Bending Horizons at DVinfo.net

J. Wilbur · November 5th, 2008, 03:25 AM

Is this normal for EX! cmos censors. Shot was a time lapse with lens wide open. Had a number of shots with the same problem. Only happened in the wide open position. No problems when lens was zoomed in

David C. Williams · November 5th, 2008, 03:32 AM

Not CMOS, it's the lens and the size of the sensor. It's pretty normal display of barrel distortion at full wide for a lens in that cost range.

Sverker Hahn · November 5th, 2008, 05:09 AM

Quote:

Originally Posted by Jason Wilbur

Is this normal for EX! cmos censors. Shot was a time lapse with lens wide open. Had a number of shots with the same problem. Only happened in the wide open position. No problems when lens was zoomed in

This could be annoying. Since the barrel-shaped distorsion disappears when zooming in a little, it is best to avoid the most wide position when it could be a problem (horizon, buildings etc.)

I use Final Cut Pro, and there is a fisheye filter, with which one can get the horizon straight again. Since it makes the outer parts of the picture unuseable, I think you have better correcting future shots with zooming in a little, rather than correcting in post.

Enabling the markers will help to find the zoom position when barrel distortion is no problem.

Tom Hardwick · November 5th, 2008, 05:37 AM

Nothing to do with the size of the sensor Jason - and all to do with the design of the lens. A trade has been made between distortion (that you're seeing) and sharpness, chromatic aberration and weight, number of elements and cost. You're getting the least distortion while still getting the image sharp at the price you've paid.

The effect will not be aperture dependent and all straight lines that don't cross through the center of the frame will be so affected. In other words if your horizon was dead center you won't see the barrel distortion (though it'll still be there of course).

But I do agree with you that barrel distortion can and does look very amateur, so I'd beware of adding any zoom-through wide-angle converter as this will just make matters worse.

tom.

Tom Roper · November 5th, 2008, 09:24 AM

I'm sorry, that's not barrel distortion. The earth is flat, and it sinks a little where the water pours over the side. Best to not get too close.

Vito DeFilippo · November 5th, 2008, 11:00 AM

If this is normal barrel distortion, why does it seem worse on the left? All barrel distortion I've seen effects left and right sides of the frame.

Warren Kawamoto · November 5th, 2008, 11:07 AM

The distortion seems worse on the left because the camera is slightly tilted to the left instead of being absolutely level.

Tom Hardwick · November 5th, 2008, 11:16 AM

It's easy to test your lens for barrel distortion. Simply set the camera up perpendicular to the front of a TV, using max wide-angle. Prepare to be upset.

Ted OMalley · November 5th, 2008, 11:29 AM

Quote:

Originally Posted by Tom Roper

I'm sorry, that's not barrel distortion. The earth is flat, and it sinks a little where the water pours over the side. Best to not get too close.

And Tom Roper celebrates his 1000th post by being helpful.

Jay Gladwell · November 5th, 2008, 11:40 AM

Quote:

Originally Posted by Tom Hardwick

It's easy to test your lens for barrel distortion. Simply set the camera up perpendicular to the front of a TV, using max wide-angle. Prepare to be upset.

Maybe there's something wrong with me, but I don't find barrel distortion upsetting. I would even venture to guess that the vast majority of the audience doesn't even notice it, until you point it out to them.

Steven Thomas · November 5th, 2008, 01:53 PM

Nothing out of the ordinanry for a lens of this price. Just zoom in a tad.

Buck Forester · November 5th, 2008, 02:03 PM

Coming from 'still' photography, even many high-end wide-angle lenses, especially zooms at their widest, have a little distortion. Tilt-shift lenses can counter this effect, which is why they are used in real estate photography where straight lines are critical. As noted the effect diminishes as you zoom in. Personally I don't mind some barrel distortion. In the case you showed it would not even be noticeable unless someone knew the horizon was supposed to be completely level.

Tom Roper · November 5th, 2008, 11:38 PM

Quote:

Originally Posted by Tom Hardwick

But I do agree with you that barrel distortion can and does look very amateur, so I'd beware of adding any zoom-through wide-angle converter as this will just make matters worse.

tom.

Being serious for a moment, I don't find the picture at all objectionable in spite of the lens flaw, because if you centered the horizon in the frame, the poor composition is what would scream amateur to me.

In other words, speaking for myself I would overlook the bending horizon and instead recognize the composition of the picture that is meant to emphasize the "heavens" or whatever message you wanted that clip to convey.

