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Near out-of-focus point, program to determine

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#26 John Russell

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Posted 21 May 2021 - 02:34 PM

Martin,

 

Telescopes and binoculars are always afocal. The eyepiece is effectively a loupe used to view the virtual image of the object in the field, formed by the objective.

The focussed image is that on the retina of the human eye, just as that of a camera lens on the film or sensor.

 

For the normally sighted the virtual image would be placed in the focal plane of the eyepiece and the emerging rays would be parallel, i.e apparently at infinity.

For the short-sighted the eyepiece would be moved inside the virtual image for divergent rays and for the far-sighted the eyepiece would be moved outside the virtual image for convergent rays.

 

The human eye/brain perceives a 0,25 mm diameter dot at 25 cm as a sharp point source. This corresponds to about 3,4 arcminutes. The depth of field would be the range of object distances on both sides of the viewed object, whose circles of confusion subtended angles of 3,4 arcminutes at the eyepiece.

Now please don't ask me to do the calculations smile.gif.

 

John



#27 MartinPond

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Posted 21 May 2021 - 02:54 PM

"Telescopes and binoculars are always afocal."

 

Nope. That I am quite sure of, in the non-focused distances.

 

Not when they are in point of fact....not currently forming an image at infinity.

Then they are not afocal....by the very definition of afocal.

 

Not when they form an image, and then you turn them to a closer object,

  and they no longer form that image at the new distance, and you are

  not allowed to refocus.

 

Do you think we are talking about refocusing the image any time the distance changes?

Then you are missing the point entirely.



#28 Henry Link

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Posted 21 May 2021 - 03:48 PM

Here are the photos of defocussed artificial stars. Three binoculars were used: a Nikon 7x50 Prostar (left PDF,) a Nikon 7x35 E (middlePDF) and a Pentax 10x50 PIF (right PDF). All three were focused on a distant target, about 200 meters away. Then, with no change in focus, all three were tripod mounted and pointed at an artificial star at 4 meters. The star is so far out of focus that it has turned into a focused image of either the full aperture objective lenses (left side) or the aperture of 35mm stopdown masks (middle Images) or the aperture of the 50mm camera lens's iris diaphragm stopped down to f/16 (hexagonal images on the right).

 

What do these images tell us? Firstly we can see that the camera sensor (just like the eye's retina) can be blocked from exposure to the binocular's full aperture either by a mask placed at the objective lens or equally well by an aperture stop smaller than the exit pupil (in this case about 3mm in diameter) placed between the eyepiece and the camera sensor in the same position that the eye's iris would be between the eyepiece and the retina. The effective clear aperture of the binocular is dependent on the dilation of the eye. If the eye's pupil is smaller than the exit pupil then the effective exit pupil of any binocular regardless of its true aperture will be stopped down to match the eye.

 

The relative sizes of the diffraction discs in the photos are also useful because they correspond to the relative sizes of the circles of confusion for each binocular at this distance from best focus. It's obvious that the 10x50  has a larger circle of confusion than the 7x binoculars both at full aperture and when stopped down. Comparing the 7x models we see no difference in the size of the circles of confusion between the two when the 7x50 is stopped down to 35mm or when both are stopped down to about 21mm by the camera iris even though the 7x50 has a longer focal length objective. The circle of confusion is larger in the 7x50 at full aperture, but to see that the eye would have to be open to 7mm and the reason for it would not be found in the binocular's optics, but in the eye, which would suffer a los of DOF as its focal ratio decreases with increasing pupil dilation.

 

I should mention here that the increase in the size of the circles of confusion in higher magnification binoculars is not because they are truly more defocussed than lower magnification binoculars. It's because the very same diffraction disk with the same number of rings is just bigger, so it just looks more defocussed.

 

Part of the confusion on the subject of binocular DOF seems to come from misinterpreted observations. In post # 25 increased DOF was attributed to the 80mm scope's high focal ratio when it was stopped down to 10mm, but remember the eye was also stopped down to a high focal ratio at the same time and that's what changed the DOF at the retina, not the telescope's focal ratio. I'm no mathematician, but I can see that inappropriate math is being shoehorned into service here. The math in Post # 19 would only be appropriate if a naked retina could somehow be positioned at the point labeled "Focal Plane of the Eyepiece" in the diagram. 

