wavefront error (1 Viewer)

It occurs to me that I have not read of Swarovski or other alpha makers measuring for wave front errors. I thought for some time that perhaps it was just the luck of the draw, sort of the "made on Monday" unidentified reason some samples tested superior to others. In fact, the only gentleman whom I had even seen mention it was over on the Cloudy Nights site where he measured wave front concerning certain samples he was evaluating. Then I read of Leupold Stevens deliberately addressing the problem for their VX6 rifle scopes. Their advertising mentioned that they had entered a new understanding of optics.
My question is--have the big boys given any consideration to eliminating wave front errors? Bro.Steve

BTW, anyone on this forum have an interferometer to test with?

I'm not sure what we would do with the (very interesting) data though, as I think it would fall under Bill's "below the threshold" comment.

bro.steve,

Forum members who work for optics companies might have access to interferometers, but don't hold your breath waiting for those kind of data to be made available.

A few of us amateurs star-test binoculars at high magnifications to evaluate aberrations. That can both reveal and explain some wavefront errors that are definitely "above the threshold" of visibility. Here's an example of binocular star-testing I did last year.

http://www.birdforum.net/showthread.php?t=285414

Henry

At the present time were stuck on Swaro focus knobs and occular condensation. ||

Thanks for the link, Henry...very helpful

A more modest initial step would be to provide actual test results for each glass. The unwillingness of any of the manufacturers to document the performance of their product makes product selection an almost entirely subjective matter of taste.
Thankfully that does nothing to impede spirited discussions of product quality. o

wavefront errors?
Sounds new to me,
since I didn't see any CA in bins* before I had heard about it,
(back then, it was said, that no bins really needed ED-glass because the focal length was so short…)
anyway, does this mean that I will start to see wavefront errors now?
:eek!:

bro.steve said:

BTW, anyone on this forum have an interferometer to test with?

Click to expand...

I know Gijs has a interferometer available at the University of Utrecht where he use to work (retired now) and test all kinds of bins on spectra for light transmission data but could somebody explain to me what a wavefront error is, how it is caused etc.
I have even never heard of the term.
Can't ask Gijs because he is on safari in Africa for the coming 6 weeks.

Jan

jan van daalen said:

I know Gijs has a interferometer available at the University of Utrecht where he use to work (retired now) and test all kinds of bins on spectra for light transmission data but could somebody explain to me what a wavefront error is, how it is caused etc.
I have even never heard of the term.
Can't ask Gijs because he is on safari in Africa for the coming 6 weeks.

Jan

Click to expand...

my guess is that start testing is much about detecting WF-errors,
found some info here

http://www.telescope-optics.net/aberrations.htm

henry link said:

bro.steve,

Forum members who work for optics companies might have access to interferometers, but don't hold your breath waiting for those kind of data to be made available.

A few of us amateurs star-test binoculars at high magnifications to evaluate aberrations. That can both reveal and explain some wavefront errors that are definitely "above the threshold" of visibility. Here's an example of binocular star-testing I did last year.

http://www.birdforum.net/showthread.php?t=285414

Henry

Click to expand...

yes, thats an interesting test you did, the HT:s really seem optimized for extreme low light observations, hmm, hopefully..

Do you see any point in having a variable aperture in larger bins, similar to camera lenses? So it would be possible to stop them down in daylight?

Vespobuteo said:

my guess is that start testing is much about detecting WF-errors,
found some info here

http://www.telescope-optics.net/aberrations.htm

Click to expand...

Thanks!

Jan

Vespobuteo,
. Your pupil, which is normally quite small in daylight will stop down the binocular automatically unless it is a very high magnification binocular.

I star test every binocular that I come across if I'm able. In the daytime I use the glint of the Sun on ballbearings for the same purpose. I have used raindrops on leaves similarly.

