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Old February 8th, 2008, 01:20 PM   #1
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Extreme is dark on left side

Hey, quick question. I'm using an XH-A1 with my newly acquired Extreme. Looks great, except I have to zoom the camera's lens in more than I'd thought to avoid a dark vignetting on the left side. I do have the ground glass centered, but the left side seems darker. Panning really reveals this, as objects leaving the left edge become brighter, and objects entering the left edge dim.

I have to zoom the camera's lens in until it cannot step above 2.8. This seems like I'm losing quite a bit of my FOV with a 28mm prime attached to the adapter, but again, I might just be uneducated. Does anyone have a comment on this?

And just to add, I am experiencing this with my 50mm lens as well. Haven't looked in depth at my 135mm yet...

UPDATE: It seems it isn't as bad with the 50mm, now that I look at it again. I can pull the camera lens out till it steps up to 2.6 without having too much of an issue. So, do different lenses exaggerate vignetting? Again, forgive me for being uneducated about this.
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Last edited by Brandon Freeman; February 8th, 2008 at 02:13 PM.
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Old February 8th, 2008, 03:04 PM   #2
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How have you got your LEX mounted... on rods? If so, you'll need to adjust how everything is sitting.
Also, the three allen key screws that you tighten need to be done it such a fashion that it doesn't pull the alignment off to one side (I've noticed that on my XHA1).
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Old February 8th, 2008, 03:20 PM   #3
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Yeah, I have the Letus rods. It's a lot more challenging to align it than I thought. But I have noticed that the wider the lens, the more difficult it is to eliminate the problem.
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Old February 9th, 2008, 09:54 AM   #4
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Is the Canon XH-A1 any relation to the HV20 camera? I seem to vaguely recall a Brevis post which suggest the camcorder imager centre is offset and causes a problem like this.

Your 28mm lens. What is the maximum aperture available?

You may have to accept zooming in closer to a smaller area of the groundglass. You may be picking up an edge of the flip path. Brighter lenses have the effect of making this less apparent.

Another issue may be if the camcorder filter thread has been crossed, you may have camera and adaptor optical centerlines which are at a slight angle not dead straight. Even if otherwise correctly centered, this may bring in an edge into the image. Is the Letus35 hard-mounted to the camcorder filter thread?

Last edited by Bob Hart; February 9th, 2008 at 10:01 AM. Reason: error
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Old February 9th, 2008, 12:09 PM   #5
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The maximum aperture on the 28mm is 2.8.

I'm not sure what hard-mounted means. I have the Letus screwed on using the filter screw. Again, I'm using rod-support, but I have found that the Letus is not entirely straight, as I had earlier thought, even utilizing the rods. Trying to figure out how to get it aligned right...

"You may be picking up an edge of the flip path. Brighter lenses have the effect of making this less apparent."

This makes sense, then, that my 50mm f1.8 has less of an issue with the left edge (though I do still have to zoom in a bit more than I'd like).
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Old February 10th, 2008, 07:02 AM   #6
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Brandon.

There is a sort of double post going on for this topic. I have address your enquiry on your other thread.

This clip probalby replicates your dark edge problem. A restricted flip path and slight offset of axes is the cause of this problem on my home-made adaptor.

http://www.youtube.com/watch?v=4gnLzWVxdnI

Last edited by Bob Hart; February 10th, 2008 at 07:05 AM. Reason: added URL
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