Filters may be made from sheets of coloured glass, plastic, or dyed gelatin, and in some cases glass cells filled with liquid have been used. Since World War II, another type of filter depending on the interference of light has been developed in which one or more metallic or other types of films of controlled thickness have been deposited on a glass plate, the layers being so thin as to cause selective interference of some wavelengths in relation to others and thus act as a nonabsorbing filter. In this case the rejected colours are reflected instead of being absorbed.

In 1690 Christiaan Huygens, a Dutch scientist, postulated that a light wave progresses because each point in it becomes the centre of a little wavelet travelling outward in all directions at the speed of light, each new wave being merely the envelope of all these expanding wavelets. When the wavelets reach the region outside the outermost rays of the light beam, they destroy each other by mutual interference wherever a crest of one wavelet falls upon a trough of another wavelet. Hence, in effect, no waves or wavelets are allowed to exist outside the geometrical light beam defined by the rays. The normal destruction of one wavelet by another, which serves to restrict the light energy to the region of the rectilinear ray paths, however, breaks down when the light beam strikes an opaque edge, for the edge then cuts off some of the interfering wavelets, allowing others to exist, which diverge slightly into the shadow area. This phenomenon is called diffraction, and it gives rise to a complicated fine structure at the edges of shadows and in optical images.
Dr. Bryant came to the NBEO after serving as Assistant Professor of Ophthalmology and Director of Contact Lens Service at Duke University Eye Center for almost ten years. Dr. Bryant has also served as a Clinical Examiner for the NBEO Part III examination and as a member of the Continuing Professional Development in Optometry (CPDO®) examination development Committee and Council. In addition, she has served as Assistant Chief Clinical Examiner of the North Carolina Board of Optometry. Dr. Bryant served as the President of the North Carolina Optometric Society in 2016-17, where she now holds the position of Immediate Past President.
I came to Standard Optical specifically for a laser surgery consult. My initial consult was with a male optometrist, whose name I can't recall. It was pretty basic and he said it seemed I'd be a good candidate for PRK. I had to do a pre-op appointment here as well, with deep dilation to get good measurements. Everyone was clear that it was possible I would arrive at the surgical center in Holladay and be told that I wasn't actually a good candidate, given my extreme near-sightedness. They told me about the possibility of an ICL surgery, but not much beyond it being more expensive and a lens is inserted. I took away one star because I feel the doctors should have been more careful in telling me I was a good PRK candidate. When I went to down to Holladay on the day of my scheduled PRK procedure, I was told by the surgeon (Dr. Williams) that I was too near-sighted (more than -10) and I would not be happy with the results. He said the doctor at the Ogden location had measured me at just less than -10, which is the cutoff, and that's fine given the different technology they have at the Holladay location. However, if the Ogden doctor knew I was right at the cusp, I would have like to have been told that and used it to make up my mind about scheduling the PRK procedure. I only have one pair of eyes, I probably wouldn't risk it if I was at the extreme edge of permissibly. Also, when they told me about the ICL procedure, all they said was that it was more expensive. Honestly, it felt more like an upsell than a "this procedure could be better for you" discussion. In actuality, once Dr. Williams explained the procedure and pricing to me, the ICL is LESS profitable for Standard Optical (you pay more than LASIK/PRK because of the surgical center fees, the portion to SO is less than the laser procedures). Regarding my appointments with Dr. Williams and my ICL surgery, I could not be more pleased. He took his time explaining the ICL surgery, drawing pictures of what he was talking about so I'd be able to understand. I was very grateful he didn't just laser off a good chunk of my eye. I had the ICL procedure performed a few weeks later. My father watched my surgery on a screen in the waiting area and was impressed by how careful and meticulous Dr. Williams was. I will need to have a LASIK touch-up to take care of my astigmatism (the ICL addressed my severe near-sightedness), but that was something that Dr. Williams let me know about at our very first discussion about the ICL, so I don't feel like I was overpromised anything in any way. I couldn't say enough good things about Standard Optical and Dr. Williams for a surgical procedure...if you've been considering it at all, call now!! The ICL procedure is expensive, but with my extreme near-sightedness, I was paying more than $600 for a pair of glasses. The cost of the ICL will easily recoup itself with me no longer having to buy expensive glasses each year! One more thing...the front ladies at the Ogden location are AWESOME! I asked a gazillion questions about the PRK procedure and had to reschedule the dates of my procedure twice. They never acted like they were put out with me, they remembered me by name every time I came into the shop, and they were so excited for me to have my surgery.
We make eye care easy at your Riverdale Target Optical located at 1135 W Riverdale Rd. Every day we deliver on our "expect more, pay less" promise by bringing together quality eye care, fashion, affordability and a simple, fun shopping experience. You always get more looks for less with your eyeglasses and sunglasses with top brands like Ray-Ban, DKNY, Armani Exchange, Oakley and more. And popular brands of contacts like Acuvue, Air Optix and specialty lenses. Whatever your choice, you get a great value on our quality lenses with a 90-day unconditional guarantee. We’re here to help you get the most from your insurance benefits and answer all your questions quickly. And when it comes to taking care of your eyes, we can't say enough about the importance of an annual eye exam. Eye exams available by Independent Doctors of Optometry next to Target Optical.
A large astronomical mirror presents many problems to the optical engineer, mainly because even a distortion of a few microns of the mirror under its own weight will cause an intolerable blurring of the image. Though many schemes for supporting a mirror without strain have been tried, including one to support it on a bag of compressed air, the problem of completely eliminating mirror distortion remains unsolved. A metal mirror, if well ribbed on the back, may be lighter than a glass mirror and therefore easier to handle, but most metals are slightly flexible and require just as careful support as glass mirrors. Since temperature changes can also cause serious distortion in a mirror, astronomers try to hold observatory temperatures as constant as possible.
For those who need professional ophthalmology treatment, we have two operating suites in our office where we can perform surgical procedures on site such as LASIK, diabetic eye disease treatment, brow lifts, and blepharoplasties. As for intraocular surgeries for glaucoma or cataracts, we perform the surgeries at a local hospital so the care you need is never far from home. We also offer 24/7 emergency assistance so we can help you when you need us most. Just contact our emergency number at (801) 625-3039. 

