PARABOLIC MIRROR REFLECTOR 37" SUPER STRONG

linkbee.com This is a quick view of the new acrylic parabolic mirrors we have been working on. Max temperature 2700F, short focal length 9" with a 46" surface area and 95% true mirror. This is not reflective stuff, near perfect mirror.

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Concave mirror formula (By - al tahir public high school khushab) part 4

This video tutorial is about how an image of an object placed in front of a concave mirror is formed? The ray from the object fall on the mirror after the reflection the ray passes from the focus and image is formed at 2F. The image is inverted. For the derivation of the equation watch the tutorial video of Algebra.

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Matter, Energy,Environment Unit Part III / VI Download Powerpoint at www.sciencepowerpoint.com

This is Part III / VI of an educational unit that covers Matter, Energy, and the Environment. The Powerpoint version of this video and entire unit can be downloaded at sciencepowerpoint.com The Matter, Energy and Environment Unit is an educational unit for students in grades 7-10 and includes an interactive and engaging Powerpoint roadmap of 2200+ slides with built in class notes (Red Slides), lab activities, project ideas, discussion questions, assessments, challenge questions with answers, review games, videos, and much more. Text is provided in large print (32 font) and is placed at the top of each slide so it can seen and read from all angles of a classroom. A shade technique and color coded text helps to increase student focus and allows teacher to control the pace of the lesson. Also included is a 14 page (Microsoft 2003 word doc.) assessment / bundled homework package that chronologically follows the Powerpoint slideshow for nightly homework and the end of the unit assessment, as well as a 8 page modified assessment. 20 pages of class notes (Word doc.) with images are also included for students who require assistance, as well as answer keys to both of the assessments for support professionals, teachers, and homeschool parents. 28 video shorts (FLV files) are provided and a slide within the slideshow cues teacher / parent when the videos are most relevant to play. Video shorts usually range from 2-7 minutes and are included in organized folders. Two Powerpoint ...

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Myopia or Short Sightedness

•Check us out at www.tutorvista.com Myopia (Greek: μυωπία, muōpia, "nearsightedness"), is a refractive defect of the eye in which collimated light produces image focus in front of the retina when accommodation is relaxed. Those with myopia see near objects clearly but far away objects appear blurred. With myopia, the eyeball is too long, or the cornea is too steep, so images are focused in the vitreous inside the eye rather than on the retina at the back of the eye. The opposite defect of myopia is hyperopia or "farsightedness" or "long-sightedness"—this is where the cornea is too flat or the eye is too small. Mainstream eye care professionals most commonly correct myopia through the use of corrective lenses, such as glasses or contact lenses. It may also be corrected by refractive surgery, but this does have many risks and side effects. The corrective lenses have a negative optical power (ie are concave) which compensates for the excessive positive diopters of the myopic eye. The Mainstream view on correction is countered by alternative theories of cause and therefore correction. The main alternative theory claims that myopia is caused by excessive near sight work. This causes the focusing muscle inside the eye to lock up into a state of near focus. Therefore the correction of myopia would be through less close work and helping the eye to do close work with the use of reading glasses

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concave lens - Thấu kính phân kỳ

concave lens - Thấu kính phân kỳ

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1960s Vicke Lindstrand vase with ground lenses and purple-black spots

www.modernistglass.com Here's our view on Lindstrand: we think his work at Kosta from 1950 to 1973 is the finest body of work, in terms of range and overall beauty, by any single mid-century glass designer. We also think it's underrated and destined to rise in price even more than other mid-century art glass (which is generally a bargain compared to new art glass anyway). This piece, mixing seemingly random ellipses of purple and concave cut lenses in a heavy, high quality crystal vase, is yet another fine example of his work. Height: 21 cm (8.25 inches) Width: 9 cm (oval shape) Weight: 2265 g Engraved "Kosta LS 605" to the base Condition: very light wear to the base, a 2.8cm long scuffmark on the side, a shallow 1mm fleck to one of the cut lenses, a couple of fairly light scratches inside (longest 3 cm) Our Reference: 2530 Pricing information Price: US $780.00 + shipping

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Plano Concave Lens

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A 17-85 Lens on a Canon HFS10, go Fish-Eye

I got a plano-concave lens from a 17-85 Canon that I broke, and then have I've mounted it on a Canon camera HSF10 to try to make it a Fish-Eye

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Phoenix 1000mm f/8 Mirror Lens with Mount for Canon EOS 30D 20D 5D Digital Rebel XT XTI & Film SLR Cameras

Buy Phoenix 1000mm f/8 Mirror Lens with Mount for Canon EOS 30D 20D 5D Digital Rebel XT XTI & Film SLR Cameras Order Today!

