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Optics Theory - This forum is aimed towards the TECHNICAL side of photographic OPTICS THEORY. There will be some overlap by camera/manufacturer, but this forum is for the heavy duty tech discussions. This is NOT the place to discuss a specific lens or lens line, do that in the appropriate forum. This is the forum to discuss optics or lenses in general, to learn about the tech behind the lenses and images. IF you have a question about a specific lens, post it in the forum about that type of camera, NOT HERE.

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Old 02-17-2011   #26
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Quote:
Originally Posted by helenhill View Post
I guess I Love Imperfections....
WOW! Such light. Delightful.
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Old 02-17-2011   #27
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Originally Posted by wjlapier View Post
Interesting how the buildings are leaning to the left on the left side of the picture and as you look to the right the buildings by the park are leaning to the right.

Looking at my first photo the buildings in the foreground are falling inward.
if film plane is tilted forward from vertical the result is diverging verticals. If film plane is tilted backwards from vertical the result is converging verticals. In this case camera is tilted forwards. Everything to left of centre leans left and everything to right of centre leans right. The reverse is the case if camera is tilting upwards. You can play with that knowledge to get some really extreme effects.
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Old 02-17-2011   #28
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Originally Posted by atlcruiser View Post
This is from my CV 21/4 on the M8. I am sure there is some distorsion but I cant really see it. As long I I keep the lens level it works like a champ.
http://farm5.static.flickr.com/4146/...7bc74335_b.jpg
I'm tempted to say that I can't see the distortion for the trees.
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Old 02-17-2011   #29
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Originally Posted by MCTuomey View Post
Apologies if this is OT, but I found your post interesting.

What happens when you've got the camera level and the framing "correct" and you find yourself with a whole lot of street/parking lot/other in the foreground that's unwanted? You can change lenses. You can crop later. Or, if you have movements you can shift upward and eliminate the unwanted foreground in a few seconds.

Ok, one doesn't "need" a view camera. Just saying there's very often a lot of value in a view camera's movements which is why I like my 35mm T-S lenses a lot.
If your framing is correct you can't shift the lens without changing the framing. So what you are suggesting is taking a different picture without the distractions in it. But you can't have it both ways.
Yes crop out what you don't want. And a lot of photographers will put their tripod on top of their car to remove that close up foreground. And there are telescopic poles you can mount your camera on to get some height to give a better viewpoint. Or use a step ladder. Or yes you can buy a view camera if you want the additional level of difficulty. All I'm saying is that there is often a simpler way of resolving compositional problems which don't involve going to a view camera. Or you can just tilt the camera and enjoy the converging/diverging verticals for their effect.
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Old 02-18-2011   #30
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Hi Chris

In nature shots, it's hard to know if a tree is really straight or not.

But with buildings and window frames, sometimes chairs or rectangular desks and tables, we assume they might be straight, and can often see the slight effects of barrel distortion.

A common explanation, usually from owners with a bunch of barrel distorted lenses, is that if you are going to shoot architecture, you shouldn't be using a rangefinder or cheap glass. But in the 21st century we live in, it's hard to find a lot of scenes without some known straight lines ...

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I'm tempted to say that I can't see the distortion for the trees.
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Old 02-18-2011   #31
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Originally Posted by ampguy View Post
In nature shots, it's hard to know if a tree is really straight or not.

But with buildings and window frames, sometimes chairs or rectangular desks and tables, we assume they might be straight, and can often see the slight effects of barrel distortion.

A common explanation, usually from owners with a bunch of barrel distorted lenses, is that if you are going to shoot architecture, you shouldn't be using a rangefinder or cheap glass. But in the 21st century we live in, it's hard to find a lot of scenes without some known straight lines ...
funny thing is that some biogons such as the Zeiss ZM C Biogon 21 F4.5 or 35 F2 exhibit virtually zero distortion which is less than most other lenses.
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right
Old 02-18-2011   #32
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right

but those are costlier than say a cv 35/2.5 which has very low distortion, and don't have hipster qualities like the hexar af lens

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Originally Posted by tlitody View Post
funny thing is that some biogons such as the Zeiss ZM C Biogon 21 F4.5 or 35 F2 exhibit virtually zero distortion which is less than most other lenses.
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Old 02-18-2011   #33
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Quote:
Originally Posted by tlitody View Post
If your framing is correct you can't shift the lens without changing the framing. So what you are suggesting is taking a different picture without the distractions in it. But you can't have it both ways.
Yes crop out what you don't want. And a lot of photographers will put their tripod on top of their car to remove that close up foreground. And there are telescopic poles you can mount your camera on to get some height to give a better viewpoint. Or use a step ladder. Or yes you can buy a view camera if you want the additional level of difficulty. All I'm saying is that there is often a simpler way of resolving compositional problems which don't involve going to a view camera. Or you can just tilt the camera and enjoy the converging/diverging verticals for their effect.
I applied quotation marks to the term correct in my earlier post to indicate that, hypothetically, the framing wasn't actually correct but had problems needing correction. I should have been clearer, sorry.