The reason why it is fairly pointless for manufactures to give us wavefront errors for binoculars is that the binocular is as it is. To improve the quality they would probably have to hand figure every component and this would vastly increase the price. This is probably worthwhile with top end binoculars costing £2000.
Also the tolerances with binoculars are quite lenient. I think that the Russians have higher standards than the West. Some common Soviet era prisms have been tested at one 20th wave.

I have it on good authority that some of the finest lenses for laser work have to be hand figured as machine figuring is just not good enough. And there are very few technicians nowadays who can do this work to high standards although there were quite a lot in the past.

I have a small Angenieux binocular which comes with a wavefront error document. The problem is that a very similar looking ancient Pentax 8×24 binocular is far superior optically and mechanically. Unfortunately the Pentax is not waterproof whereas the French one I think is waterproof. So the Pentax has some fungus in it, but I would never send it to a repairer for cleaning as I think it is quite impossible for the repairer to reassemble the binocular into the perfect optical performance that has now. Even the manufacturer might have difficulty equalling this performance. And if I bought another Pentax 8×24 it is likely to be not as good.

I had a Vivitar series 1 zoom lens that I found to be compromised optically. I sent it back to Vivitar, who then had the finest optical test bench in Britain I think, and they agreed with me and tested three similar lenses on their optical bench and sent me the best one. You might find this service now from the likes of Leica, Swarovski, Zeiss and Kowa. But I think some other importers wouldn't have a clue what you're talking about.

On another post at the moment asking what binocular I would buy again. I forgot to mention that it must be the Canon 18×50 IS, but again it is quite likely that a replacement would not be as good as the one I have.

Usually with high quality binoculars the optical performance is excellent. It is probably the design that causes problems. Every binocular is individual and as a matter of course if I was buying a binocular in a shop and they had six examples I would test everyone and buy the best. I have often done this in the past. But with expensive binoculars they are likely to have only one.

With top quality spotting scopes around 80 mm aperture, I think that they can easily take 150 times magnification. The reason why the manufacturers don't provide this is I think because they would have to guarantee the performance at 150 times. With someone like Leica their telescopes only go up to 90 times with their 1.8 times Tele converter. I think some of these scopes can probably be used at 200 times. Maybe the top quality Kowa. A Televue 80 mm can probably take something nearer 300 times before the image is likely to be compromised. The Pentax 100 mm F/12 that I had did not break down at 400 times.

But with binoculars, you basically have two poor quality telescopes side-by-side.

By the way, I don't think you can eliminate wavefront errors.
You may reduce them so that you cannot measure them with your testing methods.

Wavefront errors are something I'm not sure we really want to know.

They might be a bit disappointing.

Binastro said:

I have a small Angenieux binocular which comes with a wavefront error document.

Click to expand...

Is this the document you reference? https://www.flickr.com/photos/binocwpg/11413501874/in/album-72157623234405689/

Wavefront interferometry mesurements and certificates make sense for instruments requiring diffraction limited resolution like telescopes working well over resolving power, it's the objective lens which is tested. Only top manufacturers like Takahashi and Vixen and small companies actually do it, perhaps some high end Celestron products also benefit from it, but it takes extra time to perform these tests and most telescope users (let alone binocular users) are unaware of what it is and of the necessity of it.
In theory all quality optical instruments should have their wavefront tested but in real life, and especially for binoculars which are used at very low magnifications and well below resolving power, this is not really needed. Surely some of this work is done on samples in the background for quality checks, but you would have to pay a lot more money if it had to be done systematically.

Dear LPT,
. It is the right binocular, but until I remember where it is and where the paperwork is I'm not sure.
The photos you show are of the transmission, but I thought there were individual plots as well.
However, after several years my memory may be faulty.

I do know that the similar looking Pentax 8x24 is a much better performer. It is the Pentax that I use sometimes and that is 6 feet away.

. My optics manufacturing friends have tested the prism surfaces of Soviet binoculars and some of these are one 20th wave.
Apparently, they also tested some Maksutov military optics, which again were one 20th wave.

