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Chủ đề: CANON EOS 20Da.

  1. #1
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    CANON EOS 20Da.

    Canon EOS 20Da DSLR
    [Note the text and information in this article has been revised today (02/15/05) based on a more accurate translation of the original Japanese text]

    Today [02/14/05] Canon surprised many people with the announcement of a special order version of the EOS 20D called the EOS 20Da. Essentially it's an EOS 20D with the blocking filter which sits in front of the sensor modified to increases the sensor response to deep red wavelengths.

    The primary intended application of the 20Da appears to be astrophotography. Many emission nebulae shine in Hydrogen-alpha light which is at 656nm (deep red). Modification blocking filter increases the sensor sensitivity to Hydrogen-alpha light by about a factor of 2.5, leading to reduced exposure times and higher contrast images.

    Veil Nebula in Cygnus
    Modification of the blocking filter may enable somewhat easier terrestrial IR photography too, though Canon don't talk about this on their EOS 20D-A webpage (in Japanese). It's not clear what the transmssion characteristics of the new filter are. It certainly allows more Hydrogen-alpha light to pass, and in doing so it may possibly also allow more near infrared light too, enabling somewhat shorter exposures for work with a filter such as the Hoya R72. The fact that Canon don't mention such an appliction presumably means that there isn't a huge enhancement of IR sensitivity. However since the red edge of the filter has been pushed out past 656nm, it's reasonable to guess that transmission at short IR wavelengths may also be somewhat increased. The standard filter does allow a very small amount of IR to pass, as evidenced by the fact that you can obtain images using a Hoya R72 filter, though exposure times are long. If the new filter passes more 720nm IR, shorter exposure times with an R72 filter would be possible.

    An additional feature of the EOS 20Da is that the mirror can be locked up, the shutter opened, and the camera's LCD used for focusing a "live" image (with 5x and 10x magnification options). If you've ever done any astrophotography you'll know why this would be very valuable. It's very difficult to focus on an extremely dim object using the reflex viewfinder. This sounds a bit like the sensor cleaning mode on the 20D (mirror up, shutter open), with some firmware (and possibly hardware) mods to allow the sensor to operate and display an image on the LCD. It should be noted that manual focus in this "live preview" mode can only be done using lenses with fully mechanical focusing. Some older "L" series lenses use electronic focusing even in manual mode and so cannot be used to focus with "live preview". These lenses are:

    EF300mm F2.8L USM
    EF50mm F1.0L USM
    EF28-80mm F2.8-4L USM
    EF1200mm F5.6L USM
    EF200mm F1.8L USM
    EF600mm F4L USM
    EF85mm F1.2L USM
    EF400mm F2.8L USM
    EF500mm F4.5L USM
    EF400mm F2.8LII USM
    No price has been announced for the EOS 20Da and it's not yet clear whether it will be offered outside Japan. The Japanese website suggests that it may be a special order item with 3 month delivery. Orders are being accepted in Japan starting February 15th 2005. The Product code for the EOS 20Da is: 0639B001/JAN cord/code: 4960999278773

    UPDATE [02/16/05]: Thanks to a Japanese speaking reader, I'm informed that the price of the EOS 20Da is 250,000 Yen ($2400) and orders will be accepted from Japanese addresses ONLY and for delivery ONLY to Japanese addresses. Delivery will be within 3 months of the order being placed.

    The ordering information is here (in Japanese):

    The order form itself is here (in Japanese):

    For those who don't want to wait 3 months or order from Japan, there are companies here in the US selling the Digital Rebel and the EOS 20D with modified or removed IR blocking filters. One such company is Hutech Astronomical Products. They will also convert your existing camera for around $500-$600. You can select filters to pass hydogen-alpha, or you can select a clear filter which also fully passes infrared for IR photography. You don't get the "live preview" LCD screen focusing though.
    Được sửa bởi az04 lúc 01:41 PM ngày 18-04-2005

  2. #2
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    TKS Anh AZ, nhưng mà để thế này, mỗi khi đọc phải kèm cuốn từ điển ,chắc chết bà con luôn rồi.
    Yêu quá, body ơi !!

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