Pixel Grid in Lens flare? at DVinfo.net

Colin Levy · June 23rd, 2007, 01:06 AM

Hey guys, I just got a Canon A1 this week and I'm really excited about it. Today I went out to shoot some test footage.

Here's a clip.

And here's a still with the problem I'm having.

As you can see, there seems to be an ugly grid of colored pixels in the highlights. I guess I was pointing the camera directly at the sun, which is not a good idea, but I was wondering - what's physically happening here? I assume those pixels are from the CCD. Is light hitting the CCD's and reflecting back into the prism?

Anyway, I was not using an ND filter when I was shooting this. Would that have solved the problem? I thought that since I barely even had to stop down the aperture there was no point in using the ND filter, but I don't really know what I'm doing... Next time I'll experiment.

Anyway, has anyone else encountered this problem? Do you know what's happening? And will the ND filter solve it even if it's exposed the same way?

Thanks!

--Colin

James Miller · June 26th, 2007, 06:40 AM

Hi is this one of the areas you are talking about, it looks normal, the tiny grid artifacts look like HDV compression.

James

Colin Levy · June 26th, 2007, 03:58 PM

Hey James, thanks for the response. No, I'm not talking about the artifacting due to the HDV compression, I'm talking about the big bright colored dots that show up in the flare.

The offset red, green, and blue circles. Like this:

Know why that's happening?

Don Palomaki · June 27th, 2007, 07:02 AM

Some folks would probably pay to have that effect available as a filter in their NLE.

What f-stop was the image?

The sun is bright, perhaps 10,000-to-100,000 times brighter than the rest of the stuff in the image. What that means is even a wee bit of stray reflection or refraction in the optical path can cause the direct sun component to appear bright in the image, and going through the 3-CCD beam splitter may cause it to be displaced giving the rainbow effect. You are probably seeing the results of a stray internal reflection/refraction. The several distinct spots may relate the the number of blades in the iris.

Solution is to keep the direct sun out of the image; e.g., move the camera a bit to shade the lens from the direct sun. Using a ND would not have helped if you were interested in things other than the sun, because it effects the whole image, not just the direct sun.

James Miller · June 27th, 2007, 07:52 AM

Sorry Colin, I see what you mean now.

I love that look, I sometimes simulate the colour shift using FCP filter Prism.

As Don said move the camera so the sun is not in direct view. Or put a Matte Box on the front with french flag and keep the same camera angle. Formatt do a cheap robust box £175 FM-500.

A couple of links with pics.

http://www.formatt.co.uk/matte-boxes/products.aspx
http://www.mvsvideo.co.uk/equipment_formatt.htm

James

Colin Levy · June 27th, 2007, 12:43 PM

Hmm! I had no idea this was actually desirable...

I don't know, I love a good lens flare - you know, the photoshop variety.... But the grid surrounding the entire sun is just very distracting to me. I think if it truly was a rainbow effect, with more blending between the three distinct colors maybe it would look better.

Anyway, thanks for your tips and explanations, guys! I appreciate it. Don, I believe my iris was at around f8, but I don't remember exactly. I'll play around with the aperture next time and see if it has any effect on the number of iterations it has.

--Colin

June 23rd, 2007, 01:06 AM	#1
Colin Levy Regular Crew Join Date: May 2005 Posts: 29	Pixel Grid in Lens flare? Hey guys, I just got a Canon A1 this week and I'm really excited about it. Today I went out to shoot some test footage. Here's a clip. And here's a still with the problem I'm having. As you can see, there seems to be an ugly grid of colored pixels in the highlights. I guess I was pointing the camera directly at the sun, which is not a good idea, but I was wondering - what's physically happening here? I assume those pixels are from the CCD. Is light hitting the CCD's and reflecting back into the prism? Anyway, I was not using an ND filter when I was shooting this. Would that have solved the problem? I thought that since I barely even had to stop down the aperture there was no point in using the ND filter, but I don't really know what I'm doing... Next time I'll experiment. Anyway, has anyone else encountered this problem? Do you know what's happening? And will the ND filter solve it even if it's exposed the same way? Thanks! --Colin

June 26th, 2007, 06:40 AM	#2
James Miller Major Player Join Date: Mar 2007 Location: Sussex, UK Posts: 317	Hi is this one of the areas you are talking about, it looks normal, the tiny grid artifacts look like HDV compression. James Attached Images

June 26th, 2007, 03:58 PM	#3
Colin Levy Regular Crew Join Date: May 2005 Posts: 29	Hey James, thanks for the response. No, I'm not talking about the artifacting due to the HDV compression, I'm talking about the big bright colored dots that show up in the flare. The offset red, green, and blue circles. Like this: Know why that's happening? Attached Images

June 27th, 2007, 07:02 AM	#4
Don Palomaki Wrangler Join Date: Sep 2001 Location: Northern VA Posts: 4,488	Some folks would probably pay to have that effect available as a filter in their NLE. What f-stop was the image? The sun is bright, perhaps 10,000-to-100,000 times brighter than the rest of the stuff in the image. What that means is even a wee bit of stray reflection or refraction in the optical path can cause the direct sun component to appear bright in the image, and going through the 3-CCD beam splitter may cause it to be displaced giving the rainbow effect. You are probably seeing the results of a stray internal reflection/refraction. The several distinct spots may relate the the number of blades in the iris. Solution is to keep the direct sun out of the image; e.g., move the camera a bit to shade the lens from the direct sun. Using a ND would not have helped if you were interested in things other than the sun, because it effects the whole image, not just the direct sun. __________________ dpalomaki@dspalomaki.com

June 27th, 2007, 12:43 PM	#6
Colin Levy Regular Crew Join Date: May 2005 Posts: 29	Hmm! I had no idea this was actually desirable... I don't know, I love a good lens flare - you know, the photoshop variety.... But the grid surrounding the entire sun is just very distracting to me. I think if it truly was a rainbow effect, with more blending between the three distinct colors maybe it would look better. Anyway, thanks for your tips and explanations, guys! I appreciate it. Don, I believe my iris was at around f8, but I don't remember exactly. I'll play around with the aperture next time and see if it has any effect on the number of iterations it has. --Colin __________________ My Film, Animation and Visual Effects Work: http://www.colinlevy.com

June 27th, 2007, 07:52 AM	#5
James Miller Major Player Join Date: Mar 2007 Location: Sussex, UK Posts: 317	Sorry Colin, I see what you mean now. I love that look, I sometimes simulate the colour shift using FCP filter Prism. As Don said move the camera so the sun is not in direct view. Or put a Matte Box on the front with french flag and keep the same camera angle. Formatt do a cheap robust box £175 FM-500. A couple of links with pics. http://www.formatt.co.uk/matte-boxes/products.aspx http://www.mvsvideo.co.uk/equipment_formatt.htm James