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APM 100ED v.s. Kowa Highlander

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#26 APM M.Ludes

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Posted 01 May 2011 - 11:04 AM

In mine its just fully ilimited , and thats how many telescopes , even some high end , are build and it shows off axis no dimmer image then on -axis, same as MN Telescopes with tiny illuminated field

#27 Rich V.

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Posted 01 May 2011 - 11:33 AM

Hi, Markus, I can understand how a telescope would show a fully illuminated exit pupil but a binocular design like the Kowa or Miyauchi has quite a long internal prism light path through the Schmidt roof and rhomb prisms to contend with. I don't see how this "prism tunnel" wouldn't cause at least some vignette of off axis light. I've never seen a bino that doesn't. What I see in Tammy's photos is just what would be expected. "Half-vignetted FOV" is one of the optical design parameters of the prism assy. in a binocular.

Are you saying that with an eyepiece in the focuser, your Kowas don't show the "cats eye" shape as viewed along objective edge/baffles that Tammy's photos show?

Rich V

#28 Tamiji Homma

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Posted 01 May 2011 - 11:47 AM

Tamiji,

look again the pictures ...do you see you did not fully line up the edge and baffles ?
If you want to do it right, use a pinhole adapter with a 1,2,3,4,5, mm hole , put it into the eyepiece focusers and then line up again , but perfectly from objective edge over baffles


Hi Markus,

Have you taken a shot yourself? :)

It is kind of difficult to get the line of sight perfectly aligned if you do it yourself without any help.

In order to move scope while you are behind camera finder, you have to be able to reach the scope, i.e.: your hands are within reach of the scope, not that far away.

When you focus to objective lens edge, light circle from eyepiece is completely out of focus, just a big blob. You move the scope until the big blob circle becomes vignetting and then refocus to the light circle, object lens goes completely out of focus due to lack of DoF in camera finder. You use the highest f stop (my case at f/22) to get as much as DoF in the image. I could have done focusing with aperture f/22 to see both lens edge and light circle, but it was too dark to get focus right at f/22.

So when you look through camera finder, light circle and objective lens edge are never be in focus to see they are aligned. You may be able to do that with P&S camera but not with SLR with f/2.8 lens on it. Oh by the way, I had to use LED flashlight on left hand to have enough light to show inside the scope, right hand moving scope, focusing and pushing shutter button :) Flash for my camera is away off axis (no builtin flash), I can't use it to get the shot. I probably need to buy macro flash to get decent shot.

As Rich said, it was the best effort for time I had.

Tammy

#29 Rich V.

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Posted 01 May 2011 - 12:03 PM

A good thing I see in Tammy's photos is that in the Kowas we don't see any chordal cutoff caused by the off axis intrusion of a Schmidt prism edge like we see in the Miyauchis and their clones.

Admittedly, the Miyas and clones are 100mm not 82mm, but the result of prism size vs. objective size vs. focal length in the Kowas looks to be a good combination.

Rich V

#30 rodb

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Posted 01 May 2011 - 02:16 PM

Yes, yes, all well and good. (I try not to glaze over while digesting these tech measurements.:confused: But glad you're doing them.)

But, Tammy, when will you be able to actually star test the Kowa, and make comparisons with the APM? And give us a deliciously detailed report (easy for me to say, ay?).

On the one hand, I'd be thrilled if the Kowa were terrific in comparison, even allowing for the aperture differences, given the superior optics and the smaller form factor, among other advantages.

On the other, I'd be thrilled if it didn't quite measure up. Then I'd save a heap o' $$ in going with the APM or Garrett BT 100s. Well, not that much savings, as I'd want two premium EP sets. (Then there's the Orion BT 100/90*, which might be? in line for a fix of the reduced aperture - not holding my breath - but would, as I mentioned in another thread, save me $$ because of a contact I have there.)

Win-win, I say. :grin:

Regards, Rod

#31 Jawaid I. Abbasi

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Posted 01 May 2011 - 02:31 PM

Rod,
If you are interesting in BT-100 (ST) then EDZ is selling it and if you pickup then it will be $600.00.

PM edz and find out.
Thank you,

#32 APM M.Ludes

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Posted 02 May 2011 - 08:35 AM

Hi Rich

yes of course I see the cats eye, here some pictures I took of my kowa, handheld

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  • 4556736-Kowa-1.jpg


#33 APM M.Ludes

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Posted 02 May 2011 - 08:36 AM

another angle

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  • 4556738-Kowa 2.jpg


#34 APM M.Ludes

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Posted 02 May 2011 - 08:37 AM

and now left and right prism shape

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  • 4556740-Kowa 3.jpg


#35 APM M.Ludes

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Posted 02 May 2011 - 08:38 AM

next

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  • 4556743-Kowa 4.jpg


#36 GamesForOne

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Posted 02 May 2011 - 09:33 AM

Hi Rich

yes of course I see the cats eye, here some pictures I took of my kowa, handheld


Doesn't the cat's eye then indicate off-axis vignetting? The only bino I've seen here that doesn't display off-axis vignetting is the f/7.5 Saturn III Miyas. The trade-off is reduced field of view due to the longer focal length.

