# Idea on how to eliminate the mirror and still have a SLR design



## kphoto99 (Jan 29, 2014)

I was looking at the sensor and noticed that it is very reflective, so I thought that maybe it could be used as the mirror.
Basically if the sensor was mounted at 45 degree angle and reflected the light up into the viewfinder during focusing and when the shutter released button was pressed it would swing down to 90 degrees to take the picture. The sensor would have the DPAF from the 70D for focusing.

The shutter mechanism would have to be relocated forward, maybe something like a leaf shutter just after the mount.

Possible problem would be vibration from the sensor pivoting into vertical position.

Has anything like this been tried before?


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## bchernicoff (Jan 29, 2014)

If the surface of the sensor was reflective enough to effectively replace the mirror, I don't think it would let enough light through to be an effective sensor. Also, the sensor itself is a delicate bit of electronics. I would be concerned with it's durability when bouncing around as well as the durability of the flexible electrical leads connecting it to the rest of the camera's circuitry.


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## viggen61 (Jan 29, 2014)

But you're not, as you say, "eliminating the mirror". You are using the sensor as the mirror.

I see several major issues:

A sensor isn't nearly as reflective as a mirror is. The mirror reflects close to 99% of all light that hits it. The viewfinder would be, at the very least, extremely dark.
Live view would not work
moving the sensor around very fast, and just before exposure is fraught with problems. The mirror can move quickly because it's light, AND the only thing you care about is that it is out of the light path. Moving the sensor to vertical requires very precise positioning, and no bouncing.
Leaf shutters are used in medium format SLRs, but there are limitations to leaf shutter construction. I'm not sure speeds of 1/8000 are practical in a leaf shutter. Add to that, the leaf has to be open for focus and metering, then shut, then opened & shut, then opened again. Sports photogs and wildlife photogs would probably not be too interested...
The DPAF wouldn't work properly. With the sensor/mirror at a 45 degree angle, correct focus is different between the top of the sensor and the bottom. 


I don't think we'll be losing the mirrors all that soon. Not until a really high-quality EVF comes along, anyway.


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## Mt Spokane Photography (Jan 29, 2014)

The sensor has to be perpendicular to the axis of the lens to a very tiny tolerance, like 1/10000 inch. Putting it at a angle would seem to be impossible, only a tiny 1/10000 inch slice of the image would be infocus.


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## kphoto99 (Jan 29, 2014)

Mt Spokane Photography said:


> The sensor has to be perpendicular to the axis of the lens to a very tiny tolerance, like 1/10000 inch. Putting it at a angle would seem to be impossible, only a tiny 1/10000 inch slice of the image would be infocus.



When the picture is being taken the sensor would be back to the standard location.

Same thing for live view.


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## Mantanuska (Jan 29, 2014)

Wouldn't this still take up just as much space as having a mirror?


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## kphoto99 (Jan 29, 2014)

viggen61 said:


> But you're not, as you say, "eliminating the mirror". You are using the sensor as the mirror.
> 
> I see several major issues:
> 
> ...



The mirror allows a lot of light to the autofocus points that are behind it, so not all of it is reflected.

The sensor reflects quite a bit of light (I don't know if enough), a nano coating could be optimized to increase the reflectivity at 45 degrees.

Live view would work just like now, the sensor would go into vertical position.

The sensor would not be attached at the edge, but it would be through the middle, it would pivot on this axis. It would move half the distance that the mirror does now.

Vibration seems to be the biggest problem to me.


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## kphoto99 (Jan 29, 2014)

Mantanuska said:


> Wouldn't this still take up just as much space as having a mirror?



In theory about half, since the sensor would be mounted on an axis through the middle of the sensor. Unlike the mirror that needs to move forward as much as the sensor is high. Pivoting would need half the distance.


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## neuroanatomist (Jan 29, 2014)

kphoto99 said:


> Mt Spokane Photography said:
> 
> 
> > The sensor has to be perpendicular to the axis of the lens to a very tiny tolerance, like 1/10000 inch. Putting it at a angle would seem to be impossible, only a tiny 1/10000 inch slice of the image would be infocus.
> ...



The point is tolerances. I can guarantee you that every time the mirror flips up and down it doesn't seat in exactly the same place, every single time. Given the nature of the optical viewfinder, a little bit of slop in the positioning is not an issue. But if the image sensor is not seated perfectly, it will be an issue for every picture taken. Translational movement is fine, there's just a few pixels of offset which can be easily compensated by a slightly larger than necessary sensor (as is the case for sensor shift image stabilization). But angular displacement of the sensor is problematic.

Yes, the system could be designed such that the sensor is perfectly positioned after every movement. But the costs of such a high degree of mechanical tolerance would result in an exorbitantly priced camera, and that would not work in the marketplace.


