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Author Topic: June 2009: Removing the Blindfold from the dSLR  (Read 41801 times)
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« on: May 28, 2009, 10:46:39 PM »

June 2009: Removing the Blindfold from the dSLR


Background

Last month I discussed the new Micro Four Thirds format being offered in cameras such as the Panasonic G1 and GH1.  Note that Olympus/Panasonic have used Four Thirds format for years, it's the "Micro" part that makes Micro Four Thirds interesting as it removes the mirror mechanism from the camera.  Last month it was merely a promising technical curiosity but this month I got my hands on a G1 and this new technology has become much more than just a curiosity.  Right away I started noticing what a dSLR can do when there is no blindfold (mirror) obstructing the main sensor for important operations like focus, metering, and framing. Of course, when you remove the mirror from the dSLR, it is no longer technically a dSLR but such a camera still feels and operates very much like a dSLR with some very interesting added perks!  Let's take a look at what a dSLR style camera can really do when you remove the mirror and open the camera's eye to the world it is about to photograph.

 

Focus

Traditional dSLR: It might seem like an odd statement but as far as focus, the traditional dSLR is handicapped at the starting line!  When you activate a dSLR's auto-focus, you can see through the lens but the primary sensor (the sensor that is about to capture your image) is completely blind to what you are about to shoot.  Instead, light is bounced into a secondary focus mechanism near the top of the camera that performs some phase based calculations to calculate where the focus ring on the lens should be turned in order to achieve proper focus.  Due to slack in the lens' servo mechanism and slight errors caused by the positioning of the focus mechanism and lens, focus on a traditional dSLR is based on prediction only.  When the mirror is flipped out of the way and the shutter is opened, slight errors in the prediction can sometimes cause auto-focus errors.  This is why we hear so much talk about people getting their lenses calibrated to their camera bodies.  Seldom do a lens/body pair match so perfectly that you get perfect focus for the entire zoom range (on a zoom lens).

Mirrorless "dSLR": The mirrorless dSLR sees the world clearly because the main image sensor is always being exposed to the scene.  Fast contrast detection auto focus like that implemented on the Panasonic G1 and GH1 simply look at the part of the image that is in the focus point in the viewfinder and adjusts focus until perfect focus is achieved.  Since this operation is a honing and confirmation process, there is no error involved and the camera will give perfect focus every time because the sensor can see what it is about to capture.  Well, perfect provided you don't do something silly like try to focus on a featureless white wall.  Gone are the days of worrying about sending camera bodies and lenses in to the manufacturer for calibration or spending hours fiddling with lens fine tuning in a camera menu only to find that the adjustments only work for part of the zoom range on your zoom lens!

 

Metering

Traditional dSLR: Again, the dSLR cannot "see" when you are giving the shutter button a half press.  If you can see through the lens, the sensor cannot, so light is rerouted to what (typically) amounts to a tiny 32 pixel sensor in the top of the camera that tries to detect the amount of light in the scene.  While it is a very course measurement, it usually works pretty well but the pitfalls include exposure surprises where the matrix (32 pixel array) overestimated/underestimated how big that specular highlight or reflection really was.

Mirrorless "dSLR": With its sensor continuously exposed to the entire image, the mirrorless dSLR is free to look at the entire image at much higher resolution.  The result is far fewer surprises when it comes to metering!

 

Viewfinder Error

Traditional dSLR: If you are someone who has used traditional dSLR's for years like me, you're used to framing the subject through the viewfinder only to find that the camera actually captured a little more than what you had framed.  The difference is caused by the viewfinder having a slightly different angle of view than when the light goes to the actual image sensor.  Some cameras/lenses suffer more from this effect than others.

Mirrorless "dSLR": Because the mirrorless dSLR has no optical viewfinder, what you see through the electronic viewfinder is exactly what you'll get in the photograph.  This is because you are looking at what the sensor is actually seeing.  Now you can see exactly how your subject is being framed.

 

Camera Size

Traditional dSLR: Due to the added mechanical complexity involved in having a mirror and separate focus and metering mechanisms, the traditional dSLR is normally a pretty bulky tool to carry.

