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MrBill's new APM Apos....

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#26 Mike Harvey

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Posted 05 June 2014 - 01:10 PM

More troublesome is the off axis ghost images of nearby bright stars which sweep through the field diagonally in the reverse direction of the sweep.

Not a dealbreaker in itself but plenty annoying, especially given the cost of these.

Just poor design...strange nobody else mentioned this.

:tonofbricks:


Hi Mr. Bill... I certainly WOULD have mentioned it - but I'm not seeing it!
(Same setup w/ Docter eyepieces).
Might this be isolated to your sample, or to a limited number of examples?

I HAVE, however, noticed the "finernail" effect from time to time. It seems to be related to eye placement. If I stay right on axis I've never noticed it.
Only seen it a few times when I'm moving my eye around the eyepiece and there is a fairly bright object being observed or right at the edge of the field.

#27 Mr. Bill

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Posted 05 June 2014 - 01:17 PM


More troublesome is the off axis ghost images of nearby bright stars which sweep through the field diagonally in the reverse direction of the sweep.

Not a dealbreaker in itself but plenty annoying, especially given the cost of these.

Just poor design...strange nobody else mentioned this.

:tonofbricks:


Hi Mr. Bill... I certainly WOULD have mentioned it - but I'm not seeing it!
(Same setup w/ Docter eyepieces).
Might this be isolated to your sample, or to a limited number of examples?

I HAVE, however, noticed the "finernail" effect from time to time. It seems to be related to eye placement. If I stay right on axis I've never noticed it.
Only seen it a few times when I'm moving my eye around the eyepiece and there is a fairly bright object being observed or right at the edge of the field.


Try observing the moon off axis....bet you see the "ghost" moons. Hard to believe you have different optics.

This is obviously a design issue, not sample variablity.

I have the same issue with my Fuji 10x50s, but am willing to put up with it because they are outstanding in all other respects.

I sent back Vixen BT80s because of a real extreme problem with off axis light bleed (and 70mm effective aperture). See my past thread.

You would not notice the star ghosts unless you are sweeping. This is what I do to detect very low contrast edges on dark nebulae.

#28 Mr. Bill

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Posted 05 June 2014 - 01:44 PM


The bad news...

The fingernails in the exit pupil shown above manifest themselves as off axis light leakage.

5 degrees either side of the crescent moon showed distinct reversed images of the moon, the right barrel when looking right and the left barrel looking left.

More troublesome is the off axis ghost images of nearby bright stars which sweep through the field diagonally in the reverse direction of the sweep.


I don't recall having any problem with ghost images. Is this observed only with the 24 Pan, or all EPs you've tried?

I'll have to look again more closely with mine, but I think I would find what you describe distracting as well which leads me to believe I've not seen the same thing. In fact on a night with the Moon with both the Semi and APO models side-by-side, I thought the APOs did a much better job of suppressing off-axis moonlight.

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I just checked exit pupils on 24 Pans, 19 Pans, 14 Denks, and 12.5 Docters. The prominence of the fingernails is definitely related to the size of the fieldstop. This is still a design deficiency....should be able to use full prism rear aperture without this being an issue.

Another reason to buy the Docters. :grin:

Look down the barrels with the ep removed and you'll see the fingernail slivers around the on axis view.

What eyepiece are you using?

#29 GamesForOne

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Posted 05 June 2014 - 02:06 PM

I just checked exit pupils on 24 Pans, 19 Pans, 14 Denks, and 12.5 Docters. The prominence of the fingernails is definitely related to the size of the fieldstop. This is still a design deficiency....should be able to use full prism rear aperture without this being an issue.
[...]
Look down the barrels with the ep removed and you'll see the fingernail slivers around the on axis view.

What eyepiece are you using?


I primarily use Pentax 10XW and 20XW pairs. I also have pairs of WO 20mm SWAN and 24mm TeleVue Widefield with the rubber eyecups.

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#30 Mr. Bill

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Posted 05 June 2014 - 03:03 PM

You see this easily with the 24mm Pans (if you don't with 24mm Widefields it's because they have smaller fieldstop)....especially since the fieldstop is larger than the prism rear aperture.

Easily seen in daylight...in fact, good way to check how much each ep set shows light leakage. Just move eye off axis around the on axis exit pupil.

