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21mm And Distortion
Old 02-16-2011   #1
wjlapier
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21mm And Distortion

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.
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Old 02-16-2011   #2
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That isn't distortion, it's just the planar projection of the lens
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Old 02-16-2011   #3
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To avoid the converging verticals, try shooting with the camera exactly level - with the camera aimed at a point the same height as your eye. Do you have any samples like that? I'll bet they show the vertical lines standing true (but perhaps slightly curved). Even my Hasselblad SWC (famous for its lack of distortion) captures converging vertical lines if I point the camera upwards.
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Old 02-16-2011   #4
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In 35mm, the best lens with regards to distortion (and almost everything else IMO!) has been the Contax G 21mm. Compared to SLR lenses or the Voigtlander lenses I have tried, it's in a different league.
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Old 02-16-2011   #5
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There are three separate issues here.

First, true distortion ('pincushion' or 'barrel', according to whether straight lines near the edge of the frame are 'sucked in' or 'blown out'). Biogons (the f/4.5 models) are generally reckoned to be the winner. I don't really see this in your pics.

Second, converging/diverging verticals. These are caused by departures from holding the camera dead level. All suffer from this to the same extent. This is quite marked in your pics.

Third, something I was taught to refer to as 'true wide-angle distortion', where, for example, spheres are stretched into ovals. This is especially distressing when it happens to people's heads. As far as I know, most wide-angles suffer about equally from this, though optical designs may have some effect. Some people take exception to the term 'true wide angle distortion', but regardless of what you call it, it exists, and it 'stretches' things near the sides of the image. I don't really see this in your pics either.

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Old 02-16-2011   #6
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Quote:
Originally Posted by ChrisN View Post
To avoid the converging verticals, try shooting with the camera exactly level - with the camera aimed at a point the same height as your eye. Do you have any samples like that? I'll bet they show the vertical lines standing true (but perhaps slightly curved). Even my Hasselblad SWC (famous for its lack of distortion) captures converging vertical lines if I point the camera upwards.
I was thinking it might be how I aimed the lens. I like this little lens alot. Colors are basically true to what I saw that day--see yellow painted winery.
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Old 02-16-2011   #7
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Oh hello William
its exactly that 'Look' that made Me fall for a 21 SA...the Exaggerated sense of Proportion
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Old 02-16-2011   #8
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I guess I Love Imperfections....
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Old 02-16-2011   #9
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the 21 SA again...
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Old 02-16-2011   #10
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Hi Helen,

Love them all, especially the first one.

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Old 02-16-2011   #11
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The Super Angulon is technical wide angle perfection with regard to lack of distortion. You won't find any curved lines which are straight in real life as you would with lesser lenses. Aiming it so the planes aren't parallel with the film plane will cause the converging lines but that happens with all lenses. Wide angles just show it prominently.
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Old 02-16-2011   #12
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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.
I can't detect any distortion there. Its just converging verticals from film plane not being vertical.
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Old 02-16-2011   #13
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Quote:
Originally Posted by wjlapier View Post
I was thinking it might be how I aimed the lens. I like this little lens alot. Colors are basically true to what I saw that day--see yellow painted winery.
That's it - excellent! I see why you like it.

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Originally Posted by helenhill View Post
Oh hello William
its exactly that 'Look' that made Me fall for a 21 SA...the Exaggerated sense of Proportion
And Helen - this is wonderful! LOVE this photo!
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Old 02-16-2011   #14
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Quote:
Originally Posted by Roger Hicks View Post
There are three separate issues here.

First, true distortion ('pincushion' or 'barrel', according to whether straight lines near the edge of the frame are 'sucked in' or 'blown out'). Biogons (the f/4.5 models) are generally reckoned to be the winner. I don't really see this in your pics.

Second, converging/diverging verticals. These are caused by departures from holding the camera dead level. All suffer from this to the same extent. This is quite marked in your pics.

Third, something I was taught to refer to as 'true wide-angle distortion', where, for example, spheres are stretched into ovals. This is especially distressing when it happens to people's heads. As far as I know, most wide-angles suffer about equally from this, though optical designs may have some effect. Some people take exception to the term 'true wide angle distortion', but regardless of what you call it, it exists, and it 'stretches' things near the sides of the image. I don't really see this in your pics either.

Cheers,

R.
My chance to teach the teacher. Roger, make a fairly large print of a shot you have taken with, say, a 21mm or wider lens. Well, OK, even a 24mm is wide enough to make the point. Then try viewing the print from a distance close enough so that your viewing angle across the print matches the angle of view of the taking lens. When you get the distance right,

VIOLA! The "distortion" will be gone.

The apparent distortion is caused by a mismatch between the angle at which the picture was photographed, and the viewing angle when viewing the print.

Try it! It works! Really!
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Old 02-17-2011   #15
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Quote:
Originally Posted by Rob-F View Post
My chance to teach the teacher. Roger, make a fairly large print of a shot you have taken with, say, a 21mm or wider lens. Well, OK, even a 24mm is wide enough to make the point. Then try viewing the print from a distance close enough so that your viewing angle across the print matches the angle of view of the taking lens. When you get the distance right,

VIOLA! The "distortion" will be gone.

