Thursday, August 25, 2011

Avoiding the Siren's Song

Sony α77 with 16-50mm f/2.8 zoom
Once he hears to his heart's content, sails on, a wiser man.
Homer, "The Odyssey"
In the midst of earthquakes, eminent hurricane disaster, the fall of Libya's Kadafi (Gadhafi?) and the resignation of Jobs, comes news of a mega-product release from Sony which includes the Sony α77.

As is all too typical for such things, the Internets are awash with gushing superlatives about the camera, the new lens, and in particular the brand-spanking new 24.3 megapickles APS-C sensor. I will be taking a contrarian view of this release, so that this post will not fall into the gushing group.

As a current Olympus user, I can't help but feel the siren's call of this camera with its sensor that is twice the resolution of the current Olympus 4/3rds sensors and has 40% greater areal space. And then there's the magnesium-built body's environmental (dust and moisture) sealing and the new Sony DT 16-50mm constant f/2.8 with the same environmental sealing. Add the sensor-based image stabilization and dust-busting sensor shake, and on "paper" the Sony α77 makes a for a powerful replacement for both the Olympus E-3 and the E-5.

But that's at first blush. Digging deeper and reading many of the pre-release reviews, I came across the Imaging Resource's review and this particular paragraph:
From what we can tell, there is no strategy for keeping dust off the translucent mirror, except to blow the surface gently with air; it cannot be cleaned, and should never be touched. A fingerprint would require replacement at a service center.
This is what I was afraid might be delivered. What use is an environmentally sealed body and lens when, by removing the lens and violating the totally sealed system, something happens to fall on the pellicle mirror that requires a trip to the service center? The Sony α77, at a suggested MSRP of $1,400 body only, is a bit too rich to have to send to a service center due to a wayward fingerprint, or any other contaminant that might wind up on the pellicle mirror. It may be that there's no danger, that this is a red herring, a false alarm. And then again, maybe not.

The pellicle mirror violates a basic rule of simplification by permanently affixing a critically vulnerable optical element in the light path between the lens and the sensor. Mirrorless systems get rid of the mirror. Future mirrorless systems may even eliminate the mechanical shutter. But the Sony design, while brilliant in so many ways, has what I consider a fatal design flaw, the fixed pellicle.

I live and work outdoors in a messy environment. That's why I have an E-1 and an E-3. Most of the time I fix a lens on the body and just leave it that way until I'm finished, never changing the lens until I'm back indoors. But there are times when I have to swap a lens, such as the 50mm macro onto one of the bodies. More often than not that's "out in the wild." I have the ability to carefully clean sensors and mirrors of something falls on them. I would be extremely annoyed if something inadvertently splashed on a pellicle requiring a clean and fix at a repair depot.

In a way I wish the NEX-7, with the same sensor and EVF as the Sony α77, were also weather sealed. Then I might consider replacing both regular and µ4/3rds bodies and lenses with the NEX-7 and equivalent E-mount weather sealed lenses (assuming such were to be ever released).

It's a tough old world. Sony's pellicle design is meant to provide blazing fast and accurate phase-detect autofocus, both in stills and video. On paper it looks wonderful. But Panasonic and Sony have also shown that you can now have blazing fast and accurate contrast-detect autofocus without having anything in the light path, not even a pellicle mirror. I consider the Panasonic and Olympus a better engineering solution than Sony's, but that's not the complete story. It never is.

The best course of action for me is to continue to use what I've got and bide my time. I can afford to wait. I have heard the Sony α77's song to my heart's content and move on a wiser man.

Update 30 August

Came across this image on another site. Although it's a photo of the focus select dial, you can see into the mirror box, and see that there's no cover over the mirror.


  1. You raise a very interesting question.

    I also got excited about this camera, and didn't even think of the problems that might be associated with a fixed mirror in the optical path.

    And you might be right that if this really is a problem, it becomes a deal breaker.

    But the SLT cameras have been around for exactly one year now, and they all share this same mirror design. I would guess that quite a few A33 and A55 cameras are being used every day, with some used very heavily.

    If there was a big problem with this, then surely we would be reading about it in the gear forums.

  2. Semitransparent mirrors also were used in the film-era Canon EOS RT and in the even older Pellix and Pellix QL SLRs, plus various limited-production Canon and Nikon high-speed-motor models.

    Certainly they have their limitations, and if you can't manage to keep your fingers out of the mirror box then you shouldn't buy one. But that doesn't mean they're a bad idea for everybody.

    Panasonic has certainly upped the speed of contrast-detect AF (and I can say this with authority, owning a G1, GH1, and GH2) but one area in which phase detect is still superior is action tracking: phase detect can determine WHICH WAY the subject has gone out of focus, which contrast detect can't.

  3. From a practical standpoint you both may be right. Both of you have certainly pointed out older implementations. And Ranger 9 is certainly correct to note that if you can't keep your fingers out of the mirror box then you probably shouldn't own it (or any regular camera for that matter).

    However, to reiterate and expand a bit, having something in the light path that can't be easily kept clean when something more substantial than dust settles on it makes it a risk.

    Ranger-9, when I made my comments about autofocus, I was not considering action tracking. Accurate active tracking would be of far more interest to videography than stills photography. I can see why Sony, being a video company, would develop the pellicle mirror.

    But I also have to point out that regular moving mirror D/SLRs far outnumber pellicle mirrored cameras, both film and digital. If pellicle is as good in practice as in theory, it should have been more prevalent.

  4. The a33 and a55 have ben out for a year and I don't remember hearing any horror stories about people getting their sensors dirty and needing to send them in for cleaning. Have you?

  5. I owned a Canon RT with the pellicle mirror and one of the selling points was the extremely short shutter lag. Something like 22 ms. I owned the camera for years and at first I was worried about dust on the mirror but it's far enough away from the imaging plane that it was never in focus. A little compressed air was enough for any small trash on the front. Also consider that they may have an IR or other filter in front of the mirror like Kodak did with their 660 and 760 cameras which would block intrusion of dust and allow user cleaning of the outside surface. Win, win, win. I don't think Sony would let this one off the leash without having dealt with a very obvious possible source of customer dissatisfaction. We'll see.

  6. @kirk_tuck "I don't think Sony would let this one off the leash without having dealt with a very obvious possible source of customer dissatisfaction. We'll see."

    You would think Sony would have a solution, which is why I kept saying "might" and "may". As you said, we'll see.

    Besides, I want to go somewhere and hold this in my hands. That, and the NEX-7.

  7. My greatest interest in the pellicle mirror (I too remember the Pellix) was the potential for very quiet operation.
    Though I have not handled the 77 the 55 was louder than the Nikon D5100 thus negating the potential for me.


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