#31 Westseen

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Posted 05 June 2014 - 09:27 PM

How is the collimation? Have to checked at higher power (>50x) ?

#32 GlennLeDrew

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Posted 05 June 2014 - 10:21 PM

These light-leaking 'fingernail' reflections lie essenttially in the plane of the exit pupil (actually a bit fartber out than the e.p. due to its origin in a prism which is closer to the eyepiece than the objective). If your iris is larger than the exit pupil, or you otherwise let the iris drift laterally so as to admit this light leak, you will see its contribution superimposed with the primary image.

Can the origin be identified; is it created by the Schmidt or the rhomboid prism? Adjust the IPD to see if the 'fingernail' rotates as well, or instead remains fixed with respect to the body.

#33 RichD

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Posted 06 June 2014 - 03:10 AM

Ah, the dreaded fingernail phenomenon again.

I remember not seeing this in the Fuji 10x50 FMT until you pointed it out Bill - i'm not a sweeper so I had to use that method to really see it. I'd bet the guys above who haven't seen it yet are also not "sweepers".

Once you've noticed it there's no missing it. It doesn't bother me in the fujis as they are so good and I tend to view static fields, but you are right to say it's an annoyance and you might not expect to see it on a premium instrument.

I'm left thinking that as we have two premium instruments here that show it, that it must be a costly problem to rectify as these binos are otherwise fundamentally sound and at the higher end of the market.

#34 Mr. Bill

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Posted 06 June 2014 - 10:04 AM

In a previous discussion on this, I believe Glenn said that this problem could be easily fixed by grooving and blackening the prism edges.

If it's that simple... :shrug:

#35 Mr. Bill

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Posted 06 June 2014 - 10:07 AM

How is the collimation? Have to checked at higher power (>50x) ?


Only to 44x...12.5mm Docters. May invest in a pair of 10mm Delos to give 55x...about as high a power as I care to use.

:cool:

#36 GamesForOne

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Posted 06 June 2014 - 10:22 AM

How is the collimation? Have to checked at higher power (>50x) ?


Only to 44x...12.5mm Docters. May invest in a pair of 10mm Delos to give 55x...about as high a power as I care to use.

:cool:


Ah geez. That is wimpy power. :kitty: Should be no problem.

When you defocus one side are the images coincident, as in exactly centered with each other as you suggested I check mine?

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#37 Mr. Bill

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Posted 06 June 2014 - 10:29 AM

Doesn't need to be exactly centered; if superimposed on small disc, good enough.

I find I can make minute adjustments by rotating one of the eps and relocking. Markus suggests that most eyepieces have a small amount of runout in optics which, of course, will be more noticeable at high powers.

#38 Mr. Bill

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Posted 06 June 2014 - 10:30 AM

Perfect fit in carrier bag....carry on legal.

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#39 Mr. Bill

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Posted 06 June 2014 - 10:35 AM

Closeup showing mounting arm "borrowed" from UA P-mount. This really gives solid support even at high powers. Uses dovetail clamping system for quick removal.

Will still use Manfrotto 375/501 combo when traveling.

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#40 Mr. Bill

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Posted 06 June 2014 - 10:37 AM

Another...note hash mark to return quickly to IPD setting. Handy if more than myself is viewing.

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#41 Rich V.

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Posted 06 June 2014 - 11:01 AM

Bill, have you popped a short focal length eyepiece into either side of these binos to do a star test?

I'd like to know if these APMs put up an Airy disk like a refractor telescope would. My experience with the other BTs is that stars are blobby looking at higher mags (60x-75x and above) due to SA and who knows what other aberrations that prevent fine focus. I've never seen a star through a BT that comes close to what is seen in a good refractor; exact focus is always a bit ambiguous. I figured it was because of a less stringent objective lens figure compounded by a complicated prism design.

Can I assume that the apos can focus stars to finer "points" than our other BTs do? Of course this matters less at lower mags but even then, fainter stars should be resolved.

Rich

#42 Mr. Bill

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Posted 06 June 2014 - 11:05 AM

Rich...unfortunately, I don't own any eps less than 10mm and don't have a decent Barlow.

Leave that for you to do at GSSP.... :cool:

What I will say is that optics are good enough to notice ep defects like the field curvature in my 19mm Pans.

The 24mm Pans, 14mm Denks and 12.5mm Docter are all pinpoint stars to the fieldstop in all quadrants.

