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Proper Focusing of lens for Video


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#1 Drew Fortier

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Posted 22 August 2005 - 05:11 PM

Don't know if this is the write foum for this, but I am shooting some stop-motion, on video. And i am having trouble properly focusing the lens'. I seem to be getting some vinyeting on the very edges of the frame.

THe camera's are JVC KY-F1030's and they are mounted with Fujinon Lens' (a threaded mount).

Anyways, the cameras have a back focus, and so do the lens'. I can properly focus using an Accu-chart. and once i do that I can zoom in and out, and not loose focus. But as soon as I go wide (7.5mm to 14mm), I totally use focus on the edge of my frame. I am shooting at 5.6 to 8 so I would think that should give ample enough depth of field.

anyways.. I am just wondering if anyone has any sugestions or tips for me to try and fix this, or to prove that these lens' are in fact crap...

thanks in advance
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#2 Drew Fortier

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Posted 26 August 2005 - 07:01 AM

well I guess no one has sny sugestions for me.. maybe someone can recomend a better forum to post this question? Or does the question not make sence.....


any help would be greatly apprecieated!
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#3 Tim J Durham

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Posted 26 August 2005 - 09:44 AM

Don't know if this is the write foum for this, but I am shooting some stop-motion, on video. And i am having trouble properly focusing the lens'.  I seem to be getting some vinyeting on the very edges of the frame.

THe camera's are JVC KY-F1030's and they are mounted with Fujinon Lens' (a threaded mount).

Anyways, the cameras have a back focus, and so do the lens'.  I can properly focus using an Accu-chart.  and once i do that I can zoom in and out, and not loose focus.  But as soon as I go wide (7.5mm to 14mm), I totally use focus on the edge of my frame.  I am shooting at 5.6 to 8 so I would think that should give ample enough depth of field.

anyways.. I am just wondering if anyone has any sugestions or tips for me to try and fix this, or to prove that these lens' are in fact crap...

thanks in advance

<{POST_SNAPBACK}>

I've never heard of a screw-mount video lens but the edge abberations sound like the result of it being a cheap lens. I would take it up with tech support at Fuji if you can get them on the phone and see what they have to say. In the meantime, try to set-up your shot so that you are not shooting that wide. Either that or use the edge focus problem to your advantage OR get a different camera/lens.
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#4 Tim Tyler

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Posted 26 August 2005 - 10:14 AM

Anyways, the cameras have a back focus, and so do the lens'.  I can properly focus using an Accu-chart. 


I think you need to adjust the backfocus.

Zoom the lens out to its WIDEST focal length.
Open the aperture to its WIDEST stop, like f1.8 or f2.
Adjust the lens focus ring to its INFINITY mark, but not past infinity.
Adjust the back focus so that the image of a distant object is as sharp as possible.
Your lens should now retain focus throughout the zoom range at any f-stop.
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#5 Tim J Durham

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Posted 26 August 2005 - 10:51 AM

I think you need to adjust the backfocus.

Zoom the lens out to its WIDEST focal length.
Open the aperture to its WIDEST stop, like f1.8 or f2.
Adjust the lens focus ring to its INFINITY mark, but not past infinity.
Adjust the back focus so that the image of a distant object is as sharp as possible.
Your lens should now retain focus throughout the zoom range at any f-stop.

<{POST_SNAPBACK}>

It sounded like he was saying that it was sharp in the center but soft around the edges. That didn't sound like back-focus to me.
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#6 Tim Tyler

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Posted 26 August 2005 - 08:09 PM

That didn't sound like back-focus to me.

Oh, yeah - you're right :huh:

The 1030 has a 1/2" CCD. Perhaps you're using a lens designed for smaller CCD's?
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