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focus issue with DVX100B
We shot a ballet performance in a theater over the weekend – the DVX100B was at the back of the auditorium pretty much straight on… anyway looking over the captured footage (using FCP 4.5) I’m seeing a strange issue. In scenes where the stage lighting was low (e.g., blue overhead stage lighting) the subjects on the left side of the frame appear less focused than the subjects on the right side. In more brightly lit scenes this effect isn’t noticable. It’s not depth of field since the subjects are all at the same distance (the left side isn’t closer or further away). The camera is fairly new (less than 20 hours) and has never even been bumped.
Does this sound like anything anyone has seen or heard of before? Thanks. -
14 Replies
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DV pukes under solid blue and solid red. You’re experiencing the effects of low chroma sampling (4:1:1 on US versions, 4:2:0 on PAL versions). When something is solid blue or solid red, your effective resolution drops from 720×480 down to 180×480, which makes everything look blurry.
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Thanks Barry – I’m still wondering why the left edge of the frame and not the right?
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Can you post a grab?
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I’m at work now – will have to save a sample at home this evening … advice on the best way to do this? a single frame? how is it uploaded / posted? Thanks again.
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Hi again – I used a web acct at work to display 3 freeze frames saved as jpgs… they can be seen at:
http://www.ithaca.edu/staff/estabroo
Thanks for your input on this.
Fred -
Those are pretty small so it’s hard to tell. Does it just look like the left 1/3 is soft all the time? Is there something optically wrong with the camera? What about a regular shot in broad daylight — is the left 1/3 still soft?
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Barry – My camera person and I have been looking at the original footage on a good monitor and doing some testing of the dvx100b today and have determined that the focus problem (again, always on the left side of the frame) is most evident when the aperture is wide open (very low light conditions w/various colors, not just red or blue)- problem is non-existent or hardly visible at f2.8 or higher (no db gain). Theories? Thanks! F.E.
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I’d still want to see a full-rez frame grab before speculating.
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Barry – I put up a larger sample this morning – but based on our careful testing on saturday, could it really be anything but a technical problem with the camera? as I mentioned in earlier posts, it’s definitely happening only on the left (1/3?) half of the frame and definitely only when the aperture is wide open… (we isolated a sequence where the scene started out lit very dim and gradually brightened – the camera operator manually closed the iris to compensate and as soon as the iris changed from wide open the focus problem went away) what does this specific info suggest to you? Thanks again, F.E.
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Assuming they’re all in a line (same distance from the camera), then it seems like it should be a repair issue.
At wide open the depth of field is at its shallowest, so if those people on the left were notably closer to the lens than those on the right, that would make sense as to why they were out of focus, and why stopping down the lens would bring them back into focus.
But it doesn’t look like that was the case, was it? Looks like they were all equally distant from the lens, in the same basic focal plane, and for some bizarre reason the left side is out of focus… which I’ve never seen before, and can’t imagine how that would be occurring unless one of the lens elements was actually misaligned or something. Which is why I think that yes, it’s probably due for a trip to the service department…
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Get the most from your DVX camera. The DVX Book and DVX DVD are now available on ebay and at Amazon (https://www.fiftv.com/db)
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