 

OK. I'm done again, and I don't intend to be dragged into anyone's convoluted thinking in this subject again. I've been around this block a few times too many already.

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Edited by Henry Link, 21 May 2021 - 06:35 PM.

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#29 MartinPond

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Posted 21 May 2021 - 04:18 PM

I'm not shoehorning the 10mm mask into anything.

I'm saying it happens, and it is an extreme case, and it has

   nothing to do with my effect, .which is....except for a teeny aperture,

   under very un-challenging distances, simple focus, and going out of focus, dominates.

 

 

 

 

"I don't intend to be dragged into anyone's convoluted thinking"

 

...Ummmm, the very first chapter of an optics text is not convoluted thinking.

 

I focus for 1000meters.     1/infinity + 1/i = 1/focal-length    ---> i is then the focal length

I then look at 20 meters.

It is a fact,   1/o + 1/i = 1/f : 

   o goes down....1/o goes up.....the image has moved from the focal length.

This is is not convoluted at all.

It is the lens equation.

 

Binoculars have focusers.

At a new closer distance, you have to move the focuser back.

But ---> that is not allowed, if we are talking about the in-focus range <----

If you can constantly refocs, the range is always  infinite and as closer as the focuser allows.

 

So...the image goes out of focus.

If you don't move the focuser, the image goes out of focus.

According to some standard of resolution, this is the inner distance of the range.

Change the standard: the distance only changes a little.

It is going out  of   focus.

 

Nowhere near convoluted.

Obvious even without the equation.

And....when you look at something at 20 meters...... not  afocal any  more.

The exiting rays are not, in fact, parallel anymore.

This violates the definition of afocal.   

 

1/o  + 1/i = 1/f

o is infinite (or very long)  i === f    fact

o goes down, i goes up   fact

 

Simple.

Not convoluted.


Edited by MartinPond, 21 May 2021 - 04:31 PM.

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#30 Henry Link

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Posted 21 May 2021 - 04:31 PM

Nothing would change in the photos from using closer distances, as long as the artificial star remaines the same number of diopters out of focus. A less defocussed star would just make smaller diffraction discs, but the ratios of the disk sizes would remain the same.


Edited by Henry Link, 21 May 2021 - 05:17 PM.


#31 MartinPond

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Posted 21 May 2021 - 05:01 PM

At least I understand now: you are not describing the phenomenon of 

increasingly close objects going out of focus from the original distant focus.

So it was worth looking at the slides.


Edited by MartinPond, 21 May 2021 - 05:02 PM.


#32 John Russell

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Posted 21 May 2021 - 05:27 PM

"Telescopes and binoculars are always afocal."

 

Nope. That I am quite sure of, in the non-focused distances.

 

Not when they are in point of fact....not currently forming an image at infinity.

Then they are not afocal....by the very definition of afocal.

 

Not when they form an image, and then you turn them to a closer object,

  and they no longer form that image at the new distance, and you are

  not allowed to refocus.

 

Do you think we are talking about refocusing the image any time the distance changes?

Then you are missing the point entirely.

Try pointing your binoculars or scope at the sun (without lokking through them of course). Now hold a sheet of paper behind the eyepiece at the exit pupil.

Nothing's going to happen.

Now try this with a weak 2,5x hand loupe and focus the image of the sun on the paper.  It's going to burn!

That's the difference between focal and afocal.

Like Henry, I'm now out.

 

John



#33 MartinPond

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Posted 21 May 2021 - 08:21 PM

Try pointing your binoculars or scope at the sun (without lokking through them of course). Now hold a sheet of paper behind the eyepiece at the exit pupil.

Nothing's going to happen.

Now try this with a weak 2,5x hand loupe and focus the image of the sun on the paper.  It's going to burn!

That's the difference between focal and afocal.

Like Henry, I'm now out.

 

John

What is an afocal system?

Here is one explanation:

https://en.wikipedia...i/Afocal_system

"produces no net convergence or divergence of the beam,"

parallel in, parallel out.  Always, apparently.

No matter what the distance of the target?

 

I shall concentrate on this seemingly always afocal system...that 

    will be a more efficient use of time than careful work denied.

 

More later.

