Doug Kerr
Well-known member
Electronic viewfinders
An electronic viewfinder (EVF) is a an electronic display that shows what the camera is aimed at.
The digital image display panel of a typical compact camera is an EVF, but we don't often caal it that (except in the case of dedicated video cameras). In fact, we often call it the "LCD" even though (a) it may not be implemented as an LCD and (b) there may be other displays on the camera that are implemented as LCD's.
In the case of a mostly-still digital camera, we tend to reserve the moniker "EVF" for an EVF that is viewed through an "eyepiece".
But what I say here in general applies to any EVF.
Functions of an electronic viewfinder
Simplistically, we may look to an EVF to one of these two rather distinct things for us:
A. Allow us to see the portion of the scene that will be captured by the camera in as close as possible to the very same way if looks it we view it directly.
B. Allow us to see the portion of the scene that will be captured by the camera in a way that reveals to us certain aspects of the way the scene will be captured in the digital image that will be delivered by the camera.
Now what in particular does B mean? Well, it differs from camera-to-camera, and possibly with various option choices the user has. But typically the "image chain behavior" aspects that are revealed include these two biggies:
• The gross impact of the current ISO sensitivity and photographic exposure settings, insofar as what portions of the scene are "blown out" and what portions" go to black".
• The application of in-camera white balance color correction.
The "dynamic range" of the EVF itself
One way that an EVF (itself) can "let us down" with respect to function A (and to a lesser extent, function B) is that it not not present to us all the detail, over a range of the luminance in the scene, that the human eye can appreciate.
For example, in a scene looking into a shed, with part of the contents well illuminated by sunlight, there may be a pile of horse tack in a dark corner, which we would see in direct viewing of the scene, and in viewing the scene thorough various types of optical viewfinder, that would be "lost in the shadows" as the scene is presented to us via an EVF.
Now if we wanted, in giving specifications for an EVF we would really like, what objective property of the EVF would we ask to have "improved" to alleviate this?
Well, just as in other cases where we speak of the "dynamic range" of a camera, this is a bit tricky.
Before I proceed, let me call your attention to an interesting article in Luminous landscape that reads on this matter:
http://www.luminous-landscape.com/reviews/cameras/why_i_hate_evfs.shtml
Here, to illustrate the point, the author has prepared two images, which I take the liberty of live-linking to here:
From Luminous landscape
The author says:
Now, is that really so? For example, is the range of luminance between the brightest region of the image and the darkest not-black portion correspond to the actual ratio of the luminance of those regions in the scene (and as would land on the retina of the eye)? Not likely. Actual luminance ratios in outdoor scenes such as this are usually many times greater than the ratio that can be presented to us in this Web image.
So what might be more accurate to say is that the left-hand image maps all the luminance values in the scene to values within the range of the whole display chain (to my computer's screen), allowing us to see on-screen all the things we could see with the naked eye of through and optical viewfinder.
But not with the luminance ratios the scene actually had. And we would know that if we had that delivered image on my screen and the actual scene visible outside my window.
So what is it that the EVF display lacks? Is it contrast ratio (the ratio of the maximum to minimum luminance it can generate? Probably not. In the optically-isolated environment provided by the eyepiece system (assume we have an eyecup to block extraneous light, just as we need to have for a reflex OVF), the lowest luminance ("full black") is probably very near to zero, and so the contract ratio is probably rather large.
More likely, what the EVF lacks is:
• A high resolution for luminance (we often say, rather imprecisely, "bit depth").
• Being proceeded by an appropriate luminance mapping for its job (whichever job we look to it to do for us at the moment).
Basically, if our friend at LL was able to have all the objects in that scene visible in the image that ended up on my laptop's feeble display screen. a camera manufacturer should be able to have them all show up on an EVF display.
Assuming, of course, that such is what we want.
Best regards,
Doug
An electronic viewfinder (EVF) is a an electronic display that shows what the camera is aimed at.
