wearing glasses while observing?

[yeti monster]

As I do!

That post should be a sticky me thinks, excellent advice.

[Specman]

Just as an aside,

Grit and swarf are a nightmare, its unbelievable what just one or two grains of sand, swarf or grit can do to optical products.

A friend of mine who purchased some bino's from me about 6 months ago returned them because one of the twist up eye caps kept falling down during use.

When I checked them over I couldn't believe the amount of crud in all the hard to reach places. I spotted the cause of the problem straight away. Dirt and a few grains of sand or grit had got under the cap, as it has being twisted up and down over the last few months, this grit has sanded down the material between the cap and the EP!

During use the EP's must have steamed up or got grubby and in her haste, I suspect they have been hastily wipped with gloved hands or the edge of a T-shirt, because said grit has cut circular scratches into the reflection free coating!

Vigilance and caution! Its easy done, a lesson to us all I think.

Clear skies

Mark

[Mikea]

The other thing you shouldn't do with spectacles is put them in one of those confounded ultrasonic cleaners. Makes the coatings come off! A friend of mine did this......ahem.

[yeti monster]

^^^ rather silly of them...........

[Specman]

We use ultrasonic cleaners in the lab on a daily basis for cleaning spectacles. However there are ultrasonic cleaners and there are ultrasonic cleaners! Ultrasonic cleaning is a science in itself and its not the place to get into it here.

Suffice to say that used appropiately and correctly they do not damage coatings. If a coating comes off in one of our cleaners then the coating is rubbish, simple as that!

Be aware that in the optical industry there are a lot of cheap HMAR coatings about. Thirty years ago cheap, single layer AR's had a pink reflex and the better quality multi-layer coatings were green/gold. Faking a good coating was impossible, then along came somebody (China probably) and figured it out, now a coating can be any colour you want it to be regardless of quality.

There is still a way to tell though. Top quality, anti reflective coatings don't need a colour reflex these days, the only problem is that when one company tried to sell achromatic coatings they couldn't make it work because the customer couldn't see it! Hence the reflex!

A top quality coating shouldn't be obvious, you should see through the lens and not just see reflex. Take the green coatings for example, the greener, more emerald and obvious the coating is, the cheaper it is. The better quality green coatings are more golden, straw like green and subtle.

If you opt for branded lenses like Essilor, Seiko, Zeiss, Hoya etc you can always be sure of a good coating. If you go for free or own brand lenses from your optician its rather like ordering house wine! You gets what you pay for!

Quality coatings don't just lie on the lens surface, they are multilayer and the base layer is an etch coat that adhers to the lens surface.

What can happen is if the items are heated or cooled rapidly is a break down between lens surface and coating. The base lens and the coating can expand and contract at different rates causing crazing and irreparable damage to the coating. For example, wearing coated spectacle lenses in a sauna/cold shower or leaving your specs on the dashboard of a hot car.

Some more industrial type of ultrasonic cleaners have built in heater that can bring the water temp closer to boiling, this will damage your coatings, as will dipping a plastic frame with coated lenses into a cup of hot water to remove the lenses. Or boiling them in a pan of hot water to clean them ( I've seen it done!).

From an Astronomy point of view as winter comes and kit starts to frost up, don't be tempted to put your EP's on the heater to defrost when you come in. If your optics get frozen, defrost at ambient temperature.

In summary, a good, modern, top quality anti-reflective coating is scratch resistant, hydrophobic, anti smudge and dust repellant and if treated correctly will give years of service and still look as good as new.

http://www.essilor.co.uk/lensinfo/pdfs/Crizal_2010_Range_Brochure.pdf

Hope this is some help.

Clear skies!

Mark

[Mikea]

^^^ rather silly of them...........

Yes it was. It was my wife.... er... his wife's idea...

[Tantalus]

I wish I'd read this a month ago. I bought a new pair of specs from one of the more 'upmarket' opticians in the hope that I'd get the better product. I paid extra for anti-glare coatings and although there is no noticable colour from the coatings when I'm wearing them, any lights reflected on the front on the lenses do have a green colour. And they weren't cheap!

Specman - What's your opinion on Retinal Photography. Is it really helpful or just a waste of money (albeit only a tenner) ? And do eye exercises work?