 

------------------------

"Now hold a sheet of paper behind the eyepiece at the exit pupil.

Nothing's going to happen."

 

Seems like cheating to me. not allowing the binoculars to vary position

   to focus the Sun.  It is, isn't it?  How can you see convergance or divergance

   if not allowed to vary distance to paper?   A proper afocal system

   would show the same spot at 1,2,5,10 inches....

 

And....a binocular tuned to be afocal with the Sun couldn't possibly

    be afocal with something 20 feet away, not way out in space.

    What would be the purpose of a focuser wheel?

---------------------

 

There may be some experiments more suited...more later.



#34 MartinPond

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Posted 21 May 2021 - 10:05 PM

Aha....

   what happens when you focus the Sun through binoculars?

 

  Shine on paper through binoculars?

 

Well here it is:

 

https://www.timeandd...ed on the paper.

 

Of course:   you project an image of the Sun.

 

It does not burn because the angular size of the sun on the screen

    is much bigger than the angular size you see in the sky.

 

We call that "angular magnification".  It's what binoculars and telescopes do.

 

BUT:

Is it afocal?

Well it forms a real image, not a virtual one...(this is not afocal)

...and you need to adjust the focuser to make the image on the screen sharp..

...so that image of the sun is only at its sharpest when the light converges

   to make the image.

Converges:   that it is definitely not afocal.

 

So binoculars are not magically afocal all the time.

When you aren't focusing your corrected eyes, at the rated eye relief,

   on the stars......they are not afocal at all.

 

Sure, you can focus on a tree 45 feet away and see a nice virtual image

   at infinity.   But:  that would be <divergent in> <parallel out>  ....definitely not afocal,

    which is <parallel in> <parallel out>, by definition.  

 

 

 

"Does not burn" is a bad test for "afocal".


Edited by MartinPond, 22 May 2021 - 02:31 AM.


#35 John Russell

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Posted 22 May 2021 - 07:42 AM

A final attempt: With that Wikipedia article you have linked an excellent explanation of an afocal system but still don't seem to have understood it.

An instrument does not cease being afocal if it can be used on objects at finite distances or adjusted for the viewer'eyesight.

The rays from an object at any finite distance diverge slightly towards the objective.

That's only 1,3° when I look at my feet through my binoculars with 1,5 m close-"focus".

If I am far-sighted with a correction of +1 dioptre and view without specs I would adjust the instrument so that the rays from the eyepiece converge to a point 100 cm from the eyepiece. The focus is achieved with my eye on the retina.

In an afocal instrument you are viewing the magnified virtual image of the object. This virtual image is reversed and inverted and has to be rectified with prisms.

On other sites there have been discussions on the correct distance of an object to adjust the dioptre control of a CF binocular.

If you use the same object for both barrels, it just doesn't matter because you always place the virtual image in the same plane, irrespective of object distance.

 

John


Edited by John Russell, 22 May 2021 - 08:07 AM.


#36 MartinPond

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Posted 22 May 2021 - 09:35 AM

"

An instrument does not cease being afocal if it can be used

on objects at finite distances or adjusted for the viewer'eyesight.

"

Yes it does cease to be afocal...it violates the definition...no more parallel-in, parallel-out.

The rays from the tree at 45 feet are diverging.

 

"

The rays from an object at any finite distance diverge slightly towards the objective.

That's only 1,3° when I look at my feet through my binoculars with 1,5 m close-"focus".

"

 

1.3 degrees is massive, especially for a 50mm objective with a 200mm FL.

More to the point,  in fact , it displaces

   the focal plane PAST the focal length of the objective.

  And that is exactly what restricts the in-focus-no-adjustment range.

   If you don't touch the focuser...you are.....out of focus!  That is a plain truth.

 

"

I f I am far-sighted with a correction of +1 dioptre and view without specs

  I would adjust the instrument so that the rays from the eyepiece converge

 to a point 100 cm from the eyepiece. The focus is achieved with my eye on the retina.

"

So far so good.....If you are focusing for a very far object, that is.

 The afocal instrument includes a bit of the eye. I am cool with that.

If your target is at 45 ft and you do not focus.....not afocal at all.

 

 

"

In an afocal instrument you are viewing the magnified virtual image of the object.

