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Color Shift in snap zoom on F900


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#1 Nathan D. Lee

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Posted 04 February 2008 - 12:02 PM

Saturday I was shooting a few camera tests for a short I am shooting starting this weekend. We are using a F900 with a Canon HD 4.5mm to 55mm zoom.
I mostly have shot film before and have been working hard to understand the depths of the various menus and options on this camera.

Right at the end of the day I was zoomed in extremely close on our actress and did a quick snap back to wide. In the zoom her skin tone went green! I could hardly believe it, so I did it a few more times with the same results. Thinking it might have been a issue with my HD monitor (Panasonic 1080p) I recorded it to play back. Sure enough it was recorded, a green face!
(Note: We were only using tungsten lighting)
After this I was frightened and tried to repeat this occurrence but it did not do it as badly the second time.
Thinking it might be some automatic function I did not know about on the camera I tried whip panning in and out of light to see if it would do anything weird. Nothing happened.

Later today I will capture the footage and look at it closely on a Waveform and Vectorscope. I will try to upload a QT file of the zoom. But until then what could the issue be?

Note: There are not going to be any snap zooms or anything close on this film, but I still need to know why it happened so I don't miss it if it happens any other time, since i will be operating with the B&W viewfinder.
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#2 Nathan D. Lee

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Posted 04 February 2008 - 11:02 PM

Okay, so I have captured the footage and it does not nearly look as bad on proper monitors as it did when we shot it. but there is definitely a shift of some kind.

Here is a link to a small sample. Sorry i did not hold the shot longer i need to shoot another test ASAP.

http://www.fridayfea...om/adeltest.mov

I slowed the shot down to 25%, note the color of her skin tone right after the initial zoom in. It gains color zoomed in and looses it zoomed out.

according to the waveform monitor the red channel raises about 8% after the snap in. Its almost like some electronics are adjusting but I don't know what.

Please help!

NOTE: I forgot to render fast start, its an 8meg file, give it a sec it will load.
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#3 David Mullen ASC

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Posted 04 February 2008 - 11:56 PM

I haven't had this problem, but there are some things to check out.

Auto white balance, which I don't think the F900 can do, would create such an effect -- you fill the frame with a pink face and the camera would add some green to compensate. But as I said, I don't think the F900 has an auto white balance feature.

It could be some sort of DCC (Auto Knee) artifact, perhaps in conjunction with the REC 709 color space -- try turning one or both off and see if it happens again. I've had some chroma clipping problems and weird solarizing of strong colors like purple neon due to the REC 709 Color Matrix setting, perhaps interacting with the knee.
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#4 John Brawley

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Posted 05 February 2008 - 01:08 AM

Right at the end of the day I was zoomed in extremely close on our actress and did a quick snap back to wide. In the zoom her skin tone went green! I could hardly believe it, so I did it a few more times with the same results.



It might have been a slight change due to the ramping of exposure during the zoom. Saturation increases as you snap in. Then washes out and de-saturates a little in the highlight area on her cheek.

Might also be the actual lens shading ? (i mean electronic, not cutting the lens)

jb
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#5 Serge Teulon

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Posted 05 February 2008 - 06:38 AM

Good old digital...your RGB changes can be seen on vectorscope.
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#6 Serge Teulon

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Posted 05 February 2008 - 06:43 AM

pressed 'post' before I completed my reply.......

That has also never happened to me. It could be that the camera needs some maintenance or the lens is buggered.
I've seen some shocking examples of mistreatment of equipment in some rental houses.
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#7 Jeffrey Cirbes

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Posted 08 February 2008 - 10:02 AM

try turning off the "flare comp" in the paint menu
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#8 Etienne van Leeuwen

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Posted 08 February 2008 - 10:08 AM

Right at the end of the day I was zoomed in extremely close on our actress and did a quick snap back to wide. In the zoom her skin tone went green! I could hardly believe it, so I did it a few more times with the same results.


Could this be a lens flare problem??
This is a setting-page wich I think should only be touched by technicians. Very dangerous!

Was the set checked before YOU started the project?



Could you please keep us informed about this?

Good Luck,
Etienne.
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#9 Jeffrey Cirbes

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Posted 08 February 2008 - 11:44 AM

Could this be a lens flare problem??


Look at the shot he's talking about...
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#10 Etienne van Leeuwen

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Posted 08 February 2008 - 12:43 PM

Look at the shot he's talking about...


Hi Jeffrey,
we read the topic at the same time, but you write faster. After I pressed "add reply" I saw your message......
I allready thought it was a little strange because of the zoom, but having no real experience with this problem I could only think in this direction.
I'm sorry
;)

Etienne.
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#11 Jonathan Bowerbank

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Posted 08 February 2008 - 12:44 PM

Look at the shot he's talking about...


Ha ha! Yeah, notice he posted the footage a few posts above.

It did look like an Auto Knee correction. You can see when you zoom in that the contrast in her face lowers a bit, so the lighter side of her face becomes just a little darker to hold the detail. Just turn it off and go through the image menus to make sure all "auto" settings are turned off, perhaps that'll correct it.
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#12 Nathan D. Lee

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Posted 11 February 2008 - 12:20 PM

Thanks for all the help. In the next day or so i will post more test.

Nathan
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#13 Mark Henderson

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Posted 15 February 2008 - 03:17 AM

Chromatic aberration of the lens during the snap.

Mark
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