Mirrorless "dSLR": With reduced mechanical complexity comes the freedom to reduce physical size.  The lens to sensor distance and overall bulk can be reduced in mirrorless designs making cameras more compact.

 

Perks of a Mirrorless Design: Lots of Perks!

It's amazing what can be done once you remove that blindfold we call a mirror from the dSLR!  With the main sensor's eye to the world open and an electronic viewfinder for you to see through, here's what cameras like the Panasonic G1/G1H can offer in addition to the main advantages above.  These are what I consider to be icing on the cake:

  • Real time histograms: Look through the viewfinder and there it is: a real time histogram of the scene being displayed continuously before the picture is taken!  Remember, with the mirrorless design, you are not the only one who can see that scene you are about to shoot: the camera can see it too.

  • Intelligent ISO: The G1 has something called "Intelligent ISO".  Going beyond the traditional auto-ISO found on other cameras, intelligent ISO not only looks at the amount of light and the current zoom (focal length) of the lens, it can watch the subject and determine if an even higher ISO speed is needed due to the subject moving in the scene!  Once again, because the main sensor can see what is happening, it can see that the flower you are about to photograph is moving in the breeze and based on the amount of movement, it might increase the ISO speed further to compensate based on the movement that is occurring the instant you press the shutter button.  The result is that you get exactly the amount of ISO speed you need for the current capture, no more, no less!

  • Viewfinder menus: Because the viewfinder is actually a high resolution digital display, you can open/operate camera menus without ever taking your eye away from the viewfinder!  I find that I almost never use the rear LCD for these tasks any more: I leave it closed and the screen facing in to protect it.  When I want to activate a function or change a custom function, I use my thumb on the menu/direction pad and just operate the menus directly from the viewfinder.

  • Viewfinder blackout: Because there is nothing that has to obstruct the viewfinder while taking a shot, your view through the lens does not disappear when you press the shutter like a typical dSLR.  Instead, the image is captured instantly and it appears as if you have frozen time: the subject simply stops moving and you see the still instantly.  I didn't think this was a big deal until I realized now you can see things that happen the moment the shutter is actuated such as people moving at the last second and creating motion blur, someone blinking, etc.

  • Mirror noise/vibration: While it isn't a big deal to me, a mirrorless design offers quieter performance and no mirror slap that can sometimes blur shots from a typical dSLR.  The G1 does have a mechanical shutter of sorts, but it is nowhere near as loud as a typical dSLR because it's primary purpose is to block light from the sensor during part of the image acquisition phase.  Basically the sensor needs to be in darkness so that no further charge is accumulated on the chip while the data is read from the sensor.

  • Viewfinder display freedom: Because the viewfinder is electronic, there's a lot more freedom to display important information, icons, and things like real time histograms right in the viewfinder.  Want to see a rule-of-thirds overlay for this shot?  No problem: activate the feature and it pops up as a template in the viewfinder.  When you capture a shot, the shot is displayed in high resolution in the viewfinder too, so no need to pull the camera away from your face to view the preview on the LCD: it's right there where you were already looking and focusing your eyes.

 

What About "Live View" on traditional dSLR's?

While some late model traditional dSLR's offer a live view mode where the main sensor is open to the scene, truth be told these operate more like a kludge on most current models than a feature you can really use.  Because the rest of the camera wasn't designed to make use of the live view, the main autofocus and metering mechanisms are "blind" while in live view mode.  Some cameras offer a (slow) contrast detect autofocus while in live view mode but it is so slow that you wouldn't want to use it.  In addition, the LCD screen just isn't good enough to judge focus while the electronic viewfinder on the G1 works well for manual focus, is bright, and is unaffected by the sun.  Live view on a traditional dSLR is more a bandaid to allow access to some features (like video).  When you think about it, in one hand you have autofocus and metering and in the other hand live view.  The mirror can only be in one place at any given time so either you are using live view and blinding your autofocus/metering system or vice versa: you enable those and blind the image sensor.  With a mirrorless design, you get the best of both worlds.

