[jsherman999]

I am sorry. I thought the argument was effect of cropping an image in regards to perspective--say, using a full-frame senor vs. a APC sensor with the same lens would not impact perspective.

...(summation/paraphrase - off on a tangental discussion about another aspect of perspective),,.

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Hmm.. Maybe another approach is needed. Do you see how the image sequences I've placed in this thread have more to do with the original subject than your post? Do you see how the effects of perspective radically change the subject's relationship to the background when you move to reframe the shot at a different focal length, attempting to keep the 'subject' size the same?

Understanding this relationship is very important when you talk about cropping a FF image to match the aps-c FOV (in which case it doesn't change the perspective, because you didn't move)










...or moving closer to reframe to the aps-c FOV (in which case it does change the perspective, sometimes radically.)



100mm

70mm

50mm

28mm



That's what the discussion started to be about, and the images I've shown flesh these issues out perfectly. That's exactly what photographers are talking about when they object to 'moving to get the same FOV' on either format with a prime lens, for example. Your thoughts on linear perspective are interesting, but tangental to the original concern.




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Last edited by jsherman999; 01-16-2012 at 08:24 AM.

[Yamanobori]

Quote: Well, if linear perspective has do do with converging lines, why do the parallel lines of a building converge when you look up? Why is it called "perspective correction" when you make them appear parallel again.

Yes, you are correcting for linear perspective, but it has no impact on your positional perspective.

I don't understand. You are saying the perspective of an image is related to where you stand. So how can that not be related to linear perspective? Aren't the converging lines in a building related to where you view the building from?

[Yamanobori]

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Hmm.. Maybe another approach is needed. Do you see how the image sequences I've placed in this thread have more to do with the original subject than your post? Do you see how the effects of perspective radically change the subject's relationship to the background when you move to reframe the shot at a different focal length, attempting to keep the 'subject' size the same?

I jumped in at post 163--I think it is on page 11. I was answering a very specific claim which is quoted in the post. I have given evidence to support my argument. That is the topic I have been addressing. This is what I have been talking about--perhaps it is not me that has been misreading the thread.

If you read my posts, you will also see that I address what you have been showing: the ratio of images sizes of objects in a frame is directly related to the ratio of object distances. You illustrate this. It is not a specific object distance, but a ratio. With objects 2' and 4' from the camera, the ratio of their sizes will be the same as if they were 3' and 6' or 4' and 8' or 5' and 10', etc. Which is simply giving clarification that a particular object distance will result in particular ratio of object size ratios. Because there has been some confusion regarding perspective and object distance, I discussed this and it limits in the context of the issue in my original post--163.

Your last series is changing the ratio of object distances while maintain the FoV. And here you see the change in image size from foreground to background. You are also compounding the effect of the change in FoV, which is harder to see. I have not really been trying to show how two factors impact an image at the same time.

So I understand what you are showing. But if you return to post 163, that is not what I was addressing.

[jsherman999]

I jumped in at post 163--I think it is on page 11. I was answering a very specific claim which is quoted in the post....

So I understand what you are showing. But if you return to post 163, that is not what I was addressing.

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In post 163, you were addressing alohadave's:

"If I stand 10 feet from a person, my perspective does not change if I crop the picture from one lens or use two different lenses."

And he was right, as the images I posted illustrate. You expanded the concept of perspective to talk about a different aspect of linear perspective, how fast radial lines seem to converge in a cropped image, but that's not what Dave was concerned with, nor are most photographers when they talk about maintaining the same perspective by not moving, and cropping or using a different focal length. I happened to know what he meant (perspective as it relates to object distance,) because I see this question constantly


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Last edited by jsherman999; 01-16-2012 at 09:21 AM.

[RioRico]

There is no such thing as 'greater' nor 'lesser' perspective. Perspective is qualitative, not quantitative -- it can't be computed, unlike FOV. A shorter lens has greater (wider) FOV; a longer lens has smaller (narrower) FOV. But shots taken from the same distance with various lenses ALL have the same perspective, the same relationship of elements throughout the subject field.

If perspective is "qualitative" how do you know that the elements have the same relationship? Can't you quantify that?

Please point me to an online perspective calculator.
With DOF, we can plug-in the numbers (frame size, focal length, aperture, lens-subject distance, COC, etc) and compute a DOF range. What is the parallel for perspective? What usable numbers would a perspective function return?

