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Olympus Zuiko 21mm/3.5: Is this distortion normal?
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PostPosted: Mon Dec 07, 2009 7:34 pm    Post subject: Olympus Zuiko 21mm/3.5: Is this distortion normal? Reply with quote
Hey everyone,

I just got myself one of those Zuiko Lenses, the 21/3.5 and haven't had the chance to do in-depth tests with it but have just been using it here and there a little.

I've never owned any wide lens like that, and I must say I'm a little startled by the extreme amount of pincushion distortion that the lens has towards the corners. When I took pictures with a group of people on it, the people outside the center were too distorted for the pictures actually being really usable. I don't know if this one is the best one to illustrate, but here's a pic:



Is this normal for superwide-angle lenses? Are there any alternatives that do a little better? In my extensive research I did before getting this one, I got the impression that the Zuiko lenses are rather a choice lens in that category.

Thanks in advance for your feedback!

Best,
Chris


PostPosted: Mon Dec 07, 2009 8:35 pm    Post subject: Reply with quote
Chris - I don't think what you're seeing in this pic is actually pincushion distortion. Rather, it's an exageration of perspective. You've pointed the camera slightly down when taking the picture and this is a typical result. Was this done on a full frame negative? Maybe you could post one or two more to let us see what's going on in them?


PostPosted: Mon Dec 07, 2009 8:37 pm    Post subject: Reply with quote
Do you mean the effect, which can be described as diagonal stretch of near-edge objects? This is not distorsion, but perspective emphasized by the extreme wide-angle linear projection.

There was an article by Zeiss about distorsions - if I find it, I'll post a link.

//edit: here:

http://www.zeiss.com/C12567A8003B8B6F/EmbedTitelIntern/CLN_33_Distortion_EN/$File/CLN33_Distortion_Article.pdf

see page 21 Smile


PostPosted: Mon Dec 07, 2009 9:36 pm    Post subject: Reply with quote
Yep, no distortion but camera tilt.


PostPosted: Mon Dec 07, 2009 10:28 pm    Post subject: Reply with quote
I agree with the others. To check for either pincushion or barrel distortion, I align the edge of the frame with either a vertical or horizontal straight line. I prefer doing this along the longest edges of the frame, so it would be a horizontal line unless you hold the camera for portrait-style photos. Insure that you are holding the camera such that lens centerline is exactly parallel with the ground (i.e., no tilt). Then take the photo, and examine it for distortion.


PostPosted: Tue Dec 08, 2009 12:20 am    Post subject: Reply with quote
Nah, sorry. Yes, in the picture, there's a camera tilt upwards, but objects are *always* "pulled out" towards the edges with this lens. A disco ball (i.e. an object for which it doesn't matter what angle you approach it from), that I put near the edge of the picture will always receive deforming to an egg shape. That's cool for disco balls, but it's not so cool if there's peoples faces (or bodies) getting distorted...

I only have pictures of people I know and who wouldn't want them to be posted so far, so I'll try to take some more universal pix tomorrow.

Thanks for your assessments so far!

Best,
Chris

P.S.: Yes, it's full-frame.


PostPosted: Tue Dec 08, 2009 1:06 am    Post subject: Reply with quote
I understand what Chris is talking about.

Yes, some of that is normal in the superwide lenses. Even though I typically see it from 18mm downwards.
Yes objects tend to be stretched near the corners, where the curvature of field is more apparent
That has not to do with pincushion distortion - actually pincushion distortion is very difficult to be seen in wide angle prime lenses, it is more typical of tele prime lenses or zoom lenses.
Normally, in awide lens you would find distortion of the barrel type.

no the Olympus 21 is not known for giving much distortion. It is in fact considered one of the best 21mm lenses around.
Make some full frame tests and watch carefully the corners at all f/stops.
If in the corners wide open you see "comet-tail halo" effect of luminous points (such as night lights), your lens has coma, and that might come from misalignement of elements.
If the four corners behave the same way, it's good news.
Try to shoot at f/11 and watch the corner sharpness. It should be on par with central sharpness, or at least near.
If at f/11 the corner sharpness is visibly worse than the central sharpness, then your lens probably has some issue and should be visited by a lens doctor.


PostPosted: Tue Dec 08, 2009 2:00 am    Post subject: Re: Olympus Zuiko 21mm/3.5: Is this distortion normal? Reply with quote
chris_weinert wrote:
Hey everyone,

I've never owned any wide lens like that, and I must say I'm a little startled by the extreme amount of pincushion distortion that the lens has towards the corners...Is this normal for superwide-angle lenses? Are there any alternatives that do a little better?
Thanks in advance for your feedback!

