Showing posts with label Review. Show all posts
Showing posts with label Review. Show all posts

Sunday, 24 April 2011

Formation Of An Image By a Concave Mirror

Check us out at www.tutorvista.com To view an object in any type of mirror, a person must sight along a line at the image of the object. All persons capable of seeing the image must sight along a line of sight directed towards the precise image location. As a person sights in a mirror at the image of an object, there will be a reflected ray of light coming from the mirror to that person's eye. The origin of this light ray is the object. A multitude of light rays from the object are incident on the mirror in a variety of directions; yet as you sight at the image, only a small portion of the many rays will reflect off the mirror and travel to your eye. To see an object in a mirror, you must sight at the image; and when you do reflected rays of light will travel from the mirror to your eye along your line of sight. Not all people who are viewing the object in the mirror will sight along the same geometrical line of sight. The precise direction of the sight line depends on the location of the object, the location of the person, and the type of mirror. Yet all of the lines of sight, regardless of their direction, will pass through the image location. In fact, the image location is defined as the location where reflected rays intersect. Since all people see a reflected ray of light as they sight at an image in the mirror, then the image location must be the intersection point of these reflected rays.

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Thursday, 14 April 2011

PNW Optics: Concave Mirrors

On February 2, 2008, Physics Northwest Organization of Chicago provided a free workshop on optics. This video shows a variety of demos used to teach about image location in concave mirrors. To learn more about Physics Northwest visit their website at: www.edline.net

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Thursday, 16 December 2010

Samsung 50-Inch 1080p DLP HDTV Review

Are you thinking of buying a Samsung 50-inch 1080p DLP HDTV?

This is a popular DLP HDTV model, and is a bestseller in many different shops. It has been around for just over half-a-year, and the customer base and comments has grown enough that we can now get a good feel for its pros and cons. I've consolidated a number of customer reviews from around the net. Overall opinion is that HDTV model is good and cheap, but not perfect.

Here is a useful rule of thumb: If you want to buy a HDTV, find out the watching distance in feet and multiply that with 5. That's the size of the screen you need. For example, if your watching distance is 10 feet, 10 times 5 is 50. So choose a 50-inch TV.

Good Points

Even when Samsung 50-inch 1080p DLP HDTV first came into the market, it was one of the cheaper 50-inch HDTVs. Now that the model is half-a-year old, it is even cheaper if you buy it from online retailers like Amazon. You are likely to see about $500 of savings off the list price. You also save on certain taxes and shipping costs. Additionally, if you find that the price has dropped between the time you bought the TV and the time you received it, you can ask the retailer to refund the difference. Reputable companies like Amazon actually honor such requests.

Although electronics tend to become obsolete quickly, this HDTV was leading edge when it came out. It already had 1080p resolution - many broadcasters are still catching up to this latest standard. Even now, its technology is quite advanced, and will likely remain so for the next few years.

Samsung 50-inch 1080p DLP HDTV uses an advanced technology called LED light engine. What it means for you is that the pictures are clear and detailed, and the colors look natural and true. Movement and action is much better rendered compared to normal LCD technology, and you won't see blurring or loss of detail. This HDTV also does well in bright rooms with considerable daylight penetration.

The built-in 2-speaker surround sound is of good quality. Do make sure the surround sound mode is turned on. HD broadcasts received over a simple, cheap, indoor antenna look great. Other content (Regular DVDs, SD/HD broadcasts, Nintendo Wii, DVD, Xbox 360, etc.) also look fantastic.

You probably already know its dimensions: 45.2"(W) x 31.8"(H) x 13.4"(D) 61.3 Lbs. This 50-inch DLP HDTV is thinner than many of its competitors, and is light enough for 2 persons to move around.

There are abundant connection inputs for HDMI, S-video, RGB component, digital, optical and analog sound, and RCA jacks, and they are located on the right side of the set for convenient access - this makes it easy to hook up. Unfortunately, this can be an issue if you place your TV in a cabinet.

Samsung 50-inch DLP HDTV is pretty user-friendly. The user manual is good and extensive (although not written for novices). The remote is intuitive and the menu system is straightforward. Note that it may not have as many functions as more expensive systems.

