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A little help/advice

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#26 KennyJ

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Posted 29 February 2004 - 04:14 AM

Even though it has become apparant ( if hadn't already done so previously ) that this unit needs to be sent back to Kevin and replaced ,the problems seem so rare and so difficult to explain away that it could almost be worth purchasing this unit on behalf of the CN "Lab test" section for a kind of"post -mortem" examination to verify the precise symptoms of the ailments and reveal the true nature of the faults.

Of course if these problems can be corrected the binos could always be re -sold to a CN member to cover most of the the initial outlay.

Anyone agree ?

Regards --Kenny.

#27 sftonkin

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Posted 29 February 2004 - 04:44 AM

(...)it could almost be worth purchasing this unit on behalf of the CN "Lab test" section for a kind of"post -mortem" examination to verify the precise symptoms of the ailments and reveal the true nature of the faults.
[...]
Anyone agree ?


To the extent that I am intrigued by the nature of the fault and would dearly love to know what it is, I agree, but I know insufficient about the procedures around the CN test lab to know whether this sort of thing is a starter.

#28 EdZ

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Posted 29 February 2004 - 10:41 AM

I think, as Stephen suggests, there may be multiple aberations and one might mask the other making it extremely difficult to tell what is really going on.

If you remember, a few weeks back we had a good thread related to a very unusual aberation seen in this same model, that of radial spikes. I've been using one of these binoculars that has that same radial spikes aberation and having discussions with Kevin about it. Rather than just send it back we already recognized the opportunity to observe and makes notes on this aberation and then compare notes after we both have the chance to see the same aberation. So We may already be doing what Kenny suggests.

It is a very unusual appearance in the image. Also, it appears to be an anomoly. Kevin had to search through a dozen pairs to find one that showed the aberation.

Chris seems to have identified potential astigmatism. While it is not uncommon for binoculars to show minor astigmatism, if it interferes with achieving precise focus, it is too much. I've been reading Suiter on astigmatism. His comments would indicate that, first some minor astigmastism is almost always present and second many of the causes of astigmatism can be corrected. One of those causes being collimation. Suiter is not talking about the alignment of two sides of a binocular here, he is referring to the collimation of the mirror or in this case a refractor. So astigmatism in a binoc is not related to the merging of the images at all, but isolated within the optical axis of each barrel. That doesn't mean it's not in the prisms. But if the prisms need to be moved to adjust the light path, then it is likely the center of the objective is not precisely aligned to the center of the optical axis. Whether the objective is not centered or tilted is unidentified. We're talking possibly only fractions of a mm here, but with the fast f# of binocs it shows up quicker.

I have tested a number of binoculars and looked closely for any appearance in the diffraction image in all of them. At powers of 15x or below, separation in the diffraction rings cannot even be seen. At 16x it can barely be noticed. At 20x the first real definition of the diffraction rings begins to appear.

I checked the diffraction image on other binocs. In the 15x70/'03, I got nice round images both inside and outside of focus. I was not able to see clearly defined separated circles in the images, and the outer edge of the image was a little rough, not a perfectly smooth circle, but there was no spiking or spokes visible at any time in the smooth light across the image.

With this model, the 20x80 standards, exhibiting an unusual aberation, this is what I have see in the difraction pattern. The inside of focus difraction ring is unbroken, prominent, with some very faint spokes of light inside the rings. The outer ring is the thickest and brightest. I can clearly see the next two very thin rings in from the outer edge. Three rings seen, then the inner portion is just the rest of the light, too close to detect separate rings. Note my comment that the outer ring has most of the light visible in the rings.

The outside of focus image never forms any separate difraction rings. It is a distorted circular blur right from the start. The radial spikes distort the edges.

As the focused star image is moved towards the edge of the binocular field of view, the focused image becomes a bright point with long thin extentded wings, like a chevron. The point always faces the center. The birds wings always towards the outside. The closer the image is moved to the edge, the larger the wings get to be.

Based on this last note, I thought it might be coma. Coma shows up as a flared image, with the flare towards the outside, but I think coma shows up as a flared wedge. This is like a point with long slightly curved wings, like what you see children draw as birds. This is the closest thing I have found so far to what is being seen in the image.

The following is what Chris described
[First the left tube. When I focused in, the star turned into an oval shape. When focused out, the image turned into the blob I tried to draw, and it extended down and away from the star. When out of focus (in and out) the image looked really grainy - like a rough mirror.