Best,
Chris


Chris,

Super wide angle lenses are full of surprises.

In general, the nearer to the edge the more the "distortion". Also, there is a stretching of the object in the near to far dimension (so circles become ovals, limbs and bodies become impossibly long and rapidly diminish in size with distance from the lens)

Also, they are very sensitive to a tilting of the film plane. (Your picture shows the symptoms of having tilted the camera upwards. If it had been tilted downwards, the linear objects, e.g. the people, would appear to tilt outwards rather than inwards.)

Wide angle requires a rethinking in your technique. Smile

This is just par for the course: get used to it! Smile


PostPosted: Tue Dec 08, 2009 4:01 am    Post subject: Reply with quote
With the angular ends must learn to locate people in the central areas to a greater or lesser extent distort or exaggerate the perspective.
It is also important that the axis of camera (lens) is perpendicular to the ground. This is to portray people, to architecture is very good for me these "defects".
In the example, than the Sharp, if the camera had not been pointing up, the man would not be distorted.
It is my humble opinion.
Greetings

Con los angulares extremos hay que aprender a ubicar a las personas en las zonas centrales, en mayor o menor medida distorsionan o exageran la perspectiva.
Tambien es importante que el eje de camara (lente) sea perpendicular al suelo. Esto para retratar personas, para arquitectura es muy bueno para mi esos "defectos".
En el ejemplo, aparte del Sharp, si la camara no hubiera estado apuntando hacia arriba,el hombre no estaría distorsionado. Smile Smile


PostPosted: Tue Dec 08, 2009 4:13 am    Post subject: Reply with quote
To illustrate Banjo's points, here are a couple of photos I took with a Vivitar 17mm f/3.8 lens mounted to a Canon F-1 35mm camera. I have already determined that this lens has a small but detectable amount of barrel distortion. And as well all know, 17mm is actually a lot wider than 21mm, so anything you see in these photos should be exaggerated more.

The first image was taken with the camera tilted slightly upward. The second was taken with the camera parallel to the ground. Note how in the first image the post with the stop sign seems not just to slant inward but to bow inward noticeably. But note how in the second image, observing both the stop sign post and the power pole, the bowing due to barrel distortion is almost undetectable. My point is that pointing the camera away from horizontal can exaggerate things and cause one to think that there are defects that aren't there, or that they are worse than they really are.




Last edited by cooltouch on Tue Dec 08, 2009 5:26 am; edited 1 time in total


PostPosted: Tue Dec 08, 2009 5:23 am    Post subject: Reply with quote

This photo was taken with a 24mm Sigma Super W II, which is less than the zuiko 21mm but also distorts.
And the zuiko is better than the sigma, you have a good lens. You just have to know.
Congratulations


PostPosted: Tue Dec 08, 2009 5:39 am    Post subject: Reply with quote
francotirador wrote:

This photo was taken with a 24mm Sigma Super W II, which is less than the zuiko 21mm but also distorts.
And the zuiko is better than the sigma, you have a good lens. You just have to know.
Congratulations


Chris,

Notice how francotirador has cleverly not only kept the film-plane perpendicular (so there is no "tiliting" of the subjects), but also positioned his subjects (in particular, the woman's arms and legs) so their longest dimension is parallel to the film-plane (otherwise there would have been a gross and unsightly elongation of them).Smile


PostPosted: Tue Dec 08, 2009 6:35 am    Post subject: Reply with quote
Banjo wrote:
Notice how francotirador has cleverly not only kept the film-plane perpendicular (so there is no "tiliting" of the subjects), but also positioned his subjects (in particular, the woman's arms and legs) so their longest dimension is parallel to the film-plane (otherwise there would have been a gross and unsightly elongation of them).Smile


Good observation. In fact, most of the straight lines in francotirador's photo are horizontal, which will not distort. It's a quite remarkable photo, really. Hard to tell such a wide angle lens was used. The only noticeable distortion I can detect is the man's torso on the left side seems to be a bit stretched compared to his right.

In the case of the photos I posted above, the whole point of them when I took them was to judge distortion, since it had been many years since I had shot with that old Vivitar 17mm. So I chose a scene where I had two verticals situated toward the edge of the frame. And as you can see, when the camera is positioned correctly, it isn't so obvious that these photos -- especially the second -- were taken with a 17mm on an FF camera.


