Lens Cleaning

The surface of glass is porous and you can tell that from a new
lens, the cloth actually squeaks when you first wipe it across
within weeks muck from the air starts to fill the pores in and
any attempts to clean it with a soft cloth compacts more muck
than it removes. The best cleaner would probably be a gel that
sets and then brings all the muck out of the pores when you
pull it off. Most glass cleaners simply apply a polish on top
of what's already there.

I'm not familiar with the technology, but I would imagine
that Pilkingtons self cleaning glass is very basically glass
in which they have sealed the pores and applied a smooth
coating.

I take it that you've never bought a lens off Rocky

How can this be true of Pentax SMC lenses? SMC was 7 coats according to Bojidar - how can it possibly be still porous?

How is this evidence for pores? I can believe it's evidence for it being initially cleaner than it is after weeks of use, but pores??? Really?

As far as I know glass is effectively a supercooled fluid and it is not porous.

There may be small depressions/"pores"/imperfections in the surface of the glass.

When I think porous, I think terracotta or pumice.

My BS detector is trembling almost as much as when I heard the price of the Q!

[EDIT] Oh no!!! I just read this ..... link

Glass is made from the same material used in sandpaper
If it was a solid you wouldn't be able to see through it!

Lenses have been ground and polished using methods that will
leave slight grooves and break off minute pieces of glass.

I'm off to drink some 'Codswallop' anyway

As dougf8 discovered from reading the link in his most recent post, glass is not a super-cooled liquid, but an amorphous (non-crystalline) solid. For the inveterately curious, a comprehensive review of the physical and chemical properties of glass can be found here: link

Pre-formed glass can be made porous, at a molecular level, by chemical treatment, but is now also possible to manufacture glass substrates with defined pore sizes that have many applications in biomedical research.

I do not know whether or not the glass found in optical lens elements contains pores, but that it should do so by design seems counterintuitive, as this would have the effect of making it a 'dust magnet' and very difficult to keep clean. For this reason alone, I share Chris A's scepticism that it does.

Perhaps you can enlighten us further, Algi

Jon

I have some radio valves (with glass envelopes) that were manufacture during WW2 and they still work ie they still have a vacuum inside them.

Surely if porosity was a problem then gas would leak in (it does very very very slowly and the valves eventually cease to work. Note also that the glass in valves is less than 10thousand of an inch - not the thickness of lens glass)

My point is that if the pores are so small then dust would not be absorbed into the surface

Bernard

The OP just asked about cleaning lenses It seems that
no one knows the difference between clean glass
and dirty glass

I suppose porous is a bit too broad to describe the surface of
glass? The correct term is hydrophilic link

The surface of glass when greatly magnified looks more
like Sterling board.

Kenko now have filters with an Ultra Smooth Surface link

Ultra Smooth Surface - Nano Glass Technology

Our Nano Glass Technology creates an ultra smooth surface
from the finest particles of glass, making it stain and
scratch resistant without any effect to the image.

This should stay a lot cleaner... so just leave a UV(0) filter
on you lens all the time to keep the front element clean.
It doesn't degrade picture quality and can actually improve
landscapes.

I can't see any point in taking this thread any further it's
already slightly off topic

It totaly agree this has gone totaly off subject all I wanted to know was.
"When the time comes should the rear optic be cleaned the same as the front optic or should it be left to a professional? Any special precautions or useful links etc would be greatly appreciated"

Kind thanks for all the advice and input, but it's now gone too technical for me to understand or cope with.
Regards David

Good idea John.... put a UV filter on it

I am now confident that it's OK to use carefull normal methods to clean the rear optic the same as I do the front. Because of the risk to the mechanics of the lenses, if required I will only use cleaner fluid by putting it on the cloth rather than spraying it onto the lens.
Thanks to all David

If it's hydrophilic, it attracts water**.

So why is that ROR product aimed at removing residual oil?

Has anyone here actually used it? TBH, I don't think I'd take the chance - as JR said, it sounds more like snake oil. And I'm still rolling my eyes over the 1.5 stops claim. See:

IMO, an advert for a lens cleaning fluid that makes ludicrous claims is not at all off-topic, if the thread title is 'Lens Cleaning'.

And I still don't see the relevance of any alleged porosity or hydrophilicity, if Pentax apply 7 coats of something that presumably bonds very tightly to the glass.

Edit:

Incidentally, water in the air that gets bound to the glass is something that you can simply do nothing about. At room temperature and ordinary levels of humidity, dried glass readsorbs (sic) water so quickly that to all intents and purposes, it's always present unless you take special precautions to exclude it.

There's simply no possibility that you could buy a brand new lens and have it somehow drier than it would be after a few weeks. The notion that the presence of water molecules on/in the structure of the glass is undesirable and somehow affects the optics is similarly without basis.

__________________________________
** I can vouch for that from direct experience, BTW - in my days as a chemist I often used to do anhydrous reactions, which involved baking the glassware at high temperature for several hours, and allowing it to cool in a desiccator under vacuum, which was then refilled with argon prior to handling the glass. Since argon is denser than air, the idea was to get a stopper into the flask before the argon could be displaced by moist air. Solvents used in such anhydrous reactions also had to be dried, but that's another story.

ROR is superb stuff and my daughter uses it to clean her sight trial lenses, don't think Optometrists would use snake oil.

Lenspen make a microfibre cloth that comes in their Lenspen sets, strange then to read the last few words of this paragraph

Micro Klear - Deluxe Microfibre Suede Cleaning Cloth for cleaning the housings of digital cameras, photo equipment, camcorders, cellular/PCS phones, televisions, stereo equipment, CD's, CD-ROMs, DVDs, computers, photocopiers, jewelry, musical instruments, glassware, crystal and much more. (Not recommended for high quality lenses).

Great that we have an actual user!

Can you be a bit more specific, about why it's so good (and what are sight trials?)?

I take it these lenses don't really let three times as much light through after cleaning with ROR??!!