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Old October 12th, 2007, 03:42 PM   #1
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Problem with Chromatic Aberration?

I have footage shot at a football field at dusk with purple flares around the white helmet as well as footage shot at an ice rink where there is a purple flare around the sodium lights. Is this CA or is it a setting in my camera that can correct this obvious problem? I hope that it is not the lens as it is the Fujinon 13X3.5 wide angle which is a very expensive lens. Please help!
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Old October 12th, 2007, 04:03 PM   #2
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Do post a frame for us to assess. I have an hd100 and am aware of certain limitations of the fujinon in the long end (telephoto) of the zoom lens.

Ted
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Old October 12th, 2007, 04:05 PM   #3
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I'm trying to upload a few seconds of each clip but it isn't working???
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Old October 12th, 2007, 04:17 PM   #4
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Quote:
Originally Posted by Ted Ramasola View Post
Do post a frame for us to assess. I have an hd100 and am aware of certain limitations of the fujinon in the long end (telephoto) of the zoom lens.

Ted
Hi Ted, could you let me know the best way to upload this file from FCP.
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Old October 12th, 2007, 04:34 PM   #5
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Here are the shots
Attached Files
File Type: mov Hockey CA.mov (259.2 KB, 219 views)
File Type: mov Football CA.mov (706.9 KB, 199 views)
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Old October 12th, 2007, 07:33 PM   #6
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I'm not a lens expert by any means, so this is just my opinion and not my professional advice. But, I don't see anything wrong with the hockey footage. That all looks normal and I don't see the purple halo.

The football footage definitely looks like chroma. I doubt you can get rid of it completely, but you could probably take some steps to help it. The first thing is to make sure you have a proper white balance. The game probably started earlier and had some sunlight, but with the lights on it changes the color temp. Your footage is really blue and you should have taken a white balance at some point.
Another thing you can do is not push in so tight. Widen the shot a bit so that you're not at the end of the lens. That will definitely help the lens to function better.
Next, you can close the iris a little to help control the light. The portions with problems are all areas that are blownout. Either from stadium light reflection, or from whites being overexposed. If there were no problems with chroma I'd say the image is exposed perfectly, but with the problems your having try and close the iris just a hair more so you get less blowout.

Using any lens it's important to try and hit the sweet spot. In sports you have less control over that, but sometimes the little things can add up and help the image.

I hope that helps out a little.

Ben
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Old October 13th, 2007, 12:01 AM   #7
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Thanks Ben. In fact all shots were done on full auto, so the white balance should take care of itself- no? I have also included two more pictures, one being a close up a nissan emblem on a car and another example of the Hockey scenario. Perhaps you could have a look.

On a similar note, can anyone pass along the best settings for shooting ice rink scenarios, as I'm working on a doc that mostly takes place indoors at various rinks. Or is full auto, perhaps, the best way to go?
Attached Thumbnails
Problem with Chromatic Aberration?-hockey2-ca.png   Problem with Chromatic Aberration?-nissan-ca.png  

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Old October 13th, 2007, 12:20 AM   #8
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I'm with Ben. I think it's your white balance more than anything else. Or maybe your color settings. In the football shot the midtone whites (pants) are not white, they're blue - so the highlight whites will be blue too, only they'll stand out more. I tried to use auto aperture the other day because I was panning all around the sky following jets around. It did automatically adjust itself, but not to where I wanted it to be. I wouldn't trust auto anything.
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Old October 13th, 2007, 01:48 AM   #9
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Scott,
With the football shot at night, you have everything against you which allows CA to be at its worse.
I imagine your aperture was wide to near wide open, and you're using the tele end of the lens. I realized this may not of been avoidable based on lighting needs.

Also, your white balance needs to be corrected in post, it's way cool. This will improve the look of this footage. Maybe you had your cam set to 5600K under those lights?

Well, I guess I should of read above. I agree with Ben on this.

Remember that CA is worse when zoomed in and at a wide aperture.
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Old October 13th, 2007, 02:34 AM   #10
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Scott,

Ive seen the clips and yeah, they are CA. I tried a batch process i use to correct CA in photoshop but it didnt help much. Especially since in this particular instance the CA were in the highlights and blown out areas. The lens correction filter in photoshop is usually effective with CA in the edges of images with contrast.

In your case you were in telephoto where this usually appears on this type of lens and also the fujinon usually exhibits CA in blown out highlights and in its bokeh.

I also dont think you should use this camera in full auto. always check your white balance to get the best from this camera.

Ted
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Old October 13th, 2007, 09:56 AM   #11
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Scott,

In my experience with this camera, it has the worst auto white ability of any camera I've ever used. It adjusts itself on a whim, it's inaccurate, and it has a tendency to use the wrong color temp. You'll be much better off with a manual white balance.

On the Nissan logo you can see that everything is fine except for the portions that are blown out. Those area's just have too much light coming in and will make almost any lens look bad. You have to control the lighting or really what the exposure.

As for auto exposure, if you notice this chroma a lot, which it appears you do, then you'll need to run the exposure in manual. The camera is reasonably good at picking the right exposure but only during normal conditions. When the lens needs help then you need to make the adjustments yourself and run the iris in manual.

Once you run the camera on manual a few times you'll get in the feel for the controls and you won't think about the changes your making, it will just be natural. You may want to try it once and see if it helps the results any.

Ben
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Old October 13th, 2007, 10:15 AM   #12
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Guys, this is problem is called imager overload. I've seen it countless times on many cameras both still and video. No amount of white balancing will get rid of it. I've got examples of my own, both from a Kodak Easyshare digital camera, to my XDCAM HD camera with a $16K lens. Bright lights at night will almost always have that purple or blue fringing because you're exposing for the darker areas. That leaves those bright points of light as small areas with very dark areas adjacent. It shows up really bad on the long end of the lens because you are magnifying the problem.

Chrome in the image creates strong specular reflections that will also overload the imager. I'd be willing to bet that the Nissan shot was done during the middle of the day which creates a high key light.

Scott, from the frame grabs you posted, I'd say your camera/lens is well within the capabilities of most cameras to deal with this situation.

BTW, this same thing was just discussed in another HD100 thread.

-gb-
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Old October 13th, 2007, 11:36 AM   #13
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Well this is all very helpful, I appreciate everyones input. Again, if someone could give me a recipe for shooting inside various ice rinks(with sodium lights being the main source)I'd really appreciate it. The reason I've been shooting full auto is I also have the coach on a wireless mic with the another one for ambient sound and the full auto is the only way I can control spikes in the sound.
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Old October 13th, 2007, 11:56 AM   #14
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Quote:
Originally Posted by Scott Harper View Post
Well this is all very helpful, I appreciate everyones input. Again, if someone could give me a recipe for shooting inside various ice rinks(with sodium lights being the main source)I'd really appreciate it. The reason I've been shooting full auto is I also have the coach on a wireless mic with the another one for ambient sound and the full auto is the only way I can control spikes in the sound.
Do you like Zebras? Not the African kind, the other ones. I find them useful.
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Old October 13th, 2007, 01:06 PM   #15
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Quote:
Originally Posted by Scott Harper View Post
The reason I've been shooting full auto is I also have the coach on a wireless mic with the another one for ambient sound and the full auto is the only way I can control spikes in the sound.
Can you not set the audio on auto by itself - while the rest of the cam functions are still on manual with the HD100? Because I know you can on the 200. Worth a check.
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