PostPosted: Tue Dec 08, 2009 8:12 am    Post subject: Reply with quote
Hahaha! Wow!!! You people all ROCK!

Thanks for the illustrated 101 in wide angle photography, really helpful! How cool is this!

Best,
Chris


PostPosted: Tue Dec 08, 2009 2:30 pm    Post subject: Reply with quote
Chris,

Notice how francotirador has cleverly not only kept the film-plane perpendicular (so there is no "tiliting" of the subjects), but also positioned his subjects (in particular, the woman's arms and legs) so their longest dimension is parallel to the film-plane (otherwise there would have been a gross and unsightly elongation of them).Smile[/quote]
Yes sir, that is the question, knowing the defects allowed to use them for the photo
Greetings. Smile


PostPosted: Tue Dec 08, 2009 11:02 pm    Post subject: Reply with quote
Hello again,

so I didn't manage to take any good pics today with people on them, so I just took this extremely well composed picture with dirty wine glasses in our extremely classy kitchen. This time, I kept the film plane perpendicular and didn't tilt. Yesyes, I know, close up, but the effect is really similar with people in larger distances. In the middle you see the actual shape of the glasses, and to the sides you can see the nice distortion I was talking about (as well as the barrel distortion):



So are you guys are saying that this is the same or even worse with other superwide angle lenses?

Ok, now I'm gonna download that Zeiss article that no-X posted...

Best,
Chris


PostPosted: Wed Dec 09, 2009 12:11 am    Post subject: Reply with quote
Ok, the article is really nice... and actually page 21ff is a reply to my last post. Rolling Eyes I slowly understand the problem, or rather the tradeoff.

Again, thanks a lot to everyone for your tips and explanations, and for posting the examples, too!

Best,
Chris


PostPosted: Wed Dec 09, 2009 2:39 am    Post subject: Reply with quote
chris_weinert wrote:

so I didn't manage to take any good pics today with people on them, so I just took this extremely well composed picture with dirty wine glasses in our extremely classy kitchen.


Heh. Classier than mine, even with the dirty wine glasses and the well-used espresso machine.

Good test, though. You did a good job of lining up two horizontal surfaces with the top and bottom frame lines of the image area.

Yes, your lens is exhibiting what I would consider to be a rather pronounced amount of barrel distortion. On my 21.5" screen (55cm), I'm seeing about 3mm of distortion with the top and bottom horizontal lines. My Vivitar 17mm exhibits a similar amount.

Since I use my 17mm mostly for panoramics and scenics, a bit of barrel distortion generally has no detectable effect on the images I've taken with it. With those images I have taken where the distortion is evident, I still don't mind because usually it's a situation where no other lens I own can possibly encompass the desired subject area.

I would be much more concerned about sharpness, contrast, flare, etc. And in that respect your lens performs very well.


PostPosted: Wed Dec 16, 2009 11:36 pm    Post subject: Reply with quote
I'm slowly getting a feel for the 21mm... Meanwhile, I also came across this article on KenRockwell.com, where he shows why in some cases you exactly *should* tilt the camera when using super-wide angle lenses. For those who haven't read it, here it is:

http://www.kenrockwell.com/tech/how-to-use-ultra-wide-lenses.htm

Best regards,
Chris


PostPosted: Fri Dec 18, 2009 4:06 am    Post subject: Reply with quote
how much the different, between using that lens (21mm) at 1,5 & 2x crop factor in showing the width?


PostPosted: Fri Dec 18, 2009 11:49 am    Post subject: Reply with quote
Sorry, what do you mean exactly?

Thanks,
Chris


PostPosted: Fri Dec 18, 2009 1:00 pm    Post subject: Reply with quote
chris_weinert wrote:
Sorry, what do you mean exactly?

Thanks,
Chris


I mean using 21mm wide lens in Canon with 1,5x crop factor(CF) compare with using it Olympus 2x CF, how much different in width? is it much?


PostPosted: Fri Dec 18, 2009 1:06 pm    Post subject: Reply with quote
21mm at 1.5x crop camera = 21 * 1.5 = 31.5mm lens
21mm at 2x crop camera = 21 * 2 = 42mm lens


PostPosted: Fri Dec 18, 2009 1:37 pm    Post subject: Reply with quote
no-X wrote:
21mm at 1.5x crop camera = 21 * 1.5 = 31.5mm lens
21mm at 2x crop camera = 21 * 2 = 42mm lens


Embarassed ...sorry


PostPosted: Fri Dec 18, 2009 1:40 pm    Post subject: Reply with quote
No problem Wink
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