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Magenta Top Green Bottom Error: Using S16 Arri Zoom Lens on HDV


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#1 kalkarman

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Posted 13 November 2007 - 06:19 PM

I recently used an Arri/Zeiss Super16MM Zoom lens on my JVCHD200 with PL mount adaptor and the strangest thing happened:

From the center of the image, i get a magenta gradient going up and a green gradient going down (on the image, camera is fixed... various light situations etc..)

This does not happen when I use Primes.

Anyone have any clue how/why this would happen?

Also, I notice that on any cine lens used with this adaptor, that I get vignetting when closing past f 4.0. Reason why?

Curious,

Kal
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#2 Stephen Williams

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Posted 14 November 2007 - 02:28 AM

I recently used an Arri/Zeiss Super16MM Zoom lens on my JVCHD200 with PL mount adaptor and the strangest thing happened:

From the center of the image, i get a magenta gradient going up and a green gradient going down (on the image, camera is fixed... various light situations etc..)

This does not happen when I use Primes.

Anyone have any clue how/why this would happen?

Also, I notice that on any cine lens used with this adaptor, that I get vignetting when closing past f 4.0. Reason why?

Curious,

Kal



Hi,

You need to look for 'shading' adjustments in the menu. I don't know if you will find them in that camera as I have never used one.

What were the 'cine' lenses.

Stephen
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#3 Michael Nash

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Posted 14 November 2007 - 03:32 AM

I recently used an Arri/Zeiss Super16MM Zoom lens on my JVCHD200 with PL mount adaptor and the strangest thing happened:

From the center of the image, i get a magenta gradient going up and a green gradient going down (on the image, camera is fixed... various light situations etc..)

This does not happen when I use Primes.


Yes, this is what "white shading" is for. It's in the manual.

Lens shading or white shading should ideally be done for EACH lens a video camera uses; it just so happens to be most visible with the zoom you were using.
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#4 kalkarman

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Posted 07 April 2008 - 08:35 AM

Yes, this is what "white shading" is for. It's in the manual.

Lens shading or white shading should ideally be done for EACH lens a video camera uses; it juts so happens to be most visible with the zoom you were using.




I use the JVC HD200 with the PL adaptor, and I find extreme white shading problems when using any zoom, (16mm or 35mm). And while I follow the instructions perfectly on adjusting the white shading parameters in the advanced white balance menu, I am unable to find a setting that can work at any F stop.... In other words: yes the problem can be corrected, but as soon as you change the F stop, the problem is back.

The problem is much less noticeable with prime lenses.

I am forced to work using my set of ND's, to keep the aperature always wide open.


Am I missing something?
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#5 Michael Nash

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Posted 07 April 2008 - 11:26 PM

Am I missing something?


Probably not. I'm guessing you just can't expect optical perfection from such a relay lens system + zoom. Try a different zoom, maybe?
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#6 kalkarman

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Posted 08 April 2008 - 02:04 AM

Probably not. I'm guessing you just can't expect optical perfection from such a relay lens system + zoom. Try a different zoom, maybe?



Thanks Michael,

I also tried an enormous 35mm zoom, just to check the problem. Same thing.


So I guess our friends at JVC didn't get it all right this time.

:(
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#7 Sam Wells

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Posted 08 April 2008 - 10:21 AM

If the zooms are that inherently non-telecentric shading is a vain effort I'm afraid.

-Sam
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#8 kalkarman

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Posted 08 April 2008 - 11:52 AM

If the zooms are that inherently non-telecentric shading is a vain effort I'm afraid.

-Sam



Hey Sam, well I read on wikipedia what Telecentric means, and I'm afraid my smarts won't do me any good.


In simple terms: Does that mean that ANY zoom won't work, or must I look for a specific kind of zoom
with "telecentric" properties?


Thanks,

Kal
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#9 Phil Rhodes

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Posted 08 April 2008 - 11:59 AM

This always happens to some extent. I always understood it was to do with parallel collimation of light entering the splitter block, which might explain why it's worse on a film lens.

With any zoom, it can only really be "right" at one point in the zoom. The cheaper the zoom the worse it will be.

