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Thread: Williams Optics

  1. #1
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    Default Williams Optics



    Ok guys just stumbled across this company. Looks like they have some good equipment. Anyone own or know of their products?

    Thanks,
    Mitch
    Last edited by Tangovino; 01-17-2009 at 04:41 PM. Reason: added sentence

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    Default

    Hi Mitch,

    Williams Optics has been around for a long time. Many people have said that they were quite pleased with their products and service. I do not have any of their products but I believe Vinnie does.

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    Hi Mitch.

    I don't have any WO scopes but I do use some of their accessories, and I have looked at and through quite a few of their scopes. I have to say that their products have outstanding fit and finish, but this also comes at a price.

    Frankly (and I can feel the wolves circling ) I think that WO scopes are a little overpriced.

    Keep in mind here that I do own several ED and Apo refractors (actually 2 ED doublets and an apo triplet)

    Head to head a given ED doublet of say FPL53 glass of any of the more common asian brands is just that, and so the optics of these are very much the same.

    What you are paying for with WO are very sweet focusers and very appealing fit and finish, retracting dew shields, etc.

    But the other Asian manufacturers are now offering similar products, like SW's Equinox series, and Celestron's Onyx for example

    Also there are several proprietary brands here in Aus now that are offering outstanding Apo triplets at very acceptable prices.

    Just FYI also the name of the company is "William Optics USA" Which is a bit strange for a Taiwanese corporation. The "William" is from the founders name William Yang

    Would I own a WO refractor? Absolutely. Superb Products.

    Would I pay the current Aus market price for one? Probably not

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    Vin,
    Just back from my trip and the wife suprised me with the green light to start in earnest the persuit of more research. She isn't so much for her to get involved in it as much as she wasnt to see how my learning curve will convince her that I will be producing pretty pictures of the heavens for her. My wife is a one of a kind woman. We're still fixing up three hot rods and she now is on the Internet helping me price and locate items that can be added to our wish list. The story of her help should have a new name: 'Budget with a Boost, from my Baby!" Tomorrow we are headed for thr largest Astronomy store here in our home town. Once again I want to touch and feel and look at the various parts that will someday become my beginning set of equipment. BTW Thanks for the advice on the WO products.

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    With the APO triplet compared to the ED doublets and getting into FOV differences, what suits you better? Maybe a features list of what APO aperture is compared to the ED apertures. I am sure different lengths come into play. Could you in a show in a chart how they compare? Say features? And not to be a royal pain in the neck the different uses they do. One for DSO and one for planetary. Or What.

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    Mitch you are confusing a couple of issues here, and that could well be my fault.

    So lets look at some definitions and some real rough and ready theory.

    Just to start though, these days a lot of people, and most manufacturers, define ED doublets, as well as triplets, as apochromats. Apo is the modern day catch cry that sells refractors and is often loosely bandied for that reason. One school of thought (the one that I follow) is the the ED scopes aren't quite true apochromats and so I usually differentiate. This is an opinion, and often controversial.

    Also just to really throw some confusion in the mix, two words, achromat, and apochromat, in the eyes of a linguist, both mean the same thing ie "without colour"

    Now the idea of a telescope lens is to bend light through it to down to a common focal point. Unfortunately this is not a simple thing as the light bends at a different rate depending on the thickness of the lens (A convex lens for example is thicker in the middle and thinner at its circumference), and the fact that visible light is made up of different wavelengths which due to being slowed at different rates as they move through the glass disperse.

    Remember when you were in high school and the teacher shone a light through a prism and you saw a rainbow.

    So if you put a lens in one end of a tube, and provided the lens is truly symmetrical, the refracted light doesn't arrive all at one point, but arrives in a line along the central axis, and wherever you put your eye in that line what you will see is an image that has fuzzy discolouration. This is called chromatic aberration (CA)

    The traditional means of reducing CA has been the use of the achromatic objective (the Achro). Here the objective is a cell consisting of two lenses, typically one of "Crown" glass and one of "Flint" glass. The combination of the two allows different wavelengths to bend more closely to a common focal point, and the colour correction is usually aimed at the red and blue areas of the spectrum.

    Short focal length achros, however often do display quite annoying CA when observing bright objects, so the old style planetary achros used very long f ratios, often out to f/15 and up to around f/20. At these ratios the lens curvature is quite slight, and more light arrives at the same point. The problem here is that a 6" f/15 refractor is about 8 feet long. Hardly portable, and very expensive to mount

    More recent technology has introduced the so called ED scopes. ED meaning "Extra Low Dispersion" and refers to a type of glass, usually fluorite crystal. The ED scopes still only have a two lens objective cell (doublet) but by introducing one element of ED glass the dispersion is significantly reduced. These scopes usually correct colour in the Red and Blue and also partly in the green. Whilst these scopes are not necessarily completely free of CA, the design has enabled much shorter focal lengths to be satisfactorily used. Hence we typically see f ratios of around f/6 to f/8 that really do have excellent colour correction.

    To get maximum colour correction, or absolute minimal to non apparent CA, however, requires the introduction of a third lens in the cell, (so it is now a triplet) and at least one of those lenses needs to be of ED glass. Here the colour correction is complete in Red, Green and Blue. This is the design that I (and many others) regard as the "True" apochromat or Apo. Again this allows shorter focal lengths, and so lighter more compact scopes that are cheaper to mount.

