #5638982 - 01/23/13 01:57 PM

Ok, here's another question.

I have medium format camera lens 150mm/F2.8. It's front element is 82mm in diameter. Say I want 30x magnification. This will give me 82/30=2.7mm, which is fine. Considering the zoom needed, eyepiece should be 150/30=5mm.

OK

Now, above mentioned 1000mm lens can provide same exit pupil at 100/2.77=36x magnification. Not that much difference, right?

So, regarding the image, in which case from above mentioned, it will be brighter? if this was a photography question, I definetly know that F2.8 lens provides much much brighter image than F10 lens. But, in astronomy, where pupil matters, F number has no use?


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Patrik Iver
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Reged: 07/29/03

Loc: Kaarina, Finland
Re: Need advice on mechanical quality of zoom binos new [Re: CuriousOne]
      #5639048 - 01/23/13 02:52 PM

Quote:

Since I have two of these 1000mm/F10 reflex lenses, maybe there's some solution to join them together, to form a giant "binoculars?"




These are Maksutov-type, right?

Then they are probably focused by adjusting the distance between the meniscus/secondary and the primary mirror. To get the focal plane pushed far enough back through the porro prism cluster for you to reach the eyepiece focal plane (thus reaching infinity focus) might be difficult using the standard tele-lens body, as the focal plane in a camera is pretty close to the lens rear port, and they probably never were designed to focus that far back. And even assuming it can be done, I think you might get some other aberrations from locating the meniscus/secondary closer to the primary than originally intended, plus the effective focal length will increase (giving higher magnification) and the effective aperture might decrease.

Still, an interesting concept to experiment with, but I pessimistically predict that reaching and maintaining collimation will be mechanically very challenging.

Being a pessimist means you rarely get disapponted, and when you are proven wrong, you get pleasantly surprised! Win-win


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CuriousOne
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Reged: 01/22/13

Re: Need advice on mechanical quality of zoom binos new [Re: Patrik Iver]
      #5639067 - 01/23/13 03:10 PM

Yes, these are Maksutov type. Model is MC MTO 11: http://lzos.ru/en/index.php?page=shop.product_details&flypage=shop.flypag...

Focus is done via rotating the parts against each other, which itself changes the distance between them. Interesting, they do not have "infinity" focus, for example, after I focus on moon, I still have about half of a turn to rotate. It was designed for deep space exploration?

In soviet times, focuser/eyepiece attachments were manufactured and sold for this lens, but they are almost impossible to get now.


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Mark9473
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Reged: 07/21/05

Loc: 51°N 4°E
Re: Need advice on mechanical quality of zoom binos new [Re: CuriousOne]
      #5639151 - 01/23/13 04:04 PM

Quote:

So, regarding the image, in which case from above mentioned, it will be brighter? if this was a photography question, I definetly know that F2.8 lens provides much much brighter image than F10 lens. But, in astronomy, where pupil matters, F number has no use?




That's correct. The focal ratio only determines the focal length and therefore the magnification. For questions about brightness, specifically for daytime use, exit pupil is what you need to look at. For nighttime use, when it comes to point sources (stars) it is the aperture that matters; the exit pupil will then determine the brightness of the sky background and the very diffuse nebulous objects.


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BillC
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Loc: Lake Stevens, WA, USA
Re: Need advice on mechanical quality of zoom binos new [Re: Mark9473]
      #5639466 - 01/23/13 07:35 PM

“I have medium format camera lens 150mm/F2.8. It's front element is 82mm in diameter. Say I want 30x magnification. This will give me 82/30=2.7mm, which is fine. Considering the zoom needed, eyepiece should be 150/30=5mm.”

Curious:

When I read phrases like “Considering the zoom needed . . .,” I am left to believe you still don’t understand what “zoom” connotates in the world of optics. If I am correct, it is going to be difficult to impossible to answer some of your questions accurately—at least without covering the same topic again and again. Reading between the lines for your meaning, I think you would do well to forget the term “zoom” exists.

Because of my often too matter of fact mannerisms, I am frequently thought to be harsh when I have no such intention. So PLEASE take what I am about to say as just an old fool trying to be helpful.

Phrases like “A stitch in time saves nine” (popular, but not totally original structure) and “Don’t put the cart before of the horse,” came to be out of necessity and they seem germane to where this thread has gone . . . at light speed. And, while getting many very good responses, I don’t believe you are at the point of putting it all together, just yet. This is NO reflection on any language barrier or issue of aptitude, as you appear quite bright. It is, instead, an issue of general optics knowledge.

Newton or Leibniz could have the total attention of a 9-year old for an hour without having the youngster grasp the simplest point of calculus (You can substitute “BillC” for “9-year old,” if you want; I was just trying to save face.)

And, again, there are things with which only we opto-twidgits are going to be familiar.
For example: in GENERAL TERMS, 1000mm lens in camera talk refers to FOCAL LENGTH. Telescope makers might speak of a 1000mm objective in terms of DIAMETER.

EdZ and Glenn know the math you need and, if required, Stan could pull up a link for the best method of cleaning a rusty grill using banana oil in about .08 seconds. Ask those guys to send you some downloads pertinent to your questions. And, don’t forget the PDF I offered you.

Then, get a bowl of popcorn, a Coke, a highlighting marker and tell your wife, “Not tonight dear; I have a headache.” Then, get in bed with a good bedside lamp and read away!

There no shame in reading; I kept optics books by my bedside for 30 years . . . they make great coasters.

Go over the material, and over the material and over the material, until it becomes part of you. As you do, you will find that answers to your questions will become more understandable. Heck, with enough reading, you might even be able to understand KennyJ. Hey . . . it could happen!