This virtual image is reversed and inverted and has to be rectified with prisms.

"

In an instrument close to the target you are also looking at a

    virtual image is reversed and inverted that has to be rectified with prisms.

The rays from your nearby object are divergent.

The system is not afocal.

 

 

 

Actually, I don't care much about the afocal incantation,

   except that it is used to avoid  admitting that looking at a nearby object

   displaces the focal plane to beyond the focal length of the objective.

  

 

1/(outer) +1/(innerdistance) = 1/FL(of objective)

 

In baby-steps:

 

1/i  =  1/FL - 1/o

          1/200 -  1/13716            (13716 is 45 ft in millimeters)

1/i  =   0.005  -   0.00007291

   i =    202.96 mm   <------ i is the inner focal distance....and it  is  NOT 200mm 

                                         ...it has walked 3mm onto the FL of the eyepiece

 

 

Are you denying that looking at a nearby object

   displaces the focal plane to beyond the focal length of the objective?

  That has not been answered for days now...


Edited by MartinPond, 22 May 2021 - 09:58 AM.


#37 Henry Link

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Posted 22 May 2021 - 11:12 AM

I'll just add that the link about eyepiece projection Martin provided has been misinterpreted. What happens in eyepiece projection is that the exit pupil acts just like the entrance pupil of a Camera obscura, converting the afocal light that emerges from the eyepiece to focal light that can form an image at some distance behind the exit pupil. The light in front of the exit pupil, between it and the eyepiece (the eye relief distance) is afocal.

 

The eye does the same thing with the afocal light that falls on its pupil, whether that light comes directly from the world or from the eyepiece of a binocular. The eye can't do anything with focal light that falls directly its the pupil. It can only function by applying refraction to afocal light, thus converting it to the focal light that forms the image on the retina.


Edited by Henry Link, 22 May 2021 - 01:12 PM.


#38 ECP M42

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Posted 22 May 2021 - 01:50 PM

Part of the confusion on the subject of binocular DOF seems to come from ...

Hi Henry, flowerred.gif I'm happy to see you again and
I see that here too another nice "circle of confusion" has been created!

 

Poor Martin, is right when he talks about the object displaced by two or three mm with respect to the focus of the objective referred to infinity. Why don't you admit it to him? Do it for him, he has every right. 

 

In my opinion we should all keep in mind that reality always remains the same, equal to itself, regardless of how you or someone else describe it. Thus, it is better to stick to reality. 

 

And speaking of reality, I'm going to ask you at least one question, to try to understand what you see as reality, because it seemed to me that you have toyed with some "fantastic mathematics", which seems to deviate from the reality of optics. We know that 16 years is a long time and that fatigue is always at the door, but try to make a last effort while you are here. bow.gif

 

The question is always the same waytogo.gif :

 

Why can DOF change as a function of the iris, but not as a function of the masked aperture?

 

Henry, the question is quite easy, we talk about the focal-ratio, but if you need me to explain it to you in detail I will do it, God forbid.


Edited by ECP M42, 22 May 2021 - 01:52 PM.

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#39 Henry Link

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Posted 22 May 2021 - 04:48 PM

Hi Henry,

 

I haven't responded to most of Martin's posts because I don't want to be sucked down a rabbit hole into the irrelevant subjects of depth of focus and depth of field in focal optics, like binocular objectives and camera lenses. 

 

The DOF of a binocular as experienced by an observer changes only when the focal ratio of the observer's eye changes. That can happen at the eye's iris as it dilates and shrinks, but only as long as the eye's entrance pupil remains  smaller than the binocular's exit pupil. It can also happen if a mask is placed over the objective lens, but only if the resulting masked aperture creates an exit pupil that is smaller than the eye's entrance pupil. As I mentioned before the decrease in apparent DOF that occurs from an increase in magnification is not a true change in defocus, as defined by the number of diffraction rings, but simply the magnification of the same number of rings. 

 

The principles involved here are not as complex as these two recent threads suggest. When something is fundamentally misunderstood it takes a load of complex arguments to try to make make that misunderstanding seem right. Consider poor Ptolemy. ;)

 

Henry



#40 MartinPond

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Posted 22 May 2021 - 06:54 PM

"

In my opinion we should all keep in mind that reality always remains the same, equal to itself, regardless of how you or someone else describe it. Thus, it is better to stick to reality.