    Of course there is a big trade off here, and that's called dollar. Achros are relatively cheap to make. Introducing exotic glass into the equation gets quite expensive although these days the EDs are usually quite well priced. Moving up to the triplets, however, is not a good idea if don't like sudden shocks when you get your mastercard statement.

    So the question was more on FOV but I wanted to clear that bit up first. I'll come back to the FOV bit later.

    HTH

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    Vin,
    Not so much confusion but data assimillation. I have my mind around the different glass. I understand performance vs. price. But will standby for FOV chat. Today wifey and I are going to local shop to get deeper into the research. The local community college has a great astronomy club and I will frequent them for some hands-on comparisons. So far this has been an exciting endeavour.
    Thanks again for putting up with digging up the bones regarding the basics.

    Mitch

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    Ok Mitch I'm back

    So the prime purpose of an astro telescope is to "collect" as might faint light as possible.

    Now light collection is a direct function of a scope's aperture (the hole at the front that lets the light in). Nothing else counts, not focal length, not various different EPs (eyepieces) not f ratios. Just how much light can get in through the objective lens in a refractor or down to the primary mirror in a reflector.

    Having said that, maximum possible light collection, and therefore maximum affordable aperture, is not always the main concern. Examples are for a visual observer who is mainly interested in the planets or the moon (which are bright objects), or in your case as an aspiring astro photographer, because the camera is far more light sensitive than your eyes.

    Before we go any further you need to be familiar with a couple of simple sums.

    The f ratio of a Telescope is its focal length (FL) divided by its aperture (all in mms), so a 100mm scope of any type having a FL of 1000mm is an f/10

    Magnification is determined by the EP, and is calculated by the scope's FL divided by the Eyepiece focal length (EPFL). That number is in mms and is marked on the EP

    So if you use a 10mm EP in our 100mm x 1000mm FL scope, you are getting a magnification of 100x

    So to Field of View. We talk about two different FOV's these being AFOV (apparent field of view) and TFOV (True field of view)

    AFOV is a fixed characteristic of an EP and describes the angular field (in degrees) that can be seen in the EP. TFOV is the actual width (well I guess diameter might be a better idea) of the section of sky that you can see in the EP, again in degrees.

    AFOV for an EP is a manufacturer's spec

    TFOV is calculated by dividing the AFOV by the magnification (This is a rough sum, but is close enough for comparative purposes)

    So lets take two scopes, both at 100mm aperture, one at f/5 so it has a FL of 500mm, and another at f/10, so it has a FL of 1000mm

    Now fit a standard Plossl EP of 20mm FL and AFOV of 50° (which is common)

    In the f/5 the magnification is 500 divided by 20 = 25x and the TFOV is 50 divided by 25 = 2°

    But in the f/10 the mag is 50x but the TFOV has come back to 1°

    Of course you could achieve the same Mag and TFOV through both if say you put a 10mm EP in the f/5 and left the 20mm in the f/10, and so on.

    Now lets go a bit further. Lets take an 100mm f/15 (sometimes still seen in Maks) and our 100m f/5 (which could ne a reflector or a refractor) and put in a 5mm EP at 50° AFOV

    The f/15 comes in at 300x but at a mere 0.16° TFOV great for splitting doubles or looking at planets, but not much use to look at the nebulosity of M42 which cover about 0.8° of sky

    And the f/5 comes in at 100x but has a TFOV of 0.5° , so you fit a lot more sky in at a good sort of mid range Mag

    The downside of very short FL scopes is that EPs can be "Fussy" with a sharp light cone and in reflectors they are more sensitive to collimation error and coma. and in refractors more sensitive to CA, but clearly give wider TFOV's with common EP's

    Hence the popularity of the ED refractors around the f/7 to f/8 region (we did start off here talking refractors) sort of getting an all round or best of both performance.

    Now you are more interested in the AP side. So to set a relative standard (again not completely accurate, but good enough for comparative purposes) we generally regard a DSLR in prime focus ( that is camera body only, attached straight to the scope's focuser) as being equivalent to a common 50mm EP. but the camera takes a rectangular shot and is regarded as having an AFOV of 27° x 40° so now the sums go past my simple skills (or more like lack of skills). Anyhow, again for a simple comparison, you can only fit a 27° circle in that area. Now do remember that this is very very rough, we are just doing this for comparisons

    Now again lets take a 100mm scopes at f/15, f/10 and f/5 and attach a camera

    At f/15 the mag is 30x and TFOV is 0.9°

    At f/10 the mag is 20x and TFOV is 1.35°

    At f/5 the mag is 10x and TFOV is 2.7°

    The deal here is that from the photographer's point of view the wider field is a big advantage, and the shorter FL means shorter exposure times.

    Again this lends to the ED's around that f/6, f/7 ish as top all rounders. (again staying with the refractor theme)

    Again I really have to emphasise that none of the calculations here regarding FOV's are particularly accurate. I really don't have the education to be able to use the complex formulae involved, the whole thing is just to get a comparative idea.

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    Mitch this post just came in from another of our members, the point of interest to you I guess is that these are images produced from a DSLR with an f/7 ED80 on an EQ6 mount.

    NGC3293-NGC3324 Carina

    Sure its not as simple as just hooking up the camera and just hitting the shutter release and that's never been the suggestion, but it should give you some idea

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