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Phoenix
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Date Created :
Nov 01, 2010 11:17:08

Kit includes:
♦ 1) Phoenix 500mm f/8 Mirror Lens
♦ 2) Phoenix 2x Teleconverter
♦ 3) Precision Design T-Mount for Canon EOS (Autofocus)
♦ 4) Rear Lens Cap

Phoenix 500mm f/8 Mirror Lens includes: Filter Set (ND-2X, ND-4X, Skylight); Soft Pouch; Front and Rear Caps; Instruction Manual; Phoenix USA Warranty

This super-telephoto 500mm mirror lens and 2x teleconverter are incredibly compact and lightweight. Using multi-coated optics and an advanced reflex design, they're ideally suited for wildlife, nature and sports photography. The included 2x teleconverter will double the focal length to 1000mm, equivalent to the magnification a 20x high-power binocular and for additional control, a set of 3 filters (Skylight, ND-2X and ND-4X) are also supplied. Macro focusing capability provides an image to subject ratio of 1:2.7 and with the 2X teleconverter, incredibly detailed, almost life-size (1:1.35) images can be obtained. Designed to be easy to use, hold and transport, this super-telephoto lens kit offers incredible magnification and value.

Will mount to ANY Canon EOS AutoFocus Film or Canon Digital SLR Camera Including: Rebel X, Rebel XS, Rebel G, Rebel GII, Rebel 2000, Rebel Ti, Rebel T2, Rebel K2, Rebel S, Elan 7, Elan 7E, Elan 7n, Elan 7ne, EOS 1V, EOS 3, EOS 1Ds Mark II III, EOS 1D Mark II III, 10D, 20D, 30D, 40D, 5D, Digital Rebel (300D), Digital Rebel XT (350D), Digital Rebel XTi (400D), & Digital Rebel XSi (450D), Rebel XS (1000D) etc.

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This is a catadioptric lens. That means that it is very similar to a reflex, or mirror, telescope, and that it mixes mirror elements with refractive elements. The light comes in the front of the lens, goes right to the back of the lens, where it hits a large (full lens circumference) concave mirror, which then focuses all that light more tightly back in the direction it came. In the middle of the business end of the lens is another mirror, which then sends the light down the center of the lens back toward the camera, where standard refractive optical elements further magnify and focus the incoming light prior to hitting the film or sensor. A lens of this type is not only similar to a reflector telescope, it can actually perform as one, and you can find eyepiece attachments for just that purpose.

One of the significant benefits of a catadioptric lens is that you get less chromatic aberration, and so with subjects like the moon, which you expect to be grey, you actually get a grey image. With a standard refractor telephoto, you're quite likely to get colored fringes on sharp bright/dark boundaries - this is an area where reflectors can and do excel, and this lens is no exception.

Here's why: Light bends when it crosses the boundary between materials of two different densities. With normal lenses, light goes from air, into the material of the lens, and back into the air. So it bends twice. But light of differing colors bends slightly differently, and so the more bending (also known as refraction) goes on, the more likely you are to see colored edges - typically at the blue or red end of the spectrum - or even both. But a reflector system is made with mirrored surfaces, and light doesn't enter these mirrors, it just bounces right off the mirror surface, and it bounces at the same angle no matter what color it is - hence, there is no difference in the path light of various colors follows. This is why a well made reflector system doesn't present chromatic aberration, or CA, which is just a fancy term for what I just described to you.

Something else to keep in mind is that the background blur, or bokeh, of a catadioptric lens is donut shaped, instead of spherical - this is because of the light blockage at the center of the lens by the second mirror. That in turn means that you won't be shooting many images with creative depth of field with this lens; either the subject matter is in focus and the rest, if anything, irrelevant to the shot, or you probably won't be happy. Shooting distant things with no foreground like the sky or scenery on the skyline? No problem. Try a portrait with out-of-focus point light sources... ouch. Donuts! Just a word to the wise.

This particular lens has a screw type fitting that is not, by itself, compatible with the Canon mount. Consequently, there is a screw-to-Canon adapter supplied as part of this kit as well.

The lens sports a 500mm focal length, so you're looking at about a 10x magnification at the rated f/8 fixed aperture. But the kit comes with a physically separate 2x magnification element, which effectively increases the focal length to 1000mm and about 20x magnification, although of course this cuts the amount of light considerably, raising the lens' effective f-stop and requiring either a slower shutter speed or a higher ASA to get the same relative exposure for any given scene.

You don't have to use the 2x adapter; you can attach the screw-to-Canon adapter directly to the Phoenix lens and use it as 500mm, f/8. The only downside to this is that it takes a physical act to change from one mode to the other, one that exposes both the camera and the lens to dust and other environmental gremlins. As the focal length is fixed, I strongly suggest you think carefully about what you're going to shoot before you shoot it so that you don't have to fool with switching the 2x adapter in and out in the field.

The quality of the 2x adapter - or at least, lets say the quality of photos taken with the 2x adapter attached to the Phoenix - is, in my opinion, unsatisfactory for any use. The Phoenix by itself seems fine, so I think we can safely point the finger at the 2x adapter.

The lens is manual focus, focusing is smooth and positive, which was a relief to me after purchasing a much more expensive lens (0) recently and running into some unexpected and entirely unwelcome backlash problems. The focusing ring is broad and well textured, providing a positive grip that you'll be thankful for when you're trying to get that last little bit of focus accuracy. The Phoenix is a very, very sharp lens for the money and the focal length; when you get the focus exactly right, I think you'll be delighted with the degree of telescopic detail achieved. I know I am.