"

 

Observed reality? Yes!  That is how Science keeps from turning into foloklore.

It is always equal to itself, not bending as minds bend....it is what is.

But beliefs are stretched to try and cover the unexpected,....and they break.

 

I believed that power was the dominant range-eater.

Experiments proved me wrong, other that that little pip of length of the

 EP fl...that produces a shadow of effect....not enough at all.

 

I myself believed that f-ratio alone altered range, on a few occaisions....

I mean, look at the cameras.

Well, it didn't seem to, at all, dark or light day or time of day.

Then I pushed it, and it suddenly made a difference, albeit at extreme f-ratios.

Useless? Not really.   Barlowing an eyepiece on a long barrel is not

 uncommon.   A dimmer image with more perfect edges at high power

 is just what you want for the Moon and some planetary. 

 

Reality is not simple....but reality will not be ignored.

Reality will crush doctrines and folklore that grow without testing.

And reality needs to be real: real conditions the inference is needed for,

    real object, not artificial stars.  Not just what happens to one point

    but how points actually combine to make a woodpecker.

 

I went back to first principles, as Marcus Aurelius would say:

   "Of each thing ask, what is it in itself; what is its nature?"

 

Well...it....first and foremost..It is a LENS. 

Then  another lens.

   What is the nature of each?

  What is its nature? 

Of course, I forget in the mumbo-jumbo:

  Its nature is:  THE LENS EQUATION Book of Lens Optics, Chap.1

   Anything else is a smaller  2nd-order effect.

 

So...I coded it up, programmed it

  so as to try different combinations easily.

And lo and behold: it predicted  the range for common binoculars

 almost perfectly.

And then I tried odd combinations...and then I realized:

    length was the key, more than other factors, clearly.

 

But why did almost everyone say power?

Then I saw: most popular binocular powers are achieved by 

    scaling the power, aperture and the focal length simultaneously.

  Makes sense....maintain brightness, avoid tiny EPs and eye reliefs.

 That fit the hundreds of eyepieces I have pillaged from binoculars.

  The 6x30 , 7x35 , 8x40 , 10x50 , 12x60 .....most have the same size eyepiece.

 

And why all the talk about the amazing changes brought about by the eye's iris?

   Well, I almost never noticed that, through bright and dim, theough there is that

    ultra-small mask result...but guess what?

   I never look through binocs that way in the daytime.   And at night....to the sky?

     It doesn't matter.

    So the eye's sizes seemed mostly like a long string of red herring..

     ..if one bothers to experiment with real targets.

 

And then, someone else would believe, without careful testing and observation, that power

   was everything.  And that became folklore.  And that developed a strange Canon

   and special things to measure that even avoided images.  And then it hardened

   into doctrine.   This is when a single concept happens.

    People need one answer..just one.

    And then things are said to be this magic word, like "afocal", in cases where they

     are obviously not at all.  Hints of religion. 

    Like water is wine is blood, crackers are flesh, meat.

 

But reality goes on, and real experience and evidence chafes, and the defense of doctrine

   never ends, because the wrong turn is never fixed, because "the turn was never wrong"

   says the driver. And the driver goes round and round (just as he said), telling people

   in strange destinations they don't live in this right town, they are mistaken about where they are.

 

I am happy by myself, but I had to abandon a lot of misconception.

   I have tools that predict accurately and I know how

  to navigate my resources.  If I admit to certain exceptions, trends, and how they really

  apply, like how aperture really creeps into this.....I will discover new and cool things to try and do.

 

I am an explorer, and a Physicist trained with a few Optics courses.  I am not a priest.

Thank you Karl Popper.

Thank you Marcus Aurelius (and Hannibal Lecter, heh).

And for the Sociology I am learning in this, (quite by surprise), Thanks to 

Galileo, and Henri Bergson. 

 Columbus set out to find a short-cut to India: he learned a few surprises.

  You never know what you'll find in the world of souls.

   They alter even ordinary things.


Edited by MartinPond, 22 May 2021 - 07:26 PM.

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#41 MartinPond

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Posted 22 May 2021 - 07:35 PM

.....

.....

