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A challenge to GH1 ? New Sony A55 - translucent fixed mirror design

Discussion in 'Other Systems' started by blue, Aug 24, 2010.

  1. blue

    blue Mu-43 Veteran

    280
    Jun 1, 2010
    UK
  2. Herman

    Herman Mu-43 All-Pro

    Feb 7, 2010
    The Netherlands
    Yes, I wanna congratulate Sony, they did a good job, gold award from dpreview for the
    A55. I notice that these cameras do not support many aspect ratios.
     
  3. julienrl

    julienrl Mu-43 Regular

    100
    Jul 28, 2010
    Ottawa, Ontario
    won't a refractive mirror that does not get out of the way simply reduce the amount of available light\make for a fairly dark viewfinder? Or are they using some material similar to electronic shutters where the "mirror" (prism at this point) changes properties at the time of shooting? If not, does this mean optical view finder video shooting?
     
  4. oris642

    oris642 Mu-43 Regular

    It uses an electronic viewfinder.
     
  5. naturecloseups

    naturecloseups Mu-43 Regular

    93
    Jun 10, 2010
    As anyone can guess -- with advances in CDAF and EVF, the reflex mechanism is on its way out, but for Sony half of it is still in.
     
  6. pxpaulx

    pxpaulx Mu-43 All-Pro

    Jan 19, 2010
    Midwest
    Paul
    The translucent mirror partially reflects to a secondary 15 point AF sensor which is used solely for phase detect autofocus. Essentially you won't ever 'see' the loss of light to the sensor, but it is stated that a 1/3 stop of light is lost through the translucent mirror. The display gain will obviously compensate in lower light anyway, so you won't see the difference, but there is a slight loss of light for the actual image (if you can call 1/3EV slight...).

    Has anyone read the rumors on the new regular 4/3 cameras from Olympus? Sounds like a similar system but using a mirror that has liquid crystals capable of switching between 50% light transmission (to enable the live view) and 100% light transmission when the shot is taken, so no light is lost. That is still pure speculation and rumor, but its out there!

    All-around, the bottom line is we are seeing camera developments that are going to creat more competition, which is always good for the end user (us!). Photokina news will be a lot of fun this year.
     
  7. JoepLX3

    JoepLX3 Mu-43 Top Veteran

    509
    Jun 13, 2010
    Japan
    The mirror is great to support better LV performance on LCD, but stupid that it doesn't use an OVF anymore.
    - The only reason I can think of is money, EVF with "dummy" mirror is probably cheaper than OVF with "Real" mirror functionality.

    I still prefer the Pentax K-x :wink:
    - Just hope the price will drop further (or discount on non-kit lens)
     
  8. Shinka

    Shinka Mu-43 Rookie

    16
    Jun 19, 2010
    Lawrence, KS, USA
    Not stupid, impossible with this type of design. The mirror only reflects 1/3 of the light hitting it, making an OVF useless. The EVF sees what the main sensor sees providing continuous phase-detect AF. This means it can focus even as the shot is being taken.
     
  9. julienrl

    julienrl Mu-43 Regular

    100
    Jul 28, 2010
    Ottawa, Ontario
    I don't think its a third of a stop but a third of the light, period. (as read on dpreview).. But with a larger sensor it can be probably still do better than a 4\3 pixel for pixel as far as light goes, but its size seems to be closer to regular DSLRs giving it a disadvantage from what I can see ..... I am just confused about this move.
     
  10. Rudi

    Rudi Mu-43 Top Veteran

    574
    Aug 16, 2010
    Australia
    This isn't a new idea! Canon used this sort of technology in their EOS RT, all the way back in 1989: >>>Canon EOS RT<<<
     
  11. JoepLX3

    JoepLX3 Mu-43 Top Veteran

    509
    Jun 13, 2010
    Japan
    That one is better, it still has OVF :wink:
     
  12. Rudi

    Rudi Mu-43 Top Veteran

    574
    Aug 16, 2010
    Australia
    Exactly! :smile:
     
  13. Brian S

    Brian S Mu-43 Top Veteran

    714
    Apr 11, 2009
    Canon used this technology in the Canon Pellix in 1965. Nikon also made a Nikon F with a fixed mirror. The pellicle mirrors deteriorate easily and will cause problems on the image, like looking through a lens with separation. I had a good one, kept an F1.2 lens on it.

    Canon Camera Museum | Camera Hall - Film Cameras
     
  14. dwig

    dwig Mu-43 Top Veteran

    621
    Jun 26, 2010
    Key West FL
    Using semi-transparent mirror or beam splitters for metering and for the viewfinder is an ancient technique. What's new here is that the semi-transparent mirror is used for AF. The VF is electronic, done from the actual sensor.

    On the plus side it can use phase detect AF for faster AF.

    On the minus side:
    1. optical issues (reflection, dust, minor chromatic smearing) from the mirror being in the optical path at all times.
    2. 1/3 stop light loss, you have to shoot at ISO 500 to get the same f/stop and shutter speed as an SLR or true mirrorless system would get shooting at ISO 400.
    3. Lens mount still must extend fairly far from the sensor preventing adapting a large percentage of legacy lenses that can be adapted to true mirrorless cameras.
     
    • Like Like x 1
  15. Pelao

    Pelao Mu-43 Top Veteran

    959
    Feb 3, 2010
    Ontario, Canada
  16. pictor

    pictor Mu-43 Top Veteran

    635
    Jul 17, 2010
    This system Sony introduced here has big advantages for video, because one has phase detection autofocus during filming. The new Sony cameras are the only cameras which can do this, so do not underestimate this innovation! For video an EVF is the better solution than an OVF and therefore Sony implemented the better solution for what the new camera is best at.
     
  17. pxpaulx

    pxpaulx Mu-43 All-Pro

    Jan 19, 2010
    Midwest
    Paul
    Looking back at the dpreview review, they state it equates to 1/2EV loss of light to the sensor. It is like putting a 1/2 ND filter between the lens and sensor. Whether making f1.4 an f1.7, or f8 f11, it should always be the same relative loss of light (correct me if I am wrong!). I realize there are various filters on sensors already, but permanently having some sort of glass between the lens and sensor just kind of bothers me! (being the filter-hating sort that I am)
     
  18. JoepLX3

    JoepLX3 Mu-43 Top Veteran

    509
    Jun 13, 2010
    Japan
    For video the LCD with phase detection auto focus is indeed very good.
    - FYI: For video I see myself mainly putting the camera on a tripod or holding it like a P&S and arm length distance.
     
  19. Herman

    Herman Mu-43 All-Pro

    Feb 7, 2010
    The Netherlands
    GPS system

    The A55 has GPS on board. How long does it take to find the satellites, my car navi system (TomTom) needs more then 1-2 seconds. I assume that the GPS unit will be powered only when power is switched on.
     
  20. pxpaulx

    pxpaulx Mu-43 All-Pro

    Jan 19, 2010
    Midwest
    Paul
    Have you read the luminous landscape article abou the a55? I found the AF comment quite interesting for video - essentially that it is the best video AF he had ever experienced of anything currently available in the video world today. I suppose if current camcorders/HD cams all use CDAF, then replacing that with live phase detect AF would be better.