Double Lens

Double Lens

Be Sure About Your Contact Lens

Contact lenses have revolutionized the way people with eyesight troubles look at the world. Gone are the days when one had to deal with eye glasses and lug around a Carry Case to put them in when the eyes felt too tired or they just needed to take a nap. With discount contact lenses available all over the internet, even those with the lowest budgets are now turning to them.

But before you start wearing contact lenses, you must get yourself a proper prescription from an ophthalmologist, optometrist or perhaps an optician. This stands true even if you don't normally wear glasses and are just looking to by contacts to change your eye color.

The eye doctor will check your eyes to make sure it's okay for you to wear contacts; while it is safe for nearly everyone, there are a few who can't be prescribed lenses. Once you have your prescription, you might wish to look towards the best deal for your contact lenses. And what better place to find contact lenses at discount prices than the internet.

The World Wide Web is today awash with sites offering discount contact lenses - with most of them providing the Full Range of branded ones from top companies. The selection of contact lenses available can only be described as "vast." It is necessary not to become overwhelmed by the selection and check out the different categories of contact lenses available to decide which one best suit your requirements.

To give a brief idea about the different types of lenses - contact lenses are made of many different types of plastic, but are divided into two main groups

• Soft - contacts containing from 25% to 79% water, which are very easy to adapt to and quite comfortable to wear.

• Rigid gas permeable (RGP lenses, now called GP lenses) - rigid gas permeable contact lenses take longer to adapt to, but are more durable and more resistant to deposit buildup. While upfront cost is higher, these lenses tend to be less expensive over the life of the lens because of lower cost of care.

While the advent of online buying has made for time and money saving, there are certain important factors that need to be kept in mind when ordering contacts online - more so from the discount stores. The first point to be remembered is contact lenses are a medical device requiring proper fitting, wear and care. Other necessary guidelines include:

• Keep up with your regular eye check ups with your eye-doctor

• Always check and double check the order you are placing and also confirm the name of the brand and company that you are ordering

• Never accept an alternate brand or type other than the one prescribed by your doctor without first confirming with the medico

• Always check if the product delivered to you is well within its expiration date as soon as you receive it

• Never buy contact lenses from a site the claims discount prices but does not confirm if your prescription is current. A legitimate distributor will always confirm this with every order.

• Lastly, always compare the prices at multiple sites and also check the credentials of the provider through multiple sources before placing your order.

About the Author

Ian Koch
is an internet publisher who likes to publish
Information about Contact Lenses
. Check out
1st-in-contact-lenses.net
for more

Double- Convex lens, Diagram ?

I have a question in my physics assignment which goes as follows,
10. A thin air - filled plastic shell in the shape of a double convex lens is placed in water . Use a diagram to explain whether it acts as a converging or a diverging lens.

Right so im lost on this one.
Nebby , why does the lens change from converging to diverging once it is underwater rather rather then air?

You could draw some approximate rays through the lens, showing what happens when parallel rays enter the lens at different distances from the center of the lens, i.e. what directions they take after passing through the second surface of the lens.

A ray drawn right through the center will not be bent at all.

A ray drawn parallel to the first (centerline) ray but offset up or down from the centerline, when it hits the first surface, will be bent away from the center of the lens. You can see this by the rule of thumb that a ray moving from a low-refractivity medium to a high-refractivity medium is bent toward the normal to the surface (and vice versa: a ray moving from a high-refractivity medium to a low-refractivity medium is bent AWAY FROM the normal to the surface).

As this off-center ray hits the second surface after passing through the air-filled cavity, it may hit it nearly perpendicularly to the surface, but if not, then you would just apply the above rule again. You'll find that this lens is a diverging lens, when it's in water.

Macro - Double Lens setup