What's more "normal"...

*FHPhotographer* · 10-21-2009, 03:54 PM

... a 35 or 43mm lens?

The problem: normal vision is very broad at about 120 degrees, but it apparently focuses best on a field of view about 40-45 degrees.

On an APS-C camera, the DA-35 = 42 degree viewing angle and the FA-43 = 35 degrees (approximately). Therefore, the DA-35mm lens I use is approximately a "normal " lens, but the image, seems to be "smaller" than what I see, and doesn't "seem" correct until previewed at 1.2x in the camera. Does that mean for an image to accurately represent what I saw, I should be using a lens in that 43mm range ? Or am I confusing apples and kumquats?

I know this oversimplifies a very complex question, and pardon me for any misuse of terms, but any input would help,
Brian

Class A · 10-21-2009, 07:19 PM

Originally Posted by FHPhotographer

... a 35 or 43mm lens?

If you are looking for a lens that has a FOV that corresponds to your perception of the world with your naked eyes, don't look for a normal lens.

The latter is defined to produce images that have no perspective distortion when viewed at a normal viewing distance. As a normal viewing distance is roughly the diagonal of the image (the larger the image, the further away you'll typically be from it), a normal lens has a focal length that corresponds to the film/sensor diagonal.

The APS-C normal focal lens is therefore ~28mm. Note that the normal focal lens for FF really is ~43mm but 50mm was chosen for the "kit lens" since it was easier to get better sharpness for a slightly longer focal length.

If you are not interested in perspective distortion but FOV, good luck.

It is very hard to work out what FOV your naked eyes have as you need to distinguish between FOV of sharpest vision (very small), subjective FOV (varies between people), peripheral FOV, etc. Just make sure that you don't want to match what you see through the viewfinder as the latter adds its own (<1) magnification.

**Marc Sabatella** · 10-21-2009, 09:29 PM

I'd suggest browsing the forum for any of the other many discussions of this topic. But I can address some of your specific questions:

Originally Posted by FHPhotographer

The problem: normal vision is very broad at about 120 degrees, but it apparently focuses best on a field of view about 40-45 degrees.

And focuses better still on a field of view of about 6 degrees that about what the "fovea" (a term I just learned in one of those other discussions last week) covers. Not sure where you got the 120 degree or 40-45 numbers from, but you're right, vision is very broad in general, but much of that is "peripheral", and the normal usable part is smaller. So there are senses in which our vision is best represented by the something like 120 degrees number, other sense in which it best represented by something like 40-45 degrees, and other senses in which it is best represented by 6 degrees.

None of this really explains why certain focal length are called "normal", though. As Class A says, it's about what happens when you print the image (at a typical size - this doesn't work for very small or very large prints) and then view the print from a typical distance for that size. A "normal" focal length is one that, when printed and viewed in this manner, produces no perspective distortion - all objects in the picture look to be the same sizes they did when you took the picture.

Put another way, a "normal" focal length would be one in which if you looked at a print on the wall from what felt like a typical distance, you could *just* fit it in the viewfinder if you tried to take a picture of the print itself.

Therefore, the DA-35mm lens I use is approximately a "normal " lens, but the image, seems to be "smaller" than what I see

You mean, in the viewfinder? That's simply because the viewfinder doesn't magnify the image enough. What you see in the viewfinder has nothing to do with what makes the image "normal" - it's all about what is actually captured.

and doesn't "seem" correct until previewed at 1.2x in the camera.

I assume now you're talking about the LCD. Now your problem is what I mentioned about thigns not holding for prints that are too small or too large. The LCD is basically a tiny print from this perspective, and you're viewing it from too far away for it to work out as it would if you printed, say, 8x12, and hung it on a wall.

audiobomber · 10-21-2009, 10:15 PM

As others said, "normal" is not about FOV, it's about perspective. The example above shows a photo that is "not normal". I don't know if you'll be ablie to see it, or if it's so obvious to me because I was there. The photo was taken at 250mm FL and shows severe compression of perspective. The neighbourhood behind the train yard seems all jammed up against the trains, and the water tower is way too big and imposing compared to the real scene as I saw it with my eyes. If I had shot the scene with a wide angle, the water tower would have looked very unimposing and distant. A normal lens would have given the photo a normal perspective, with the houses and tower moving back into realistic relative sizes and proper depth perspective.

*FHPhotographer* · 10-22-2009, 01:08 AM

Thanks for the feedback; I know know that "normal" is perspective-normal not FOV-normal, and thanks for that.

I should have started out with this image to get my question across (this is, after all, a forum dedicated to a visual art).

Using the power lines in the foreground as a measurement, the red line drawn on the image is (approximately) what my eye saw.

.
I'm not saying there's a right perspective or FOV, just that I would like on landscape shots like this that the relationship of the parts to the whole would be close to my vision. In this case, if I had used a 28mm the image would have more closely conformed to the "real" relationship of objects in the image?
Brian

*DavidWasch* · 10-22-2009, 08:07 AM

Originally Posted by Marc Sabatella

I'd suggest browsing the forum for any of the other many discussions of this topic. But I can address some of your specific questions:

And focuses better still on a field of view of about 6 degrees that about what the "fovea" (a term I just learned in one of those other discussions last week) covers. Not sure where you got the 120 degree or 40-45 numbers from, but you're right, vision is very broad in general, but much of that is "peripheral", and the normal usable part is smaller. So there are senses in which our vision is best represented by the something like 120 degrees number, other sense in which it best represented by something like 40-45 degrees, and other senses in which it is best represented by 6 degrees.

