QC, Alphas, Pete Dunne, Internet vs. Specialty Store.... (1 Viewer)

Some time ago, I read that Pete Dunne once noted a distinct difference in the optical quality of two "identical" alphas right out of the box and, thus, advised to try out several of the same bin before purchasing.

One: While I don't expect someone to test drive each Dodge or Chevy, I do expect someone at the factory to "test drive" each alpha binocular before it leaves the factory. Is that done?

Two: If so, and at the alpha level, is the acceptable range so great as to be obvious other than on an optical test stand (Pete's experience)?

Three: If so, is there any reason to purchase "sight unseen" over the Internet as opposed to from a specialty shop?

Lastly, If not, and other than obvious mechanical flaws, is there a short list of things to note when performing an in-store, side-by-side comparison?

Thanks,
Mike

Hi Mike, some reading here while you await a lemon fresh response :
http://www.birdforum.net/showthread.php?t=40197
http://www.birdforum.net/showthread.php?t=38542

Thanks for the links, Norm. I don't think anything has changed in the last seven years since those threads.

Thanks Norm.

St. Elmo said:

Some time ago, I read that Pete Dunne once noted a distinct difference in the optical quality of two "identical" alphas right out of the box and, thus, advised to try out several of the same bin before purchasing.

One: While I don't expect someone to test drive each Dodge or Chevy, I do expect someone at the factory to "test drive" each alpha binocular before it leaves the factory. Is that done?

Two: If so, and at the alpha level, is the acceptable range so great as to be obvious other than on an optical test stand (Pete's experience)?

Three: If so, is there any reason to purchase "sight unseen" over the Internet as opposed to from a specialty shop?

Lastly, If not, and other than obvious mechanical flaws, is there a short list of things to note when performing an in-store, side-by-side comparison?

Thanks,
Mike

Click to expand...

There is some useful information in the threads linked to but they tend towards the astronomer not the birder in my view, or at least there are some questions that arise in my mind. This post is interesting:

http://www.birdforum.net/showpost.php?p=384902&postcount=7

When he says "Now here are my impressions of sharpness when looking trough the binoculars in normal use" does he mean on the night sky, or for birding? From later comments, it seems he refers to low light viewing, so his tests are from the point of view of an astronomer, not a birder. This is important given his conclusions.

As an aside, later on he says you cannot see CA from a 40mm objective with a low power eyepiece, so 8x40 binoculars should not have CA, which is clearly wrong, as they do have obvious CA, due to the internal focussing, and/or the eyepieces. (My Nikon 8x32 SE has slight but obvious CA, but no internal focussing.) NB: The calculations he refers to might be on-axis.

There is a good reason to ask how he measured resolution. As many/most here know, on the night sky, you are testing the instrument with your irises dilated, so for an 8x40mm bin, you are using it at full aperture, and seeing full aperture aberrations. In daylight outdoors, your iris stops the binocular down. I have not seen a clear proof that the open aperture on axis resolution correlates directly to the stopped down resolution. Does someone have measurements?

Also, for birding a visual unaided test in good light (outdoors, sunny) against a resolution chart is perhaps a good test. Has anyone done tests to see if there is much sample variation? One check would be to compare each optical assembly. If both give very similar resolutions, the divergence being less than that between different models, then that adds support for the test.

As to the questions, a few comments:

1) Manufacturers do have quality control checks. We might hope that more expensive bins have better QC.
2) I have seen several instruments with obvious defects. One was a Nikon 8x42 HG i.e. a high end instrument. One side was out of collimation, and depth of field was lacking. It might have occurred in use. You will find such an instrument more tiring to use.
3) Buying sight unseen is risky. But at least (in the UK anyway) you have the right to return a product bought online, or on the phone.

You can buy from a specialist dealer, in the UK many dealers keep only one sample of each high end instrument in stock, as they are so expensive. If you consider the one in stock to be sub-par, as a result of testing, is the dealer going to order another on the off-chance that a customer might buy it? How many are you going to check? Do you know what is acceptable for that model? Some dealers only keep a demonstrator, and order in a sample if you want to buy. That was and might still be the case with the RSPB and premium scopes. So you cannot choose, and you do not have the right to return it in 14 days.

I take the view that you should be able to determine whether or not the instrument provides a good view by visual use. There is the issue of the image quality that is characteristic of the given model (off axis aberrations, distortion, chromatic aberration, field of view and so on). These differences can be quite large. You compare one sample of each model to determine which you like, assuming that each is 'okay'. Then you check the one you intend to buy, both optical assemblies should show similar sharpness and depth of field. I am sure there are some people who will test a binocular on a tripod with a point source, but I am not in that camp, and I suspect that none of the most respected birders star test their binoculars.

