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05-28-2009, 12:42 PM   #16
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QuoteOriginally posted by PentaxPoke Quote
yes nanok, there is so much confusion now amongst consumers as to what magnification and coverage actually mean, that it seems pointless to continue to rate them this way. I almost wish they would simply switch to rating the viewfinders on diagonal dimension, like they do for the LCD. Then the manufacturers would all be scrambling to make larger viewfinders.
but if they get bigger they are not as bright, because the light will be spread out further off the little mirror in the ASP-C format mirror box.

05-28-2009, 12:53 PM   #17
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good point. and to offset that, they would make brighter (and shittier for DOF preview) focusing screens. arggghh.

but still, confusion helps noone, what the hell, just be honest for $#^%s sake.
05-28-2009, 04:35 PM   #18
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QuoteOriginally posted by regor Quote
I always understood that maginification of the viewfinder was a percentage of the size of the image on the focusing screen relative to the size of the sensor. i.e. a 0.92 magnification means the size of the image on the focusing screen is 8% smaller than the actual size of the sensor; hence why the 0.92x of an APS-C sized image is much smaller than a 0.92x of a FF sensor image.
That's not my understanding of how it's done, although I don't claim expertise here. I've always understood it to measure the apparent magnification to the eye - relative to without the viewfinder, as is the case with binoculars - measured using a 50mm lens, as Ken mentions. The fine print in camera specs virtually always specifically mention that they are measuring using a 50mm lens, which wouldn't really be relevant if it was simply measuring the size of the image on the focus screen relative to sensor.

In fact, I would think something would have to be terribly wrong if the size of the image on the focus screen was anything other than *exactly* the same as the size on the sensor, since as far as I know the *distance* from lens to screen and sensor has to be identical in order for MF to work. Seems physics would prevent the two images from ever being anything but exactly the same size if they are at the same distance.

Anyhow, bottom line is, as far as I can see, Ken is absolutely right. This touches on something Robin and I just stumbled upon on in another recent thread: the 35mm format happened to be a kind of "magic" format where a lens that many people perceived as providing a natural field of view (although *nothing* like the field of view of the unaided eye, as is sometimes claimed) also happened to provide something close to 100% magnification using using a basic viewfinder design without additional optics. So a "normal" lens happened to provide close to 100% magnification as well a "natural" field of view. Whereas APS-C provides the same field of view only with a much shorter focal length and an equivalently smaller magnification.

Conversely, one might expect a larger (than 35mm) format camera to provide 100% magnification only with a wide angle lens - with a "normal" field of view, the magnification might be bigger than 100%, unless the camera is so much bigger that it moves the focus screen further away and thus reducing the apparent magnification, which is entirely possible - I don't know that I've ever looked through a viewfinder on a larger format camera.
05-28-2009, 06:14 PM   #19
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QuoteOriginally posted by Marc Sabatella Quote
This touches on something Robin and I just stumbled upon on in another recent thread: the 35mm format happened to be a kind of "magic" format where a lens that many people perceived as providing a natural field of view (although *nothing* like the field of view of the unaided eye, as is sometimes claimed) also happened to provide something close to 100% magnification using using a basic viewfinder design without additional optics. So a "normal" lens happened to provide close to 100% magnification as well a "natural" field of view. Whereas APS-C provides the same field of view only with a much shorter focal length and an equivalently smaller magnification.
This is something that has bugged me for over a year, since soon after I got my FA43. I am still amazed it is not a more well known phenomenon.

05-28-2009, 06:48 PM   #20
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might this be related to the minimum (confortable) viewing distance of the human eye? meaning that the 35mm frame is about as small as you can get and still bring the image close enough to the eye so the perceived size is natural with the normal lens, without making it disconfortable. for larger formats, you can either bring the image further adn have the same effect (if you have the space) or you will have a "bigger viewfidner", for smaller formats, you will have to put the image further via optics other than the pentaprism (lenses), because you don't want to do it with a prism of the same size as for 35mm (it would take too much space), and at the same time enlarge it so as to avoid the tunnel effect, this means it gets inefficient as you go to a smaller frame (image on the matte screen), and you start losing light twofold (additional lenses, and enlarging the image/pushing it further -- thus "stretching" the available amount of light).

not sure if i'm making any sense, it's late and i'm thinking out loud
05-28-2009, 09:19 PM   #21
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QuoteOriginally posted by Marc Sabatella Quote
I've always understood it to measure the apparent magnification to the eye - relative to without the viewfinder, as is the case with binoculars - measured using a 50mm lens, as Ken mentions.
That's right. And Ken has a point that one cannot use viewfinder magnification figures across different formats to compare apparent size of the image in the viewfinder. But I don't get the fuzz. Viewfinder magnification is clearly defined in terms of a 50mm lens (not in terms of a format normal, which would change with the format), so there is no cheating.

