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Old March 22nd, 2003, 11:20 AM   #1
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barrel distortion from Leica

I've just watched a lot of footage shot in New York The place is fullof tall, parallel sided buildings with rectangular windows and doors, right? Not on this film.

The MX350's 12x Leica zoom is abysmal at the wide-angle end, curving everything it can lay its hands on. I got so annoyed at seeing everything so barrel distorted I would have accepted a lower level of sharpness to have straight lines rendered as straight.

I find it really unacceptable, but then few films show off this lens failing as much as a city-scape movie. Of course the lens barrel distorts everything at wide-angle, faces and bicycles and elephants. It's just that it's not so obvious with some subjects.

tom.
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Old March 22nd, 2003, 04:36 PM   #2
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And..., you know, the MX350 has less barrel distortion than the MX300, according to Panasonic. But perhaps you notice a depth of field difference at 12X instead of barrel distortion?
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Old March 22nd, 2003, 08:00 PM   #3
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Hi.

Err, I'm not familliar with the term "barrel distortion". Can somebody explain it to me?

I gather it has something to do with lines that should be straight (outside the camera), looking bowed in the camera?

I believe this is normal.

Have you considered that the more wide angle you go, the more "fisheye" your shots will be, and the more curved effect you will see?

If you use a fisheye lens / adaptor and make your MX equivalent to a SLR camera's lens 24mm, you will see everything like through a fishbowl :)

The MX300 at it's widest angle (0x) is equivalent to a SLR camera's lens at 38mm. Not very wide angle, but you will see the curved effect.

If you zoom to about 2.5x or 3x onwards, then there will no longer be any curved effect - 'cos it's now equivalent to SLR camera's lens at around 50mm (like our eye's).

The MX500 isn't as wide angle as the MX300 & MX350, therefore it will have less of the curved effect. Unless you attach a WideAngle adaptor!
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Old March 23rd, 2003, 01:33 AM   #4
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First to Frank - I'm not sure what you mean when you say : "perhaps you notice a depth of field difference at 12X instead of barrel distortion?" The distortion is only present at the wide-angle end of the zoom and DOF doesn't come into it.

To Steven: Barrel distortion is a lens design failing that renders all straight lines (that don't pass through the centre of the frame) as bowed outwards towards the edge of the frame. Pincushion distortion is lines that bow inwards.

Contary to what you say, this is not "normal" in the sence that it is desirable. It may well be dished up to us by camcorder manufacturers, but it sure is unwelcome in my book.

You say that "the more wide angle you go, the more "fisheye" your shots will be, and the more curved effect you will see", and again, this is not necessarily so. I have aspheric element wide-angle converters that give no barrel or pincushion distortion at all, and of course my prime 20mm lens for my Canon SLR is totally without distortion, so it's certainly not a design requirement.

All zooms fitted to camcorders have design limitations, and the 12x on my VX2k also barrel distorts at the wide-angle end, though not as much as the 350. It's a design trade off, where the manufacturer ballances the sharpness vs the speed vs the compactness vs the distortions they think we'll find acceptable at the price. I just think that Leica should think twice befoe signing their name on such a distorting optic.

tom.
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Old March 23rd, 2003, 01:49 AM   #5
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www.dpreview.com :

Barrel Distortion
By Phil Askey

Barrel distortion is a lens effect which causes images to be spherised at their center. Barrel distortion is associated with wide angle lenses and only occurs at the wide end of a zoom lens. Most noticeable when you have a very straight edge near the side of the image frame. Some people find this to be an unacceptable fault of the camera, my own personal feelings are that although barrel distortion can be visible sometimes it would not be noticeable in 90% of your photography.


We measure barrel distortion in our reviews as the amount a reference line is bent as a percentage of picture height, for most consumer digital cameras this figure is normally around 1%. See also the opposite effect, pincushion distortion.

Tom, it was only a suggestion.
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Old March 23rd, 2003, 08:28 PM   #6
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Thanks, Tom & Frank.

I'm really enlightened!

I can "see" clearly now ;)

Seriously, though, I suppose that Aspherical WideAngles are really really expensive since it has to be designed to remove all / most of the barrel distortion.

And most consumer cams will be shipped with not so good non - Aspherical (spherical?) lenses because of cost issues.

Maybe because of the trend to make smaller lens elements makes it more distorted? i.e. JVC's into 27mm filter thread / lenses for vidcams now, Sony's been doing 37mm, our MX is at 43mm, while the big pro's cams are 58mm MINIMUM.

Say, Tom, what WideAngles would you be using for your vidcam? Century Optics? Tiffen?

Thanks in advance!
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Old March 23rd, 2003, 08:54 PM   #7
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This article on lens defects on DV Info may be helpful. Aspherical lens elements help with minimizing Barrel Distortion, but add to the cost of the lens.

Leica needs to make a profit like any other company. Just because it says Leica (or Zeiss, etc.) is no guarantee as to optical perfection.
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Old March 24th, 2003, 12:04 AM   #8
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Like you I really find distortion in camera lenses annoying. Unfortunately it seems to be typical of cheaper imaging systems in all categories.

