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11-29-2014, 02:50 AM - 3 Likes   #1
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Is this Pentax's future? Translucent mirror with adjustable transmission rate patent

Semi-transparent stationary reflex mirror in an SLR is nothing new. Canon Pellix in 1965 used such mirror to let about two-thirds of the light from the lens pass directly through to the film, while the rest was reflected to the viewfinder and CdS meter cell for the TTL exposure measurement.

Sony's Single-Lens Translucent technology uses a semi-transparent fixed mirror which diverts about 30% of the incoming light to a phase-detection autofocus sensor, while the remaining 70% strikes the image sensor, which in turn feeds the electronic viewfinder. This design allows for full-time phase-detection autofocus during electronic viewfinder, live view, and video recording operation.

The drawback of these technologies is the loss of light:

- Canon Pellix: about - 0.5 EV in the exposure through the semitransparent mirror and about - 1.7 EV dimmer finder compared to using a fully reflecting mirror
- Sony SLT: about - 0.5 EV in exposure because of the portion of incoming light diverted to the autofocus sensor.

Ricoh were just (11 November 2014) granted a patent on a translucent mirror with adjustable transmission rate: light transmission rate is adjustable from 50 to 100%, i.e. reflection rate varies from 50 to 0%.

Ricoh ???????????????????????????????So-net???

With such a device, you can either, and successively, improve the efficiency of the autofocus sensor in low light by increasing the reflection rate and improve that of the image sensor by increasing the transmission rate (SLT scheme with an electronic viewfinder) or, if you keep the optical viewfinder (Pellix scheme), successively improve the brightness of the viewfinder by increasing the reflection rate then the efficiency of the imaging sensor in increasing the transmission rate.

The better of both worlds.


Last edited by Mistral75; 11-29-2014 at 07:03 AM.
11-29-2014, 03:51 AM   #2
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As I recall the Pentax LX has a semi-transparent area on the mirror.
11-29-2014, 04:36 AM   #3
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But still consuming light we would rather use to take an image.
11-29-2014, 05:11 AM   #4
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QuoteOriginally posted by RonHendriks1966 Quote
But still consuming light we would rather use to take an image.
No, it does not, transmittance reaches up to 100 per cent.

11-29-2014, 06:54 AM   #5
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Merci Mistral, very interesting !

I would bet for such a system, in conjunction with the possibility to include more customisable informations in the view finder, using 'electronic-powered' focussing screens.
11-29-2014, 07:33 AM   #6
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This is pretty exciting. The arrangement shown in the diagram looks very much like Sony's SLT system, but without the light loss. SLT is much maligned, but it has a number of desirable features - higher frame rates, being able to use the dedicated PDAF sensor during video, using PDAF and CDAF at the same time, and probably more that I haven't thought of. Of course you lose the OVF, which would probably be divisive. I'd be interested to hear how long the mirror takes to change between its fully transparent and semitransparent states. If it was fast enough, it would mean the camera could reflect light to the PDAF to achieve focus, then let all the light through for capture, perhaps even at high frame rates.

The other possibility is to use it in an arrangement where it reflects the image up to a prism, as Mistral75 said, but that doesn't seem to be what's illustrated in these diagrams.
11-29-2014, 08:30 AM   #7
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100% I find it difficult to believe...
But even if it's only 98% or so, Ill take it, esp. over the 70% of Sony's setup...
Nowadays however I'm increasingly inclined to accept an EVF in place of a traditional OVF..
11-29-2014, 08:37 AM   #8
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QuoteOriginally posted by JPT Quote
This is pretty exciting. The arrangement shown in the diagram looks very much like Sony's SLT system, but without the light loss. SLT is much maligned, but it has a number of desirable features - higher frame rates, being able to use the dedicated PDAF sensor during video, using PDAF and CDAF at the same time, and probably more that I haven't thought of. Of course you lose the OVF, which would probably be divisive. I'd be interested to hear how long the mirror takes to change between its fully transparent and semitransparent states. If it was fast enough, it would mean the camera could reflect light to the PDAF to achieve focus, then let all the light through for capture, perhaps even at high frame rates.

The other possibility is to use it in an arrangement where it reflects the image up to a prism, as Mistral75 said, but that doesn't seem to be what's illustrated in these diagrams.
With the emergence of on-sensor PDAF, are the advantages of SLT largely superseded? This patent would theoretically allow full light transmission to the sensor but that would not be possible in C.AF mode and video (I think). In other words, Sony's true C.AF relies on the fact that light is being split between the AF sensor and the image sensor.

On-sensor PDAF, by contrast, allows for simultaneous image capture and focusing.

