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Kowa BDII-XD - september 2019

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Old Monday 28th October 2019, 12:37   #326
mwhogue
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RB,

No trouble at all and thanks for the kind words. I enjoyed our exchange.

Mike
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Old Wednesday 30th October 2019, 14:35   #327
iri
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Hi. I am new here, but I read all about this serie of Kowa. Thanks to all who did writes about that. I believe that I will buy a 6,5 or 8. That's what I founded today on allbinos
https://www.allbinos.com/177.1-artic..._hands-on.html

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Old Sunday 10th November 2019, 17:13   #328
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I got the 8x32 of these yesterday and have been trying them out today, largely in comparison to my 8x30 m7. The Kowa has a nice sturdy feel and the large eyecups fit me well. They are brighter and sharper than the m7 with a wider FOV. They show some glare, but less so than the m7. They show quite a bit of CA outside of the sweet spot (which is modestly sized), which I found a bit distracting. The m7s are definitely better in this regard, although CA is essentially absent in the sweet spot of both. There is some 'rolling ball' due to field curvature on the edges, but it's not bad and didn't bother me at all.

If not for the CA, I would call these perfect. Instead they represent a good value buy, probably a better purchase than the m7s if the ergonomics suit you. If you are particularly averse to CA I would probably look elsewhere, at least for the 8x32 pair.
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Old Tuesday 26th November 2019, 07:08   #329
range
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According to pixels of the pics attached,
If the Nikon E2 is 8.8°,then Kowa 8x32 should be 8.24°.
That's actually an ordinary number for a 8x32. What a disappointment!
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Old Tuesday 26th November 2019, 13:03   #330
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Quote:
Originally Posted by range View Post
According to pixels of the pics attached,
If the Nikon E2 is 8.8°,then Kowa 8x32 should be 8.24°.
That's actually an ordinary number for a 8x32. What a disappointment!

That is disappointing. I can say that my kowa has a larger FOV than my 8x30 m7 when compared side by side and the m7 lists as 8.3 degrees. Maybe I can set up a comparison like yours this weekend between those two
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Old Friday 29th November 2019, 18:37   #331
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I've had some fun with the images attached to range's post #329. Ideally they could tell us quite a bit about the comparative magnifications, AFOV and distortion characteristics of the binoculars, but that is somewhat qualified here because we don't know what kind or amount of distortion is being added or subtracted by the camera lens. Still, since the camera lens affects both to about the same degree a few things can be reasonably deduced.

Firstly, the center field magnifications of the two binoculars are nearly identical, so we know that the Kowa's smaller real field is not caused by higher real magnification.

Secondly, there's no doubt that the Nikon has much more pincushion distortion and therefore much less angular magnification distortion than Kowa. Notice that the wooden slat at the bottom of the image shows pincushion distortion in the Nikon image in contrast to slight barrel distortion in the Kowa. Also notice the difference in shape of the window at the extreme left of the image. It's more horizontally compressed in the Kowa image from higher angular magnification distortion. That, combined with the Kowa's smaller real FOV, give it a substantially smaller true AFOV compared to the Nikon. If we assume that the field circles in the photos are the eyepiece field stops of the binoculars then by simply measuring and comparing the diameters of the circles we find that the true AFOV of the Kowa is about 62.4º compared to the 66.5º true AFOV I've measured for the Nikon EII.

Looks like I'll get a chance in a couple of weeks to test a BDII 10x42 XD that a friend has decided to purchase. I should be able to provide some measurements and hopefully some explanations of the subjective impressions we've had so far.

Last edited by henry link : Friday 29th November 2019 at 19:01.
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Old Friday 29th November 2019, 19:34   #332
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Quote:
Originally Posted by henry link View Post
Looks like I'll get a chance in a couple of weeks to test a BDII 10x42 XD that a friend has decided to purchase. I should be able to provide some measurements and hopefully some explanations of the subjective impressions we've had so far.
I'll be very interested in your impressions of the 10x42. That is a hole in my arsenal right now and the Kowas are a strong candidate to fill it.
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Old Saturday 7th December 2019, 15:29   #333
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Well, I got my shot at evaluating the BDII 10x42 XD yesterday.

In brief, I didn't like what I saw. Full aperture resolution was poor (5.6" left, 6.5' right) due to a brew of excessive spherical aberration, astigmatism, coma and very poorly made roof prisms in both sides. Longitudinal CA was well corrected, but latitudinal CA was quite high, even near the field center. Glare resistance was below average, in part due to undersized prisms. Real FOV was slightly below 7º, compared to Kowa's 7.2º spec, while the true AFOV was only 64º, far below Kowa's spec of 72º. The oddly small AFOV was caused by a fairly extreme mustache distortion. I recommended that my friend return the Kowa's for a refund.

I will write more and post photos of bad roof prisms, distortion and glare in a few days.

