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Kowa BDII-XD - september 2019 (1 Viewer)

I saw that. I liked the Kowa 6.5x32 BDII XD so much I bought the Kowa 10x42 BDII XD from Binocular USA. A 72 degree AFOV should be WOW. Here is an example of why do you don't keep the world's most dangerous bird the Cassowary as a pet. They can weigh 160 pounds and have razor sharp talons. Kind of like a small Velociraptor!

https://www.cnn.com/videos/us/2019/04/15/cassowary-kills-florida-man-es-vpx.cnn
 
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I just received my Kowa BD II 6.5X32 today, I ordered online from Optics4birding after a relatively lengthy conversation with Steve regarding their qualities, he was favorably impressed with them. When I got them out of the box I immediately took them out to the front porch to verify their usefulness while wearing eyeglasses I found that I was able to get a full field of view and I was very impressed with the view (like looking out a picture window and not a port hole). This was just a quick first impression to see if I wanted to keep these binoculars and that is what I will be doing.
 
wdc said:
Now, wait a minute. Steve.... Do you want to meet, or beat, that offer? ;)

I'll even take your response in a PM.

-Bill
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Gentlemen

I can see this has arisen innocently so this is just a reminder that the Birdforum binoculars sub-forum is not a bazaar where dealers and customers negotiate.

Bill is right to suggest that this goes to Personal Messages and if Optics4Birding want to publicise offers and discounts they should have a word with Birdforum Admin about posting in the Retailers and Dealers Offers sub-forum.

Thanks.

Lee
Moderator
 
Steve O4B said:
Hi Sage,


For need low light performance, I would avoid all 30mm or 32mm binoculars in favor of the 42mm models. A 42mm binocular will receive about 70% more light than a 32mm binocular. That's a little more than 2/3 of a f/stop. So, given equivalent glass and coatings, the 42 will be the better choice.



Between an 8x42 and a 10x42 of the same binocular series, the 10x will give you better low light performance. If you don't believe me, do the test. The reason for this is physiological as well as optical. All 42mm binoculars receive the same amount of light in any given circumstance. The objective lens doesn't know which eyepiece the binocular has. The 8x delivers more total light to your eyes because of the wider field of view - you have photons coming from more things, but it delivers the same amount of light from the bird as the 10x. The problem is that the photons from the extra field of view of the 8x reach your retinas and tell your brain that there is more light, so your brain doesn't dilate your pupils as quickly. That means you get less light from the bird with the 8x. When your pupil diameter maxes out with the 10x, the pupils would still be only partially dilated with the 8x. This is the effect called twilight factor.
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Hi Steve,

I find this very interesting. With 8x the image brightness is ~56% brighter than with 10x, so I have always claimed that 8x is better than 10x in low light. This is obvious if looking at an even colored wall. Also if using the binocular at low light condition 8x with the larger exit pupil will provide a brighter image. But I know the increased image scale can reveal more details despite the image is dimmer. This is providing the exit pupil is not too small. Just an extreme example: 100x42 will not work at all in real low light condition despite a very high twilight factor(magnified darkness = darkness)
Regarding what you are talking about: when it comes to the total light amount of light sources due to the difference in field of view it can impact the perceptive brightness. I would like to try it out!
 
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Swedpat said:
Hi Steve,

I find this very interesting. With 8x the image brightness is ~56% brighter than with 10x, so I have always claimed that 8x is better than 10x in low light. This is obvious if looking at an even colored wall. Also if using the binocular at low light condition 8x with the larger exit pupil will provide a brighter image. But I know the increased image scale can reveal more details despite the image is dimmer. This is providing the exit pupil is not too small. Just an extreme example: 100x42 will not work at all in real low light condition despite a very high twilight factor(magnified darkness = darkness)
Regarding what you are talking about: when it comes to the total light amount of light sources due to the difference in field of view it can impact the perceptive brightness. I would like to try it out!
Click to expand...


