Lemons? (1 Viewer)

Before joining this forum it never crossed my mind that the scope I bought could be defective ( a Lemon ) Whenever I buy anything I always buy quality and I must admit, I am surprised that the quality of spotting scopes, especially from world class optic manufactures are subject to quality variations.

What is it that make these Lemons defective? Is it the lenses, alignment or something else. Are these top end optics not checked before they are sent out, surely they would have some means of checking them?

Personally I've always been happy the optics I've bought, and I have to admit I'm a bit sceptical that there are that many out there that you need to do a star test before you buy.

Just spotted this.

Star testing a telescope can be a great way to determine if any errors are present in the optical system and what those errors are. The star test is very critical and can show even slight aberrations. It does require a sharp eye and some experience to really get the most out of it. This section will describe how to star test a telescope and give examples of the most common aberrations. For more details on the errors you might see, check out the Optical Aberrations page.

Note: First a warning. The images shown below are idealized examples. Unless you paid as much as a small car and waited on a list for the better part of a decade to get your telescope, do not expect flawless optics. Most mass produced telescopes--even good ones--can show minor flaws if you look closely enough. The real test of a telescope is what you see when you look through the eyepiece under normal conditions. Almost without exception, all telescopes from reputable manufacturers will perform well enough that you could never notice any errors. If you plan on using your telescope to look at high-power, out-of-focus star images, maybe a star test is a practical examination of the scope's optics. But in reality, as long as the telescope shows good images under normal use, a star test doesn't mean too much. However, for advanced users who want to compare different instruments or determine what the limiting factors of their optics may be, the star test is a great way to learn a lot about a telescope.

In my experience there are too many lemons to ignore the possibility, even with expensive scopes. Besides, a simple star-test of the kind that would reveal serious flaws literally takes about ten seconds and can be done in daylight with an artificial star..

The paragraph quoted really applies to using star-testing for bragging rights among the owners of ultra-fine astronomical telescopes where having a scope with less than a 0.99 Strehl ratio gets you tossed out of the club.

What I can't understand though is, if the failure rate, ( for want of a better phrase ) is so high and from your experiences with Kowa, it's 25%. Why don't they test them before they ship them out.
Can these Lemons be fixed, do they need some sort of adjustment, or are they scrap?

They do probably test them, but meet their adequate consumer tests.
I would expect a Kowa 88mm scope to take a magnification of 180x before the image began to break down.

My Pentax 100mm f/12 took 400x without the image breaking down. It was Pentax's own demonstrator.
The 312mm Dall Kirkham custom took 750x with no sign of breakdown. Yet the makers of the D.K told me that one quadrant was not up to their standards. The makers were the best several in the U.K.

Also a lens element can slip slightly out of alignment and give poor performance.

I would expect all telescopes to give slightly differing star test images.

In actual use most consumers would not know the difference.

I often observe through double glazing. Obviously my 1970s double glazing must be better than some because others report image degradation at 10x or 20x.
I see no sign of degradation till 60x, more noticeable at 100x on planets.

Also small scopes are less affected by window glass.

I have had many photos published taken through window glass. Not once has anybody complained or noticed a flaw.

The real cause of image degradation is our atmosphere.

Nikon lenses have high reputations yet a 30cm f.4.5 Nikon lens gave ludicrously bad images. Every star was double nearing the edge.
Compared with a TTH 12inch f/4 it was utter rubbish.
Did professional photographers or magazine editors care or notice? Probably not.

I asked a top U.K. maker of optics whether his optics were as good as he could make them.
He said, No.
It would be far too expensive to make them better than they were.

In the 1980s I saw several military hand figured lenses that cost £250,000 each. That was as good as could be made.
An adequate consumer version might have cost £20,000.

Why?

My guess is many new owners cannot tell the difference,
so companies benefit from "ignorance is bliss".

I just ordered the Kowa 883 from B&H,
so this thread is not helping me.

edj

Hi Ed,
Just learn to to do simple star tests and you can then rest easy.
Make sure the air is steady, say mornings or afternoon with no rapid temperature changes.
Or in a large controlled building setting.