 

Mirrorless in Operation

By now some of you are probably wondering how an electronic viewfinder and contrast autofocus work in the real world.  Surely there must be a down side to using a camera like the G1.  People are used to contrast detection autofocus being super slow.  Is it on the G1?  People say that electronic viewfinders don't offer a good view and are laggy and noisy?  Does the G1 viewfinder lag and get noisy and is it useless for manual focus?  In short, the contrast detection autofocus is just as fast or at least very close to the speed of my past dSLR cameras.  In addition, when the G1 locks on, you know for a fact your image will be in focus and the area where you focused is exactly where the focus will be when you see the final image: no surprises or front/back focus errors.  As for the viewfinder, I was amazed at the resolution and brightness of the electronic viewfinder in the G1.  Outdoors or in bright light, you don't really even notice it is an electronic viewfinder.  Only in (very) low light does it get laggy, meaning jerky/slow like a very slow framerate video.  To be honest, when I point the G1 at the area under my computer desk where the shadows are quite dark, the G1's viewfinder gets very grainy and only updates maybe 5 times a second.  It doesn't look pretty but it actually gives a brighter picture than your eyes can even see.  When I point my other traditional dSLR's at the same area, the viewfinder is almost completely black.  So even though noisy and slow, if you aren't shooting fast moving objects, you can still see more through the G1's viewfinder.  Overall I have yet to find a single drawback to the G1 that gets in the way of my shooting.  It isn't a particularly fast camera at only 3 frames per second but that really has nothing to do with the mirrorless design.  The G1 is also not at the top of the heap as far as image quality and low noise at high ISO like some other high end dSLR's but it isn't far off and to me, the benefits far outweigh something like a 10% hit in image performance.  Due to the design, I find myself getting a very noticeable increase in the ratio of "keepers" versus "toss" photos compared to other cameras.

 

Summary

I'm happy to say that I am very excited about the mirrorless dSLR both in concept and in practice when using the Panasonic G1.  Considering the Panasonic G1 is the first dSLR-like camera to sport a mirrorless design and given all that it can do, the traditional dSLR may really be evolving into something better.  Technology of any new design is sure to improve over time and considering that the G1 has blown me away at the starting gate, I see only good things to come with the mirrorless dSLR design.  The G1 may not have the silky smooth ISO 1600 performance of a high end dSLR or the shallow depth of field offered by a full frame dSLR but it sure does eliminate a lot of the pitfalls of the traditional dSLR that have become my pet peeves over the years.  I look forward to more models using a mirrorless design in the future.

 

Mike Chaney

« Last Edit: June 02, 2009, 02:57:26 PM by Mike Chaney » Logged
johngie
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« Reply #1 on: May 29, 2009, 03:05:05 PM »

Wow, shades (no pun intended!) of the old Canon Pellix!

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« Reply #2 on: May 29, 2009, 03:14:15 PM »

Very informative. I'm looking forward for more like this. Thanks, Mike.
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« Reply #3 on: May 29, 2009, 05:35:21 PM »

Thanks for this informative article. I am a Olympus user and they expect to launch their micro 4/3 in the next few months, this make me even more interested to see what enhancements they produce.
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« Reply #4 on: June 10, 2009, 06:32:04 PM »

 Smiley Sounds very familiar to Minolta A2 users. I have a Minolta A1, which is not as highly spec'd as the A2, but they both have many of the features of the Panasonic G1, and they have both been around for many years now. I realise the Panasonic G1/GH1 have somewhat better performance, but also somewhat higher price. In the meantime my A1 is giving me good performance for the money, and I cannot afford to update to the latest/greatest new camera every few years. Thanks for the excellent article and forum.
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« Reply #5 on: July 08, 2009, 01:22:00 PM »

The only thing missing was the downside of that technology, at least for now.

Carrying such a rig while the system is still on can really burn up some pixels as it bounces into full view of the sun, etc.  The mirror protects that until the system powers down.

The other thing on an interchangeable lens camera is dust.  Right now, although sensors get dirty, the mirror catches most of it.  I know there is a filter and/or cover over the sensor, but the extra barrier is a blessing more often than not.