This is the difference between total light and light from your subject. The 8x and 10x each receive photons from their entire field of view. The 8x has a larger FOV, so more total photons because it sees more stuff. On a plain wall of any color, this means more photons of that color, so it appears brighter. But in the field, both receive the same number of photons from a single bird. When you're studying the bird in bright daylight, the bird will appear equally bright in either binocular. But as the light starts to fail, because the total number of photons are fewer with the 10x due to the smaller fov, your pupils start to dilate earlier, which then delivers more photons from the bird to your retina than with the 8x because the aperture of your pupil is larger.
 
Steve O4B said:
This is the difference between total light and light from your subject. The 8x and 10x each receive photons from their entire field of view. The 8x has a larger FOV, so more total photons because it sees more stuff. On a plain wall of any color, this means more photons of that color, so it appears brighter. But in the field, both receive the same number of photons from a single bird. When you're studying the bird in bright daylight, the bird will appear equally bright in either binocular. But as the light starts to fail, because the total number of photons are fewer with the 10x due to the smaller fov, your pupils start to dilate earlier, which then delivers more photons from the bird to your retina than with the 8x because the aperture of your pupil is larger.
Click to expand...

Thanks for explanation.
Several years ago I have in some thread wondered about the difference if comparing different AFOV with the same magnification and aperture for stargazing. For example: two 10x50s, one with 50 deg AFOV and the other with 65deg. My thought was that with the narrower FOV less stars will be visible and therefore less light amount hitting the eye. I don't think stars will impact pupil size in a binocular but could a narrower field improve dark adaption for dim objects?
 
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Kowa

jremmons said:
Thanks for the quick and concise review, Andy.
With regards to the out of focus edges, can they be refocused or is the lack of focus more due to astigmatism? I've found with a lot of 8x32s, including the 8x32 Victory T*FL which I owned for a bit, that eye placement is hypercritical due to astigmatism. If it is introduced distortion (e.g. pincushion or what have you) that blurs the edges, I don't seem to notice the eye placement issue as being so pronounced.
Also, of slightly less importance, is the focus-knob metal? I always liked the metal, knurled knob of the Genesis series; I still find it the most please focus I've used.

Justin
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I tried it a bit today while out in the field, some sneak peeks.

Now this is the 8X32 - not the best for glare, not one of the strong points.
The sweet spot is if I were to put a % on it maybe 30%, the edges can be focused but only at the edge, slightly off the field stop it becomes out of focus.
To be clear these will be a great truck glass for me, though a porro, the EII is still the king of the wide FOV.

The depth of field is OK from 150 feet to infinity, but any closer it resembles in visual observation as a flat field, no depth of focus, or significant depth of field. There is significant pincushion distortion.
The FOV is wide, and it is well built, good grab and go econo glass for the money.

The 6.5X32 is likely different.

Andy W.
 
To your right (clockwise) Chosen. And I am not sure of the composition of the wheel itself, although I suspect a composite plastic.

Andy W.
 
dries1 said:
To your right (clockwise) Chosen. And I am not sure of the composition of the wheel itself, although I suspect a composite plastic.

Andy W.
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Thanks Andy - good to see they've followed 'alpha' convention - happens to be my preferred direction too :t:

Could one of these wide angle Kowa formats cause me to break my one bin rule? Not sure I'm ready for the nuthouse just yet ! :-O




Chosun :gh:
 
dries1 said:
To your right (clockwise) Chosen. And I am not sure of the composition of the wheel itself, although I suspect a composite plastic.

Andy W.
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Yeah , the focus wheel on my old BDXD Prominar is plastic , the BDII's are most likely plastic as well , although they do LOOK like aluminium , I tested this with a metal detecting pointer.

Cheers.
 
Troubador, can you get your German Kowa contact to clear up the focus wheel material question with regards to the BD? Seems strange to me that they would use metal for one and plastic for the other but end up with an almost indistinguishable product.
 
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