Tunnel vision or vignetting at DVinfo.net

Josh Bass · February 2nd, 2003, 09:18 PM

I've noticed recently that the corners of the frames of my XL1s's images frames are slightly darker than the rest of my image, with the effect getting worse at the telephoto end of a zoom. This is with either lens (IS II or the manual 16x). It sort of looks like vignetting, but I don't see how that could be. I don't remember seeing it before. When zoomed fully in, it looks like a I have some sort of tube pressed up to the lens, and I'm looking through it. Some weird function of the iris? It seems more noticable when fully open, but I'm doing these tests inside under not very good lighting. Do your cameras all do this?

Don Palomaki · February 3rd, 2003, 05:03 AM

Photo-optical lenses have some fall-off at the corners. Check the lens reviews in photo magazines like Popular Photography for some quantitative data. Best way to demonstrate it it is with flat shubects (e.g., a white wall) that are somewhat underexposed.

Jeff Donald · February 3rd, 2003, 05:57 AM

Are you shooting with something attached to the front of the lens (filters, hoods) that you didn't in the past attach? If so, the filter etc. is causing vignetting. The edges of the filter are intruding into the frame and the result is dark corners. Other wise you're observing, as Don suggests, fall off of the light. This is most common at the wide angle position on lenses.

Dylan Couper · February 3rd, 2003, 12:35 PM

Josh I get the same thing when I'm using a filter, but not all the time.

Josh Bass · February 3rd, 2003, 12:55 PM

No filter, yes, using the lens hood. Maybe I've just never noticed before. I can make some screen grabs if someone wants.

Andre De Clercq · February 3rd, 2003, 12:59 PM

Johs, you probably see "portholing". Do a search in this forum and you will find some answers.

Jeff Donald · February 3rd, 2003, 01:05 PM

If you want to find out what it is you'll need to make some grabs with different aperture settings. As you stop the lens down (go from F/2.0 to F/16 or higher) you are increasing DOF and the likeliness of the outer edges of a filter or hood protruding into the scene. The wider the angle of view the greater the chance of light fall off and vignetting. So, run some tests and keep track of F/ Number, lens to subject distance, and angle of view.

Ken Tanaka · February 3rd, 2003, 01:22 PM

Josh,
Your observation sounds very similar to a phenomenon I observed on my GL2 last summer. I've never observed it on my XL1s. After lengthy discussions and further study I am convinced that, as Jeff and Don suggested, it's an optical characteristic of the lenses.

Josh Bass · February 3rd, 2003, 01:46 PM

I'm guessing you're right. . .but I've never noticed it before. I guess the corners are outside the safe area, so they only show up on a computer monitor when editing, not when played on a TV.

February 2nd, 2003, 09:18 PM	#1
Josh Bass Slash Rules! Join Date: Apr 2002 Location: Houston, Texas Posts: 5,472	Tunnel vision or vignetting I've noticed recently that the corners of the frames of my XL1s's images frames are slightly darker than the rest of my image, with the effect getting worse at the telephoto end of a zoom. This is with either lens (IS II or the manual 16x). It sort of looks like vignetting, but I don't see how that could be. I don't remember seeing it before. When zoomed fully in, it looks like a I have some sort of tube pressed up to the lens, and I'm looking through it. Some weird function of the iris? It seems more noticable when fully open, but I'm doing these tests inside under not very good lighting. Do your cameras all do this? __________________ The Bass' camerawork The Bass on IMDB

February 3rd, 2003, 05:57 AM	#3
Jeff Donald Warden Join Date: Mar 2002 Location: Clearwater, FL Posts: 8,287	Are you shooting with something attached to the front of the lens (filters, hoods) that you didn't in the past attach? If so, the filter etc. is causing vignetting. The edges of the filter are intruding into the frame and the result is dark corners. Other wise you're observing, as Don suggests, fall off of the light. This is most common at the wide angle position on lenses. __________________ Jeff Donald Carpe Diem Search DVinfo.net for quick answers \| Where to Buy? From the best in the business: DVinfo.net sponsors

February 3rd, 2003, 12:55 PM	#5
Josh Bass Slash Rules! Join Date: Apr 2002 Location: Houston, Texas Posts: 5,472	No filter, yes, using the lens hood. Maybe I've just never noticed before. I can make some screen grabs if someone wants. __________________ The Bass' camerawork The Bass on IMDB

February 3rd, 2003, 01:05 PM	#7
Jeff Donald Warden Join Date: Mar 2002 Location: Clearwater, FL Posts: 8,287	If you want to find out what it is you'll need to make some grabs with different aperture settings. As you stop the lens down (go from F/2.0 to F/16 or higher) you are increasing DOF and the likeliness of the outer edges of a filter or hood protruding into the scene. The wider the angle of view the greater the chance of light fall off and vignetting. So, run some tests and keep track of F/ Number, lens to subject distance, and angle of view. __________________ Jeff Donald Carpe Diem Search DVinfo.net for quick answers \| Where to Buy? From the best in the business: DVinfo.net sponsors

February 3rd, 2003, 01:22 PM	#8
Ken Tanaka Retired DV Info Net Almunus Join Date: Dec 2001 Location: Chicago, IL Posts: 6,943	Josh, Your observation sounds very similar to a phenomenon I observed on my GL2 last summer. I've never observed it on my XL1s. After lengthy discussions and further study I am convinced that, as Jeff and Don suggested, it's an optical characteristic of the lenses. __________________ Lady X Films: A lady with a boring wardrobe...and a global mission. Hey, you don't have enough stuff! Buy with confidence from our sponsors. Hand-picked as the best in the business...Really! See some of my work one frame at a time: www.KenTanaka.com

February 3rd, 2003, 05:03 AM	#2
Don Palomaki Wrangler Join Date: Sep 2001 Location: Northern VA Posts: 4,488	Photo-optical lenses have some fall-off at the corners. Check the lens reviews in photo magazines like Popular Photography for some quantitative data. Best way to demonstrate it it is with flat shubects (e.g., a white wall) that are somewhat underexposed.

February 3rd, 2003, 12:35 PM	#4
Dylan Couper Wrangler Join Date: Jun 2002 Location: Vancouver, British Columbia Posts: 8,314	Josh I get the same thing when I'm using a filter, but not all the time.

February 3rd, 2003, 12:59 PM	#6
Andre De Clercq Major Player Join Date: Sep 2002 Location: Belgium Posts: 804	Johs, you probably see "portholing". Do a search in this forum and you will find some answers.

February 3rd, 2003, 01:46 PM	#9
Josh Bass Slash Rules! Join Date: Apr 2002 Location: Houston, Texas Posts: 5,472	I'm guessing you're right. . .but I've never noticed it before. I guess the corners are outside the safe area, so they only show up on a computer monitor when editing, not when played on a TV. __________________ The Bass' camerawork The Bass on IMDB