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07-06-2012, 06:54 AM   #31
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QuoteOriginally posted by TomTextura Quote
I never understood that to be the case. I could very well be wrong though. I remember reading, and it seemed to make sense, that spacial compression and distortion is dependent on focal length and that those characteristics of focal lengths that are much wider or longer than ~50mm are not normal looking. I thought that, aside from AOV, lens characteristics mostly remain the same across the two formats. I realize that AOV is the main thing that makes a lens normal but something about the definition of it as purely that has never quite satisfied me. I inevitably end up coming across a definition that says something along the lines of: when the printed picture is viewed at typical or normal viewing distances for its size. However, I've never been able to find any examples of what that "normal" viewing distance is for a given print size. I somehow intuitively feel, though again perhaps incorrectly, that spatial compression, distortion, and magnification also play a part in giving a focal length the sense that it is normal. Maybe this discussion belongs in its own thread though.
The perspective of a print is normal when the angles you see is the same as the saw camera when it took the photo.

So if you make a photo 10cm away from a subject and you print the photo life size and you place your face 10 cm from the photo the perspective should be natural looking, so the definition of a normal lens is a bit loose because of that.
That's why like you said we look at the typical viewing distance for a print.

07-06-2012, 08:53 AM   #32
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QuoteOriginally posted by TomTextura Quote
I never understood that to be the case. I could very well be wrong though. I remember reading, and it seemed to make sense, that spacial compression and distortion is dependent on focal length and that those characteristics of focal lengths that are much wider or longer than ~50mm are not normal looking.
Yes, unfortunately, in the days when most photographers dealt with only a single format - 135 aka FF - it was common for writers to make the mistake of associating certain things with focal length that should really have been associated with angle of view. if you're omly dealing with one format, you can make that association, because each focal length produces one and only AOV, changing focal length always means changing AOV and vice versa, etc. But as soon as you start dealing with multipke formats, you need to be more precise about what is due to focal length and what is due to AOV, since one given focal length might have a different AOV on different formats. And, unfortunately, no one went around re-writing all the old articles and books to clarify this. So as result, it's a quite common misunderstanding.

QuoteQuote:
I thought that, aside from AOV, lens characteristics mostly remain the same across the two formats.
Well sure, *lens* characteristics remain constant. The point is, perspective distortion is not a lens characteristic - it is a simple functin of AOV.

QuoteQuote:
I inevitably end up coming across a definition that says something along the lines of: when the printed picture is viewed at typical or normal viewing distances for its size. However, I've never been able to find any examples of what that "normal" viewing distance is for a given print size. I somehow intuitively feel, though again perhaps incorrectly, that spatial compression, distortion, and magnification also play a part in giving a focal length the sense that it is normal.
Of course - because what makes something "normal" is lack of spatial compression / distortion. And what creates the spatial distortion is a mismatch between the AOV depticed in the scene and the AOV subtended by the print vpfrom the given viewing distance. These things are all interrelated. But again, it's all about angles, not about focal length. The eye doesn't care what focal length lens is used. it only cares about angles of view.

QuoteQuote:
Maybe this discussion belongs in its own thread though.
It's been the topic of about a hundred other threads, most of them hundreds of posts long because it is such a poorly understood topic. A search might yield some answers, although it will probably keep you busy for quite a while hunting through all the results.
07-06-2012, 09:01 AM   #33
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QuoteOriginally posted by Anvh Quote
Marc not to go into discussion again but point of view is far more important then the angle of view when it comes to the distortions (if it have even effect)

Doesnt perspective not literally mean that?
Again, the term "perspectie. has two very different senses that are relevant hee.

"Llinear perspective* is dependent on shooting position (point of view) and shooting position only; angle of view has nothng to do with it. All pictures taken from a given position display the same linear perspective regardless of angle of view - att least, in this universe where light ray travel in mostly straight lines.

However, the optical illusion known as *perspective distortion* is dependent on angle of view and angle of view only; shooting position has nothing to do with it. All images taken with a given angle of view will exhibit the same sense of perspective distortion for a given print size / viewing distance, regardless of shooting position.

And what makes an image "normal" - which was the aubject of the post I was resppnding to - is the absence perspective distortion. That is, an image that displays neither the optical illusion of telephto compression nor the optical illusion of wide angle expansion . That is achieved when the AOV depticed in the image matches the angle subtended by the print/display of the image itself from a given viewing position.
07-06-2012, 10:32 AM   #34
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Though the last ten or so posts have been a bit off topic, they were good discussion all the same. Thanks all for sharing your knowledge! In my opinion, the generous sharing of knowledge is what makes this forum shine. I think I've got a better understanding now of what a "normal" lens is, at least for the time being . Would I be wrong to say that the 135 FF format hits a certain sweet spot in that the ~50mm focal length gives both a normal AOV and comes close to matching the eye's magnification.

07-06-2012, 11:07 AM   #35
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QuoteOriginally posted by TomTextura Quote
Would I be wrong to say that the 135 FF format hits a certain sweet spot in that the ~50mm focal length gives both a normal AOV and comes close to matching the eye's magnification.
Each format has its own sweet spot: around 50mm for FF, around 25mm for MFT, around 33mm for APS-C, . . .
07-06-2012, 11:23 AM   #36
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QuoteOriginally posted by lytrytyr Quote
Each format has its own sweet spot: around 50mm for FF, around 25mm for MFT, around 33mm for APS-C, . . .
Those are just the focal lengths for the normal angles of view on their respective formats though, right? For either MFT or APS-C the magnification will be less than what your eye sees. Jump up to medium format and you'll need about a 75mm FL for a normal AOV but the magnification will be greater than what you see with your eyes alone.
07-06-2012, 01:43 PM   #37
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QuoteOriginally posted by Marc Sabatella Quote
Again, the term "perspectie. has two very different senses that are relevant hee.