I don't find the magnification figures misleading either, because they refer to a magnification of the viewfinder as such, ergo it has to be relative to the format (size of the sensor). Hence, an apparent size comparison always has to take the format into account. No big revelation of a scandal, AFAIC.

QuoteOriginally posted by Marc Sabatella Quote
This touches on something Robin and I just stumbled upon on in another recent thread: the 35mm format happened to be a kind of "magic" format where a lens that many people perceived as providing a natural field of view (although *nothing* like the field of view of the unaided eye, as is sometimes claimed) also happened to provide something close to 100% magnification using using a basic viewfinder design without additional optics.
But "basic viewfinders" have optics, don't they?
I don't understand the "magic" part. The viewfinder magnification (i.e., the optics between the focusing screen and the eye) is just chosen to be 100% for a 50mm lens. Since viewfinder magnification is defined in terms of a 50mm lens, it pans out to be a 100%.

QuoteOriginally posted by Marc Sabatella Quote
Whereas APS-C provides the same field of view only with a much shorter focal length and an equivalently smaller magnification.
I agree regarding the shorter focal length, but in what sense are you using "magnification" here?
Obviously, it is possible to build a viewfinder that has 100% magnification for APS-C. With such a viewfinder your "magic" would be back, no?

If you are referring to output magnification, then this entirely depends on print size. If you print both an FF and an APS-C image in 6x9 then they will both show the same FOV and magnification provided that the respective format normal focal lengths are used (or any other pair with the correct ratio, i.e., 1.5 for Pentax APS-C).

Last edited by Class A; 05-28-2009 at 09:25 PM.
05-28-2009, 11:20 PM   #22
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QuoteOriginally posted by nanok Quote
might this be related to the minimum (confortable) viewing distance of the human eye? meaning that the 35mm frame is about as small as you can get and still bring the image close enough to the eye so the perceived size is natural with the normal lens, without making it disconfortable.
That's kind of my assumption too - a smaller frame couldn't be brought close enough. Although I'm not sure what that really means - I can't focus on normal objects that are just inches from my eyes, but I *can* focus on a viewfinder image. So in some way, my eye is presumably focusing far beyond the actual distance to the focus screen. I don't know nearly enough about optics to sort that out.
05-28-2009, 11:33 PM   #23
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QuoteOriginally posted by Class A Quote
But I don't get the fuzz. Viewfinder magnification is clearly defined in terms of a 50mm lens (not in terms of a format normal, which would change with the format), so there is no cheating.
Oh, I wouldn't say anyone is "cheating". Just that it is a nice feature of 135 format that one can get close to 100% magnification using a "normal" FOV, whereas APS_C cameras require a telephoto FOV to get anything close to 100% magnification. Perhaps it would be possible *in theory* to get 100% with a "normal" FOV lens on APS-C, but in practice, it's never happened, and I'm assuming there is a reason for that.

QuoteQuote:
But "basic viewfinders" have optics, don't they?
I don't know. It sure seems like we are just seeing an unmagnified view of the focus screen itself - same as if you imply held the focus screen up at that distance from your eye. But as I said in the other thread, even if magnifying optics are involved, it's still an interesting fact that optics to produce close to 100% magnification with a "normal" FOV are quite common for 135 format but unheard of for APS-C. I'm guessing that's because any such required optics are simple for 135 but would be impractical for APS-C.