Henry

Last edited by henry link : Saturday 7th December 2019 at 15:39.
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Old Saturday 7th December 2019, 17:05   #334
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Thank you, Henry - as always with your reports, interesting findings presented in a straightforward language with no fuss.
Your findings do not really come as a shock - the expectations for these „widefield“ binos were way too high, esp. when you consider the price of the new Kowas. There is a reason why really good, or really very good, widefield binoculars tend to be more expensive.
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Old Saturday 7th December 2019, 19:04   #335
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It is rather sad to see a firm like Kowa advertising wide field binoculars if they are not wide field.

Also the reports do not indicate high quality.
I suspect a lot of sample variation also.

In the past Kowa had a good reputation for fast and special lenses, and the spotting scopes were good.

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Old Sunday 8th December 2019, 06:30   #336
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Unhappy

Quite disappointing about the 10x42 ...... look forward to reading more analysis Henry.




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Old Sunday 8th December 2019, 11:06   #337
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Henry,

Thank you for your comments. I've only seen the pre-production samples at birdfair, but the lateral CA, was much higher than I thought acceptable for the 10x models in particular. Doesn't sound like much has changed there. I noticed moustache distortion in the 6.5x32, but can't say I paid the higher magnifications as much attention.

Did you happen to notice if the field stop was sharp? I've seen a few recently that weren't. I had supposed it was due to incorrect stop positioning. I checked out a couple more closely recently and found fov, afov, ER and magnification were all incorrect as well and wondered if something like lens spacing in the eyepiece was to blame? Any thoughts?

David
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Old Sunday 8th December 2019, 22:25   #338
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Quote:
Originally Posted by range View Post
According to pixels of the pics attached,
If the Nikon E2 is 8.8°,then Kowa 8x32 should be 8.24°.
That's actually an ordinary number for a 8x32. What a disappointment!

I just did a quick FOV test. I used my pole barn with ribbed steel siding to measure the FOV with the binos on a table and looked through the right tube. The results I got are: m7 8x30 - 8.09 degrees, edii 8x32 - 8.60 degrees, and edii 6.5x32 9.86 degrees.
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Old Monday 9th December 2019, 03:35   #339
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Thanks Brink. I have the Kowa 6.5 ed ii and the fov at medium to long distance appears noticeably wider in use than my Nikon E2 8x30 - not so dramatic at distances of less than @ 300 yards. Based on my use of the 6.5 and comparison with a number of other models and reading the reviews of the new Kowa models here including your fov testing, it may be that the 6.5 is the pick of the litter of the new Kowas. It also appears as others note there is sample variation. Mine is very good optically and mechanically especially focus function. IME the 6.5 does benefit a great deal when using eye shields made by Field Optics.

Mike
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Old Monday 9th December 2019, 15:06   #340
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Quote:
Originally Posted by typo View Post
Henry,

Thank you for your comments. I've only seen the pre-production samples at birdfair, but the lateral CA, was much higher than I thought acceptable for the 10x models in particular. Doesn't sound like much has changed there. I noticed moustache distortion in the 6.5x32, but can't say I paid the higher magnifications as much attention.

Did you happen to notice if the field stop was sharp? I've seen a few recently that weren't. I had supposed it was due to incorrect stop positioning. I checked out a couple more closely recently and found fov, afov, ER and magnification were all incorrect as well and wondered if something like lens spacing in the eyepiece was to blame? Any thoughts?

David
Hi David,

I didn't examine the sharpness of the field stop closely, but it didn't draw my attention as being especially unsharp. When I compared field stop apparent sizes between the Kowa and a Nikon 10x35 EII I didn't notice any striking difference in field stop sharpness between the two.

I forgot to measure ER, but the center field magnification measured 9.93x. From there I would expect the magnification to follow the distortion profile, increasing a little out to about half way to the edge as pincushion increases and then decreasing toward the field edge after the pincushion reverses. Magnification at the field edge is complicated by barrel distortion causing such a large amount of angular magnification distortion that the circumferential magnification near the edge is about 9.2x, but the radial magnification is only about 7.8x. Average magnification across the field is probably quite close to 10x if the outer 20% is ignored.

Henry

Last edited by henry link : Monday 9th December 2019 at 16:46.
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Old Tuesday 10th December 2019, 07:28   #341
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Henry,

Thanks for the extra detail. Doesn't seem like you found a simple explaination for the reduced fov. I can't say I've had a look at radial magnification. Something to add to the list.

I recently learned that the official ISO method for measuring ER specifies that the instrument should be stopped down to a 2mm EP, but it seems listing available ER is also permissible . Other companies list the ER for full the full EP. The ERs across the BDII XD range vary from 15mm to 17.5mm. They were all fine with my glasses so I'd guess that is the ISO method. However, the difference in effective ER can alter the AFoV.

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