The eye can't do anything with focal light that falls directly its the pupil. It can only function by applying refraction to afocal light, thus converting it to the focal light that forms the image on the retina.

....

You say the eye can only function on afocal light?

 

The eye does its best to make light focal, before it falls on the pupil...Good Lord.

"Focal light" does not drift through the cornea unaltered, yes?  Strange.

 

The eye functions by focusing light on the retina,

    from real and virtual images  and actual object....all of that!

     At various distances.

Remember the accomodation you rail on about?  Where has it gone? 

 

If the eye only worked on afocal light as you say,

   everything would be blurry under 100 feet (close enough  to afocal). or more.

   Targets at 70, 50, 20, 30, 10 feet? All not afocal.

 

 

You have a very peculiar concept of what afocal is.

You are even describing light itself as afocal, when that is not a property

   of light, it is a property of a lens system.

 

Maybe you are talking about parallel, or collimated light?

 

Calling light "afocal light"  is bordering on religion.

As opposed to magnifying light?  Who knows.

There is also no "focal light" either. Diverging or converging light.


Edited by MartinPond, 22 May 2021 - 07:39 PM.


#42 j.gardavsky

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Posted 23 May 2021 - 04:00 AM

Hi Henry,...

 

The question is always the same waytogo.gif :

 

Why can DOF change as a function of the iris, but not as a function of the masked aperture?

 

Henry, the question is quite easy, we talk about the focal-ratio, but if you need me to explain it to you in detail I will do it,

God forbid.

These are the right words,

and especially during the Pentecost Holidays,

 

JG
 


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#43 ECP M42

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Posted 23 May 2021 - 10:58 AM

Henry, I agree with you not to fall down the rabbit hole, but answer at least one question. I don't want to sound too insistent, but you haven't answered my question. You keep reading the same verse of the gospel over and over, but you avoid my question in every way. smirk.gif

 

When something is fundamentally misunderstood it takes a load of complex arguments to try to make make that misunderstanding seem right. 

 

Another thing. The iris cannot correct the aberrations of the binoculars. This is another very important point that you should re-discuss. I've always heard that music out of tune and now I've seen the bell. Today I took back my usual 7x50 and 20mm masks. I placed it on the tripod, aiming at 10m (30ft) and looking for various details with shadows and reflections from the Sun. I focused both channels perfectly, using an 8x30 as a multiplier. I masked a channel and rechecked the images. With the naked eye (7x) we see that the masked channel is better than the other, even if the DOF has changed little (we are at 30ft). But with the 8x30 multiplier, you can see very well how the aberrations of the 7x50 have almost disappeared, in the masked channel.

 

Yet my iris in that light is closed to at least 1.8mm, but it hasn't really canceled the aberrations of the 7x50. I don't know if that can tell you anything, but it should at least make you think.



#44 KennyJ

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Posted 23 May 2021 - 12:15 PM

ECP M42,

 

Just to help me to understand your last paragraph, how when viewing through the masked to 20mm channel, via a 8x30 multiplier, your eye pupil is constricted to just 1.8mm?



#45 ECP M42

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Posted 23 May 2021 - 01:31 PM

I don't know, Kenny. Maybe the iris opens to 2.5mm or maybe he doesn't have the time, but that's not the point (what's on your mind?).

 

 

The 8x multiplier produces an exit pupil which is however narrower than 1.8mm: theoretically 0.9mm for the 50mm channel and 0.36mm for the 20mm channel.

 

Therefore, the effects of the "pseudo-cancellations" of a 0.9mm iris, should already be present (evident) in the 56x50 channel, but they are not seen. The multiplier gives the same result in both channels, but in the masked one (the only variant in the test) you can admire the work of the mask, on aberrations and on the reduction of image points (diffraction figure). 

 

Try it yourself, Kenny.


Edited by ECP M42, 23 May 2021 - 01:32 PM.


#46 MartinPond

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Posted 23 May 2021 - 02:49 PM

Trying things out is a good idea.

Trying different things connotes 'generalizability'. 

 

I had an idea, to make examples that would apply to

     real observations, but simple. 

     The binoculars remain the same, the light changes.