Just a hunch... this patented technology is best used conceptually the same as in a DSLR. In essence, the light transmission has to cycle as fast or faster as a moving mirror can cycle. If the transmission can cycle at 10 times per second or faster then you're ahead of what is often achievable in a DSLR.

Or... I'm missing something critical to how this can be used.

11-29-2014, 08:44 AM   #9
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QuoteOriginally posted by Mistral75 Quote
light transmission rate is adjustable from 50 to 100%, i.e. reflection rate varies from 50 to 0%.
See, I cannot believe this. Literally. Keep in mind that in marketing speak "reaches up to" basically means "it never actually does". And I'm sure there are side effects and extra costs. But maybe it is better than the Sony SLT- Still, I doubt Pentax would want that, since Pentax lenses are compact and relatively slow in aperture. I don't think Pentax can afford to lose more light.
So interesting patent, I doubt I would buy a product with it. I would rather go full mirrorless or full SLR.
11-29-2014, 08:50 AM   #10
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and photogs have such passionate thoughts on UV filters in front of their lenses? I can only imagine the furor over a SEMI-TRANSLUCENT mirror that you can't even remove. Plus it's just one more thing to collect dust or moisture. Does the mirror come with its own windshield wipers?

I see a whole new set of problems when you start putting things between the image and the sensor that a photographer CANT control....
11-29-2014, 10:39 AM   #11
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I don't think the moisture or dust problem is as great a deal as you think. This actually would make it easier to clean the camera because the sensor would be protected behind the mirror in a (hopefully) dust proof enclosure. There might be a way to flip the mirror out of the way to actually clean the sensor too because eventually filings and lube from the shutter would get to it. This is a non issue and probably a boon for people that swap lenses a lot. The mirror would be far enough away from the sensor that dust wouldn't likely show up nearly as much unless you really stopped down.

I agree. I would totally take 97% trasmission as long as there wasn't any real downsides to resolving power. SLT also cuts into that as well. CDAF would be possible because the mirror would hopefully be fast enough to become translucent instantly to allow the shutter to fire. Introduce a global shutter and your framerates can be totally insane.

If it takes my k-mount lenses sign me up. As much as I love the OVF it is getting harder and harder to ignore the benefits of a good EVF especially focus peaking. I was actually kind of hoping for a hybrid OVF, but this would be an ok compromise and it still leaves the door open for OVF/EVF hybrid as well.
11-29-2014, 11:10 AM   #12
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QuoteOriginally posted by LensBeginner Quote

Nowadays however I'm increasingly inclined to accept an EVF in place of a traditional OVF..
Replacing OVF by EVF would actually sign the end of PENTAX as an historical and ethymological full sensed acronym...(*)
This would be actual nonsense marketingwise, also because it would probably mean K-mount's death => in japanese : a dobble HARA-KIRI !


(*) : The Pentax (derived from PENTAprism refleX) camera was the first camera to incorporate a pentaprism viewfinder and a reflex mirror system in 1952...

Last edited by Zygonyx; 11-29-2014 at 01:28 PM.
11-29-2014, 11:27 AM   #13
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QuoteOriginally posted by nomadkng Quote
and photogs have such passionate thoughts on UV filters in front of their lenses? I can only imagine the furor over a SEMI-TRANSLUCENT mirror that you can't even remove. Plus it's just one more thing to collect dust or moisture. Does the mirror come with its own windshield wipers?

I see a whole new set of problems when you start putting things between the image and the sensor that a photographer CANT control....
Apart from the adjustable transmission/reflection rate, this translucent mirror is quite similar to that in Sony SLTs and there are no particular complaints about dust or moisture problems with them.
11-29-2014, 11:40 AM   #14
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That's interesting. The new high end MILCs started sporting very fast frame rates, difficult to obtain with a classic mirror; and this technology is an obvious solution. Except for a reduced thickness, this - together with a hybrid OVF - can eliminate all the real and perceived advantages of a MILC/EVF design. Of course, the technology must reach a point where nothing significant is lost.

Personally, I'm happy with a classic OVF as I don't need 15fps; and I'm not sure the technology is close to being ready for production. Perhaps it was a "just in case" type of patent... but, who knows?
11-29-2014, 11:49 AM   #15
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QuoteOriginally posted by LensBeginner Quote
100% I find it difficult to believe...
But even if it's only 98% or so, Ill take it, esp. over the 70% of Sony's setup...
Nowadays however I'm increasingly inclined to accept an EVF in place of a traditional OVF..
I was thinking that too........

but maybe......

This is not the solution to replace the mirror in dslr, but adding pdaf to mirrorless.....
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