# Will Canon Ever Revisit their Pellicle Mirror Design?



## Sator (Apr 29, 2016)

Back in 1989 Canon introduced the first pellicle mirror, single lens translucent design in the Canon EOS RT. Its successor, the Canon EOS-1N, was capable of shooting up to 10 fps—on film. 





http://www.mir.com.my/rb/photography/hardwares/classics/eos/EOS-1nRS/index1.htm

The problem was that the view through the optical viewfinder was very dim. The pellicle reduced light transmission by 2/3 stop, and reducing this transmission would have made the viewfinder even darker. Some period tests on Canon SLT models also suggested that a translucent pellicle robbing the exposure of 2/3 of stop of light additionally degraded image quality.

Today, it is possible to amplify the dim light signal from the pellicle with an EVF. Sony has done precisely that with their A mount DSLT design, in which the pellicle reduces transmission to the sensor by 1/2 stop. However, Sony's first implementation in a full frame model was only capable of shooting at 6 fps, which is less than what Canon's film camera SLT was capable of back in 1989, and no better than what conventional DSLRs such as the 5DIII could achieve anyway. Worse still, Sony failed to eliminate black out during shooting:

http://www.darinmcquoid.com/A99.html

The predictable result of this woeful implementation was that the Sony a99 was hardly a hit on the marketplace, and rumour has it that Sony lost money on it so badly that it might have nearly bankrupted them (they were only saved by the success of their mirrorless cameras). Sony have a bad habit of prematurely releasing grossly underdeveloped beta prototypes onto the market, and in this instance they paid dearly for it

As Sony is still licking its wounds from its self-inflicted initial failure, they are only exceedingly tentatively continuing development of their DSLT design concept. Even then with the APS-C a77II, they now achieve a 12 fps frame rate on a camera body costing less than $1000 USD. That is almost as fast as the 14 fps the Canon 1DX II manages at six times the price. Although it is virtually never spoken about, this is a far more remarkable engineering achievement than anything found in their mirrorless models over which the mindless masses in the meanwhile are going irrationally gah-gah over:

http://petapixel.com/2016/04/04/sonys-full-frame-pro-mirrorless-fatal-mistake/

A pellicle design also eliminates mirror slap and the image degradation this mechanical movement causes, something that will become increasingly desirable as sensor resolutions inch towards 120MP, and become more sensitive to such movement. It also means the elimination of an expensive and heavy mechanical moving part, resulting in a weight reduction for the body. If a film EOS camera could shoot at 10 fps back in the 1990s, one can only imagine what a more convincingly executed high-end Canon DSLT design might be capable of today

The EVF further permits real time exposure preview, including a histogram, a feature normally associated with mirrorless cameras. Some would add that current EVFs have a lag, meaning that this makes them less suitable for shooting action, but EVFs are improving. Given that a higher frame rate is intended for shooting action, this would appear to be a significant design disadvantages—at least for the time being until EVF technology catches up.

From the perspective of autofocus, a DSLT uses a dedicated AF sensor for continuous PDAF, one separate from the main image sensor. This gives it a significant advantage over mirrorless designs in its AF speed. However, in the meantime, on-sensor PDAF has been developed, such as in the dual-pixel autofocus system from Canon, where AF capabilities are built into the main image sensor. Whether hybrid on-sensor plus off-sensor PDAF would confer any advantage is unknown. Perhaps, the loss of light transmission from the translucent pellicle could be reduced to somewhat less than 1/3 stop, and the resulting reduction of PDAF performance from the dedicated AF sensor be made up with some on-sensor PDAF. That is pure speculation, however.

A new Canon digital pellicle model would have all the key advantages of mirrorless, along with all of the key advantages of a DSLR. It would as fast, or faster than a DSLR, and have the electronic viewfinder of a mirrorless for live exposure preview. The result would be a hybrid of DSLR and mirrorless design concepts. This stands in marked contrast to a professional grade DSLR-sized FF mirrorless with all the disadvantages of mirrorless and none of the advantages of a DSLR.