Will borrow 17.3mm Delos at GSSP from TV rep to see if these reach focus. My measurements say yes but it's real close. These will replace the 19s if all works out.

I've gotten spoiled already with pinpoint stars acress the entire fov. :grin:

#43 GamesForOne

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Posted 06 June 2014 - 11:13 AM

Bill, have you popped a short focal length eyepiece into either side of these binos to do a star test?

I'd like to know if these APMs put up an Airy disk like a refractor telescope would. My experience with the other BTs is that stars are blobby looking at higher mags (60x-75x and above) due to SA and who knows what other aberrations that prevent fine focus. I've never seen a star through a BT that comes close to what is seen in a good refractor; exact focus is always a bit ambiguous.


Rich, I've done so and yes you see something much closer to the Airy disk like in my TMB APO refractor. With my APO bino the disk seems a little uneven to one side when I get best focus with both eyes -- the first ring is nicely round but its brightness is just a bit uneven, brighter on one side than the other.

The exact appearance could probably be tweeked by slight rotations of the EPs, or whatever, to slightly affect collimation with both eyes. Also, I've not had the best seeing conditions since I've received my sample so it might be better on the best nights.

It isn't perfect like I've seen with my TMB APO refractor, but it is definitely better than I've seen in any other bino I've used.

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#44 Mr. Bill

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Posted 06 June 2014 - 12:31 PM

Closeup of mounting bracket...1/4-20 bolts up to bino.

Plenty beefy to support bino's weight without effort.

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#45 Mr. Bill

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Posted 06 June 2014 - 01:23 PM

Rich, I've done so and yes you see something much closer to the Airy disk like in my TMB APO refractor. With my APO bino the disk seems a little uneven to one side when I get best focus with both eyes -- the first ring is nicely round but its brightness is just a bit uneven, brighter on one side than the other.

The exact appearance could probably be tweeked by slight rotations of the EPs, or whatever, to slightly affect collimation with both eyes. Also, I've not had the best seeing conditions since I've received my sample so it might be better on the best nights.

It isn't perfect like I've seen with my TMB APO refractor, but it is definitely better than I've seen in any other bino I've used.

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Michael Mc


How about comparison of one barrel to the other?

Any difference? Might speak to QC as in effect you have two samples.

#46 GlennLeDrew

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Posted 06 June 2014 - 03:45 PM

So... Is it possible to resolve in which prism the 'fingernail' originates?

#47 Mr. Bill

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Posted 06 June 2014 - 03:55 PM

So... Is it possible to resolve in which prism the 'fingernail' originates?


Moves with IPD adjustment.

#48 GlennLeDrew

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Posted 07 June 2014 - 02:04 AM

Then it's the rhomboid prism which is the culprit.

After some thought (I have no direct experience of rhomboids in this application), I wonder if the 'fingernail' reflections could well involve *only* the two 45 degree reflective faces? If so, a reflection-intercepting groove cannot be made to work.

And if one of the 'walls' (more properly, the polished surface wich is either the entrant or exit face) is involved, the limited prism volume may not permit such a groove without also causing a chordal cut in the exit pupil.

I would love to be able to examine this 'in the flesh'...

#49 Mr. Bill

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Posted 07 June 2014 - 09:33 AM

Then it's the rhomboid prism which is the culprit.

After some thought (I have no direct experience of rhomboids in this application), I wonder if the 'fingernail' reflections could well involve *only* the two 45 degree reflective faces? If so, a reflection-intercepting groove cannot be made to work.

And if one of the 'walls' (more properly, the polished surface wich is either the entrant or exit face) is involved, the limited prism volume may not permit such a groove without also causing a chordal cut in the exit pupil.

I would love to be able to examine this 'in the flesh'...


What can I do for you to further investigate, short of disassembly? :question:
And knowing what's going on isn't going to improve the problem unless they are taken apart to correct, if correctable. :foreheadslap:

Well, like my Fuji 10x50s, they are good enough in all other respects to live with the problem.

At least the BinoBox doesn't have these issues with flat mirrors. I'm beginning to think that prisms suck.

#50 Mr. Bill

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Posted 07 June 2014 - 09:39 AM

Glenn, something I haven't mentioned that may be of use to your evaluation....

If I position the off axis bright star just so, the ghost image appears as a short diagonal line, which suggests to me an edge reflection.


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