Dr. Fellows's Biography — Dr. Bradley Fellows has been in private practice for 25 years. He received his optometry degree from Pacific University, serving internships at the VA Hospital in Vancouver, Washington and Grace Peck Clinic in Portland, Oregon. Early in his practice he saw patients at the VA Hospital in Salt Lake City and served as part time staff and clinician at the U of U hospital. He served for 10 years on the Utah Optometric Association Board of Directors, serving as the UOA president in 1993. Dr. Fellows received the Young Optometrist of the Year Award in Utah in 1993. He also served on the Utah State Licensing Board of Optometry for 6 years. With his experience and training Dr. Fellows specializes in routine and medical eye care, pediatric vision care, pre and post lasik and cataract care, as well as all types of contact lens fittings and treatment of eye diseases. He loves his work and his patients who have been with him since the beginning. He loves being able to see the grandchildren and great grandchildren of his first patients from 25 years ago.
American Optometric Association: "Proper Nutrition Is Critical to Eye Health," "Antioxidants and Age-Related Eye Disease," "Diabetes Is the Leading Cause of Blindness Among Most Adults," "Good Vision Throughout Life," "Recommended Eye Exam Frequency for Pediatric Patients and Adults," "Shopping Guide for Sunglasses," "UV Protection With Contact Lenses," "Glaucoma," "Computer Vision Syndrome."

In a lens that has spherical aberration, the various rays from an axial object point will in general intersect the lens axis at different points after emerging into the image space. By tracing several rays entering the lens at different heights (i.e., distances from the axis) and extrapolating from a graph connecting ray height with image position, it would be possible to infer where a ray running very close to the axis (a paraxial ray) would intersect the axis, although such a ray could not be traced directly by the ordinary trigonometrical formulas because the angles would be too small for the sine table to be of any use. Because the sine of a small angle is equal to the radian measure of the angle itself, however, a paraxial ray can be traced by reducing the ray-tracing formulas to their limiting case for small angles and thus determining the paraxial intersection point directly. When this is done, writing paraxial-ray data with lowercase letters, it is found that the Q and Q′ above both become equal to the height of incidence y, and the formulas (3a), (3b), and (3c) become, in the paraxial limit:

If you already have a medical eye problem — such as glaucoma, macular degeneration or cataracts — it is important to seek care from an eye doctor who is highly trained and skilled in monitoring and treating your condition. In many cases, this may mean that medical or surgical eye care by a specially trained ophthalmologist is in order. In such cases, your optometrist (or general ophthalmologist) may refer you to a colleague who is a specialist in treating your condition.