Clear day here. I've just spent an hour putting the swifts through their paces alongside the Habicht, Ell and Zeiss BGATP 7x42. The swifts are doing very well at 'faint single web detection' - one of the most difficult tests that I know of as it seems to combine resolution, CA, contrast, brightness etc all in the one go. The excellent Ell can struggle at this web test sometimes. Ive only done a couple of hours of viewing at this stage, but I'd easily be putting the swifts into the above category of binoculars. What an extraordinary value.
Rathus,
What does single web detection mean? Does it refer to spider webs?
David,
The second multi-coated version had more multi-coated surfaces, but not all of them. The eyepiece reflections are clearly different, and the objectives are somewhat darker green. The fully multi-coated version that showed up in the late 1990s is even darker green. None disappoint.
Ed
...
Re The single thread test - I look for a single thread from a spider or caterpillar a few inches long (6-12inches...sometimes longer) which is usually stretched between bark or twigs. The best thread is Very fine/barely perceptible. Sometimes it's also a waving piece of thread. Shaded or sunny, this is the most ruthless test I've come up with so far for binoculars. I usually view from 30-40 feet away. Some of my sharpest binoculars can struggle with the thread test. It's almost spooky and ghost like when the thread appears in some binoculars and not others.
I walked up to the piece of thread I was viewing yesterday to check it out, and it took me a minute or so to find it from just 12inches away with the naked eye. I knew where it was but still couldnt locate it for some time. Incredibly difficult to see. A couple of the binoculars gave me a better view from 30-40 feet away.
Cheers
Rathaus
In 1941, Hecht was awarded the Frederick Ives Medal of the Optical Society of America. He was elected to the National Academy of Sciences in 1944. A director-at-large of the Optical Society of America, he also served on the editorial boards of the Journal of the Optical Society, the Biological Bulletin, and Documenta Ophthalmologica.
Very interesting! Did you make that procedure up yourself? The reason I ask is that, depending on how one defines acuity, the limit of human capability is about 0.5 arc seconds, which is well below commonly accepted grating acuity. See Wiki article, where this is discussed towards the end of the article and is doubtless based on the seminal work of Hecht & Mintz (1939) that I've attached.* So far, you are the first I've seen to incorporate this into binocular instrument evaluation. Congrats!
* Some astronomers and opticians on BF take issue with the article claiming that Hecht was old fashioned, or unfamiliar with classical optics, etc. However from his NAS obituary:
Hi Rathaus,
The code is the address In Doncaster of the binocular maker. No, actually the binocular previous owner.
It seems to be half a mile from Botany Bay.
Hi Ed.
I read the Visibility of single lines article. Thanks.
I don't think astronomers would disagree as it is astronomers who confirm the findings by observation.
However, I am not sure how accurately it tests binoculars optics, as poorer optics could expand wires to larger apparent sizes than top quality optics.
I am not sure of this, but maybe Typo commented on this.
Also illumination of beads on wires by sunliight will render them visible even when much less than 0.5 arcsecond wire diameter.
This is also why I object when people here talk of Dawes limits, when it is not Dawes limits they are seeing.
And the fact that resolution limits vary from 0.5 arcseconds to several arc minutes just shows how one cannot just talk about resolution without saying what you are measuring.
It is like pairs of binoculars, sets of binoculars compared to a binocular.
I am probably too pedantic as these terms are used in the venacular. I sometimes talk of binoculars myself when I mean binocular, but I try to be consistent.
Same with Dawes limit. Poor Rev. Dawes will be turning in his grave. He was not in the best of health when he actually made his observations. Good thing he didn't read this site.
David,
Yeah, it always seemed to me that the word binoculars is curiously redundant. Bicycles, for example, refers to more than one bicycle; so why wouldn't binoculars refer to more than one binocular? I guess folks who use the word "maths" know how to explain it, ... I don't.
:king:
Ed
Yo, Eddie:
I threatened you with being back on the 10th!
The VERY LAST page in my book will have two photos. The one on the left will be of a binocular; the one on the right will be a PAIR of binoculars. :cat:
Bill
Ed,
Too true.
I did study Maths and folks here don't know what Math is.