QuoteQuote:
I don't understand the "magic" part. The viewfinder magnification (i.e., the optics between the focusing screen and the eye) is just chosen to be 100% for a 50mm lens. Since viewfinder magnification is defined in terms of a 50mm lens, it pans out to be a 100%.
If it turns out to be true that the optics could equally well be chosen to yield 100% for any other focal length, then you're right, ther is no "magic". But I'm assuming that's not the case - any optics involved in achieving 100% magnification from a 50mm lens are "easy" to produce, but the optics involved in achieving 100% magnification from a shorter focal length length are far more complex. And my basis for assuming that is simply that if it were easy, cameras would do it!

QuoteQuote:
Obviously, it is possible to build a viewfinder that has 100% magnification for APS-C.
With a lens providing a "normal" FOV? I wouldn't say this is "obviously" true at all. The fact that no existing APS-C cameras even comes *close* to this - they are generally around what, maybe 60% when used with a "normal" FOV lens? - suggests that if it *is* possible to get 100% magnification on a "normal" FOV lens for APS-C, it must be prohibitively difficult/expensive/ineffective.

QuoteQuote:
With such a viewfinder your "magic" would be back, no?
If one were to be built, sure. But until someone shows me an existence proof that it is possible and practical, I'm leaning toward assuming it isn't.

05-29-2009, 01:30 AM   #24
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QuoteOriginally posted by Marc Sabatella Quote
That's kind of my assumption too - a smaller frame couldn't be brought close enough. Although I'm not sure what that really means - I can't focus on normal objects that are just inches from my eyes, but I *can* focus on a viewfinder image. So in some way, my eye is presumably focusing far beyond the actual distance to the focus screen. I don't know nearly enough about optics to sort that out.
first, look at the diagram of a pentaprism: the light path is not very direct, in order to straighten the image, it has quite some way to go, so the distance is not just a few cm as it might seem. second of all, as i mentioned above, the ocular piece is also doing that for you when needed: it projects a "virtual" image farther than the real image trully is (and might also enlarge it), this is commonly used in eyepieces for other instruments (including microscopes and the like), the simplest example is a magnifying glass: the image you see is not "real" (it can be projected by your eye or some other lens, but you cannot project the image directly, as you could project the image given by a lens at it's focal distance). i could explain further, but it's hard to draw on a forum (and it is really needed to explain optics, as it's mostly geometry)

try this (looks good, haven't had the time to read it through to verify though)
Free Astronomy Lesson 4 - Optical Devices

hope this sheds some light.
05-29-2009, 03:30 AM   #25
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QuoteOriginally posted by Marc Sabatella Quote
Oh, I wouldn't say anyone is "cheating".
I was referring to "Nikon attempts to deceive", "not honestly represented", and "filthy lies".

QuoteOriginally posted by Marc Sabatella Quote
APS_C cameras require a telephoto FOV to get anything close to 100% magnification.
But that's only because of their viewfinder magnification which isn't high enough.
Your point about no 100% magnification viewfinders existing w.r.t. to an APS-C normal focal length is certainly true. It could mean two things:
  1. Either it is physically possible but not economically viable, or
  2. there are physical limitations, such as a maximum magnification before the image becomes too dark for the unaided eye.
I don't know what the real reason is.

QuoteOriginally posted by Marc Sabatella Quote
It sure seems like we are just seeing an unmagnified view of the focus screen itself - same as if you imply held the focus screen up at that distance from your eye.
Hmmh, don't think so. There is definitely a lens at the eyepiece. But to be honest I don't know.


QuoteOriginally posted by Marc Sabatella Quote
I'm guessing that's because any such required optics are simple for 135 but would be impractical for APS-C.
That sounds plausible. Not sure about "impractical" vs "not cost effective".
05-29-2009, 05:55 AM   #26
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QuoteOriginally posted by Class A Quote
I don't understand the "magic" part. The viewfinder magnification (i.e., the optics between the focusing screen and the eye) is just chosen to be 100% for a 50mm lens. Since viewfinder magnification is defined in terms of a 50mm lens, it pans out to be a 100%.
Since I was the one who made the original observation about "normal" lenses some time ago, let me repeat here what I observed. I brought this up in several threads but never had a satisfactory dialogue about it until Marc engaged with the issue.

I observed the following:
1. A 43mm lens on a 35mm camera has a perfect normal field of view, defined in terms of diagonal angle of the film.
2. A 43mm lens on a 35mm camera has a perfect "eye feel", in that the image through the viewfinder has the same aspect as viewing outside the viewfinder. One can keep both eyes open and the images fuse.
3. A 28mm lens on an APS-C camera has a perfect normal field of view, defined in terms of diagonal angle of the sensor.
4. A 43mm lens on an APS-C camera has a perfect "eye feel".