I guess I think it's safer & simpler to carry a tilt-shift lens (or even a view camera) than resorting to telescopic poles, step ladders, upper floors in nearby buildings, stilts, stage heels, what-have-you. How do you fit that stuff in your domke anyway?

Anyway, imho, converging/diverging verticals and distortion can work really well - Helen's pics are wunnerful - but they aren't always pleasing.
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Old 02-18-2011   #34
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This is what I use when necessary.
http://www.kirkphoto.com/Bubble_Level.html

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Old 02-18-2011   #35
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Quote:
Originally Posted by MCTuomey View Post
I guess I think it's safer & simpler to carry a tilt-shift lens (or even a view camera) than resorting to telescopic poles, step ladders, upper floors in nearby buildings, stilts, stage heels, what-have-you. How do you fit that stuff in your domke anyway?
A tilt shift lens is an easy option for 35mm photography like tilting the camera up or down is. A view camera is not an easy option and requires a whole new system with lenses, a means to develop and scan/print.
Then if you have ever looked at the MTF charts for lens you find that distortion kicks in the further from the lens axis you move meaning there is usually very limited shift without distortion unless you have long focal length lenses with much bigger image circles than your film format. But that means longer focal lengths which means being further from sibject which introduces more foreground which can be problematic. And shift introduces abberations such as coma. With a TS lens for a 35mm camera how much shift do you get without introducing distortion. The (now old) contax 35mm F2.8 shift lens gave 2% distortion in the corners before any shift. I suspect the even shorter lenses available give even more. So use your TS lens to stop converging / diveging verticals but introduce more distortion.
I still say the optimum is to place yourself in the optimum position with a distortion free lens. But that is for absolute optimum which architectural photographers may want. Most of us don't need that level of correction as no one really worries about a tad of distortion or converging verticals unless it contains people/faces.

p.s. It's all fairly academic now that you can easily correct distortion and perspective digitally. Only if you are wet printing does it still bear some consideration.

Last edited by tlitody : 02-18-2011 at 21:29.
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Old 02-19-2011   #36
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Originally Posted by PKR View Post
This is what I use when necessary.
http://www.kirkphoto.com/Bubble_Level.html

pkr
I have one of those but wouldn't think to use it on a RFer. Though, I have to admit I did mount it next to the 21/25 VFer on my IF. But didn't go out shooting with it.
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Old 02-19-2011   #37
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Quote:
Originally Posted by ampguy View Post
What I've found is that in nature, it's pretty easy to compose with the CV 21/4, (and, while harder, even the CV 15/4.5) even though some of the distortions mentioned are still present, if you compared with say a 35 cron asph or good 50 on a tripod. The photos can still look pleasing:



But, with square and rectangular architecture, with wider than some 35s, you sometimes have to pick 2 or 3 sides of the square or rectangle, that you wish to be parallel with your frameline edges. For this image, I bracketed, but ended up liking the street, and sky, and right hand side parallel to the print edges, while the left edge of the subject building is converging. I have other images that retained the left side's known vertical perspective, but at the expense of skewing the top, bottom, or right:



The CV lenses do have a bit of barrel distortion, noticeable at the edges, but not severe, and most lenses in the price range would exhibit the same, with the exceptions of some older '70s SLR glass that is not available anymore, and much larger in size.
Ampguy: I wanted to show a method of fixing this problem that I use frequently. I use the perspective correction feature of Photoshop Elements. I'm using PSE 6 currently, since it runs on the iMac.

To do this, I first brought the picture into PSE 6. Then I clicked "new layer from background." Next, I used the perspective feature to widen out the top of the building, straightening the verticals in the process. I rotated the picture slightly clockwise, as the camera was not quite level. Finally, I used the clone stamp to fix blank areas that were created by the rotation.

I'm a stickler for correct verticals, so I also use 28mm and 35mm PC lenses on film and digital Nikons.