I suspect only amateur astronomers are interested in the full aperture aberrations revealed by a star test, perhaps because they view stars, defects are more apparent with point sources, they tend to use tripods, and their eyes will be using the full aperture.

I suspect some people here think that I am an ignorant peasant. ||

Anyway, we all know that what you really need is the DVD test. (For at least one literal minded person, please note that comment is not intended to be taken seriously.)

FWIW, at the top of the Opticron range, both the Aurora and the DBA Oasis are individually checked for defects, resolution performance etc by the owner of the business before they get to the shelf in the warehouse ready for sale. Not claiming to be an alpha, but it's where a 'brand' can add value to its product.

Similarly, all our high end (HR and GS ED) scopes are also individually checked for resolution, aberration etc. before going into sales stock.

All HDF zoom and SDL zoom eyepieces also get a visual inspection for manufacturing defects before being allocated to sales stock.

The Kaizen principle has rubbed off on our management team after many years working with Japanese suppliers

http://en.wikipedia.org/wiki/Kaizen

Cheers, Pete

Leif,

Now, in addition to full aperture tests I usually do high magnification resolution and star-tests with aperture stopdowns to simulate daylight birding conditions,... but I suppose that just adds to the general geekiness. ;-)

Henry

Firstly using the strict standards of Conrady only a 20mm f/4 objective would be considered colour error free.
a larger aperture would show false colour.
A 40mm f/4 would not be considered colour error free even with the looser standard.
A 32mmf/4 would just be considered colour free to a first approximation.
Some objectives are only f/3.5 about so they would show more false colour.

Most astronomers don't use tripods. I rarely do even with 12x 50, 15 x 70, 20 x 60 or when younger 20 x 80 which I could easily hand hold.

For critical observations I would use a tripod, but normally I just wedge it against something and hand hold.
And I prefer IS binoculars anyway, but use non IS.

I don't know why here it is stated often that astronomers use tripods, most don't under 15 x 70, and lightweight 15 x 70s are easily hand held.
Slight movement makes faint fuzzies easier to see as does tapping a telescope or tripod mounted binocular.


I have tested as many as 12 identical binoculars against each other and with modest priced binoculars there is considerable variation in Russian types and enormous variation in lower priced Chinese.
Even the best vary and the very act of collimating means you are throwing one side out of perfect allignement.
It is rare indeed for there to be two perfect star image barrels in a binocular although the best come close.
And you must know your eyesight extremely well or use perfect glasses correction to properly test perfection.
Few binoculars are perfect, some high end telescopes are.

henry link said:

Leif,

Now, in addition to full aperture tests I usually do star-tests with aperture stopdowns to simulate daylight conditions,... but I suppose that just adds to the general geekiness. ;-)

Henry

Click to expand...

Geeky maybe, but interesting. Do you stop down to ~20mm say? Do you find a correlation between full and sub aperture resolution and aberrations? Obviously aberrations do reduce, but that does not say much. It is possible that with a 20mm stop, most bins perform superbly. (A suggestion, maybe wrong.) Naively I might think that pinched optics (objectives, prisms) might not show stopped down, depending on where the strain is.

And do you measure sub-aperture results with a booster and visually, and find a strong correlation?

The chap in the post I linked to mentioned that he saw a correlation between full aperture resolution and the visual resolution in low light.

Regarding the comments from Binastro on chromatic aberration, I see CA through my Nikon 8x32 SE even on a sunny day when the effective aperture is more like 16mm. I roughly measured the focal lengths and found them to be consistent with ~F4. There will be components of CA from the objectives, and the eyepieces, I do not know which dominates. CA through a roof prism bin can be huge, and my guess is that the focus lens provides the dominant contribution to the CA, since it is of a type I've not seen through a porro, and only appears in internal focusing roofs that have a focus lens behind the objective. It is seen as purple fringing. I recently tried a B&L 8x40 Elite, and the colour fringing was appalling.

The reason I mention tripods and astronomers is because I believe Henry recommends testing on a tripod i.e. not necessarily using a tripod, but testing with one. (Yes, it is a more correct procedure.)

Back on the ranch, maybe we need a poll: "When you purchase a binocular do you a) star test it b) test it on an outdoor resolution chart c) choose the one with the nicest advert" or whatever.