You are back to the fact that the ratio of images sizes are proportional to the ratio of object distances. That is a very basic concept. Not enough for perspective which deals with the apparent depth (3-D-ness) of a 2-D image.

And how are those ratios useful when shooting in the field? What are the numerical factors that can be applied to perspective? What are 'greater' and 'lesser' perspective? Show us the numbers, please.

[Laurentiu Cristofor]

That's not an option in the field for a particular shot unless you have bodies of both formats, which is going to be a tiny percentage of people. In the field, you change lenses and walk around.

Let me give you a few examples where this misconception around perspective matters in practice.

I have seen FF users that were commenting on the use of 50mm lenses on APS-C sensors as being inappropriate for portraiture. They had this idea, because on FF a full-head shot with a 50mm requires a certain focusing distance that doesn't produce the most flattering results. But instead of associating the perspective with the distance, they associated it with the 50mm focal length, and thought that the focal length would not be appropriate on any other camera either.

Another instance of this misconception pops its head during the FF vs APS-C debates where some people bring forward the following (incorrect) argument for FF: "on an APS-C camera you are forced to use lower focal lengths to achieve the same classic fovs we are used with on FF cameras and that will produce more perspective distortion".

If you want to be precise about perspective, especially when discussing different formats, you need to be aware of what jsherman999 has been explaining.

[vonBaloney]

Let me give you a few examples where this misconception around perspective matters in practice.

I have seen FF users that were commenting on the use of 50mm lenses on APS-C sensors as being inappropriate for portraiture. They had this idea, because on FF a full-head shot with a 50mm requires a certain focusing distance that doesn't produce the most flattering results. But instead of associating the perspective with the distance, they associated it with the 50mm focal length, and thought that the focal length would not be appropriate on any other camera either.

Not exactly "in practice" -- just some FF users musing about things that haven't actually tried. If they had "in practice", they would either find out that their 50mm does work ok after all or that they still don't like it (probably for a different reason). It is a subjective question after all. And just the sort of misunderstanding about the difference between formats I was suggesting could be lessened if that difference was explained clearly, starting with the actual technical distinction between the two and then moving on to the consequences "in practice" of that distinction.

Another instance of this misconception pops its head during the FF vs APS-C debates where some people bring forward the following (incorrect) argument for FF: "on an APS-C camera you are forced to use lower focal lengths to achieve the same classic fovs we are used with on FF cameras and that will produce more perspective distortion".

How is this incorrect? You do have to use lower focal lengths.

[RBellavance]

How is this incorrect? You do have to use lower focal lengths.

It is incorrect in that perspective distortion is dependent on the distance to the subject. With that shorter focal length of APS-C, you will be standing in the same spot as you would with the longer focal length on "full frame", and perspective distortion will be the same.

[Laurentiu Cristofor]

Not exactly "in practice"

It is "in practice" in the sense that such misconceptions end up guiding buying decisions and what lenses some users are using or recommend using to others.

[Edvinas]

How is this incorrect? You do have to use lower focal lengths.

It is correct that you will need to use shorter focal lengths.
Incorrect is part about perspective: perspective won't change because of those shorter focal lengths.

[Oog]

Back in the day (about 35 years ago now) my colleagues and I worked with multiple formats daily, including systems with mounts for the same lenses on different-format cameras. We never spoke of 'equivalence' nor crap.factors. We learned how various focal lengths performed in different situations. That's all.

To me, these FF vs HF / APS arguments are absurd.

Agreed. I learned on film, and focused (ha!) on focal lengths, change in perspective with focus distance, and the resulting compression/stretch in perspective when changing focal length to keep object size the same. Those were the important things to learn about photography. That and how to actually improve my photographic skills....

Shall we argue the merits of MFT vs FF?

[RioRico]

Shall we argue the merits of MFT vs FF?

As long as it's not LS/MFT. #8-)

[Oog]

As long as it's not LS/MFT. #8-)

[Parallax]

As long as it's not LS/MFT.

Used to smoke Winston, myself. If they were good enough for Fred Flinstone, they were good enough for me.

[Anvh]

I don't understand. You are saying the perspective of an image is related to where you stand. So how can that not be related to linear perspective? Aren't the converging lines in a building related to where you view the building from?

It's your point of view, keep your camera level (not pointing up or down) and the lines will be straight.
That's why some use shift lenses.