P
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#10 Walter Graff

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Posted 08 April 2008 - 12:19 PM

Are you using a scope with RGB cascade, shooting a white card at f4 and making your red and blue targets as small as possible using the white shading menu in manual and adjusting each control? If not, then you are not doing it right.
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#11 Phil Rhodes

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Posted 08 April 2008 - 01:10 PM

On my camera, it's automatic (though it has that effect).

Not sure how it would be visible when shooting a white field, though.
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#12 Walter Graff

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Posted 08 April 2008 - 01:13 PM

On my camera, it's automatic (though it has that effect).

Not sure how it would be visible when shooting a white field, though.


It would not be visable on a white surface, but using that white card is about the simplest way of adjusting it manually with RGB cascade on a scope shooting a white card at around f4. Takes about seven seconds ot make perfect white shading.
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#13 Sam Wells

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Posted 08 April 2008 - 02:03 PM

I've seen it on other relay lenses use with 3 chip (and 3 tube) cameras and could not be fixed by shading adjustment but typically at the edges - so I'll concede I may have spoken too soon & it can be fixed but with the error changing with stop on a zoom I'm not so sure the fix would hold........

-Sam
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#14 kalkarman

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Posted 09 April 2008 - 01:58 AM

Are you using a scope with RGB cascade, shooting a white card at f4 and making your red and blue targets as small as possible using the white shading menu in manual and adjusting each control? If not, then you are not doing it right.



Hey Walter... yeah I played with it for an hour in a camera rental house, using a very expensive Arri Zoom 10-110 if I recall. I followed the instructions in the JVC manual to a T. Putting it at f4, and with the lens at half it's zoom, so about 50mm. I dialed in g50 in white shading, and the effect went away. I was shooting a white card and viewing a HD monitor. Then, after inital happiness, I moved the Fstop to make sure, and the effect comes back in a big way.


My only solution is to always shoot wide open and use my ND's instead...

I'm doing that, but I wish my very expensive PL adapter by JVC would work at all Fstops.

:(
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#15 Walter Graff

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Posted 09 April 2008 - 06:26 AM

If you are closed down past f4 you are not making an HD picture anyway since 75% of MTF in these cameras is reached at wide open. So you are doing the right thing by trying to keep the lens at wide open. In all of these 1/3 inch cameras you want to always keep your lens wide open. There is always a trade off when using various lenses that were not designed for the camera you are using. Many times its optics. Just because they make lens does not mean it is going to be the best match for a particular camera chain. Video lenses have various coatings that film lenses do not that help to correct for various abberations. Some of the best film designed lenses are bad combinations for video since they were not designed to work in a flat 3 chip plane.
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#16 kalkarman

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Posted 09 April 2008 - 07:57 AM

If you are closed down past f4 you are not making an HD picture anyway since 75% of MTF in these cameras is reached at wide open.



Thanks Walter, I feel better knowing that shooting wide open is the way to go anyways. Quick question: What does MTF stand for?

Thanks

K
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#17 Walter Graff

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Posted 09 April 2008 - 08:08 AM

Thanks Walter, I feel better knowing that shooting wide open is the way to go anyways. Quick question: What does MTF stand for?

Thanks

K


Yes, with any 1/3 inch camera you want ot be as close to wide open whenever shooting to get the most out of the lens/CCD chain. MTF is a term that describes how well and how clear a camera sees differnces in contrast. Just as an experiment, take your camera outside and shoot at f8 with no filters. Then add ND etc and get the lens as wide as possible and shoot the same shot. Now go inside and look at the footage and you will see what I mean. The stuff shot at f8 will look soft and ugly. While the wide open much more pleasing. It doesn't take much light for a 1/3 inch target to get what it needs and too much makes for ugly pictures. The general rule with a 1/3 inch camera is that if you are shooting near or above 5.6 you are not really making an HD picture. Physical laws of light make sure of that.
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#18 Hal Smith

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Posted 09 April 2008 - 10:03 AM

Hi Walter,

Are all of these shading problems hiding a telecentricity issue? Is all this related to what happens if the lens doesn't "match up" to the color separation optics inside the camera?
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#19 Sam Wells

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Posted 09 April 2008 - 12:53 PM

What you sometimes get in these cases (with non-telecentricity) are off-axis rays traveling through the dichroic filters at too steep an angle.

-Sam
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