If not, ask folks at the local astro society to test it for you.

Personally I would'nt bother with a star test, if your happy with view, and I'm sure you wiil be. Just enyjoy the scope. I don"t know, but I am not aware of anyone returning any TSN833 because the wern't happy with them.
I just can't sea company like Kowa selling their flagship scopes with defects.

I often observe through double glazing. Obviously my 1970s double glazing must be better than some because others report image degradation at 10x or 20x.
I see no sign of degradation till 60x, more noticeable at 100x on planets.

Also small scopes are less affected by window glass.

I have had many photos published taken through window glass. Not once has anybody complained or noticed a flaw.

The real cause of image degradation is our atmosphere.


Unfortunately Binastro your double glazing is not very efficent by todays standards as regards thermal insulation. All sealed unit double glazing , up to 2002, usually consisted of two sheets of clear float glass with a silver aluminium spacer tube between them and were then hermetically sealed. There was nothing else to them. Unfortunately since April 2002 the replacement windows have to have a U value of less than 2.0, and the last three years a U value of 1.6. This has led to different double glazing sealed units and triple glazing - your units most probably have a U value of something like 3.5 - this required the inner pane to have Low Emissivity glass installed which affect the visability somewhat.

Low E Glass
Low-E glass coatings having improved durability and transmissivity. In particularly preferred forms, the present invention is embodied in surface-coated glass articles which include a glass substrate and a multiple layer coating on a surface of the glass substrate, wherein the coating is comprised of a layer of a transparent dielectric material adjacent the surface of the glass substrate, a layer of nickel or nichrome, and a layer of silicon oxynitride interposed between said layer of dielectric material and said layer of nickel or nichrome. The thickness of the silicon oxynitride layer is most preferably between about 25-200 Å

giosblue said:

Personally I would'nt bother with a star test, if your happy with view, and I'm sure you wiil be. Just enyjoy the scope. I don"t know, but I am not aware of anyone returning any TSN833 because the wern't happy with them.
I just can't sea company like Kowa selling their flagship scopes with defects.

Click to expand...

One of the lemon 883s I tested was replaced by the dealer with a better one. A lemon Zeiss Diascope I tested was returned to Zeiss USA and replaced, but I've found it's not always possible to rescue happy people from their bad scopes.

Hi,

I also had the misfortune to have seen quite some not so great alpha scopes, although probably not as many as HHenry Link or Binastro. My Kowa score is better though, all I have personally looked through were at least good. I read about a really awful example of the Kowa Master Lens on cloudynights.

The two times the aperture in mm rule for max. useful magnification is for astro scopes - spotters should be allowed a little leeway in my opinion - they're usually very fast ED doublets for weight and size reasons and all the glass path of the prisms does not make things easier, especially in a fast instrument. I would regard 1.5 times the aperture in mm as the standard to meet for a spotter - most cannot get that high anyways due to limited choice of proprietary EPs and no extender available.

Joachim

Les, thanks.

I am aware that my double glazing is inefficient.
However, despite requests to have it replaced with new units I will not do so.
I much more value glass windows that make my place into an enclosed observatory.
The lower transmission does not bother me either.

In fact my heating bills are quite low.

The Mirador 30-120x70 Maksutov scope is perfectly happy at 120x through the double glazing.
The Acuter 80mm spotter shows degradation at 95x but still showed 4 belts on Jupiter.
The 90mm Skywatcher Maksutov shows no ill effects at 125x.
Some of the windows are better than others.
I use any binocular through the windows with no problem just gently touching the glass and window frame.

Horace Dall had selected single plate glass windows in his attic observatory. He selected the best and may have worked on it also.
We looked at Mars at 400x at a big angle with his own made 8 inch Maksutov.
The view was quite astonishing.

After he passed away his widow Helena said I could have the windows covering the tomatoes, which she thought came from the attic after he had double glazing installed, but they were not his attic windows. If they had been I would have installed them and happily observed at high power from indoors.
There are a few enclosed observatories with optical glass windows.