None of this really explains why certain focal length are called "normal", though. As Class A says, it's about what happens when you print the image (at a typical size - this doesn't work for very small or very large prints) and then view the print from a typical distance for that size. A "normal" focal length is one that, when printed and viewed in this manner, produces no perspective distortion - all objects in the picture look to be the same sizes they did when you took the picture.

Put another way, a "normal" focal length would be one in which if you looked at a print on the wall from what felt like a typical distance, you could *just* fit it in the viewfinder if you tried to take a picture of the print itself.

You mean, in the viewfinder? That's simply because the viewfinder doesn't magnify the image enough. What you see in the viewfinder has nothing to do with what makes the image "normal" - it's all about what is actually captured.

I assume now you're talking about the LCD. Now your problem is what I mentioned about thigns not holding for prints that are too small or too large. The LCD is basically a tiny print from this perspective, and you're viewing it from too far away for it to work out as it would if you printed, say, 8x12, and hung it on a wall.

Marc, I'm dissapointed that you didn't use the term "subtend."

Eruditass · 10-22-2009, 08:16 AM

Originally Posted by audiobomber

As others said, "normal" is not about FOV, it's about perspective. The example above shows a photo that is "not normal". I don't know if you'll be ablie to see it, or if it's so obvious to me because I was there. The photo was taken at 250mm FL and shows severe compression of perspective. The neighbourhood behind the train yard seems all jammed up against the trains, and the water tower is way too big and imposing compared to the real scene as I saw it with my eyes. If I had shot the scene with a wide angle, the water tower would have looked very unimposing and distant. A normal lens would have given the photo a normal perspective, with the houses and tower moving back into realistic relative sizes and proper depth perspective.

If you walk 20 ft back from your monitor it will appear "normal" as you saw it :-p

*newarts* · 10-22-2009, 08:33 AM

Perception of "normal" varies with the observer. I tend to mentally adjust my central area of visual interest to about the size of my hand held with elbow bent at 90 degrees (this is about the same as the area of my computer screen.) To me, like you I suspect, almost all landscapes are "too small" and almost all wide angles are "too wide".

For Binocular vision the video people have figured out that a 16:9 field (hand held sideways) is acceptable for most people (with about the same vertical AOV.) But clearly this is not true for portraits, which appear best to most when formated like your hand held vertically.

Videographers, theatrical directors, etc make sure that lighting & backgrounds effectively create a "portrait orientation" for scenes where the focus is on an individual performer...long lenses, dark, out-of-focus backgrounds, no peripheral distractions, etc. regardless of the physical format.

The foveal field (in which you actually see sharply) is only about 1 degree, about the same as your thumbnail, but our eyes dart about using the foveal view to "paint" a high res image comfortable for each of us.

You know, I'll bet this varies with age. My eye muscles probably aren't nearly as good at this "darting about" as they were 50 years ago! Neither is my foveal vision as sharp, etc.

Finally, it is pretty easy to show that we are pretty tolerant of perspective variations...I'll try to come up with an illustration of this..

Dave in Iowa

CFWhitman · 10-22-2009, 09:42 AM

Originally Posted by FHPhotographer

Thanks for the feedback; I now know that "normal" is perspective-normal not FOV-normal, and thanks for that.

I should have started out with this image to get my question across (this is, after all, a forum dedicated to a visual art).

Using the power lines in the foreground as a measurement, the red line drawn on the image is (approximately) what my eye saw.
.
I'm not saying there's a right perspective or FOV, just that I would like on landscape shots like this that the relationship of the parts to the whole would be close to my vision. In this case, if I had used a 28mm the image would have more closely conformed to the "real" relationship of objects in the image?
Brian

It sounds to me like you actually are talking about perspective (distortion) here. In that case I would have to say that some of Marc's remarks are apropos to what you are talking about.

Originally Posted by Marc Sabatella

You mean, in the viewfinder? That's simply because the viewfinder doesn't magnify the image enough. What you see in the viewfinder has nothing to do with what makes the image "normal" - it's all about what is actually captured.

With the APS-C cameras available today, the view through the finder is not going to look "normal" through a normal lens. It will appear too small and far away as though you were using a wide angle lens. As Marc said, this doesn't reflect what the feel of the actual print will be.

I assume now you're talking about the LCD. Now your problem is what I mentioned about things not holding for prints that are too small or too large. The LCD is basically a tiny print from this perspective, and you're viewing it from too far away for it to work out as it would if you printed, say, 8x12, and hung it on a wall.

Again, as Marc said, you are not getting the proper feel for your capture by looking at it on the tiny LCD screen. It may seem like it's too distant when you look at it, but that's not likely to be the case for the actual print.