My first dissapointment in this area was from an Olympus digital camera. Reviews hailed the lens as wonderfully sharp. What they failed to point out was the high degree of distortion at wide-angle settings. This was clearly a secondary requirement for the manufacturer at this price point.

Olympus make interchangeable rectillinear lenses (ie: very little distortion) for their SLR still cameras, but they cost more. Similarly, broadcast zoom lenses have less distortion, but they can cost as much as their already expensive high end cameras. You really do get what you pay for.

Frank has pointed out the DP review.com site where Phil Askey actually measures the degree of distortion in digital still cameras. We need something like this for video systems so we get hard figures on things like distortion and smear in cameras. Until then we will all be operating by the seat of our pants (like the reviewers) and discovering these things by tragic accident, sometimes after we have purchased the camera.

Jim
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Old March 24th, 2003, 02:15 AM   #9
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Hi, Tom.

Unfortunately, only a minority of us are "purist" & have very high levels of excellence (and it naturally flows into our preferences for the finer things in life) - I'm guilty too.

I suppose that even if we found out that our MX300 / MX350 / MX500 whatever has *some* barrel distortion, the price & performance factors may persuade us to get it anyways.

Sigh.

I know for one that I can't afford those high end 700+ lines of definition TV station crew camcorders with the fancy glass. Guess you get what you pay for.

So I'll have to live with my trusty MX300 which does the job, has 3 CCDs, sharp enough image, small enough, and cheap enough.

====

Perhaps the solution is to keep the MX300 at 2.5 to 3x where there's no barrel distortion, and put on a very very good wideangle converter (Century Optics) with a very wideangle i.e. 0.5x to compensate?

But then, I don't even know if Century Optics has such a good wideangle... anybody know?
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Old March 24th, 2003, 03:08 AM   #10
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A fellow from Vancouver tested the Century, Kenko Pro and Tiffen. I can't recall which cam he used. He noticed that the Tiffen had the sharpest image. There was no mention of barrel distortion.

Also, the Century is made by the same company that makes Heliopan and B&W. Furthermore, Kenko makes the Sony adaptors.

Which one is best? This would depend on the cam as well. For the MX300, I think the Panasonic is best, followed with the Tiffen---they both have their strengths and weaknesses though. I would venture to guess that the Pana has better zoom through.
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Old March 24th, 2003, 11:17 AM   #11
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Panasonic do indeed make a 0.7x zoom-through widie for the MX300 and its ilk, though like very many others it suffers barrel distortion. Of course it's not helped by being attached to a barrel-distorting zoom lens...

I have many wide-angles Steven, and I've tested a few of them for a video magazine. The Century 0.65x was the best of group test, but so it should've been at the price. Even so, my conclusions were that it gave far too much barrel distortion in this day and age and at the price.

The Schneider Kreuznach 0.65X gave absolutely zero barrel distortion (tested on a VX2000) but being a singel element aspheric means that you can only zoom a little way before it goes hopelessly out of focus.

The Raynox 0.66x is also very good at keeping straight lines straight, but the further you zoom the softer the image. Raynox make no bones about this but it's a shame when the lens is so good at wide-angle.

Your idea of zooming up a bit and fitting a wide-angle converter doesn't work Steven. Try it and see - the extra three elements add their own distortions and sharpness losses.

tom.
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Old March 24th, 2003, 10:56 PM   #12
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Hi, all.

Thanks for the interesting feedback so far.

I've been trying out my MX300 by vidcamming an open doorway at home - yes, there are barrel effects - the left & right of the doorway do stretch towards the left & right of the video frame, like it's grown fat...

Then I noticed, there is less barrel effect on the TOP & BOTTOM sides of the video frame. Hmmmm...... Maybe if you rotate the cam 90 degrees clockwise / anticlockwise you won't get such barrel effects. ;) ;) ;) ;) and rotate the video back to normal when you edit & put a black frame around the picture... err... never mind...

Seriously, the barrel effects are there, but I find it not so bad, I'll live with it.

I compared the same doorway scene to my Sony Digi8 which has a f=36mm lens (the MX300 is f=35.5mm), the Sony has LESS barrel effect i.e. still bowed a bit, but not as much as the MX300!

Then I realized that the nearer I am to the doorway, the more apparent the bowing. The futher away, the less barrel effect.

I took a bubble level to the doorframes and guess what? The doorframes aren't exactly straight! Same goes with the other doorways and some arches & some of my walls.... and the MX's barrel effect EXAGGERATES this - makes it look more crooked than it really is. Aggghhh....
So I can use my MX to spot walls etc that aren't so straight... 8O


Guess architechts and builders aren't too good at making straight walls, doors, archways & perhaps buildings?
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Old March 25th, 2003, 03:37 AM   #13
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Steven, you say:

"Then I realized that the nearer I am to the doorway, the more apparent the bowing. The futher away, the less barrel effect."

This has nothing to do with distance, only to the fact that barrel distortion only effects lines that don't pass through the centre of the frame. In other words a photo of the Union Jack flag would show a bowed outer perimiter to the flag, but all the other lines would appear straight.

So the further the lines are from the centre of the frame, the more curvature takes place. This explains why the top and bottom are less bowed - they are simply nearer the optical centre.

tom.
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