I nearly always star test or artificial star test in daylight. Also double stars real or artificial.
I never use test charts, rather clock towers with tiny detail on the clock face or tiny detail on a distant building and distant chimney pots against bright sky. Also white pillars.
These are so well known to me that I can see in seconds if the binocular is good or not.

Tripod mounting is the correct procedure but most are O.K. with improvised mounts or bean bags.

The CA mentioned by astronomers is usually the objective CA, however the whole system including prisms? contributes as do ones eyes.

In actual fact I have never found an optically perfect binocular although I have found optically perfect telescopes where I could detect no errors.

Also star tests are not the ultimate test as faint low contrast planetary detail is a much more difficult test but this applies to telescopes as binoculars are low power instruments.

Stars are rather easy as they are such high contrast but they do instantly show errors.

Binastro said:

Stars are rather easy as they are such high contrast but they do instantly show errors.

Click to expand...

Yes, they are high contrast. For birding, low contrast test subjects are also important. I feel it is wise to try bins in good light, outdoors, and poor light, outdoors.

I'm assuming this star test is just the 'final check', once you have visually checked CA, field of view, off axis IQ and so on. (Or maybe the first check, to see if you wish to do more tests.)

Binastro said:

These are so well known to me that I can see in seconds if the binocular is good or not.

Click to expand...

This is interesting and IMO worth to point out. The first seconds, when using new binoculars, provide something like an unerring look. During this short time span the eyes (=the visual system) aren't able to compensate all weaknesses of the instrument. I think when using optical instruments, there is always a process of adaption of the visual system going on.

Stargazers need binoculars with very good contrast too, when looking at deep sky objects like M33, M31 or M42, to mention only the most renowned ones.

Steve

Leif said:

Geeky maybe, but interesting. Do you stop down to ~20mm say? Do you find a correlation between full and sub aperture resolution and aberrations? Obviously aberrations do reduce, but that does not say much. It is possible that with a 20mm stop, most bins perform superbly. (A suggestion, maybe wrong.) Naively I might think that pinched optics (objectives, prisms) might not show stopped down, depending on where the strain is.

And do you measure sub-aperture results with a booster and visually, and find a strong correlation?

The chap in the post I linked to mentioned that he saw a correlation between full aperture resolution and the visual resolution in low light.

Regarding the comments from Binastro on chromatic aberration, I see CA through my Nikon 8x32 SE even on a sunny day when the effective aperture is more like 16mm. I roughly measured the focal lengths and found them to be consistent with ~F4. There will be components of CA from the objectives, and the eyepieces, I do not know which dominates. CA through a roof prism bin can be huge, and my guess is that the focus lens provides the dominant contribution to the CA, since it is of a type I've not seen through a porro, and only appears in internal focusing roofs that have a focus lens behind the objective. It is seen as purple fringing. I recently tried a B&L 8x40 Elite, and the colour fringing was appalling.

The reason I mention tripods and astronomers is because I believe Henry recommends testing on a tripod i.e. not necessarily using a tripod, but testing with one. (Yes, it is a more correct procedure.)

Back on the ranch, maybe we need a poll: "When you purchase a binocular do you a) star test it b) test it on an outdoor resolution chart c) choose the one with the nicest advert" or whatever.

Click to expand...

Leif,

Sorry for the late reply, I've been away from the computer.

The answers to your questions are:

Yes, I stop down 8x binoculars to around 20mm to simulate sunlight and star-test with a booster. However, at such a small aperture the magnification doesn't need to be any more than 25-30x for a real star-test. Yes, a good star-test is invariably linked to a clean looking high magnification image, just as it is in any telescope. As you guessed, when the aperture is reduced longitudinal CA and spherical aberration always improve, but more so for large exit pupil binoculars than small ones. Pinching and astigmatism also often improve, but coma or a poorly made roof prism don't change. The only defect I can think of that could actually worsen would be a zone near the center, which would contribute a larger percentage of light to the total wave front error when the aperture is reduced. Finally, no, not all bins perform "superbly" when they're stopped down.

As for CA, comments should always distinguish between longitudinal and lateral. Lateral is the one that is really visible in low magnification binoculars. Usually it's thought of as mostly an eyepiece aberration, but my understanding is that certain objective designs with wide air spacings can also contribute, and that I think is where internal focusing elements enter the picture.

Henry

henry link said:

Leif,

Sorry for the late reply, I've been away from the computer.

