September 30, 2014, 12:51:07 PM

Author Topic: Idea on how to eliminate the mirror and still have a SLR design  (Read 3108 times)

kphoto99

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Idea on how to eliminate the mirror and still have a SLR design
« on: January 29, 2014, 03:27:32 PM »
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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Idea on how to eliminate the mirror and still have a SLR design
« on: January 29, 2014, 03:27:32 PM »

bchernicoff

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Re: Idea on how to eliminate the mirror and still have a SLR design
« Reply #1 on: January 29, 2014, 04:00:06 PM »
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

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Re: Idea on how to eliminate the mirror and still have a SLR design
« Reply #2 on: January 29, 2014, 04:04:06 PM »
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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Re: Idea on how to eliminate the mirror and still have a SLR design
« Reply #3 on: January 29, 2014, 04:20:00 PM »
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. 

kphoto99

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Re: Idea on how to eliminate the mirror and still have a SLR design
« Reply #4 on: January 29, 2014, 04:26:59 PM »
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.


Mantanuska

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Re: Idea on how to eliminate the mirror and still have a SLR design
« Reply #5 on: January 29, 2014, 04:27:58 PM »
Wouldn't this still take up just as much space as having a mirror?

kphoto99

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Re: Idea on how to eliminate the mirror and still have a SLR design
« Reply #6 on: January 29, 2014, 04:38:30 PM »
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.


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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Re: Idea on how to eliminate the mirror and still have a SLR design
« Reply #6 on: January 29, 2014, 04:38:30 PM »

kphoto99

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Re: Idea on how to eliminate the mirror and still have a SLR design
« Reply #7 on: January 29, 2014, 04:41:54 PM »
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.

neuroanatomist

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Re: Idea on how to eliminate the mirror and still have a SLR design
« Reply #8 on: January 29, 2014, 05:00:39 PM »
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.

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

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Re: Idea on how to eliminate the mirror and still have a SLR design
« Reply #9 on: January 29, 2014, 05:01:46 PM »
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

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Re: Idea on how to eliminate the mirror and still have a SLR design
« Reply #10 on: January 29, 2014, 05:22:11 PM »
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.

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.

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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Re: Idea on how to eliminate the mirror and still have a SLR design
« Reply #11 on: January 29, 2014, 05:53:03 PM »
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.

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.

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.
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

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Re: Idea on how to eliminate the mirror and still have a SLR design
« Reply #12 on: January 29, 2014, 06:05:43 PM »
...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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Re: Idea on how to eliminate the mirror and still have a SLR design
« Reply #12 on: January 29, 2014, 06:05:43 PM »

kphoto99

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Re: Idea on how to eliminate the mirror and still have a SLR design
« Reply #13 on: January 29, 2014, 06:09:40 PM »
...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.

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 ;)

neuroanatomist

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Re: Idea on how to eliminate the mirror and still have a SLR design
« Reply #14 on: January 29, 2014, 06:15:58 PM »
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.   :o
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Re: Idea on how to eliminate the mirror and still have a SLR design
« Reply #14 on: January 29, 2014, 06:15:58 PM »