A horizon in the middle of the frame is always wrong, and boring...(to me). My $0.02

Tom Hardwick · November 6th, 2008, 02:49 AM

I agree entirely with Tom (above). Watch a lot of film and you'll see many people tend to aim, not frame. How many stills have you seen with the person's head mid-frame, cut off at the knees and a ton of 'sky' above? I don't criticise or they may start on my cooking skills...

Post #50 in this thread shows my set-up pictures.
http://www.dvinfo.net/conf/canon-xl-...hipping-4.html

tom.

November 5th, 2008, 03:25 AM	#1
J. Wilbur New Boot Join Date: Apr 2008 Location: Sydney Posts: 8	Bending Horizons Is this normal for EX! cmos censors. Shot was a time lapse with lens wide open. Had a number of shots with the same problem. Only happened in the wide open position. No problems when lens was zoomed in Attached Thumbnails

November 5th, 2008, 11:00 AM	#6
Vito DeFilippo Trustee Join Date: Mar 2006 Location: Montreal, Quebec Posts: 1,585	If this is normal barrel distortion, why does it seem worse on the left? All barrel distortion I've seen effects left and right sides of the frame. __________________ . http://www.nosmallroles.com

November 5th, 2008, 03:32 AM	#2
David C. Williams Major Player Join Date: Jun 2008 Location: melb.vic.au Posts: 447	Not CMOS, it's the lens and the size of the sensor. It's pretty normal display of barrel distortion at full wide for a lens in that cost range.

November 5th, 2008, 05:37 AM	#4
Tom Hardwick Inner Circle Join Date: Mar 2003 Location: Billericay, England UK Posts: 4,711	Nothing to do with the size of the sensor Jason - and all to do with the design of the lens. A trade has been made between distortion (that you're seeing) and sharpness, chromatic aberration and weight, number of elements and cost. You're getting the least distortion while still getting the image sharp at the price you've paid. The effect will not be aperture dependent and all straight lines that don't cross through the center of the frame will be so affected. In other words if your horizon was dead center you won't see the barrel distortion (though it'll still be there of course). But I do agree with you that barrel distortion can and does look very amateur, so I'd beware of adding any zoom-through wide-angle converter as this will just make matters worse. tom.

November 5th, 2008, 09:24 AM	#5
Tom Roper Trustee Join Date: Jun 2004 Location: Denver, Colorado Posts: 1,891	I'm sorry, that's not barrel distortion. The earth is flat, and it sinks a little where the water pours over the side. Best to not get too close.

November 5th, 2008, 11:07 AM	#7
Warren Kawamoto Trustee Join Date: Nov 2006 Location: Honolulu, HI Posts: 1,435	The distortion seems worse on the left because the camera is slightly tilted to the left instead of being absolutely level.

November 5th, 2008, 11:16 AM	#8
Tom Hardwick Inner Circle Join Date: Mar 2003 Location: Billericay, England UK Posts: 4,711	It's easy to test your lens for barrel distortion. Simply set the camera up perpendicular to the front of a TV, using max wide-angle. Prepare to be upset.

November 5th, 2008, 01:53 PM	#11
Steven Thomas Trustee Join Date: Sep 2005 Location: Gilbert, AZ Posts: 1,896	Nothing out of the ordinanry for a lens of this price. Just zoom in a tad.

November 5th, 2008, 02:03 PM	#12
Buck Forester Major Player Join Date: Feb 2008 Location: California Posts: 230	Coming from 'still' photography, even many high-end wide-angle lenses, especially zooms at their widest, have a little distortion. Tilt-shift lenses can counter this effect, which is why they are used in real estate photography where straight lines are critical. As noted the effect diminishes as you zoom in. Personally I don't mind some barrel distortion. In the case you showed it would not even be noticeable unless someone knew the horizon was supposed to be completely level.

November 6th, 2008, 02:49 AM	#14
Tom Hardwick Inner Circle Join Date: Mar 2003 Location: Billericay, England UK Posts: 4,711	I agree entirely with Tom (above). Watch a lot of film and you'll see many people tend to aim, not frame. How many stills have you seen with the person's head mid-frame, cut off at the knees and a ton of 'sky' above? I don't criticise or they may start on my cooking skills... Post #50 in this thread shows my set-up pictures. http://www.dvinfo.net/conf/canon-xl-...hipping-4.html tom.