The apparent distortion is caused by a mismatch between the angle at which the picture was photographed, and the viewing angle when viewing the print.

Try it! It works! Really!
Dear Rob,

I'll almost completely agree, and the same argument appears on my site. From
http://www.rogerandfrances.com/subsc...ctive%201.html (Perspective):

Traditional 'standard' lenses and viewing distances are all well and good until you start to consider enlargements. Obviously, very few people are going to look at 24x36mm images from a distance of 43mm (the negative diagonal), except perhaps when they are going through contact sheets with a magnifying glass. So let's imagine we use a 43mm lens (the nearest we know of is the 42.5mm Biogon for the pre-war Contax) and blow it up 6x to 144 x 216mm, a bit under 6x9 inches. The optimum viewing distance for the 'magic distance' is now 6 x 43 = 258mm or a bit over 10 inches -- an ideal viewing distance for a print that size.

Now make a 40x50cm/16x20 inch print from the same negative: people do. You'll have to crop the negative a bit to make it fit, but for a borderless print this size you are looking at almost a 17x enlargement. Your optimum viewing distance is now 17 x 43 = 731mm or about 29 inches: probably a bit closer than most people would normally look at such a big picture unless they were examining it fairly closely, for example in a gallery.

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.

For the small print, the viewing distances go from 258mm/10 inches with the 'standard' lens to 126mm (near enough 5 inches) with the 21mm and 510mm, a bit over 20 inches, for the 85mm. With the big print (optimum viewing distance 731mm/29 inches for the 43mm lens) they are 357mm, 14 inches, for the 21mm shot and 1445mm, near enough 57 inches, for the 85mm. You will have noted that because we chose focal lengths that were roughly half the 'standard' and roughly double, the viewing distances in both cases are roughly halved and doubled. Similar arguments would apply to 14mm (about 1/3) and 135mm (about triple).

Now, imagine that our 85mm shot is a portrait, and we make a 40x50cm/20x16 inch print from it. We often look at portraits of ths size from a distance of around 1.5 metres or 5 feet, so the perspective will be much more pleasing than it would have been with a 43mm portrait covering the same subject, but (necessarily) closer to the subject. Conversely, if we shot a landscape with our 21mm lens, and made a 40x50cm/20x16 inch print from that, we might well find a magical sense of being 'inside' the landscape if we stood close enough to it.


One reason I say 'almost' is that in reality, we very seldom do make such massive prints; or if we do, we seldom look at them from so close. The other is that I am reasonably confident that the 'spheres to ovals' phenomenon still applies. We normally turn our heads to look at things off to one side, and besides, the brain does an awful lot of post-processing, so we literally see what we expect to see.

I say only 'reasonably confident' on the basis of optical theory and the psychology of vision. I'm thinking in particular of a 21mm shot I took of the interior of a classroom in India where the headmistress is peeking through the door on one side. Her head is grotesquely distorted. Quite honestly, I'm not going to make a 20x16 inch print and stand REALLY close to it to see which of us is right. I think it's me, but it might be you.

Cheers,

R.
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Old 02-17-2011   #16
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The only way out of this is with movements - a view camera...

Rockwell has a pretty good primer on ultrawides.

Wonderful pics, Helen.
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Old 02-17-2011   #17
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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.
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Old 02-17-2011   #18
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Quote:
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The only way out of this is with movements - a view camera...
The best way out is to get your taking position right so that the camera can be level and the framing is correct. That way there is simply no need for a view camera. Of course that is not always feasible but is often overlooked when it is. It's just too easy to point the camera up or down rather than move yourself to the optimum position (which might include getting yourself into a middle floor of a building opposite).
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Old 02-17-2011   #19
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Quote:
Originally Posted by tlitody View Post
I can't detect any distortion there. Its just converging verticals from film plane not being vertical.
I now see what distortion is ( not in my photos ) and what converging verticals are.

Anyway, this lens has me re-thinking CV lenses. Actually the build quality is very good.
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Old 02-17-2011   #20
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Simply gorgeous shots Helen. Especially the first one. Jim
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Old 02-17-2011   #21
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Quote:
Originally Posted by tlitody View Post
The best way out is to get your taking position right so that the camera can be level and the framing is correct. That way there is simply no need for a view camera. Of course that is not always feasible but is often overlooked when it is. It's just too easy to point the camera up or down rather than move yourself to the optimum position (which might include getting yourself into a middle floor of a building opposite).
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.
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Old 02-17-2011   #22
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Quote:
Originally Posted by helenhill View Post
Oh hello William
its exactly that 'Look' that made Me fall for a 21 SA...the Exaggerated sense of Proportion
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.
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Old 02-17-2011   #23
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I think that's because your photo was taken with the camera leaning forward (lens' axis pointing down).
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Old 02-17-2011   #24
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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.
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Old 02-17-2011   #25
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To My 'EYE' , All the shots here have a varying
Degree of Heightened Proportions.... thats why 21's are Stellar

Cheers & Thank You my Rff buddies /Bill, Chris, BigEye, Barnwulf
for the Kind Comments...
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