If you really want your images to look bigger through the finder and on the LCD screen, then you would need to go to a longer focal length rather than a shorter one (that is, say, 40mm rather than 28mm), but I think that you are letting the memory of your perception of the viewfinder and LCD views of your picture at the time you took it influence your perception of the resulting print.

*newarts* · 10-22-2009, 10:15 AM

Originally Posted by FHPhotographer

Thanks for the feedback; I know know that "normal" is perspective-normal not FOV-normal, and thanks for that.

I should have started out with this image to get my question across (this is, after all, a forum dedicated to a visual art).

Using the power lines in the foreground as a measurement, the red line drawn on the image is (approximately) what my eye saw.
.
I'm not saying there's a right perspective or FOV, just that I would like on landscape shots like this that the relationship of the parts to the whole would be close to my vision. In this case, if I had used a 28mm the image would have more closely conformed to the "real" relationship of objects in the image?
Brian

If you used a longer lens the mountains would be bigger compared to the utility pole.

Eruditass · 10-22-2009, 10:19 AM

Originally Posted by newarts

If you used a longer lens the mountains would be bigger compared to the utility poles.

Or if you used the same lens, stepped back, and cropped

CFWhitman · 10-22-2009, 10:43 AM

Originally Posted by audiobomber

As others said, "normal" is not about FOV, it's about perspective. The example above shows a photo that is "not normal". I don't know if you'll be ablie to see it, or if it's so obvious to me because I was there. The photo was taken at 250mm FL and shows severe compression of perspective. The neighbourhood behind the train yard seems all jammed up against the trains, and the water tower is way too big and imposing compared to the real scene as I saw it with my eyes. If I had shot the scene with a wide angle, the water tower would have looked very unimposing and distant. A normal lens would have given the photo a normal perspective, with the houses and tower moving back into realistic relative sizes and proper depth perspective.

This description is correct in essence, but there is something that I would like to clarify here. Whichever length lens is used to capture a photo, the sizes (and therefore apparent distances) of objects in the picture relative to each other will remain the same. However, their apparent sizes (and therefore distances) relative to the viewpoint will change.

Perspective is relative. That is, things that are farther away appear relatively closer together because they are close together compared to their distance from you. It follows that things that are closer appear relatively farther apart because they are farther apart compared to their distance from you. Therefore when you make things that are far away appear to be closer, they still look just as relatively close together as before, which is too close together compared to your altered perception of their distance from you. Also, when you make things appear to be farther away than they actually are, they still look just as relatively far apart as before, which is too far apart compared to your altered perception of their distance from you.

To put it more simply. If you make one object in a picture appear to be only one third of its actual distance from you, you make every object in the picture appear to be one third of its actual distance. So an object 90 meters away appears to be 30 meters away, and an object 120 meters away appears to be only 40 meters away. This makes the apparent distance between the objects seem to be 10 meters (assuming they are in the same direction from the viewpoint) when they actually are, and should appear to be 30 meters apart (compression distortion). Of course this holds true in reverse as well. So if you make one object appear to be twice as far away as it actually is, then every object will appear to be twice as far away and the distances between them will seem twice as much as they actually are (extension distortion).

That was probably not as clear an explanation as I would like it to be, but I tried.

*reeftool* · 10-22-2009, 11:10 AM

I have always understood that "normal" in refering to lens length was that the perceived distance of the subject was the same as we would see with our eyes or appox. that same view. I think the problem arises in that our field of vision is much wider than a "normal" lens. This isn't much of a problem with taking a bicture of a bird, person, statue, etc. where our attention is focused on a single object but makes landscape shots difficult to compose sometimes because to take in the scene thats making us go "WOW!" we have to use a wider lens and that changes the distance perspective. When I'm hiking in the mountains I have to close my eyes for a second and spend some time taking the scene in just from the viewfinder because it will never be exactly the same view. In my experience, landscapes look more like normal vision shot with a wider angle lens than "normal" and printed large. I will also add that I have difficulty doing this and while I take hundreds of landscape shots every year I am usually not too happy with the outcome and when I get a good one it's more of an accident.

CFWhitman · 10-22-2009, 11:17 AM

Originally Posted by newarts

If you used a longer lens the mountains would be bigger compared to the utility pole.

Actually with a longer lens the mountains would be the same size compared to the utility pole, but since they would both be bigger compared to your field of view, they would appear to be closer to each other as well as closer to you. This is because if you actually moved closer, the mountains would become smaller compared to the pole rather than staying the same size (that is, they would grow less in size than the pole). The mountains not growing less in size than the pole, when your brain knows that they should, is perceived as though they grew bigger in relation to the pole.

audiobomber · 10-22-2009, 11:26 AM

Originally Posted by CFWhitman

Actually with a longer lens the mountains would be the same size compared to the utility pole, but since they would both be bigger compared to your field of view, they would appear to be closer to each other as well as closer to you. This is because if you actually moved closer, the mountains would become smaller compared to the pole rather than staying the same size (that is, they would grow less in size than the pole). The mountains not growing less in size than the pole, when your brain knows that they should, is perceived as though they grew bigger in relation to the pole.

Dammit Charlie, you're making me dizzy.