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How to do a proper scratch test.


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#1 James Steven Beverly

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Posted 14 March 2006 - 12:54 AM

I'm new to 35mm and would like advice and techniques as well as what to look for when doing a scratch test. Thanks
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#2 Stephen Williams

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Posted 14 March 2006 - 03:48 AM

I'm new to 35mm and would like advice and techniques as well as what to look for when doing a scratch test. Thanks


Hi,

Run 20 feet of film through each magazine at the speeds you are going to shoot at. Then look at the film with a bright light at 45 degrees to the film. Check both sides of the film, you are looking for any evidence that the film has been run! Any marks outside the pefs need to be investigated.

Stephen
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#3 Daniel Stigler

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Posted 14 March 2006 - 05:52 AM

Do as Stephen told. And make shure those 20 feet of film used for each mag never ran through a camera before. After you tested the magazine throw the piece of film used away.
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#4 Laurent Andrieux

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Posted 14 March 2006 - 07:05 AM

Use a Maglite as to enough enlight the film when you examine it. Especially look by the perfs, so there is no problem with the pins hitting them.

When you get some processed film back from the lab, (your registration tests or lens calibration tests..) examine the film prior to any other manipulation. If you notice some fogging level by the perfs, may also reveal a problem with the pin hitting the perf, even though you didn't notice any scratch at the first place. (some scratches are so thin you might not see them at the first sight).

I recently had this problem with a BL 3
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#5 Dan Goulder

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Posted 14 March 2006 - 11:40 AM

Use a Maglite as to enough enlight the film when you examine it. Especially look by the perfs, so there is no problem with the pins hitting them.

When you get some processed film back from the lab, (your registration tests or lens calibration tests..) examine the film prior to any other manipulation. If you notice some fogging level by the perfs, may also reveal a problem with the pin hitting the perf, even though you didn't notice any scratch at the first place. (some scratches are so thin you might not see them at the first sight).

I recently had this problem with a BL 3

Did you locate the source of the scratches? Was it a mag, or within the camera itself?
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#6 John Pytlak RIP

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Posted 14 March 2006 - 11:58 AM

The best light to use for evaluating surface scratches is a very intense SPECULAR light source. Direct sunlight coming in a window is good, as is the focused light from a projector. In the field, a very bright focused flashlight/torch is good.
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#7 Laurent Andrieux

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Posted 14 March 2006 - 01:34 PM

Did you locate the source of the scratches? Was it a mag, or within the camera itself?


Yes it was the registration pin that hit the perf edge, causing a very thin scratch as well as fogging the film, like a static fogging, looking like a half circle around it. But it was far from the frame so I didn't bother that much. The reason was it's an old camera.
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#8 James Steven Beverly

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Posted 14 March 2006 - 08:50 PM

Great stuff guys, Now if I encounter any of these problems does this mean the camera and mag should be sent to a quailified repair shop immediately or are there some problems I can take care of myself? Another question I had was reguarding the mag's pressure plate. I have 3- 200 ft mags, the pressure plates seem to have a little different resistance on each mag. How much pressure should the plate exert and is that something I should have a tech do or can I judge that myself and adjust it accordingly. Also are 3-200 ft mags suffecient for second unit work or do I need to be looking at picking up a couple of 400 footers? This camera is a Konvas 1m w/ a reostate motor and lomo and jupiter lenses by the way if that makes a difference. Thanks.

Edited by Capt.Video, 14 March 2006 - 08:50 PM.

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#9 Laurent Andrieux

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Posted 14 March 2006 - 10:46 PM

Do your tests first and according to the eventual problems you might encounter, one will tell what you can do.

I suggest that you don't touch and test the pressure plates by hand.I don't think that the fact you feel one is different from another is significant, before you test them.

BTW, a default in the mag pressure plate would cause focus breathing, not a scratch nor fixity problem.

If you do lens calibration tests, read ach image as to evaluate any focus breathing, or esp. look at this when you see a projected (positive or negative) image.
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