The answers to your questions are:

Yes, I stop down 8x binoculars to around 20mm to simulate sunlight and star-test with a booster. However, at such a small aperture the magnification doesn't need to be any more than 25-30x for a real star-test. Yes, a good star-test is invariably linked to a clean looking high magnification image, just as it is in any telescope. As you guessed, when the aperture is reduced longitudinal CA and spherical aberration always improve, but more so for large exit pupil binoculars than small ones. Pinching and astigmatism also often improve, but coma or a poorly made roof prism don't change. The only defect I can think of that could actually worsen would be a zone near the center, which would contribute a larger percentage of light to the total wave front error when the aperture is reduced. Finally, no, not all bins perform "superbly" when they're stopped down.

As for CA, comments should always distinguish between longitudinal and lateral. Lateral is the one that is really visible in low magnification binoculars. Usually it's thought of as mostly an eyepiece aberration, but my understanding is that certain objective designs with wide air spacings can also contribute, and that I think is where internal focusing elements enter the picture.

Henry

Click to expand...

Henry, I don't wish to be rude, but you are rather talking down to me in your post, although that is rather par for the course for a number of Cloudy Nights posters. You might be surprised how many 'birders' here have done university courses in classical optics, or understand optics as part of their work/hobbies. Are you aware of the contribution of spherical aberration to the bokeh of a lens? Well corrected lenses tend to have poor bokeh. That is well known to photographers. Of course stopping down reduces aberrations from the lenses, apart from diffraction as you well know. I was actually asking about the amount seen in practice in binoculars i.e. do most aberrations effectively disappear on stopping down to ~16mm. Yes of course CA is generally separated into transverse and longitudinal. But I do not have access to the optical designs, or ray tracing software, so it is all rather academic, and I saw no reason to distinguish them. I am interested in the net result.

My interest is to relate the star tests you and others do to actual use by a birder. I recall comments by Kimmo Absetz on one his binocular reviews referring to astigmatism seen in a star test not being an issue in practice.

When you say; "Yes, a good star-test is invariably linked to a clean looking high magnification image, just as it is in any telescope."

I had assumed that but I am not sure we are on the same wavelength. When you star test the stopped down binocular, does the star test provide a good measure of the image quality of the instrument when used visually in good daylight, without any booster?

Sorry Leif, I certainly didn't intend to offend you. Since this is a public forum I assume there will be more readers than just you, so I try to make my posts understandable to everyone, including those who haven't taken courses in classical optics, which certainly includes me. If you have an optics education I'm not sure why you even posed the questions.

As to the final question in your last post, my answer is "usually".

Leif,

I read Henry's post #13 and then moved to your reply, and was quite surprised by your comment on "talking down." I thought Henry was being in his usual style matter of fact, straight to the point and, as he said above, trying to make sure other readers also understand. I did not sense anything even remotely ad hominem in what he wrote. Lateral and longitudinal CA are so regularly lumped together or not understood by many of the less frequent posters that it certainly made sense for him to spell it out.

Some posters on these forums may from time to time become a bit aggressive, but Henry is certainly not one of them.

Btw, it is nice to have you back posting Leif.

Kimmo

kabsetz said:

I did not sense anything even remotely ad hominem in what he wrote.

Click to expand...

For example Henry said: "As you guessed, when the aperture is reduced longitudinal CA and spherical aberration always improve"

He was suggesting I was unaware of that basic fact.

henry link said:

Sorry Leif, I certainly didn't intend to offend you. Since this is a public forum I assume there will be more readers than just you, so I try to make my posts understandable to everyone, including those who haven't taken courses in classical optics, which certainly includes me. If you have an optics education I'm not sure why you even posed the questions.

As to the final question in your last post, my answer is "usually".

Click to expand...

Henry, firstly thank you for the final comment. That is what I was trying to get to with my earlier posts i.e. how well the star tests relate to the actual user experiences given the low magnifications e.g. 8x. I star tested my scope - now sold - since it went to 60x, and it was good, but not stellar (no pun intended). I have always assumed star testing bins is going overboard, but it does look as if it is a quick(ish) way to get basic information about the bin.

You did not offend me, but I was surprised you seemed to be teaching me that aberrations reduce as the aperture is stopped down. I was trying to ask to what degree they typically reduce when stopped down to ~16mm, given your experience of testing.

Leif,

If it helps you to read "as you guessed..." as teaching you something you didn't need teaching about, that is certainly your choice. I should know better than trying to act as a peacemaker in other people's discussions.

Kimmo

Kimmo, I was just surprised to be assumed to be so ignorant, that's all.