Alpen Wings ED 10x25 Binos - Review (5 Viewers)

[clear_blue_skies]

Focus knob placement

other than that, there is absolutely nothing not to love about these if mini compacts are your pleasure.

That's not true. I don't think the position of the focusing wheel is good. It feels very unnatural having to use my non-index fingers to focus it.

I have the Alpen Wings ED 8x20. I think the optics have a lot of potential, but mine are going to need to go back to the manufacturer for repair. I will test further, but I believe the lenses in one of the barrels arrived from the factory out of alignment.

 

[james holdsworth]

Fun thread.

Although I am torn.........to a degree I agree with Dennis, I can clearly see differences in some aspects of different binoculars but I'm not sure that what I'm seeing is ''resolution.''

Some of it is probably a combination of brightness, better contrast, less stray light and glare and fewer visual abberations.

I can do a side-by-side of my Elite's and my FL's and the FL's will look strikingly better, sharper etc. I have always assumed that what I was seeing was superior resolution but now I think most of the difference is contrast and the elimination of lateral colour and CA.

Henry?

 

[ronh]

Thanks to Henry for his nice explanation (although ephemeral!) of the Barlow type lens (a negative lens ahead of the objective focal plane) in the SV eyepiece. I have used Barlows plenty in astronomical telescopes, and can verify that the use of such a lens does more good than the obvious cheap increase in magnification, and allowing greater eye relief for a given magnification. By increasing the effective focal ratio of the objective, it makes the eyepiece's job easier, and so also improves edge sharpness.

This was done a long ago in the Nikon Prostar, which has a nearly perfect sharp edge, just like the SV. I have wondered if they'd ever just stick a Nagler eyepiece on a binocular, and thought it would be too expensive. But it looks like we are getting there.

If I may run on with more superfluous details from the dark side, a book that is popular with amateur astronomers is Rutten and Van Venrooij's "Telescope Optics". This book summarizes the strengths and weakness of many eyepiece designs, and with fast objectives like those in binoculars, it is not necessarily so that "all eyepieces will appear equally sharp on axis"--in fact quite a few exceed an arcmin resolution at the center at f/5, and would be much worse at f/3.5 or f/4, and a sharp eye could see that. I doubt Swaro would ever give us anything that bad, but some cheaper binoculars might, given the other compromises that are made.

Sorry Alpen fans, this thread has derailed into a trainwreck. But you just have to jump into these little digressions wherever they pop up, sometimes they're the best thing on the forum!
Ron

 

[henry link]

Ron,

Sorry for the deletion. I got a little hot when I saw Dennis' post, but then decided not to pursue it.

I've poured over those same eyepiece spot diagrams in "Telescope Optics" and wondered how any binocular using a Kellner or Erfle could be any good at all. Of course we know part of the reason is that the most critical visual tests for center sharpness in binoculars tend to be done in daylight when the f-ratio is effectively higher (except for your double star observations), but I've also wondered why boosted magnification tests (which use the entire objective) don't reveal poor axial performance from simple binocular eyepieces, since the resolution limitations of the eyepiece should pass through the booster telescope to the eye. It would seem, for instance, that even an eyepiece with axial line pair resolution better than eyesight, say 50 arcseconds, should be the limiting factor for resolution from low magnification binoculars when the magnification is boosted after the eyepiece. Shouldn't the tack sharp 50 arcseconds become a dismal 400 arcseconds once an 8x booster is inserted behind the eyepiece? I commonly see line pair resolution of 3-4 arcseconds from 8x binoculars boosted to 64X. Wouldn't the eyepiece have to have axial line pair resolution no worse than 24-32 arcseconds for that to be possible? Any ideas?

Henry

 

[ronh]

Henry,
That is a very interesting contradiction between your (and others') boosted resolution measurements and the axial spot diagrams.

My old copy of Conrady (p 507) offers some help in the case of the Kellner eyepiece, which he calls the Achromatized Ramsden--the lens layout looks the same to me. He explains in detail why the Kellner was, around 1950, the favored binocular eyepiece. The dominant axial aberration in the eyepiece, spherical aberration, has a value of -0.0072. A typical set of Porro prisms, however, has its own spherical aberration, which is of the opposite sign. When the eyepiece and prisms are combined the net is +0.0048. Now, this doesn't sound like a great improvement, but Conrady hems and haws about how his choice of eyepiece and prism size are not realistic, and that it would be a much better nulling in the real world, if the binocular designer tried even a little bit to get it right. He concludes that the spherical aberration of the eyepiece alone is "greatly reduced". Unfortunately, I can't go from the above units to angular spot size, so I just have to trust him on this.

All prisms are thick blocks of glass with flat sides, and will have similar degrees of positive spherical aberration. Whether the sign of the spherical aberration of most eyepieces is negative, I cannot say, and R&vV are no help. But I have a hunch that in many cases it is the prism-eyepiece relationship that is being worked to make binoculars look tack sharp even though the eyepieces alone may not.

If you need further convincing, well, urban myths of unsuccessful swappings of telescope and binocular eyepieces are out there. QED!
Ron

 

[henry link]

Thanks for the information, Ron. I like the idea of nulling from complimentary aberrations. Even the fast scope/Erfle combinations in "Telescope Optics" already look good without the help of a prism.

Just for fun I did a resolution test of a Zeiss 25mm 3 element aspheric eyepiece, chosen only because it's physically easy to use as a 10x magnifier. I examined a glass slide of the USAF 1951 chart placed at the focal plane of the eyepiece. This slide goes down to 228 line pairs per mm (Group 7, Element 6). I found I could only see down to about 80 lp/mm looking directly through eyepiece, but when I placed a Zeiss 3x monocular behind the eyepiece to triple the magnification, I could easily see to the end of the chart and certainly could have done better if the chart had smaller groups. This suggests to me that the axial resolution of the eyepiece itself is probably no worse than 30 arcseconds, most likely better. This is far beyond my 90-100 arcsecond line pair eyesight acuity, but of course it might not be fully realized in a fast telescope.

Henry

 

[clear_blue_skies]

Alpen Wings ED 10x25 Binos

Seems like this thread was hijacked. Shouldn't these posts be under a separate thread?

 

[brocknroller]

Holy Arctangent, Batman! I tuned into this thread to find out how a review of a inexpensive compact could garner 87 responses, but after reading the latest posts, I had to scroll to the top to make sure I hadn't logged on Cloudy Nights by mistake!

Boy, if we could just get Professor EdZ on this thread, we'd really have ourselves a party!

Anyway, carry on, gentlemen! Let us know when you've worked out the problem and then dumb it down so even this "soft headed dreamer" can understand it. Thanks.

clear_blue_skies, sorry to hear you got a bad unit, hopefully, they will fix you up with a good one in short order.

Brock