Its pretty quiet, since it uses LED light sources instead of the more normal bulb and color wheel of most other DLPs. Since the LED engine is cooler and more energy-efficient than the bulb and color wheel, Samsung 50-inch DLP HDTV also doesn't need a powerful cooling fan. Overall, you get good energy savings - it is Energy Star rated. Another good point is that the LED lasts longer than the bulb of normal DLPs (which need to be changed every 2 or 3 years).

Some of you might be nervous about getting faulty goods by buying from online retailers. The big and reputable companies like Amazon usually have a 30-day guarantee period. When any problems crop up, they have a good reputation of honoring their commitments to replace or refund the TV. If you are not certain about your online retailer, you can check their reputation with the Better Business Bureau.

Problems Encountered By Customers

Buying this DLP HDTV is not perfect, though. Customers have reported 3 main kinds of problems.

1) Delivery & Service Problems:

a) Some customers complain about not receiving their TVs. This is more likely to happen with online retailers with their more complex supply chain and delivery procedures - either their orders were not received by the vendor supplying the TV to the online retailer, or the delivery agent did not receive the correct delivery from the vendor, etc. There are precautions you can take to minimize problems (see the section below).

b) Sometimes you get an incompetent or lazy deliveryman. He may not be able to find the place you live. Or he may not want to deliver to your doorstep. Or he may just drop your TV off at your doorstep and refuse to carry it in for you. On the other hand, there are also stories of deliverymen who go beyond the call of duty - they help you to move your old TV to its new location, then they bring your new Samsung 50-inch 1080p DLP HDTV in and install it for you. Then the even take away the packing crate for you. Sometimes they do it for free, sometimes you have to pay them a few bucks extra.

c) There are also some complaints of poor customer service from Samsung. It is typical of any large company's service - when you get a good Customer Representative, you get good service. It helps if you get their name ahead of time before you start telling them about your problems or asking them questions. If you get a jerk, you get lousy service. Don't get mad, get their name, and escalate to their boss. If that doesn't work, get a refund or replacement from your retailer.

2) Quality Control Problems affecting some individual TVs:

a) The dreaded "blue-halo" effect, which basically is a blue-ish area of light that becomes visible in dark areas of high-contrast scenes, around the lower center of the screen. This seems to be caused by a ring around the lens of the projector that should be black, but is reflective silver in some TVs.

b) There is a "hot" or bright spot in the middle of the screen and the center is a little brighter than the edges.

c) When the entire screen is one color, sometimes the four corners of the TV fade in brightness.

d) The image is skewed (left side lower than the right), there is a noticeable green tint that is not correctable via any of the user settings.

e) Picture shuts off for minutes or hours at a time - which can be a motherboard problem.

f) Spots on the screen - which can be an unfixable LED light engine problem.

If the problem crops up well within the online retailer's guarantee period (typically 1 month), then call Samsung customer service and they will send a technician in about 2 working days to fix the problem. Otherwise, make good use of your retailer's guarantee period to get a replacement. Reputable online retailers like Amazon are pretty good about honoring their guarantees without hassling their customers.

3) Problems with the model or DLP HDTV technology which affect all TVs:

a) SD images via digital cable (connected via HDMI) are sometimes a little pixellated.

b) Small amount of curvature on horizontal lines right at the top of the set (which is a common artifact with this type of set) - not generally noticeable.

c) Minor incompatibility with 480p resolution settings and DirecTV (call your DirecTV customer service to get some satellite technicians to figure this out)

d) Echo if you have both TV speakers & surround sound speakers on and the volume is high. Just mute the TV, or use 5.1 or 7.1 surround sound.

e) When viewing non-HD programming in 4:3 mode there are a set of double lines at the edge of the image. This may be too distracting for some people.

f) When playing a letterbox or widescreen DVD the 16:9 or Zoom settings are a little off. The center of the image at the top is nearly 3/4 inches lower than at the ends creating a slight "U" shape or concave appearance. This can also be very distracting for some people.

g) Slight geometry problems (noticeable bowing towards the top center portion of the screen)

h) On non-stretch mode with SD (where you have a black bar down each side of the picture), the sides of the image are bowed in a little bit.

i) Viewing angle is limited, which sucks if you have a large number of people gathered around it. Just make sure that you're in the center and can see the screen. The viewing angle is good to about 140 degrees, although it is best up to 90 degrees. Still, this is supposed to be the normal level of performance for DLPs. Basically, the best seat is the sofa in front of the TV, although anyone on the love seat has just as good a picture.

