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ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Dust, other imperfections in glass (1 Viewer)

C

CarterMT

Active member
Greetings,

Wondering if any of you would like to weigh in on what you consider to be appropriate expectations with respect to new optical equipment. I keep finding that every instrument I buy has some obvious (to me) manufacturing flaw or flaws. The latest is that my new 7x42s have some kind of imperfection in the glass that can be seen through one of the objective lenses. I didn't even look for it, instead it just jumped out at me while in the field the other day. It has since been suggested to me that all optical instruments (regardless of price) have visible flaws in the glass. Do you agree?

As ever,
CMT
 
Does a photo showed the imperfection?

Some binoculars show no visible optical flaws or dust etc.
A perfectly clean binocular does not mean that it necessarily performs well.
But usually small things don't matter.
 
CarterMT said:
Greetings,

.....
.....
It has since been suggested to me that all optical instruments (regardless of price) have visible flaws in the glass. Do you agree?
CMT
Click to expand...

All ? No.

But many do, in fact even very expensive ones.

If imperfections inside the glass are small, they usually don't really affect performance of the instrument much.
On the other hand, it can be frustrating to buy very expensive optical equipment and then realize that despite the high price and the reputation of the manufacturer, the equipment is less than perfect.

Over the years, I had to return several binos, including Zeiss/Leica/Swaro ones, for service, and some were repaired, other exchanged against a new one. In one case, a half inch sized spot in an objective lens was the cause for the exchange. This should not happen - quality control should prevent such a bino from entering the market. But it still does happen :-(

At least with the big names, service or exchange is usually not an issue, so if you are really unhappy with your bino, you might consider returning it.
 
So interesting. I readily admit limited knowledge of optics, but it's borderline astonishing to me that instruments which cost upward of $2k seem to be so frequently problematic. Part of the problem, in my view, is that those of us who are willing to pay for alpha binoculars are probably the ones most likely to closely scrutinize them.
 
come on they screwed up the Hubble Telescope.......what do you expect from commercial production binoculars, even alphas........
 
CarterMT said:
Greetings,

Wondering if any of you would like to weigh in on what you consider to be appropriate expectations with respect to new optical equipment. I keep finding that every instrument I buy has some obvious (to me) manufacturing flaw or flaws. The latest is that my new 7x42s have some kind of imperfection in the glass that can be seen through one of the objective lenses. I didn't even look for it, instead it just jumped out at me while in the field the other day. It has since been suggested to me that all optical instruments (regardless of price) have visible flaws in the glass. Do you agree?

As ever,
CMT
Click to expand...

The best glass for prisms is BaK4, Barium Crown, then comes Schott PSK3, Phosphate Crown. The Chinese use a lot of BAK4 (note the capital A) which I think is Borosilicate Crown and very similar in characteristics to PSK3 but BAK4 is allowed twice the bubble density of BaK4. This implies that even the best glass can have bubbles. Do they make a difference to the image? Not really unless they were very near the surface and the polishing broke then so they fill with polishing compound.
 
This is an interesting thread, it's not something I have thought about, but I bought a Bushnell porro a while ago, new, in original packaging, I kept it awhile, but I never used it, so decided to sell, it was then I noticed a flaw looking through the right objective, just as CMT describes, I just assumed I had been duped with a "factory second" and sold it cheap as having a fault. A few years ago, with a Leica BN, I noticed a little tiny bubble in the glass of the right eye lens, I thought it was the coating at first, but then saw it was inside the glass. Again, when I sold it, I let it go fairly cheap for a Leica, as I saw this as a rare or unusual fault, but it seems more common than I realised.
 
Around 1980 I bought a range of Hoya brand lenses for Minolta, new but half price. They looked smart and nice.

Then I noticed that they all had hundreds of small bubbles in the glass, presumably Hoya glass.

I don't think Hoya made many own brand lenses.

Not sure how the performance was as I didn't like the bubbles.

Early Hoya filters that I have are not flat.

Just now it is sunny and I noticed colour fringing on the edge of the small bit of sunlight on the carpet from a gap in the curtains.. Put a white tissue down. Definitely coloured edge, reddish. Not CA I think but diffraction.
And these are good quality curtains.

In the evening the round solar images on the wall are also coloured.
Perhaps I should ask for replacement curtains. :)
 
Binastro said:
Just now it is sunny and I noticed colour fringing on the edge of the small bit of sunlight on the carpet from a gap in the curtains.. Put a white tissue down. Definitely coloured edge, reddish. Not CA I think but diffraction.
And these are good quality curtains.

In the evening the round solar images on the wall are also coloured.
Perhaps I should ask for replacement curtains. :)
Click to expand...

David

Its a problem caused by inaccurate eye placement. If you turn around and face directly away from the phenomenon I can guarantee you will no longer be troubled by it :-O

Lee
 
Hi,

imperfections in optics will happen at all quality levels - the really important questions are:

a) are they visible when looking at the instrument or when looking through it (to cite some famous instrument maker)?

b) if a is true, how does the vendor react?

Regarding dust on and small bubbles of similar size in the glass are probably not visible in daytime viewing unless they are in focus as shown in the schott paper.
At night they might cause a tiny bit of diffraction which could result into visible contrast loss if there's a quite few specks of dust...

If you want lenses without bubbles, you can use examples made from grown crystal like the CaF2 used in some scopes (spotters or astro) but then you need one or two mating elements usually made from optical glass.

Regards,

Joachim
 
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