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S-t-r-e-t-c-h-e-d Image.


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#1 22west

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Posted 09 January 2006 - 04:30 PM

I have a problem with some footage that I now believe is process related - so I have jumped to this forum.

I recently shot a 100 ft roll of 16 mm film and had it processed - I asked for a transfer to DV and for them to return the developed negative.

Both the images on the negative reel and the transfer are slightly stretched - very slight - but noticable.

To check my lens, I looked through my view finder at an image of a circle on the wall to see if it was elliptical but it was not. As this camera is a reflex camera, I confirmed that the image created by the lens was ok (ie; the lens was not slightly cylindrical).

Is it possible that the film was shomehow shrunk slightly in length during processing?
Like I sent them 100 ft and they returned 99 ft (with much exaggeration).
This would result in my situation - a negative roll with slightly "squished" frames and a transfer of the same.
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#2 John Pytlak RIP

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Posted 09 January 2006 - 04:40 PM

Although triacetate film normally shinks about 0.1% during processing, this normal shrinkage is uniform and would not cause the kind of geometric distortion you describe. Excessive tension during processing could stretch the film slightly or damage the perfs, but it would be most apparent as unsteadiness.

The most likely cause is some geometric distortion in your display. Are you using a CRT display where misadjustment is possible? Depending on the telecine, some geometric distortion might also occur during transfer.
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#3 22west

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Posted 09 January 2006 - 05:17 PM

Although triacetate film normally shinks about 0.1% during processing, this normal shrinkage is uniform and would not cause the kind of geometric distortion you describe. Excessive tension during processing could stretch the film slightly or damage the perfs, but it would be most apparent as unsteadiness.

The most likely cause is some geometric distortion in your display. Are you using a CRT display where misadjustment is possible? Depending on the telecine, some geometric distortion might also occur during transfer.


I thought the same untill I projected the developed roll on the wall - this was also stretched.
I believe this returned roll is the one that was actually exposed in the camera.
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#4 John Pytlak RIP

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Posted 09 January 2006 - 05:22 PM

I thought the same untill I projected the developed roll on the wall - this was also stretched.
I believe this returned roll is the one that was actually exposed in the camera.


Keystone distortion during projection if the projector is at a slight angle to the screen?
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#5 Dominic Case

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Posted 09 January 2006 - 06:40 PM

Is it possible that the film was shomehow shrunk slightly in length during processing?

As John says, not enough to distort the image visbly without other far more serious effects.

You could verify whether the film is stretched by comparing a foot or two of the processed negative with the same length of raw negative stock. Hold the lengths of film together, with perfs lining up exactly at one end.

For one per cent shrinkage (100ft returned to you as 99ft), the processed film will be one complete frame shorter in 100 - that is, 2 1/2 feet.
(if you find that, then you should ask the lab for a 1% refund :lol: )

THe 0.1% shrinkage that John refers to will give you a difference of about half the height of the perforation itself.

Are you sure that you are seeing the same distortion in the projected film image as you are in the DVD? And do I understand that you are projecting the original negative?
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#6 Dominic Case

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Posted 09 January 2006 - 08:16 PM

The transfer clip you posted is a 720x480 image (1.5:1). It's certainly wide. If you redimension it to 640x480 (1.33:1) or even 600x480 (1.25:1) it looks about right. So the image is somewhere between 12% and 20% too wide.

That amount of distortion is not caused by the film itself being stretched or shrunk. Trust me on this!

Impossible to tell much from the negative image you posted. That has a massive keystone distortion itself, which makes the comparison meaningless.
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#7 Phil Rhodes

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Posted 09 January 2006 - 08:49 PM

Hi,

Are you sure you aren't just seeing pixel aspects here?

The image is 720x408 but it is not 1.5:1; it's a D1 NTSC frame, representing a 4:3 image with nonsquare pixels. It is being displayed incorrectly by the web browsers we're all using to look at it.

Download it, resize to 640x480 for a square pixel display, or load it into Photoshop with NTSC pixel aspect ratio selected, and all is well.

I don't see a problem. This is normal.

Phil
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#8 22west

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Posted 09 January 2006 - 11:46 PM

Hi,

Are you sure you aren't just seeing pixel aspects here?

The image is 720x408 but it is not 1.5:1; it's a D1 NTSC frame, representing a 4:3 image with nonsquare pixels. It is being displayed incorrectly by the web browsers we're all using to look at it.

Download it, resize to 640x480 for a square pixel display, or load it into Photoshop with NTSC pixel aspect ratio selected, and all is well.

I don't see a problem. This is normal.

Phil


Thanks very much gents.
Very useful info - I will continue my research.
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