21mm And Distortion

[awilder]

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.

 

[Rob-F]

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.
R.

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.

 

[Rob-F]

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.

 

[Roger Hicks]

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.

 

[Sparrow]

... 12 and 35 rectilinear lenses, distortion?

 

[ampguy]

Thanks Rob

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.

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

 

[Rob-F]

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

 

[ampguy]

Hi Roland

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 :angel:

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.

Roland.

 

[Roger Hicks]

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.