[Specman]

I wish I'd read this a month ago. I bought a new pair of specs from one of the more 'upmarket' opticians in the hope that I'd get the better product. I paid extra for anti-glare coatings and although there is no noticable colour from the coatings when I'm wearing them, any lights reflected on the front on the lenses do have a green colour. And they weren't cheap!

Specman - What's your opinion on Retinal Photography. Is it really helpful or just a waste of money (albeit only a tenner) ? And do eye exercises work?

I think Retinal Photography is really a good thing as it gives a very accurate, chrisp clean image of the retina, and optic nerve. Much clearer than the image from the retinascope alone (the gadget the optom uses to peer into your eyes from about an inch away from your face). What is 'normal' anatomy varies greatly from patient to patient, what really matters is CHANGE. If something changes in the back of the eye, a bleed or cupping of the optic disc for example that could be the start of something more serious and it needs to be monitored or acted upon.

Of course, this is only of benefit if you attend the same optician on a regular basis. Your patient records don't follow you about quite the same as they do in the NHS (although in theory they should).

Eye health is extremely important and the importance of the clinical side of an eye test should not be underestimated.

I am a qualified Dutch Optician and in Holland they do things very differently. They have separated the clinical side from the high street opticians to some extent. They treat the clinical, medical, health of the eyes separately by doctors, ophthamologists, orthoptists from shop keepers selling you Gucci, Dior etc.

This means that people can have their health checks without the worry of being hit with a £300+ bill! Or being made to feel they have GOT to buy new specs.

Check about. Some companies / independants offer the service free.

As for exercises to improve sight, example The Bates Method for Good Sight Without Glasses, IMO you can't correct a sight defect with exercises, though don't confuse this with exercises given to a patient / child by a Orthoptist to correct a squint (Strabismus). The evidence is rather thin on the ground on this one http://en.wikipedia.org/wiki/Bates_method, however belief is a wonderful thing as a placibo effect.

Also wearing spectacles doesn't make your vision worse, your brain simply gets used to seeing clearly, which makes it seem worse without your specs (especially for people who are shortsighted (myopes))

Clear skies

Mark

[Tantalus]

Thanks for the feedback Specman, some really useful information there.

This particular optician makes the retinal photos available online, so I now have a permanent copy for myself. I'm myopic, and without my specs I struggle to see much of the night sky - nearly everything becomes a feint fuzzy

[Specman]

Thanks for the feedback Specman, some really useful information there.

This particular optician makes the retinal photos available online, so I now have a permanent copy for myself. I'm myopic, and without my specs I struggle to see much of the night sky - nearly everything becomes a feint fuzzy

Yes thats right Tantalus. There is a tendancy for the eye to become more myopic under conditions of low illumination by as much as 0.25 - 0.50 dioptre. That is why night driving can be difficult for a myope, especially if your prescription is a little weak and out of date.

I'm as blind as a bat in the dark

Clear skies!

Mark

[yeti monster]

I'm as blind as a bat in the dark

Radio telescope???

[michael.h.f.wilkinson]

Yes thats right Tantalus. There is a tendancy for the eye to become more myopic under conditions of low illumination by as much as 0.25 - 0.50 dioptre. That is why night driving can be difficult for a myope, especially if your prescription is a little weak and out of date.

I'm as blind as a bat in the dark

Clear skies!

Mark

There is also the issue that a dilated pupil has less depth of field, so the effect of any error in the correction of myopia is increased. Furthermore, in the dark the rods are more active than the cones, and the former have larger receptive fields, decreasing overall sharpness.

Personally, I have few problems seeing in the dark, at least with my relatively new glasses. Being an amateur astronomer for some 32 years, using averted vision has become second nature, and this helps a lot in the dark.

[Specman]

There is also the issue that a dilated pupil has less depth of field, so the effect of any error in the correction of myopia is increased. Furthermore, in the dark the rods are more active than the cones, and the former have larger receptive fields, decreasing overall sharpness.

Personally, I have few problems seeing in the dark, at least with my relatively new glasses. Being an amateur astronomer for some 32 years, using averted vision has become second nature, and this helps a lot in the dark.

I couldn't have put it better myself Michael

Clear skies!

Mark

[michael.h.f.wilkinson]

I couldn't have put it better myself Michael

Clear skies!

Mark

Thanks!

No clear skies in sight yes, alas!