Now when I went over to the right tube and did the same there, I found something really weird - vertical lines! I have NO knowledge about optics whatsoever, and I've never seen or heard about this before. When the image was focused out, the vertical lines were big at the top and then they got thinner. When it was focused in, the lines where the same size (On the sketch they look really thick. This is just how I made them (Rough sketch remember ) They were actually quite thin) and this was also the only time I saw faint diffraction rings.]

What these comments have in common with what I see and read.

I do not see any astigmatism in my sample, but it does seem to be identified here. Chris identifies miscollimation and this might be the cause of the astigmatism.

It's possible what Chris saw as a slightly out of shaped image inside of focus may have been caused by not perfectly centering the target before checking out of focus images. That might relate to what I saw as potential coma.

I also see a difraction pattern ONLY inside of focus.
When focused out, the pattern turns into an undefined distorted circular blur right from the start. Radial spikes break the outer edge of the image.

I don't see the lines Chris refers to, but there are those radial spikes. I have noted at times they do not appear completely around the image. Is it possible this is related to coma?

Stephen, your knowledge of optics may be of great help here in helping to identify these aberations. Any comments?

edz

It occured to me that Chris has already shown us the location of the cutoff in the exit pupil in his left barrel. Doesn't it match with the truncated image of the difraction pattern also from the left barrel? One of the primary tenets of observing the difraction pattern for aberations is you must be observing in collimated (not barrel to barrel, but collimated like a scope, evenly centered difraction rings) optics. Otherwise the out of collimation difraction image is adding an unnecessary aberation you need to look through.

edz










#29 sftonkin

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Posted 29 February 2004 - 12:12 PM

EdZ wrote:

>If you remember, a few weeks back we had a good thread related to a
>very unusual aberation seen in this same model, that of radial spikes.

Did you find the cause? Surface roughness?


Re astigmatism:
> Whether the objective is not centered or tilted is unidentified. We're
>talking possibly only fractions of a mm here, but with the fast f# of binocs
>it shows up quicker.

Indeed. it only takes a couple of arcminutes of misalignment at f/5 to throw
it up!

One thing I suggested in my previous was that astigmatism would likely be
masked by coma if it was the eyepiece or objective responsible for it. I'm
too used to playing with reflectors and cats! With refractors that is not
necessarily the case and astigmatism can show over coma.


>Based on this last note, I thought it might be coma. Coma shows up as
>a flared image, with the flare towards the outside, but I think coma shows
>up as a flared wedge. This is like a point with long slightly curved wings,
>like what you see children draw as birds.

To my eye coma always reminds me of a shuttlecock (as used in
badminton).


I've also been thinking some more about that left hand tube. It reminds me
of the effect of tube currents. Chris: Was there any reason for that side to
have been warmer than the other? I take it the effect is there every time
you use them?


#30 Chris_H

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Posted 29 February 2004 - 07:37 PM

Ed, I just did the collimation test on Nu (v) Draco. I make it out to be 4-5 times separation.

Stephen, the lines seem to disappear as I get closer to focus. But seeing that I never reach perfect focus, they might still be there - or even be the source of the problem for all I know. I’m as new to this as you are. And no, there should be no reason for the left side to be warmer then the right side.

OK, finally got some good skies. The binocular was taken from 20 C out to -5 C and was left there for 10 minutes. I used Jupiter this time and I made two new sketches. These are as close to the real thing as I can make them.

Posted Image

Posted Image

Hopefully I will hear from Kevin one of these days :)

#31 EdZ

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Posted 29 February 2004 - 10:34 PM

Stephen,
>If you remember, a few weeks back we had a good thread related to a
>very unusual aberation seen in this same model, that of radial spikes.

>>Did you find the cause? Surface roughness?

Although I have clearly identified the symptom, I have not identified the cause. Suiter doesn't even talk about radial spikes. One book does, but only to the extent that it mentions if you see more than a few, send it back.

I was think it might be due to gross over or undercorrection. Suiter does mention there are many different ways that this aberation can manifest itself and says he will only deal with one in his photos and description.

I look at that picture above and I just don't get where those lines are coming from. The light in the left image looks sort of like an SCT with a grossly miscollimated mirror where the central light is completely off to one side and no hint of the rings can even be found (as view thru a scope with astigmatism).

The most obvious thing that should be coming out of all this is we have a binocular here with to many potential issues to try to coach someone to fix it.

perplexed,

edz



#32 sftonkin

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Posted 01 March 2004 - 01:49 AM

The most obvious thing that should be coming out of all this is we have a binocular here with to many potential issues to try to coach someone to fix it.