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## xvnm (Jan 29, 2014)

kphoto99 said:


> In theory about half, since the sensor would be mounted on an axis through the middle of the sensor. Unlike the mirror that needs to move forward as much as the sensor is high. Pivoting would need half the distance.



Man, I'm sorry. No offenses, but your idea is just plain dumb.


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## kphoto99 (Jan 29, 2014)

neuroanatomist said:


> kphoto99 said:
> 
> 
> > Mt Spokane Photography said:
> ...



I'm attaching a crude diagram, this is a side view of the sensor.
The box on the right has the sensor in the "mirror" position so the eye can see through the lens.
The box on the left has the sensor in the picture taking position.
When the sensor swings down to the picture taking position there is no lateral moment since it is anchored to the pivot point. The difficulty is making sure it stops at the precise location so the top and bottom are not out of vertical plane.

Anyway, it was an idea and I was just curios if this was ever tried before.


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## rs (Jan 29, 2014)

kphoto99 said:


> neuroanatomist said:
> 
> 
> > kphoto99 said:
> ...


It's great to see some lateral thinking, but this particular one doesn't make sense to me for the following reasons:

as stated, like a mirror, no amount of engineering at consumer prices will allow for it to return accurately without bounce, friction to hold it off the buffers after a bounce, play in the bearings, wear in the buffers, or to reduce damage, soft buffers which give a random amount of compression and alignment.
as stated, the alignment of the sensor is much more critical to image quality than mirror alignment. Any issues here will be very apparent.
rotating in the middle rather than the top frees up space needed in front of the sensor, but what for? That space is already there with EF lenses, and now you need all that space freed up at the front at the back - hence a bigger camera
if the sensor is made truly reflective at 45' and completely non reflective when perpendicular to the light, that's all well and good until it comes to off angle light in the mirror box area, such as with angle lenses and big aperture lenses


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## neuroanatomist (Jan 29, 2014)

rs said:


> ...but this particular one doesn't make sense to me for the following reasons:



Also, the mirror doesn't reflect all the light up to the VF - some of the light passes through the 'half-silvered' mirror to be reflected off the submirror for phase detect AF. Therefore, there would need to be 'holes' in the sensor for light to pass through the circuitry that underlies the photo sites.


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## kphoto99 (Jan 29, 2014)

neuroanatomist said:


> rs said:
> 
> 
> > ...but this particular one doesn't make sense to me for the following reasons:
> ...



In this "implementation" all the AF points would be on the sensor (like the sensor in 70D) so no need for 'holes'.

And yes, I see lots of problems with this idea


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## neuroanatomist (Jan 29, 2014)

kphoto99 said:


> In this "implementation" all the AF points would be on the sensor (like the sensor in 70D) so no need for 'holes'.



So you couldn't autofocus while looking through the viewfinder? Yeah, I'd call that a problem.


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## kphoto99 (Jan 29, 2014)

neuroanatomist said:


> kphoto99 said:
> 
> 
> > In this "implementation" all the AF points would be on the sensor (like the sensor in 70D) so no need for 'holes'.
> ...



No, some of the AF points would be angled 45 degrees down, so in the "mirror" mode they would be looking through the lens.


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## neuroanatomist (Jan 29, 2014)

kphoto99 said:


> No, some of the AF points would be angled 45 degrees down, so in the "mirror" mode they would be looking through the lens.



Then in imaging mode they would still be 'holes' in the image. 

Regardless, fresh ideas are great, but this one just doesn't seem practically viable.


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## kphoto99 (Jan 30, 2014)

neuroanatomist said:


> kphoto99 said:
> 
> 
> > No, some of the AF points would be angled 45 degrees down, so in the "mirror" mode they would be looking through the lens.
> ...



Why would there be holes, the 650D & 700D have extra AF points on the sensor for autofocus in video mode?


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## neuroanatomist (Jan 30, 2014)

kphoto99 said:


> Why would there be holes, the 650D & 700D have extra AF points on the sensor for autofocus in video mode?



Indeed, and it's pretty well acknowledged that the on-sensor PDAF of those cameras is slow and not terribly accurate. The dual-pixel design of the 70D is, so far, the only Canon implementation of on-sensor PDAF that approaches the performance of the dedicated AF sensor, and the latter is still superior in some applications. DPAF is so effective because ~80% of the sensor's pixels are used for AF. I suspect and implementation of '45° angled' AF pixels (or clusters) extensive enough to deliver AF performance adequate to replace the dedicated AF sensor would, indeed, leave 'holes'.


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## Sanaraken (Jan 30, 2014)

Im sure the engineers in Canon thougth of this idea, but it just not possible or else we would have it on our DSLR already. Unless your smarter than the engineers in Canon and you can give them your idea.