The digital image display panel of a typical compact camera is an EVF, but we don't often caal it that (except in the case of dedicated video cameras). In fact, we often call it the "LCD" even though (a) it may not be implemented as an LCD and (b) there may be other displays on the camera that are implemented as LCD's.
In the case of a mostly-still digital camera, we tend to reserve the moniker "EVF" for an EVF that is viewed through an "eyepiece".
But what I say here in general applies to any EVF.
Functions of an electronic viewfinder
Simplistically, we may look to an EVF to one of these two rather distinct things for us:
A. Allow us to see the portion of the scene that will be captured by the camera in as close as possible to the very same way if looks it we view it directly.
B. Allow us to see the portion of the scene that will be captured by the camera in a way that reveals to us certain aspects of the way the scene will be captured in the digital image that will be delivered by the camera.
Now what in particular does B mean? Well, it differs from camera-to-camera, and possibly with various option choices the user has. But typically the "image chain behavior" aspects that are revealed include these two biggies:
• The gross impact of the current ISO sensitivity and photographic exposure settings, insofar as what portions of the scene are "blown out" and what portions" go to black".
• The application of in-camera white balance color correction.
The "dynamic range" of the EVF itself
One way that an EVF (itself) can "let us down" with respect to function A (and to a lesser extent, function B) is that it not not present to us all the detail, over a range of the luminance in the scene, that the human eye can appreciate.
For example, in a scene looking into a shed, with part of the contents well illuminated by sunlight, there may be a pile of horse tack in a dark corner, which we would see in direct viewing of the scene, and in viewing the scene thorough various types of optical viewfinder, that would be "lost in the shadows" as the scene is presented to us via an EVF.
Now if we wanted, in giving specifications for an EVF we would really like, what objective property of the EVF would we ask to have "improved" to alleviate this?
Well, just as in other cases where we speak of the "dynamic range" of a camera, this is a bit tricky.
Before I proceed, let me call your attention to an interesting article in Luminous landscape that reads on this matter:
http://www.luminous-landscape.com/reviews/cameras/why_i_hate_evfs.shtml
Here, to illustrate the point, the author has prepared two images, which I take the liberty of live-linking to here:
From Luminous landscape
The author says:
I have edited the same frame so that the one on the left looks pretty much the way it does to the naked eye or the viewfinder of a full-frame DSLR. The one on the right more like the view through the Sony's EVF.
Now, is that really so? For example, is the range of luminance between the brightest region of the image and the darkest not-black portion correspond to the actual ratio of the luminance of those regions in the scene (and as would land on the retina of the eye)? Not likely. Actual luminance ratios in outdoor scenes such as this are usually many times greater than the ratio that can be presented to us in this Web image.
So what might be more accurate to say is that the left-hand image maps all the luminance values in the scene to values within the range of the whole display chain (to my computer's screen), allowing us to see on-screen all the things we could see with the naked eye of through and optical viewfinder.
But not with the luminance ratios the scene actually had. And we would know that if we had that delivered image on my screen and the actual scene visible outside my window.
So what is it that the EVF display lacks? Is it contrast ratio (the ratio of the maximum to minimum luminance it can generate? Probably not. In the optically-isolated environment provided by the eyepiece system (assume we have an eyecup to block extraneous light, just as we need to have for a reflex OVF), the lowest luminance ("full black") is probably very near to zero, and so the contract ratio is probably rather large.
More likely, what the EVF lacks is:
• A high resolution for luminance (we often say, rather imprecisely, "bit depth").
• Being proceeded by an appropriate luminance mapping for its job (whichever job we look to it to do for us at the moment).
Basically, if our friend at LL was able to have all the objects in that scene visible in the image that ended up on my laptop's feeble display screen. a camera manufacturer should be able to have them all show up on an EVF display.
Assuming, of course, that such is what we want.
Best regards,
Doug