Another good trick is to use a wider lens, and hold it in portrait position so as to be able to include the top of the building, while keeping the back (film or sensor plane) vertical. Then you can either crop out the excess foreground, or keep it if it is interesting. I'm finding that a photo of a tall structure often needs some extra foreground; it seems to visually "balance" the height of the building. (This might just be me, though.)

I had to reduce the file size to make it upload, so it will not really be useable to print, but I hope it's good enough to show the basic idea.

Hope this gives you a useful idea or two.

Best, Rob
Attached Images
File Type: jpg Ted's picture corrected.jpg (47.3 KB, 7 views)
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Old 02-19-2011   #38
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Quote:
Originally Posted by wjlapier View Post
Something I never really paid much attention too, until I saw it in some of my pictures. Distortion. I'll include two pics below, but I'm now curious and wondering about something. Do all 21mm lenses display this much distortion? I don't shoot this wide usually. Any other 21's better at handling distortion? BTW, lens is CV 21/4 LTM. I was using my IF with CV 21/25 finder.
You can test for optical/rectilinear distortion by overlaying straight lines in PS. Like this:



Basically, in your pics, there is none. You don't need another lens

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Old 02-19-2011   #39
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Here is an example of barrel distortion (Summilux 50/1.4 v2):



Easy to correct in PS though:

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Old 02-19-2011   #40
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Here you see what Roger calls "true wide-angle distortion" (using a 15mm, a fairly rectilinear lens).



Look at the guy on the right (my father in law). This photo made me stop using anything wider than 28.

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Old 02-19-2011   #41
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While the 21/4 CV is a nice lens for the money, the ZM 21/4.5 C-Biogon is far better in comparison, i.e. zero distortion and much better sharpness/contrast. I'd say it's the best optic I've ever used and even handily beats the Leitz 21/3.4 SA in terms of performance. The speed advantage of the SA is not great because you have to stop down to f/5.6 anyway to tame some of the corner falloff. The ZM OTOH has considerably less fall off.
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Old 02-19-2011   #42
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Quote:
Originally Posted by Roger Hicks View Post

Now change the focal length. Shoot the same scene, from the same spot, with both a 21mm lens and an 85mm lens. For the same size prints, we can establish the optimum viewing distances using our dear friends the similar triangles. For the 21mm, the viewing distance is 21/43 the distance for a 'standard' 43mm lens, and for the 85mm it is 85/43.
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Dear Roger,

I'm not sure if you meant to say this. In order to change from a 43mm lens to a 21, and then shoot the same scene you took with the 43mm, you can't do it from the same spot, unless you crop your photo to a 43mm equivalent angle of view. To take the same scene with the 21mm, using its full angle of view, you have to move closer to the scene, in the ratio of 21/43. That done, I agree we would then (theoretically) view the print from a closer distance--closer by that same ratio.

If we took a second picture with the 21mm, from the same spot, we will then include a wider view than we did with the 43mm lens. The perspective, however, will not have changed. To quote Gunter Osterloh, "Distance determines perspective: focal length determines cropping." Same spot, different lens = same perspective. different distance = different perspective (regardless of focal length).

I'm not sure there is a single answer here. It seems like it depends on whether we want to be true to the original perspective of the normal lens, or to be true to the angle of view of the lens in use. I was thinking of the latter in my earlier post.
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Old 02-19-2011   #43
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A follow-up thought: The intro to the first Cinerama film, "This is Cinerama," was narrated by Lowell Thomas. The film started with a conventional picture that occupied only perhaps 1/6 of the screen width. Then Thomas says, "This is Cinerama," the curtain opens all the way, and the picture is wall-to-wall. What Thomas did not say was, "Now everybody move closer because we used a wide-angle lens for this shot." He didn't have to, because in this case the picture width was increased in proportion to the increased taking angle; while the audience viewing distance was held constant.

This seems to argue in favor of making larger prints of pictures taken with wider lenses. That is not always practical, but it would avoid prohibitively close viewing distances for those pictures. Just something to think about.
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Old 02-19-2011   #44
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Dear Roger,

I'm not sure if you meant to say this. In order to change from a 43mm lens to a 21, and then shoot the same scene you took with the 43mm, you can't do it from the same spot, unless you crop your photo to a 43mm equivalent angle of view. To take the same scene with the 21mm, using its full angle of view, you have to move closer to the scene, in the ratio of 21/43. That done, I agree we would then (theoretically) view the print from a closer distance--closer by that same ratio.

If we took a second picture with the 21mm, from the same spot, we will then include a wider view than we did with the 43mm lens. The perspective, however, will not have changed. To quote Gunter Osterloh, "Distance determines perspective: focal length determines cropping." Same spot, different lens = same perspective. different distance = different perspective (regardless of focal length).