Cheers,

BillC


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GlennLeDrew
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Re: Need advice on mechanical quality of zoom binos new [Re: BillC]
      #5639539 - 01/23/13 08:39 PM

Just to clarify. A 150mm focal length f/2.8 imaging lens has an actual working aperture of 150 / 2.8 = 53mm. The clear aperture of 83mm is only to allow off-axis light to get through to the image plane without suffering too much vignetting. And the reason for this larger aperture is because the front element is located some not insignificant distance in front of the lens's iris, or entrance pupil, which is also known as the nodal point.

And as you seem to have divined already, an imaging objective and an afocal system are quite different items. For direct imaging, an objective's focal ratio directly controls image surface brightness at the focus. An afocal system (e.g., a telescope) sends parallel light exiting the eyepiece into the eye, which the latter focuses on the retina. And so image surface brightness is controlled by the exit pupil, or the eye's own pupil, whichever is the smaller.

As BillC has pointed out, it must be asked... When you use the word "zoom", do you mean higher magnification (fixed, but 'zoomed in', so to speak), or instead a variable magnification (where you can smoothly zoom in and out over some range)?


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CuriousOne
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Reged: 01/22/13

Re: Need advice on mechanical quality of zoom binos new [Re: GlennLeDrew]
      #5639737 - 01/23/13 10:57 PM

Well, that was my fault, yes, I used "zoom" where I should used "magnification".

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planetmalc
sage


Reged: 10/21/09

Re: Need advice on mechanical quality of zoom binos new [Re: CuriousOne]
      #5640385 - 01/24/13 10:41 AM

If you are serious about the idea of using your two Maksutovs to make a large binocular, you need to: close-focus the lens to its limit; form an image of a DISTANT object onto a screen; measure the distance between the screen and the end of the focuser; then let us know what this distance is so that we can tell you whether or not your scheme is feasible.

Edited by planetmalc (01/24/13 10:48 AM)


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Rich V.
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Loc: Lake Tahoe area, Nevada, USA
Re: Need advice on mechanical quality of zoom binos new [Re: planetmalc]
      #5640421 - 01/24/13 10:56 AM

How does one propose getting a proper interpupillary distance with two 100+mm diameter optics if these Maks are used? Do they have enough back focus for prism assys to be incorporated? Did I miss something here?

Rich


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planetmalc
sage


Reged: 10/21/09

Re: Need advice on mechanical quality of zoom binos new [Re: Rich V.]
      #5640429 - 01/24/13 10:59 AM

This is what we're trying to determine, Rich.

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BillC
on a new path
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Reged: 06/04/04

Loc: Lake Stevens, WA, USA
Re: Need advice on mechanical quality of zoom binos new [Re: planetmalc]
      #5640458 - 01/24/13 11:17 AM

Quote:

This is what we're trying to determine, Rich.




Understood. However, just as it easier to make a 6-inch mirror AND a 12.5-inch mirror than a 12.5-inch mirror alone, it will be easier for CuriousOne to make better decisions and ask more pointed questions by taking some time off to read a little on optical realities. Stuffy or not, without doing so, this thread will grow to be 10 pages in 4 more days and CuriousOne will know little more than he does now. But, I have approached that logic several times to no avail, so I will stop recommending it.

Cheers,

BillC


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Rich V.
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Re: Need advice on mechanical quality of zoom binos new [Re: BillC]
      #5640521 - 01/24/13 11:54 AM

It just seems to me that an inexpensive 30x80 bino will provide all the reasonable magnification that can be had for terrestrial use. More magnification at long distances more often than not just doesn't cut it due to surface atmospheric disturbance which has already been discussed here. A 30x80 provides a usable ~2.5mm exit pupil with a usable focusing mechanism and IPD adjustment incorporated into a handy package. Hard to beat, IMO.

For me, even my higher quality 22x binos show too much air turbulence at long distances under many circumstances.

This query seems to be headed to a lot of trouble for little realized good.

Just my opinion, of course...

Rich


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Mark9473
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Loc: 51°N 4°E
Re: Need advice on mechanical quality of zoom binos new [Re: Rich V.]
      #5640551 - 01/24/13 12:17 PM

Quote:

How does one propose getting a proper interpupillary distance with two 100+mm diameter optics if these Maks are used? Do they have enough back focus for prism assys to be incorporated? Did I miss something here?



The idea was to mount a porro binocular body with the objective barrels removed, behind the two lenses. He tried with one binocular but that wasn't wide enough. He had another one that was wide enough, but that was defective on one side.


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CuriousOne
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Reged: 01/22/13

Re: Need advice on mechanical quality of zoom binos new [Re: Mark9473]
      #5643813 - 01/26/13 05:22 AM

Say the 3 fold calendar, like this:

https://sites.google.com/site/giffitti/3FOLDSHIPPINGCALENDAR.jpg

is hang about 180 meters away and binoculars allow to distinguish and read smallest text ("week") on them. Such binoculars are considered good or bad?


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EdZ
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Re: Need advice on mechanical quality of zoom binos [Re: CuriousOne]
      #5644070 - 01/26/13 10:01 AM

Quote:

Say the 3 fold calendar, like this:

https://sites.google.com/site/giffitti/3FOLDSHIPPINGCALENDAR.jpg

is hang about 180 meters away and binoculars allow to distinguish and read smallest text ("week") on them. Such binoculars are considered good or bad?




without knowing the actual size of the letters and the power at which the binocular is used, this question, which really measures only one aspect, resolution, cannot be answered. Even if yyoou knew alll the above and were abble to ansswer the question, theres's at leastt anotheer 10 aspets of performaancce to measure to determine if ythe binocular is good or bad.


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