And a little while ago the person who made my 20.5 inch F/4 mirror told me that it was also one 20th wave, which amazed me as it was much better than I paid for. But that is how it came out.

I don't know what wavefront errors the top quality binocular manufacturers achieve.

I have been told that some of the Zeiss eyepiece elements which were meant to be cemented, were routinely so good that they stuck together without balsam. I think this meant that they had the same characteristics as if they had been cemented together.

Some Schneider lenses and also some Zeiss lenses have unbelievably good surface accuracies, at least from star testing.

Telescope flat mirrors are also routinely tested for surface accuracy.

However, the triplet objectives of the 1940s 25×105 binocular were tested, and the surface accuracies were not very good, at least for astronomical use.

Dear LPT,
. Thank you for pointing out the error regarding the Angenieux 8×24 F paperwork.
I have not used this binocular for several years and I was going by memory, which in this case was a bit faulty.
Your comments encouraged me to look for the binocular, and I found it in less than a minute.
The 20 page leaflet in French and English has the curve for transmission, which I remembered as being a surface accuracy plot. What confused me was probably the extra information.
In English it gives the definition on page 19 for the centre and edges. The distortion is quoted as less than 3%. The field curvature less than one dioptre. The longitudinal chromatism as less than 0.4 dioptres. The lateral chromatism as less than 0.8 mrad. The axes parallelism horizontal less than 1° and vertical less than 0.5°. The minimum focusing distance 2.75 m.

But this information is generic, and not measured for each binocular.

There is also a 30 year warranty card, but I'm not sure if the company still exists, or whether it has been taken over by a large conglomerate. Also I'm not sure if the 30 years is up yet, as the card is not dated.
There are quite a few exclusions, regarding the warranty, so it is not comprehensive. But there is a fault with the binocular which should be covered, although I'm not going to make use of the warranty.

. Both the French binocular and the Pentax binocular had six months shop guarantees.

I tested the Pentax binocular on the moon and the image is very good. But by the time I found the French binocular it was cloudy and now it is raining.

The actual weight of the French binocular is 438 g approximately and the quoted weight is 435 g. The Pentax binocular weighs 355 g and feels considerably lighter.
The transmission of the French binocular is given as 0.8 with the ultraviolet filters installed. These are 30.5 mm screw in filters marked with the makers name. I think this filter size is used for the rear of many mirror lenses. Polarising filters were an option but are not supplied with this binocular.
Also the binocular comes with a soft carry case but not with the hard storage case. It also has a strap.

The main problem mechanically is that the unusual dioptre arrangement is somewhat faulty probably from wear. This means that is is difficult to get both images sharp. The Pentax dioptre adjustment is normal on the right side and is very good even though the Pentax has probably had more wear that the French binocular. The Japanese sticker on the Pentax is well worn.

The eyecups are much better on the Pentax. The French binocular does not have eyecups and some light can come in from the side.

Looking at ghost images from a street light, both binoculars are quite good and are about equal.
However, the edge performance of the French binocular is much worse than the Pentax. Even though the French binocular field of view is slightly less than the Pentax.
Both binoculars have rather restricted fields of view to my tastes. The Pentax is given as 6.5° and the French binocular 6.3°.

The French binocular has much worse pincushion distortion compared with the Pentax.

I think the Pentax binocular is older than the French binocular. In its time, perhaps the late 1960s I think that the Pentax was the equal of any 8×24 or 8×25 binocular. But nowadays I'm sure that such a binocular with ED glass and top quality coatings would give better images. But I doubt whether it would be any better mechanically than the Pentax.

My impression is that the Angenieux binocular is style over substance or usefulness. The poorer performance of this French binocular is the reason why I put it away and use the Pentax.

The problem with the Pentax is that it is not waterproof. But the fungus spots internally are less bad than I remember. When the sky is clear I will see which binocular shows the fainter stars.
the French binocular is very much more expensive than the Pentax. But in my opinion the Pentax is clearly better.