I tend to agree. Instinct tells me that the problem resides in the prisms and I know from bitter experience that they can be remarkably difficult to get right. Now I do understand why it is so expensive to get it done professionally! :grin:

At least as perplexed as you...

#33 KennyJ

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Posted 01 March 2004 - 02:33 AM

Whether the cause is identified or not , I hold my hand up to Chris for some superb ilustrations .

Regards --Kenny.

#34 Chris_H

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Posted 01 March 2004 - 10:43 PM

Well I just got a reply from Kevin and he had never seen this before either, but he is very forthcoming and helpful! I must say he’s a real gentleman.

Btw, I tried to take some photographs through the tubes and though it wasn’t a complete success, you CAN see the lines (The drawing is more accurate).

Chris

#35 sftonkin

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Posted 01 March 2004 - 11:02 PM

Meeeowww!

(aka I spy very misaligned prisms)

#36 edcannon

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Posted 02 March 2004 - 12:09 AM

Chris,

I just read the thread, maybe too fast, and wonder if you turned them upside down, just to make sure it's nothing about your eyes. I don't think it is, but I think that you did leave that a little bit in question. I also know nothing about optics beyond what I've read here and other lists AND have managed to absorb.

I wonder if looking into the wrong end would show anything at all that could be a clue to the lines or anything else.

Ed Cannon - Austin, Texas, USA


#37 EdZ

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Posted 02 March 2004 - 07:07 AM

Chris,

could you please focus your binoculars out a window and stand back a bit and take of picture of the exit pupils? I already suspect what I will see, but I'd like to see it.

edz

#38 EdZ

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Posted 02 March 2004 - 10:20 AM

I think as Stephen exclaims, things are just way out of alignment. We're not talking here about images not merged, this is refractor optical axis miscollimation. Remember, you've got two refractors joined together.

I think those lines you are seeing are the edges of the diffraction rings. The Airy pattern is not even present. If you look closely at the "lines", they are not horizontal at all, but clearly show up as curved.

If you had a good SCT (easiest type of scope to see diffraction pattern) and threw the diffraction pattern out of collimation to the point where the Airy disk was no longer anywhere even visible with a few uunbroken rings, I mean really threw it out, I think it would be similar to what you are seeing here. My guess is the diffraction pattern is SOOOO off center that the edges of the diffraction rings are beginning to appear as just very long arcs (curved lines), with not even much more than a small hint of being the outside edge of a circular pattern whose center is very far off in the distance.

Proper collimation in a refractor is first achieved by working with the objective lens. In a binocular, if the objective is as it should be, then very minor adjustments can be made with the prisms to merge the two images.

If the objectives are not collimated, all bets are off, and nearly everything you do with the prisms to merge the images will have some small undesireable affect on the diffraction pattern and the exit pupil. Everything I'm seeing here seems to add up. To get the images even close, not completely merged, the prisms may have been tilted to such an extent that the diffraction image appears elongated. Astigmatism seems to be present, it's cause uncertain, but possibly due to off axis light path and a tilted prism.

I think you've already shown it way back in the beginning, but I'm waiting to see the real image of the exit pupils.

edz

#39 Chris_H

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Posted 02 March 2004 - 11:05 AM

And here they are :) They are bad since I had to rush it. If they aren't useful, I will take new ones tomorrow.

They all look pretty round to me, but I’m sure your super sharp eyes can pick out something ;)

Chris

#40 EdZ

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Posted 02 March 2004 - 02:09 PM

Sorry, that's not going to do it.

How did you get such large photos of a distorted diffraction image? Can you show me some images like that? I want to see the shape of the exit pupil. I'm not seeing much in these. Although almost actual size, difficult to see. they do appear to be slighly out of round, but photo and internet resolution makes it difficult to see the edges.

the right one's defintitely out elongated from 2 to 7 oclock.

The left one seems out slightly elongated from 10 to 4 oclock.

Don't need photos from the objective end. cannot assess the ep from that end. Best one's so far are #1 and #4

edz

#41 Chris_H

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Posted 02 March 2004 - 05:21 PM

Ah you want them like that...got it. ;)
I just used Orion’s SteadyPix camera mount adapter and hooked it up to the bino with the 2" eyepiece clamp. It fits perfectly over the 20x80's eyepieces.
You will get new pictures tomorrow, Ed.

Chris


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