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## sagittariansrock (Jan 30, 2014)

rs said:


> rotating in the middle rather than the top frees up space needed in front of the sensor, but what for? That space is already there with EF lenses, and now you need all that space freed up at the front at the back - hence a bigger camera



I think this is the biggest issue- there will be no advantage in going through this whole rigmarole (the numerous problems already so eloquently stated) since you end up with a bigger camera. In other words, it would be much ado about nothing 

Keep thinking though- successful ideas follow a bunch of failed ones


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## Halfrack (Jan 30, 2014)

More tidbits to chew on:

-You assume the back of the sensor is a flat plane, where has lots of electrical contacts plus a heat sink
-Microlenses on the sensor would throw a fit - they don't do this off axis stuff, plus would throw a lens color cast
-shutter - leaf shutters can do 1/800 of a second, period. a focal plane shutter isn't going to like being moved around
-lag time - to take a photo it would have to pivot, close the shutter, take the image, and then pivot back into focus/viewfinder mode - much slower than the current setup
-Mirror box bounce - watch some slow motion video of a few frames, and see how much that mirror box bounces over and over with each frame
-general costs - a mirror box is MUCH cheaper to have replaced compared to a sensor

IMHO, sticking with the current mirrorless setups (rangefinder or EVIL) is a safer bet.


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## AcutancePhotography (Jan 30, 2014)

I wonder if there is any advantage in a type of digital Twin Lens Reflex camera?

It would be probably an overly complicated solution to a rather simple problem though.


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## m (Jan 30, 2014)

AcutancePhotography said:


> I wonder if there is any advantage in a type of digital Twin Lens Reflex camera?



Consumers would have to buy lenses in pairs.
There's no moving mirror.


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## Sella174 (Jan 31, 2014)

m said:


> AcutancePhotography said:
> 
> 
> > I wonder if there is any advantage in a type of digital Twin Lens Reflex camera?
> ...



Canon would love it if this concept ever got off the ground ... you'll be needing two EF 24-70mm f/2.8 blah Mark II lenses and two EF 600mm blah blah lenses. Instant doubling of sales. Whoohooo!


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## Halfrack (Jan 31, 2014)

Sella174 said:


> m said:
> 
> 
> > AcutancePhotography said:
> ...



You wouldn't need to do pairs, a single lens much smaller than your current one would work for the frame & focus, and it could be a semi-superzoom with lots of AF points to cover a wide framing, but as you put on a longer lens, you'd end up with fewer points, but they'd cover the entire frame. Design it to cover the 18-200mm range, the wider frame wouldn't have as full a coverage, and the tele/supertele would literally have the AF points cover the entire frame, and able to track stuff coming in and out of the frame, so if I'm tracking a subject, and something crosses from outside the frame it ignores it.


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## viggen61 (Jan 31, 2014)

kphoto99 said:


> The mirror allows a lot of light to the autofocus points that are behind it, so not all of it is reflected.



The reflex mirror allows a small portion of the light through for AF. It makes no difference to your eye, since your eye has the greatest computer on earth letting you see the image. 



kphoto99 said:


> The sensor reflects quite a bit of light (I don't know if enough), a nano coating could be optimized to increase the reflectivity at 45 degrees.



The sensor reflects some light, but that is a natural result of having a highly polished surface. (It's like when your smartphone is turned off, you can use as a mirror in a pinch, but you wouldn't want to replace your bathroom mirror with it.) It is not the same as being a mirror. Any coating the increases reflectance will decrease the amount of light passing through it, therefore making the sensor less sensitive to light.



kphoto99 said:


> Live view would work just like now, the sensor would go into vertical position.



So how is it AFing again? I thought you said it used dual pixel?



kphoto99 said:


> The sensor would not be attached at the edge, but it would be through the middle, it would pivot on this axis. It would move half the distance that the mirror does now.



That might help a little... But one there is another issue. Your mirror box will need to be longer, unless you expect Canon to drop the EF lenses altogether, and make a whole new line based on the new, shorter, registration distance. 



kphoto99 said:


> Vibration seems to be the biggest problem to me.



That is an understatement, I believe. There is a lot more in the sensor than you can see through the lens mount...


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## 9VIII (Jan 31, 2014)

We already know there's ways to make the mirror fold up that don't involve it slapping forward toward the lens, but really, after reading about the new Sigma 50f1.4 and Zeiss Otus design, I'm not entirely sure if that's actually a problem.

What people want from mirrorless is the advantages of using live view instead of the mirror.


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## 100 (Feb 1, 2014)

This thread made me wonder if anything can be done with the light that gets wasted due to the use of a Bayer sensor.
A Bayer sensor only uses 1/3 of the total amount of light hitting the sensor due to the color filters (RGBG). Could it somehow be possible to use the rest of the light for autofocus and/or some form of an optical view finder?


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