So it would certainly be interesting to see if Canon have ever considered revisiting their pellicle mirror SLR designs for the digital age. They have extensive experience with it, and this will help them succeed in digitalising the technology where Sony have hitherto failed—although that too may soon change. Developing a Canon DSLT would also have the advantage over starting up a full frame mirrorless system in that it would not require the expensive development of a new full frame mirrorless lens mount, as it would be able to take EF mount lenses. Nor would users have to buy new lenses to adopt the new technology as they would for a full frame mirrorless system from Canon.


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## privatebydesign (Apr 29, 2016)

No they won't, not unless they can overcome the dramatic shortfalls of the technology by inventing switchable mirrors with next to zero lose of light when deactivated for exposure (which also means viewfinder blackout.

The RT was the third Canon camera with a pellicle mirror, the first was the Pellix QL in 1965, then there was a special F1 for the 1972 Olympics.


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## Mt Spokane Photography (Apr 29, 2016)

After the third flop (The one you think was first), Canon seems unlikely to try again.


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## Bennymiata (Apr 29, 2016)

My father had a Canon Pelix which he bought new around 1966 and he reckoned that it was good in bright lighting conditions, but hard to see through the viewfinder in low light.
The Pelix was a popular camera in its day too.
For my 13th birthday in early 1968, he bought me a Canon FT-QL, which was basically the same camera but with a flippy mirror.
The FT was better to use in low light as the ovf was much brighter.

To me, the light loss you get with pellicle mirrors is just too much to be useful.


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## Mt Spokane Photography (Apr 29, 2016)

I never owned a Pellix QL, but the guy next to me at work bought one. The viewfinder was very dim. I have a FTQL.


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## Sator (Apr 29, 2016)

The early Pellix models are certainly before my time! 

It's easy to dismiss it as an outdated technology, but the first reflex mirror design was found on a camera obscura dating from 1676. DSLRs are just a modernised digital version of an 1676 design concept. As for mirrorless cameras, a 19th century daguerreotype camera is also mirrorless:





People talk about "mirrorless" as though it were a startlingly original novelty that appeared like a lightning bolt out of the blue. In actuality, if you look at the big picture you find that "there is nothing new under the sun".

Analogue pellicle mirrors would have had to have a greater loss of light because otherwise the OVF would be too dim. In the case of the Canon pellicle design, you got a 2/3 stop loss of light. If you amplified that view with a EVF, you overcome the dimness (but replace the dimness with the problem of EVF lag), thus allowing the engineer to make the pellicle more translucent without causing the viewfinder to become unacceptably dim. 

If Sony can get a sub $1000 USD APS-C DSLT body to shoot at 12 fps, imagine what Canon could achieve with a premium product from an optimal DSLT design using an updated design involving minimal pellicle light loss and a quality EVF. Sony have got the transmission loss down from the 2/3 stop of Canon film era pellicle models to a 1/2 stop of light, but this could surely be much improved on as well.


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## Mt Spokane Photography (Apr 29, 2016)

Sator said:


> The early Pellix models are certainly before my time!
> 
> It's easy to dismiss it as an outdated technology, but the first reflex mirror design was found on a camera obscura dating from 1676. DSLRs are just a modernised digital version of an 1676 design concept. As for mirrorless cameras, a 19th century daguerreotype camera is also mirrorless:



Its not outdated, it was not a commercial success because only 1/3 of the light goes to the viewfinder, and 2/3 to the sensor. 

Trying to manually focus with a dim viewfinder was the main reason it was not liked. Then, having to use higher ASA settings or longer exposures was not popular.

Now that we have digital sensors, a dim viewfinder and the need for a longer exposure or ISO setting is still not popular. The dim viewfinder limited practical use of the camera to bright daylight.

There are some other issues, shadows due to light reflecting from both sides of the pellicle mirror that appear on the image. It all adds up to poor acceptance by pro photographers.

Although the shadows are weak and only visible on careful examination, its just an additional strike against it.


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## retroreflection (Apr 30, 2016)

It seems that you want this to be a path to higher frames per second.
Mirror lockup when high fps are desired fixes the mirror cycle limit, but data transmission and other bottlenecks are also serious hurdles. Pellicle mirrors hurt there, too. The loss of light increases exposure time, more scenarios would need exposures longer than the time available (1/fps - shutter reset time).


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