Precautions To Take

1) If you buy from an online retailer like Amazon, make sure the TV is sold directly by Amazon. Amazon sometimes acts like a storefront for other companies. This means that you are the other company's customer, not Amazon's. How can you tell? Look for this sentence on the 1st page after Amazon lists the "Price" of the TV - "Availability: In Stock. Ships from and sold by Amazon.com." Other online retailers should have something similar.

2) Print the receipt. Although this is common sense, sometimes we forget. Or something else happens, for example, your printer breaks down. If this happens, just take a screen capture and save the picture to Microsoft Word.

3) Remember: You are probably buying online to take advantage of lower costs and free shipping. Don't expect 5-star service. Take the initiative to find out the contact of the actual supplier and delivery agent so that you can keep track of your order and delivery. Call the online retailer's customer support if you have any doubts.

4) If you think there is a problem with your Samsung 50-inch 1080p DLP HDTV, take advantage of the 30-day guarantee period to get a replacement or refund. Don't suffer problems for 3 months before complaining. By this time, it is too late.

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Thursday, 9 September 2010

Physics: optics of lenses and mirrors (4)

Physics: Introduction to the optics of lenses and mirrors. Concave, convex, converging, diverging; real, virtual; upright, inverted, magnified, shrunk. Sign conventions for focal length, image distance, object distance, magnification. The lens/mirror equation; the magnification equation. Introduction to ray tracing. This is arecording of a tutoring session, posted with the student's permission. These videos are offered on a "pay-what-you-like" basis. You can pay for the use of the videos at my website: www.freelance-teacher.com For printable documents containing the "handout" and problems discussed in this video series, go to my website. For a list of all the available video series, arranged in suggested viewing order, go to my website. For a playlist containing all the videos in this series, click here: www.youtube.com (1) The lens/mirror equation. Focal length distance, object distance. Convex, concave, diverging, converging (2) Image distance. Real, virtual (3) Continued. Magnified, shrunk (4) Continued. Upright, inverted (5) Continued. Magnification equation (6) Continued. The lens/mirror chart (7) A problem (8) Continued. Ray tracing (9) Continued (10) Another problem (11) Continued

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Saturday, 3 July 2010

Essential Parts of a Microscope

The basic design of the microscope has not changed that much over time. They have evolved, but the basic concept is still the same. There are several key parts that many types of microscopes have in common. All of the parts of a microscope must function properly for the microscope to work well. If one part is substandard, it can render the microscope useless. The major parts of a microscope are the lenses, the arm, the tube, the illuminator, the stage, and the adjustment knobs.

There are two kinds of lenses on a microscope. The eyepiece lens, also known as the ocular lens is at the top of the microscope. This is the part that people look through. The ocular lens is not adjustable on most models. The objective lens provides much of the microscope's magnification. A microscope usually has a few different objective lenses that vary in strength. The objective lenses are contained on a circular part placed between the eyepiece and the stage. Different objective lenses are chosen based on their strength. When someone wants to use a different strength of objective lens, they turn the circular disk to put another lens over the stage.

Other than the lenses, the other parts of a microscope are the tube, the arm, the stage, the illuminator and the adjustment knobs. The tube connects the ocular lens and the objective lens. People look through the ocular lens and tube and see out of the objective lens at the bottom. The arm connects the lenses and the stage. It protrudes to the side and provides a handle to carry the microscope as well. The stage is where the object is placed for examination. Stage clamps secure the microscope slides to the stage. The microscope slides contain specimens such as blood or other liquids. The illuminator is below the stage. This part provides light to make the specimen easier to see. The illuminator is either an actual light or a mirror.

Most microscopes feature two adjustment knobs to help focus the lenses. The coarse adjustment knob is the larger of the two and brings the lens and the stage closer together. The fine adjustment knob is smaller and is used after the coarse adjustment knob to provide any small adjustments to bring the item into sharp focus.

These parts of a microscope are common to nearly all models. Some microscopes use slightly different parts. For example, electron microscopes use electron beams instead of illuminators.

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