Until Nikon and Canon come up with a reliable way to clean a sensor in the camera, having that mirror there when changing lenses at football, NASCAR, Indy--even some landscapes--is a blessing.
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« Reply #6 on: July 08, 2009, 03:30:55 PM »

The only thing missing was the downside of that technology, at least for now.

Carrying such a rig while the system is still on can really burn up some pixels as it bounces into full view of the sun, etc.  The mirror protects that until the system powers down.

The other thing on an interchangeable lens camera is dust.  Right now, although sensors get dirty, the mirror catches most of it.  I know there is a filter and/or cover over the sensor, but the extra barrier is a blessing more often than not.

Until Nikon and Canon come up with a reliable way to clean a sensor in the camera, having that mirror there when changing lenses at football, NASCAR, Indy--even some landscapes--is a blessing.

Interesting but I'm not convinced either of those is a significant down side.  When I'm carrying the camera, it usually has the lens cap on and even if it was off, I'm not sure light is going to ruin pixels.  The mirror being in the way of the sensor for dust is of less concern than something accidentally poking the sensor while the lens is off.  Dust tends to fall around the mirror anyway and the mirror just makes it harder to clean the sensor in the long run.  My main concern is if you change lenses in the field, a branch, screwdriver, etc. might accidentally scratch the exposed sensor.

Mike
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« Reply #7 on: July 08, 2009, 06:37:22 PM »

When I'm carrying the camera, it usually has the lens cap on and even if it was off, I'm not sure light is going to ruin pixels. 

What I meant is that focused beam on the sensor.  I have seen it burn through shutters in the "old days."  Dunno.

Quote
The mirror being in the way of the sensor for dust is of less concern than something accidentally poking the sensor while the lens is off.  Dust tends to fall around the mirror anyway and the mirror just makes it harder to clean the sensor in the long run. 

In PJ you just have no choice.  You're even supposed to urn the camera off when changing; we just don't can't do that in a fast moving situation.  I agree about the mirror, somewhat.  Of curse the D300 has a sensor clean (some kind of oscillation) but the D3 does not.  Go figure.  I have always wondered about those cleanings though.  Where the heck can the dust go except hang around to blow back on at some point !?!?!  It's not like they have a waste tank like printers do <GGGG>.
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« Reply #8 on: July 14, 2009, 09:26:28 PM »

The vibration cleaning systems work very well. I had to clean the sensor in my previous DSLR all the time, but my Canon 40D has only needed a wet cleaning once in 2 years. In the newer Canons, there's a patch of sticky material somewhere in the mirror chamber where the dust is supposed to accumulate after it falls off the sensor (off the anti-aliasing filter in front of the sensor, to be precise). I don't see the dust ever overwhelming that system.

I'd like to see someone run a test on noise generated by these live-feed sensors. As long as the sensor is operating, it generates heat, which should produce more noise. I've seen people suggest anecdotally that the live view cameras spike up in noise quite a bit when live view is engaged for a long time, say 30 seconds or so. I haven't seen it in my DSLR yet, but I only use live view for focus confirmation and so forth. Full HD video has got to really put heat in a sensor. Maybe what's needed is an active cooling system, like the ones used on astro imaging equipment.

I'm one of those guys who might have a real problem with the sun-on-the-sensor deal. I hardly ever use lens caps in potential shooting situations, preferring to leave lens hoods on all the time to protect the glass. I could easily imagine letting the sun accidentally fry whatever was at the focal plane. [Some years ago, I was shooting a snow scene on top of a mountain near Albuquerque with a Rolleiflex. I set up a scene with the sun visible. The air was very dry and cold. The sun beating down on the shutter blades caused them to warm up, and when I tripped the shutter, I got a blast of static electricity between shutter and film that ruined several frames. You can see from the negative that it started where the sun was in the frame.] A minor point to be sure, but it is something to consider.

I'll be interested in where this idea goes. Something like a ruggedized G1 might be ideal for underwater photography. The water bath would draw heat away from the camera, eliminating sensor heat buildup. Contrast focus would probably be great in that situation too. You could switch on the LCD for easier viewing through a mask. Could be a real winner.
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