Although you do have to stand off from your subject a bit, this lens can also serve as a perfectly reasonable macro lens. With the 2x adapter, you can get 1.35 macro shots on a film camera, and with a digital camera that uses a c-size sensor, you add an additional 1.5x so you're really getting close to a 1:1 full macro at that point. Again, here is an area where the catadioptric lens ability to basically do away with chromatic aberration serves to get you a considerably better image overall, and the lens' overall sharpness contributes a lot (as long as the object has a very flat focal plane, of course.)

There is visible, though not particularly offensive, vignetting that occurs around the center of the image. Sometimes this can work for you; so much so that it is a common effect you can add in many image processing packages. But there are times you won't want it, and with this lens, that means using post-processing to remove it, not impossible, but not trivial, either.

The lens is moderately heavy at 360 grams (12.7 oz), and with the approximate one and half inch 2x doubling tube attached, it sticks out pretty far so there's some leverage working on you along with the weight. It isn't so much that a standard tripod is overwhelmed, but if you're going to be shooting hand-held (presumably with a lot of light!) this thing will get your wrists tired in short order, no question about it.

One thing about any fixed f-stop lens, and this lens being no exception, is that the depth of field is limited. There isn't much you can do about it. For instance, at a distance of 12 feet, the DOF of this lens is about 1/4 inch. This has a number of consequences. The obvious one is the type of subject matter you will want to shoot with this lens will be limited to that which has a relatively shallow depth of field compared to the distance you'll be shooting at. Another, perhaps not immediately obvious consequence is that focus adjustment requires you to take great care or you'll find the focal plane is not collinear with your subject matter. In my case, I'm using the lens with a Canon EOS 40D, which provides for a live LCD view which can zoom the FOV in for a 1:1 pixel (LCD:Sensor) view; this allows me to see precisely how well I'm focused (or not.) In this sense, this lens is very well-suited to my camera (or vice versa.) If you are limited to a TTL viewfinder, you may find that focusing this lens perfectly is quite challenging. The lack of backlash helps, but even so, a very slight rotation of the focusing ring does move the focal plane a considerable distance. No question about it, this is one of the tricky areas for this type of lens.

As a manual focus lens and a fixed f-stop lens, it doesn't really tell the camera anything about itself. Your aperture readout will probably show a clueless 0.0 value; don't worry about it too much. If you set the camera to aperture priority, the camera will set the shutter speed appropriately and you'll get a properly exposed image. Or you can use full manual and tweak till you find what you're looking for. Given that shutter speed affects the blur of motion in an image as well as the available exposure time, and ASA (if your camera provides for adjustable ASA) affects the exposure time and the graininess and noise of the image, it may take some experimentation before you find the optimum combination of ASA and shutter speed that works best for your particular camera. Modern digital cameras have such large megapixel counts that in many cases, you can reduce noise after the fact by trading in some resolution; for instance, if you have a 10 mp camera like my EOS 40D, you can cut the resolution by half in both dimensions (proportionally) and this results in the light values of four adjacent pixels being combined into one new one in a final 2.5 mp image, which will serve to average out a great deal of sensor noise - at the cost of some detail, of course. In the case of a not perfectly focused image, though, which I think you'll find you take quite often with this lens because the DOF is so limited, there is little down side to such a reduction in pixel dimensions - and remember, noise occurs in an image regardless of focus because it comes from the sensor, not the image.

The kit comes with several filters which need to be mounted internally; they're more for film cameras which have fewer options for easily managing light (for instance, they can't adjust ASA without actually changing a film cannister.) They're quite inconvenient as they mount inside the lens at the adapter end, and so I have not even tried to use them. Nor do I really see a huge need for them in my situation. The only exception is related to the fact that filters can increase contrast as they block out ranges of light which may be obliterating certain features by virtue (or lack thereof) its abundance. So your mileage may vary; the filters are there if you choose to use them.

Last but not least, the lens comes with all the caps you need to keep dust off it, as well as a handy soft bag you can use to protect the fine surface features. It's a typical soft bag and it won't serve to protect the lens if, for instance, you were so unfortunate as to drop it. For that, you need a camera bag. As with all lenses, this baby is delicate, and the very first thing you should invest in is a bag that will keep the slings and arrows of outrageous fortune from lodging in your lens collection.

In summary, there can be no question that this is a special purpose lens, but when you are shooting distant objects on the ground or in the sky, it really comes into its own. It is all metal, at least on the outside, and feels very solid and frankly, it also feels expensive. Given the price, which is more than reasonable, and the build quality, which in my opinion is quite high, I think almost anyone who likes to really experiment with different types of images should have this lens in their kit bag. I recommend it enthusiastically and with great cheer. I'm very happy to have it myself, and I'd immediately and without any question replace it with the same model if something unfortunate happened to mine.

You can't put 500mm of telephoto capability in your camera bag at anywhere near this price point using standard lens designs; if you are willing to put out more money, you can get a better result, no question about it, but this is still a terrific way to start with telephoto photography.

In the next few days and evenings, I'm going to prepare some sample images taken with this lens specifically to go along with this review; please check the images section if you'd like to see them.

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