Also, why are there no baffles in the APM ED100? To keep costs down?

Thanks,

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Michael Mc

#37 Rich V.

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Posted 02 May 2011 - 09:54 AM

Thanks, Markus, the Kowas are beautiful binoculars even if they have some off axis vignette. No big deal. It's a shame there aren't more eyepiece options, though (also a shame their eyepieces are so expen$ive to begin with!).

Like Miyauchi, Kowa has chosen to put the eyepiece field stop further down inside the focuser barrel and closer to the rear rhomb prism face, preventing the choice of using unmodified telescope eyepieces as an option. Milt Wilcox found that the shoulder of a Nagler eyepiece could be machined down so as to come to focus in the Kowa. You stated above that you also use modified Nagler eyepieces in yours. Could you give some further details as to how this was accomplished?

At least Kowa stayed with the 1-1/4" format rather than the oddball 1.3" and 1.338" formats used by Miyauchi!

Rich V

#38 Andresin150

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Posted 02 May 2011 - 11:31 AM

Tamiji, with what eps did you take the photos? does the percentage of full illumination changes with different eps used? is it possible EDZ?
It looks like at higher F ratio or at higher magnification compared to apperture illumination improves...?

#39 EdZ

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Posted 02 May 2011 - 11:58 AM

does the percentage of full illumination changes with different eps used? is it possible EDZ?



yes very much so.

Percentage of full illumination is measured as
at what position in the field is the fov still fully 100% illuminated?

We can take this same question another way by asking,
what is the percent illumination at various points across the fov.

In general, eyepieces with smaller field stops will be fully illuminated to a greater extent (further out in the fov) than eyepieces with wider field stops. But I think in part it may also have to do with how far the field stop is behind the rear prism aperture.

Here are some examples using original straight thru Oberwerk BT100 (+/-5%)
Celestron Ultima 30mm ep - fs dia 26.3mm - 2.4° fov at 21x - fully illuminated to 35% of fov
Oberwerk stock 24.5mm ep - fs dia 27mm - ~2.5° fov at 25x - fully illuminated to 35% of fov
Meade 4000 18mm SWA - fs dia 19.7mm - 1.8° fov at 34.4x - fully illuminated to 50%
Televue plossl 20 ep - fs dia 17.1mm - 1.6° fov at 31x - fully illuminated to 60%
Oberwerk stock 10mm ep - fs dia 10.5mm - ~1° fov at 62x - fully illuminated to 80% of fov

If we were comparing two eyepieces of the same focal length, the one with the wider Afov would have a lower percentage of the fov fully illuminated. Here we are comparing eyepieces of different focal lengths.


edz

#40 Andresin150

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Posted 02 May 2011 - 12:36 PM

Thanks EDZ.
So, for better near 100% illumination, we'll need shorter focal length eps, longer focal length objectives/system and preferably not too wide (AFOV) eps.
Now that's a good explanation why the Taks perform so good, of course combined with the fluorite apo and perfect mechanic execution.
So, I'll suppose, given equal conditions, the 40x150's should have better percentage of illumination than the 25x150's, I'm I right?

#41 Tamiji Homma

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Posted 02 May 2011 - 12:37 PM

Tamiji, with what eps did you take the photos? does the percentage of full illumination changes with different eps used? is it possible EDZ?
It looks like at higher F ratio or at higher magnification compared to apperture illumination improves...?


It was with 14mm eyepiece (32x, field stop 17.5mm). If I get a chance later today, I will post photo with 9mm eyepiece (field stop 10.5mm).

As Edz already answered, I would expect 9mm eyepiece shows better illumination. We'll see.

Tammy

#42 EdZ

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Posted 02 May 2011 - 12:51 PM

that would be my guess.

Yes this certianly does expalin the Taks.

You might find it interesting to note that the size (dia in degrees) of the central field that is fully illuminated is nearly the same in all cases.

Good binoculars are designed with eyepieces that are wide enough to provide a good field of view, with prisms large enough to provide good area of full illumination, and that do no fall off to poor illumination at the field edge. There are always some tradeoffs in those choices. Some binoculars are down to 20% illumination at the edge, while others only drop off to 50% at the edge.

edz

#43 Rich V.

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Posted 02 May 2011 - 01:12 PM

Here Glenn LeDrew gives an explanation of the effect of eyepiece field stop size as it effects off axis illumination:

From the thread "General comments on angled binos" (3/31/10)

Off axis vignette is most apparent with the largest field stop eyepieces (widest TFOV).

Here's a worksheet from an optical design class that shows how prism size and eyepiece lens size effect off axis vignette. The ray trace diagrams towards the bottom of the page should be helpful even if the math is a bit complicated. The text and diagrams are enough to get the idea, I think. ;)

Arizona.edu Porro Prism Binoculars-Solutions .pdf

Rich V

#44 GlennLeDrew

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Posted 02 May 2011 - 01:30 PM

Rich,
Thanks for posting the link to that very useful PDF! I've seen that stuff before, but it's always useful to periodically remind others of it here; it encapsulates a lot of good info.

