Porthole in XA20 at DVinfo.net

Go Back   DV Info Net > Canon EOS / MXF / AVCHD / HDV / DV Camera Systems > Canon XA and VIXIA Series AVCHD Camcorders

Canon XA and VIXIA Series AVCHD Camcorders
For the Canon XA25, XA20, XA10 and all VIXIA / LEGRIA Series AVCHD camcorders.


Reply
 
Thread Tools Search this Thread
Old December 1st, 2015, 03:38 AM   #1
Major Player
 
Join Date: Jan 2009
Location: Veenendaal, Holland
Posts: 210
Porthole in XA20

Does anyone have a remedie to avoid the nasty porthole effect in the XA20 yet?
Jo Ouwejan is offline   Reply With Quote
Old December 1st, 2015, 09:51 AM   #2
Wrangler
 
Join Date: Sep 2001
Location: Northern VA
Posts: 4,298
Re: Porthole in XA20

Porhole Effect? Do you mean vignetting or something else??
__________________
dpalomaki@dspalomaki.com
Don Palomaki is offline   Reply With Quote
Old December 1st, 2015, 10:07 AM   #3
Major Player
 
Join Date: Jan 2009
Location: Veenendaal, Holland
Posts: 210
Re: Porthole in XA20

I've been told, that it was known as the porthole effect. Under brighter conditions, the corners of the image are somewhat gey.
Jo Ouwejan is offline   Reply With Quote
Old December 1st, 2015, 05:11 PM   #4
Major Player
 
Join Date: Jun 2008
Location: Sutton, Australia
Posts: 328
Re: Porthole in XA20

I own an XA20 and I've heard the effect occurs sometimes on full zoom, bright light, ND on, stabilisation on, handheld. Kudos to those who found it and noticed it, I never have and I very much doubt a typical viewer would notice. Why are you asking? If you are considering buying an XA20, I seriously wouldn't be put off by these reports.
Rainer Listing is offline   Reply With Quote
Old December 1st, 2015, 06:48 PM   #5
Wrangler
 
Join Date: Sep 2001
Location: Northern VA
Posts: 4,298
Re: Porthole in XA20

That would be corner brightness fall-off type of vignetting, common to ALL lenses, both video and photo, and is one of the lens design considerations..

It is more apparent with flat images with large expanses of feature-less image, like blank walls, or a clear or uniformly overcast sky. It is less apparent in images with a lot of varied content. You can control it to some degree by adjusting the zoom and aperture settings.

See Canon Lens Vignetting (Light Fall-off) for more discussion.

The Paul van Walree link at the end of the above article gives more optical theory with math on the subject.
__________________
dpalomaki@dspalomaki.com
Don Palomaki is offline   Reply With Quote
Old December 2nd, 2015, 02:12 AM   #6
Major Player
 
Join Date: Jan 2009
Location: Veenendaal, Holland
Posts: 210
Re: Porthole in XA20

Thanks for your explanation Don. Fine to find out, that there is something I can do about it.
Jo Ouwejan is offline   Reply With Quote
Old December 2nd, 2015, 08:02 AM   #7
Wrangler
 
Join Date: Sep 2001
Location: Northern VA
Posts: 4,298
Re: Porthole in XA20

The articles suggest avoiding wide open apertures and wide zoom to minimize the corner fall off.

Ensure no physical items such as filter stacks or lens hoods obstruct the light path at the edges/corner of the frame.

If you can, avoid wide expanses of feature-less background and avoid lighting that causes hot spots mid frame (unless that you your intent) such as narrow beam lights on the camcorder that can make it worse.
__________________
dpalomaki@dspalomaki.com
Don Palomaki is offline   Reply With Quote
Old December 2nd, 2015, 09:17 AM   #8
Major Player
 
Join Date: Jan 2009
Location: Veenendaal, Holland
Posts: 210
Re: Porthole in XA20

Your recomendations in regard of the feature-less background and lighting midframe showed to be useless at the saltflats of Uyuni, Bolivia, where I sufffered the porthole most some weeks ago. But I will pay more attention to the zoomfactor and the aperture next time.
Jo Ouwejan is offline   Reply With Quote
Old December 2nd, 2015, 03:08 PM   #9
Major Player
 
Join Date: Jun 2008
Location: Sutton, Australia
Posts: 328
Re: Porthole in XA20

Jo, it seems you encountered an extreme example - can you post a frame?
Rainer Listing is offline   Reply With Quote
Old December 3rd, 2015, 04:21 AM   #10
Major Player
 
Join Date: Jan 2009
Location: Veenendaal, Holland
Posts: 210
Re: Porthole in XA20

These are two frames, that I saved from the actual footage:
Attached Thumbnails
Porthole in XA20-image1.jpg   Porthole in XA20-image3.jpg  

Jo Ouwejan is offline   Reply With Quote
Old December 3rd, 2015, 06:17 AM   #11
Wrangler
 
Join Date: Sep 2001
Location: Northern VA
Posts: 4,298
Re: Porthole in XA20

As was discussed in the link above the corner fall-off tends to draw the eye to the center of the frame. Not always a bad thing. However, you may be able to apply some form of gradient filter in post to brighten the corners a bit.
__________________
dpalomaki@dspalomaki.com
Don Palomaki is offline   Reply With Quote
Old December 3rd, 2015, 06:00 PM   #12
Major Player
 
Join Date: Jun 2008
Location: Sutton, Australia
Posts: 328
Re: Porthole in XA20

Thanks Jo. Like Don says, and if it does bother you, and I don't think it should, there probably are a number of post fixes - I had a quick go in Vegas, just a soft edge mask and increased brightness, I think you'd do better with curves, gradients, secondary color, depends how much time you think is worth spending.
Attached Thumbnails
Porthole in XA20-image1.jpg  
Rainer Listing is offline   Reply With Quote
Old December 4th, 2015, 09:50 PM   #13
Wrangler
 
Join Date: Sep 2001
Location: Northern VA
Posts: 4,298
Re: Porthole in XA20

The Adobe Lens Correction filter vignetting settings might work
__________________
dpalomaki@dspalomaki.com
Don Palomaki is offline   Reply
Reply

DV Info Net refers all where-to-buy and where-to-rent questions exclusively to these trusted full line dealers and rental houses...

Professional Video
(800) 833-4801
Portland, OR

B&H Photo Video
(866) 521-7381
New York, NY

Z.G.C.
(973) 335-4460
Mountain Lakes, NJ

Abel Cine Tech
(888) 700-4416
N.Y. NY & L.A. CA

Precision Camera
(800) 677-1023
Austin, TX

DV Info Net also encourages you to support local businesses and buy from an authorized dealer in your neighborhood.
  You are here: DV Info Net > Canon EOS / MXF / AVCHD / HDV / DV Camera Systems > Canon XA and VIXIA Series AVCHD Camcorders

Thread Tools Search this Thread
Search this Thread:

Advanced Search

 



Google
 

All times are GMT -6. The time now is 09:00 PM.


DV Info Net -- Real Names, Real People, Real Info!
1998-2017 The Digital Video Information Network