 

Test #1:

----in a very well-lit dining room (6 100w equiv white LED lights),

      I check with my eye, just the eye, with no (-4D) glasses:

       (glasses off simply makes the range closer, easier to measure)

     *With no filter, the 'doesn't look blurry' range:   6 --- 10 inches

     *With a 12% transmission Moon filter:              4 --- 11 inches

  

    So far, so good: only 1 lens, in the eye, and it is acting a bit like a camera.

     I can't come up with any alternate explanation to the "changing iris" theory.

     ...sold.

 

 

Test #2:

  ----in a very well-lit dining room (6 100w equiv white LED lights),

       looking through a 6x30 bincular barreI, with no (-4D) glasses,

       focuser all the way out.  Near and far points (before 'fuzzy')

       With no Moon filter:          10 -- 11 ft.

       With the 12% Moon filter:  10 -- almost 12 ft.

               The effect is....waning.

 

 

                 (the day outside is slightly bright, overcast)

Test #3:    same 6x30 binoculars, a 12%filtered barrel and a non-filtered barrel,

                looking out the window, I focus for infinity and find nearest distance before 'fuzzy'

                 Range, no filter on:     infinity to 45 feet

                 Range, 12% filter on:  infinity to 43 feet    

 

 

So:

---The eye, by itself, seems to act like a camera.

----The 6x30 binocular plus eye close in and indoors is not much like a camera.

----The iris/camera effect is almost completely  gone looking out the window.

 

It seems, through observation,

     that the eye acts like a camera only without the binocular.


Edited by MartinPond, 23 May 2021 - 09:20 PM.


#47 MartinPond

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Posted 23 May 2021 - 02:53 PM

ECP M42:

"

 but in the masked one (the only variant in the test) you can admire the work of the mask, on aberrations and on the reduction of image points (diffraction figure).

"

 

This is why I still like to 35mm mask the 7x50s. 

The range doesn't change, but the quality is enhanced. 

I would add: stunning contrast.  The daylight world is a lot worse for

   stray light. Add more contrast to less aberrations, and

    the results are quite nice.


Edited by MartinPond, 23 May 2021 - 02:55 PM.

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#48 KennyJ

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Posted 23 May 2021 - 06:17 PM

Sorry I’m so late responding.

 

It’s after midnight now and the first chance I’ve had following a day with many other things on my mind apart from what prompted me to ask why an effective 0.36mm exit pupil would cause the eye pupil to become so tiny.

 

In my experiences, only excessive brightness has had that effect, with eye pupils normally reacting to relative darkness by natural dilation.

 

It seemed a very simple expression of surprise on my part.

 

I’ve probably spent more time playing around with aperture masks over the past 20 years or so than most other binocular users have, but must admit to never having thought much about, let alone discovered a method of accurately measuring my eye pupil sizes during the precise moments of my eyes being scrunched into the oculars.

 

Kenny



#49 Henry Link

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Posted 23 May 2021 - 09:40 PM

"Henry, I agree with you not to fall down the rabbit hole, but answer at least one question. I don't want to sound too insistent, but you haven't answered my question. You keep reading the same verse of the gospel over and over, but you avoid my question in every way. smirk.gif"

 

I think I've lost track of which question you mean.

 

"Another thing. The iris cannot correct the aberrations of the binoculars. This is another very important point that you should re-discuss." 

 

I'll post a simple test for this tomorrow. No time to write it up tonight



#50 MartinPond

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Posted 23 May 2021 - 09:41 PM

I changed the 2-stage-lens program

   so it will accept the focal length of the objective directly

   (instead of assuming FL = 4 *diam for binoculars).

 

I have a nice Keplerian spyglass with an achromat

    and a fine Plossl EP. It makes you woozy to hold the

    fully-inverted and reversed image steady, but the clarity is amazing.

Anyway, it is longer than a 30mm binocular would be.

 

When I put an objective FL of 186mm (F6) and a power of 10 into the

    2-stage lens program, I come up with an infinity-focused near range

    distance of:  122 feet.

    Testing this out the window, I come up with an observed near-edge of range

      of :   130 ft. (the object is at 130, couldn't pick exact distances to trunks).

 

So.....the range modeling looks very good at F6 and various powers of F4...still great. 

I can add other long-barrel range tests now..


Edited by MartinPond, 23 May 2021 - 09:43 PM.

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