Markus,
Regarding your suggestion of the 'pinhole' adapter to use when checking on vignetting. It's important that any such device be placed at the location of the focus. That is, it must be at least close to where the eyepiece field stop would be located. If this item were to be placed either too far inward or outward, it would affect the result, in that with increasing outward distance the vignetting would appear to be worsening. (And too far inward would artificially improve things.)

I find an easier thing to do is simply leave the eyepiece in place (a shorter f.l. being better), and aim the eyepiece directly toward some easily identifiable, small object. A single light source works well. With said object nicely centered in the reduced view produced by the eyepiece, it acts exactly like the pinhole adapter. It only requires to adjust focus to near that for infinity.

#45 GamesForOne

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Posted 02 May 2011 - 02:32 PM

Off axis vignette is most apparent with the largest field stop eyepieces (widest TFOV).


That's very interesting because I personally found that the Pentax XW10 seemed to perform better, with respect to full field illumination, in my APM ED100 than the XW20. When I made the comment, I interpreted the replies from the experts in this group that field illumination was independent of exit pupil size -- as long as the field stop of the eyepiece did not exceed the clear aperture.

Now I see that it is dependent? This makes all the "sighting through the objective" tests (which I personally do not like) even more subjective, especially with binos that can accept multiple eyepieces.

I also noted that the image circle with the XW10, when viewed in the sighting through the objectives position, seemed to be less clipped than the XW20. Given my misunderstanding, I chalked it up to a smaller circle being more difficult to see.

I guess my impressions at the eyepiece have been correct after all. You guys confuse me at times... :grin:

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Michael Mc

#46 EdZ

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Posted 02 May 2011 - 04:02 PM

I interpreted the replies from the experts in this group that field illumination was independent of exit pupil size -- as long as the field stop of the eyepiece did not exceed the clear aperture.

Now I see that it is dependent?



Well, be careful here. It's not really dependant on exit pupil size, you are simply making that relationship and it could be correct in some instances. but it won't be always. However it will always be dependant on field stop diameter.

For example
same binocular with these different eyepieces
a 50° 20mm eyepiece
a 60° 20mm and
a 70° 20mm and
a 80° 20mm

all will have exactly the same exit pupil size, but the illumination will improve from 80 to 70 and from 70 to 60 and then again from 60 to 50. So by this example you can see illumination IS NOT dependant on exit pupil size.

edz

#47 GlennLeDrew

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Posted 02 May 2011 - 04:56 PM

To put the 'sighting-through-the-objective' test into better perspective, note that the eyepiece-produced image, after being collimated by the objective, has an apparent angle equal to the instrument's TFoV. Magnification and hence exit pupil diameter have no role here; it's the diameter of the field stop only which controls this.

The foregoing presupposes that the full field stop is seen, and not clipped by some other aperture between objective and field stop. If a too-large field stop is employed, clipping is quite likely (and the field edge during observation will be noticeably darkened, and possibly even reduced.) I suppose it's approximately true that a reduced field stop as seen through the objective would still be indicative of the TFoV, but the fact that the clipping aperture lies some distance ahead of the field stop results in parallax, which introduces no small uncertainty.

#48 Rich V.

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Posted 02 May 2011 - 04:57 PM

Michael, I think your initial perceptions were correct; the XW10 should show less vignette than the XW20. Glenn's point #7 in the above linked post is in agreement.

Another quote from one of Glenn's posts in the above linked "General comments" thread seems to answer your question also:

"The illumination delivered to the focal surface is a fixed quantity if all the eyepieces to be used have their field stops ahead of all optical elements. In such case, no matter what the eyepiece focal length, the linear image brightness profile across the field is unchanged.

Let's say the illumination profile is of this form:
90% on-axis (reduced by, say, a too-small prism)
80% 5mm off axis (10mm diam. circle)
70% 10mm off axis (20mm diam. circle)
60% 15mm off axis (30mm diam. circle)

A low power eyepiece having a 25mm diameter field stop will have 90% illumination at the center and ~65% at the field edge.

A high power eyepiece having a 10mm diameter field stop will have the same 90% illumination at the center, but a higher 80% at the field edge.


Sounds good to me. :)

Rich V

#49 Tamiji Homma

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Posted 02 May 2011 - 05:18 PM

Here is follow up with 9mm eyepiece (10.5mm field stop)

Looks like a little better than 14mm but not much. Now I am done with taking photos :)

Posted Image Posted Image Posted Image Posted Image Posted Image

Tammy

#50 JimP

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Posted 02 May 2011 - 07:51 PM

Tammy, my suggestion is to look through the darn things and quit looking At them :^). They truly are exceptional binoculars in my opinion. And, yes, I sold them to help fund the purchase of a TOA 150B but I do miss them...

Have a blast with them Day or Night.

best,

JimP


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