There are far more lemons than peaches in my experience when it comes to scopes and binoculars.

Binastro said:

I asked a top U.K. maker of optics whether his optics were as good as he could make them.
He said, No.
It would be far too expensive to make them better than they were.

In the 1980s I saw several military hand figured lenses that cost £250,000 each. That was as good as could be made.
An adequate consumer version might have cost £20,000.

Click to expand...

It's not a question of can they make them better. I don't think anyone would not be happy with a good example of a Kowa TSN833. The problem seems to be, can they make them of consistent high quality. The answer, for some reason seems to be, no they can't. The question I'm asking is, why not, what do they have to do make a consistantly high quality product. Is it just the nature of the beast that these are made to such fine tolerances it's difficult, without increasing the price?
What is wrong with these sub standard scopes? Is is something that is easily sorted or are they scrap?

Hi giosblue,
It could be that the alignment is just out and they need to be put on an optical bench and realigned.
They can probably be improved although there may be some lens elements or prisms that are not up to specification.
If Kowa get a bad example back they can if they want improve it.

Binastro said:

Hi giosblue,
It could be that the alignment is just out and they need to be put on an optical bench and realigned.
They can probably be improved although there may be some lens elements or prisms that are not up to specification.
If Kowa get a bad example back they can if they want improve it.

Click to expand...

Is it not, 'when, not if' Kowa get a bad example back?
These are not exactly massed produced, surely it woun't be too difficult for them to test each scope before it was shipped. They must some sort measuring equipment they use during assembly. These are massive world class company's, If I was head of Kowa and we got a single scope back that didn't meet it's spec. It would thoughly investigated so it didn't happen again.


Oh and a Merry Christmas to all the members for wonderful forum. All the best for 2018

Hi edj,

edwincjones said:

I just ordered the Kowa 883 from B&H,
so this thread is not helping me.

Click to expand...

Maybe this test of multiple 883s will ease your mind a bit:

http://www.tvwg.nl/testrapporten/telescoop/spreiding_in_optische_kwaliteit_bij_telescopen2.shtml

Part 1 tested Zeiss scopes:

http://www.tvwg.nl/testrapporten/telescoop/spreiding_in_optische_kwaliteit_bij_telescopen.shtml

Regards,

Henning

Thanks for the link, Henning.

I only have time now for a couple of comments. Firstly, to make sense of Jan Meijerink's resolution figures you have to double them because he derives his figures from lines per millimeter on his chart rather than the more usual practice of using line pairs per millimeter. Once you've made that adjustment all of these scopes look like lemons. The resolution of the best one works out to about 140/Diameter of the objective lens and the worst one about 156/D (a diffraction limited scope would be about 116/D). I doubt that they are all lemons. It's more likely that the imaging camera or the 60x maximum magnification is acting as the limit on the test resolution for the best specimens.

Notice that the worst performers show evidence of coma (red fringes of lateral color) and astigmatism (unfocused lines perpendicular to focused lines). A star-test would confirm the presence of those and any other defects.

Henry

Some of the lemons may be because delivery workers used the parcel as a football.
There was footage on the news a few days ago showing how poorly paid delivery workers routinely deal with parcels.
It reminded me of the envelopes marked, 'Photographs don't bend'. The mail workers replied, 'Yes they do'.

I have seen military optics that are extremely well packed and have warnings on bad handling.
In addition the parcel has g meters.
If the g forces exceed the set limits the optics are rejected and the maker informed why. The g limits are not high.
Other military optics can deal with very high g forces.

From what height can a Kowa 883 be dropped without getting out of alignment?

This is a very interesting thread. I always try to pack any optics a little overkill, but maybe I should go a little bit more overkill.

Edj you have until Feb. 1 2018 to return the Kowa with the extended return for the Holidays at B&H.

I am actually serious about dropping scopes and other optics.

Any optics receiving the abuse shown on the T.V. news is likely to suffer damage unless seriously well packed.
Preferably lots of bubble wrap in a box and then placed inside another protected box.