"Llinear perspective* is dependent on shooting position (point of view) and shooting position only; angle of view has nothng to do with it. All pictures taken from a given position display the same linear perspective regardless of angle of view - att least, in this universe where light ray travel in mostly straight lines.

However, the optical illusion known as *perspective distortion* is dependent on angle of view and angle of view only; shooting position has nothing to do with it. All images taken with a given angle of view will exhibit the same sense of perspective distortion for a given print size / viewing distance, regardless of shooting position.

And what makes an image "normal" - which was the aubject of the post I was resppnding to - is the absence perspective distortion. That is, an image that displays neither the optical illusion of telephto compression nor the optical illusion of wide angle expansion . That is achieved when the AOV depticed in the image matches the angle subtended by the print/display of the image itself from a given viewing position.
Actually we are talking about precisely the same thing but we explain it differently.

Forget about the camera for the moment and think about what effects the angle of view of the viewer of the print.
07-06-2012, 01:47 PM   #38
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QuoteOriginally posted by lytrytyr Quote
Each format has its own sweet spot: around 50mm for FF, around 25mm for MFT, around 33mm for APS-C, . . .
It's actually 43mm, and around 28~30mm for APS-C

07-06-2012, 02:05 PM   #39
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QuoteOriginally posted by TomTextura Quote
Those are just the focal lengths for the normal angles of view on their respective formats though, right? For either MFT or APS-C the magnification will be less than what your eye sees. Jump up to medium format and you'll need about a 75mm FL for a normal AOV but the magnification will be greater than what you see with your eyes alone.
Won't the magnification depend on the optics of the viewfinder?
07-06-2012, 02:19 PM   #40
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QuoteOriginally posted by lytrytyr Quote
Won't the magnification depend on the optics of the viewfinder?
No the lens only, it's about how large the projected image is compared to the real life image.
So if a bug appears 2 cm long and it is projected as 2 cm long on the film then the magnification is 1:1

But magnification has nothing to do with perspective though.
07-06-2012, 02:38 PM   #41
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Between the 3 in the thread title I'd take the da35/2.4.

However I'd take the fa35, sigma 30 and fa31 over any of those choices (budget aside of course)
07-06-2012, 02:48 PM   #42
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QuoteOriginally posted by lytrytyr Quote
Won't the magnification depend on the optics of the viewfinder?
Yes, of course. I was assuming ~1x magnification in the VF. I realize that can be worked around with an add on loupe. I just know that when I put a 50mm lens on my K-5 and put the VF up to my right eye and leave my left eye open, the magnification is darn close to the same. I think having that along with the normal AOV would be pretty nice. I'm sure having greater magnification would be even better with either medium format (totally out of the question for me) or an EVF (not my preference by any means).
07-07-2012, 08:31 AM   #43
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The thing is, 1x magnification in viewfinder is an arbitrary figure - it is simply calculated as that which produces the effect in question when using a 50mm lens. Really, APS-C cameras should calculate their magnifications based on a 35mm lens, but they don't, so we're left with the mistaken impression we have "95%" magnification when of course we really don't n any meaningful sense. APS-C camera that had 1x magnification as measured with a 35mm lens would have the property you seek. However, they don't exist. The physical sizes and distances involved are such that your basic observation is sound - on 135 format, it does happen to be the case that many camera provide 100% magnification with a normal lens, while other formats typically do not.
07-07-2012, 08:34 AM   #44
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QuoteOriginally posted by Anvh Quote
No the lens only, it's about how large the projected image is compared to the real life image.
So if a bug appears 2 cm long and it is projected as 2 cm long on the film then the magnification is 1:1

But magnification has nothing to do with perspective though.
As with perspective, there are two very different senses of the word magnification. You are using the sense that applies to macro photography. But the issue of viewfinder magnification is entirely separate. Two completely unrelated topics that just happen to share the same word.

It is true that neither sense of the word magnification has anything to do with either sense of the word perspective, though..
07-07-2012, 08:45 AM   #45
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QuoteOriginally posted by Anvh Quote
Actually we are talking about precisely the same thing but we explain it differently.
Not true. You erroneously stated that point of view has an effect on perspective distortion. It does not. It affects linear perspective, but not perspective distortion. Only angle of view affects the optical illusion known as perspective distortion, for any givenrint size / viewing distance. You conti ue to not acknowledge or understamd this difference. Linear perspective is not the same as perspective distortion, although to be sure, linear perspective is a *component* of perspective distortion.

QuoteQuote:
Forget about the camera for the moment
Forgetting the camera is only relevant when discissing linear persepctive. You cannot forget the camera when discussing the optical illusion known as perspective distortion, because this illusion can pnly happen when looking at a printed/displayed image that was taken with a specific angle of view. You need a camera to produce that, so how can you forget the camera?

QuoteQuote:
think about what effects the angle of view of the viewer of the print.
Not sure what you mean by .angle of view of the viewer of print"? If you mean, the angle subtended by the print itsrlf from the viewing position, then the answer is as I have been stating: size of and viewing distance from the print. But wheter or not this will result in the optical illusion known as perspective distortion depends on whether that angle matches the angle of view depicted in the image or not.
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