I'm not sure there is a single answer here. It seems like it depends on whether we want to be true to the original perspective of the normal lens, or to be true to the angle of view of the lens in use. I was thinking of the latter in my earlier post.
Dear Rob,

I'm pretty sure I meant what I said. The 21mm shot from the same viewpoint will indeed cover a much wider field of view, and will therefore need to be printed bigger for the picture elements to subtend the same angle as the objects in the original scene subtended. In effect, you're adding more picture around the outside of the 43mm crop. This perfectly matches your example of Cinerama (constant viewing distance).

Or, alternatively, for a constant print size for two pictures shot from the same spot with the two lenses, you'll need to view the one taken with the wide-angle from closer.

Cheers,

R.
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Last edited by Roger Hicks : 02-19-2011 at 10:09.
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Old 02-19-2011   #45
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... 12 and 35 rectilinear lenses, distortion?
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Thanks Rob
Old 02-19-2011   #46
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Thanks Rob

I don't use PS, I do have elements 8, and iphoto. I do use Picasa for resizing.

I'm aware of what PS can do. You can also dial out barrel/pincusion distortion with the lens correction factors.

It's just something I don't like to do. Same with cropping, other than to fit a given frame size.

Quote:
Originally Posted by Rob-F View Post
Ampguy: I wanted to show a method of fixing this problem that I use frequently. I use the perspective correction feature of Photoshop Elements. I'm using PSE 6 currently, since it runs on the iMac.

To do this, I first brought the picture into PSE 6. Then I clicked "new layer from background." Next, I used the perspective feature to widen out the top of the building, straightening the verticals in the process. I rotated the picture slightly clockwise, as the camera was not quite level. Finally, I used the clone stamp to fix blank areas that were created by the rotation.

I'm a stickler for correct verticals, so I also use 28mm and 35mm PC lenses on film and digital Nikons.

Another good trick is to use a wider lens, and hold it in portrait position so as to be able to include the top of the building, while keeping the back (film or sensor plane) vertical. Then you can either crop out the excess foreground, or keep it if it is interesting. I'm finding that a photo of a tall structure often needs some extra foreground; it seems to visually "balance" the height of the building. (This might just be me, though.)

I had to reduce the file size to make it upload, so it will not really be useable to print, but I hope it's good enough to show the basic idea.

Hope this gives you a useful idea or two.

Best, Rob
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Old 02-19-2011   #47
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Originally Posted by Roger Hicks View Post
Dear Rob,

I'm pretty sure I meant what I said. The 21mm shot from the same viewpoint will indeed cover a much wider field of view, and will therefore need to be printed bigger for the picture elements to subtend the same angle as the objects in the original scene subtended. In effect, you're adding more picture around the outside of the 43mm crop. This perfectly matches your example of Cinerama (constant viewing distance).

Or, alternatively, for a constant print size for two pictures shot from the same spot with the two lenses, you'll need to view the one taken with the wide-angle from closer.

Cheers,

R.
Roger,

I think we are in agreement, I just have reservations about calling the wide-angle shot "the same scene," since it includes a lot more real estate. If I wanted it to be the same scene, I would move in tighter with my wide-angle lens, covering about the same ground with a more expanded perspective. I do agree on the idea of printing wider scenes larger!

Best,

Rob
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Hi Roland
Old 02-19-2011   #48
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Hi Roland

I think it's a fine photo. What I would have done, is to just yell at the folks close-up to "get out of the way, I'm taking a photo" which I think is common to do in Europe.

Oh, and get your father-in-law tan pants

Quote:
Originally Posted by ferider View Post
Here you see what Roger calls "true wide-angle distortion" (using a 15mm, a fairly rectilinear lens).

...

Look at the guy on the right (my father in law). This photo made me stop using anything wider than 28.

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Old 02-19-2011   #49
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Roger,

I think we are in agreement, I just have reservations about calling the wide-angle shot "the same scene," since it includes a lot more real estate. If I wanted it to be the same scene, I would move in tighter with my wide-angle lens, covering about the same ground with a more expanded perspective. I do agree on the idea of printing wider scenes larger!

Best,

Rob
Dear Rob,

A classic example of both of us thinking "I know what I mean". I can see your reservations about calling the wide-angle shot "the same scene," but equally, given the Osterloh quote about perspective and crop, I think you will see why I would call it 'the same scene'.

But at least we've managed to resolve it amicably, and with any luck, we may have enlightened one or two others who were interested.

Cheers,

R.
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