(Yes, I realise that there are other definitions of "normal". And I realise our vision is far more complex than any simple definition of angle of view.)

The point here is that 4. is an unexpected outcome. This makes working with 35mm more pleasing overall. There is something "magic" about that format.

The tentative explanation was that viewfinder magnifications on APS-C are all wrong. This conforms to what Rockwell is saying. I can't believe I'm actually agreeing with him about something, but the truth is he is only agreeing with Marc and I -- we sorted this out first!
05-29-2009, 08:21 AM   #27
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QuoteOriginally posted by rparmar Quote
4. A 43mm lens on an APS-C camera has a perfect "eye feel".

The point here is that 4. is an unexpected outcome. This makes working with 35mm more pleasing overall. There is something "magic" about that format.
I dunno, why would it be unexpected? Again, the basic issue is that the viewfinder image in an APS-C cameras has a smaller apparent size - that's the cause of everything you've stated.

You could design the viewfinder optics to give an image that's the same apparent size of a 35mm viewfinder - and if you did then you'd get a close-to-1X magnification image with a lens that's "normal" for APS-C. The downside is that the viewfinder would be dimmer (which would diminish the "magic").

One of the nice things about the Panasonic G1 is that it has a very large viewfinder image despite it's even smaller 4/3 sensor. The electronic viewfinder has freed them from the size/brightness limitation.
05-29-2009, 10:09 AM   #28
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QuoteOriginally posted by Class A Quote
Ah. That's clearly just hype. But the phenomenon itself is real enough.

QuoteQuote:
Your point about no 100% magnification viewfinders existing w.r.t. to an APS-C normal focal length is certainly true. It could mean two things:
  1. Either it is physically possible but not economically viable, or
  2. there are physical limitations, such as a maximum magnification before the image becomes too dark for the unaided eye.
I don't know what the real reason is.
Bingo. I'm glad you pointed out the potential physical limitation issue - darkness in particular. That's actually what I had in mind when I used the word "ineffective" in offering possible reasons why it isn't done. Darkness, also perhaps issues with being able to see the whole image at once - eyepoint, I guess?
05-29-2009, 10:14 AM   #29
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QuoteOriginally posted by rparmar Quote
The tentative explanation was that viewfinder magnifications on APS-C are all wrong. This conforms to what Rockwell is saying. I can't believe I'm actually agreeing with him about something, but the truth is he is only agreeing with Marc and I -- we sorted this out first!
Maybe he got word of our exchange and decided to go off on it himself?

I actually have no preconceived ideas about Ken Rockwell. I hear the name very often, and I've probably read an article or two of his along the line, but I remember nothing in particular he's ever written. I gather a lot of people read him, but his opinions are often controversial. No idea what any of them are, though.
05-29-2009, 10:19 AM   #30
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QuoteOriginally posted by Sean Nelson Quote
I dunno, why would it be unexpected? Again, the basic issue is that the viewfinder image in an APS-C cameras has a smaller apparent size - that's the cause of everything you've stated.
Of course; it's expected once someone thinks about the physics of it all. But unexpected from a naive standpoint of having always associated "normal" FOV with 100% magnification. To the point where many people are in the habit of *defining* a normal lens as "one that gives 100% magnification", because it happened to work out that way on 135.

QuoteQuote:
You could design the viewfinder optics to give an image that's the same apparent size of a 35mm viewfinder - and if you did then you'd get a close-to-1X magnification image with a lens that's "normal" for APS-C. The downside is that the viewfinder would be dimmer (which would diminish the "magic").
This is more or less what I assume, but I wonder if there wouln't be other issues too (eyepoint, distortion, cost, etc).

QuoteQuote:
One of the nice things about the Panasonic G1 is that it has a very large viewfinder image despite it's even smaller 4/3 sensor. The electronic viewfinder has freed them from the size/brightness limitation.
And someday I expect to own an "EVIL" like that - although preferably one that takes my Pentax lenses! So far though, it seems the resolution, responsiveness, and noise levels of EVF's are not up to snuff.
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