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Kalle Folke

Arri Sr2 "moving gate" problem

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Hi!

I'm happy owner of a used Arri Sr2. I come from the "video world" and shooting film has been a life long dream to me. I'm very great full for this forum and have had a lot of help from it.

After doing my first tests I have a million questions… It would be a bit too overwhelming to write everything now, so I'll start with my main concern.

 

See this:

https://vimeo.com/90344273

 

I've uploaded a test on Vimeo, I'm not sure what the english word is (in Swedish I think it's bildstilleståndstest- a unique word with no match on google, haha). In the video you'll see that the whole gate is moving a bit, but the lines that are double exposed seems to move consistently. From what I've understood this should mean that the camera produces a stable image. Why then is the whole frame moving? Is this a problem with scanning?

 

On my Vimeo: http://vimeo.com/folkefolke I've also uploaded more from my first test with Kodak 7219. Any feedback would be appreciated, and I'm sure I'll keep the post's with questions coming...

 

Hope I managed to make sense even if I'm lacking the technical terms in english.

 

Thank you/Kalle

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I think you might be talking about "Gate Weave" but I don't see much evidence of this. Your footage looks mostly stable.

You can see the perfs on the left hand side and they move very little.

 

I'm thus not sure what you mean.

 

Freya

Edited by Freya Black

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I think you might be talking about "Gate Weave" but I don't see much evidence of this. Your footage looks mostly stable.

You can see the perfs on the left hand side and they move very little.

 

I'm thus not sure what you mean.

 

Freya

 

Thanks for your reply. What is "Gate Weave"?

 

Even if the perfs look stable the whole frame is moving. You also see it clearly in this video after 03.25: https://vimeo.com/89728141

That test shot is on a locked off tripod but the frame is still moving. I mostly shot my test handheld and then it's not as noticeable.

The first picture steadiness test is shoot on an expired Kodak 7207 250D and everything else on a fresh Kodak 7219 500T, so it shouldn't be a problem caused by the film.

 

Looking forward to hear any thoughts.

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Hi again,

Did some quick research on gate weave and could it be that this is a general problem with all Sr's before the Sr3 Advanced with it's improved gate?

If this is considered "normal" I guess I'll have to shoot hand held all the time...

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Hi Kalle,

congratulations on your new camera.

 

The technical term in English would be "steady test" or "registration test". Your camera looks to be rock solid. You only need to look for movement between the 2 grids, and your test shows none at all. Any movement of the whole picture is due to something external to your camera, like the transfer.

 

SR1s and 2s don't really have a problem with gate weave normally, they just have fixed side rails in the gate which after a lot of film has passed through can wear a groove that allows some lateral movement. Once detected it's easily fixed with new rails or another gate. The SR3 Advanced gate uses saphire spring-guides which never wear.

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I agree with Dom on the lateral movement part. The "registration" is nearly perfect. But the film does seem to weave back and forth just a hair.

 

The reason the double exposure test footage looks solid may be that the perfs are not perfectly solid on the film itself thus causing the film to move just a hair and the slightly warn gate allowing for that lateral movement. I have seen lateral movement caused by lateral movement in the perforations before. The pitch can be perfectly registered on the film (so no vertical movement or variation in space between frames), but the location of the perforations relative to the edge of the film may be weaving slightly and the not particularly tight gate allowing for it.

 

That's my take anyhow.

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Thank you both for you input, makes total sense. I can't really see any groove on the rails/gate, but I guess it could still be worn. I don't know any detailed history about the camera except that it's been used by a German tv-network. So even if the Super16 gate can't be very old there's probably been a good amount of film passing the gate.

 

My guess is that changing to a unused gate (a Sr3 Advanced gate would be best maybe?) would be more expensive than what I payed for the camera (1800€ for complete kit). Is this correct, or do you know about any good places to look, preferably in Europe? I'd love to find a service tech in Sweden...

 

A lot of things to learn, but also very exiting. Thanks again!

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The reason the double exposure test footage looks solid may be that the perfs are not perfectly solid on the film itself thus causing the film to move just a hair and the slightly warn gate allowing for that lateral movement..

 

Hi David,

the gate isn't worn, the camera registration is good. The important thing is that the grids are locked together, which means that on separate passes the image is not moving. If there was any play in the registration the two grids would be moving independently, quite obvious when you see it.

 

Lateral registration in SRs (or any 16mm camera or projector really) is controlled by the film edge not the perfs, the registration pin only secures the vertical position, it doesn't fill the perf width. Slight variations in the lateral position of a particular stock's perforations won't affect a camera's registration, but it could affect the steadiness of a scan if only the perf is used as an anchor.

 

I'm not really up with developments in scanning software, but aren't there pretty good stabilisation programs these days anyway?

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There are very good stabilization functions even just built into Adobe after effects and apple motion.

 

But, in the case of this footage, the perfs appear to stay rock solid but the frame sways side to side. That tells me the film is swaying back and forth in the gate. Ya probably happening evenly and equally in each pass because the gate is edge guided.

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You can definitely try another transfer to confirm. But, if you review the footage, you can see that the perfs stay perfectly registered and the frame moves laterally. It does so perfectly for both exposures. So, it sounds to me like the edges of the film itself were non-uniform and following the edges of the gate.

 

This is a natural and expected result of "edge guided" lateral centering. There's nothing much that can be done about it.

 

If you shoot in a locked position on a tripod, and the movement is noticeable, you will be able to "fix" it with motion stability software. You likely will not get a different result with a different camera.

 

This scan was probably done using a perforation only centering mechanism (in a computer). You would likely not see this problem as badly on an edge-guided setup such as a Spirit.

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I'd try getting your film transfered at another facility to check if it's the transfer,

 

Well, problem is it's the only lab in Scandinavia still running so not sure where to send it… Also now when it's more of a personal development project I can't spend too much money on it. But will keep it in mind if I can't live with the issue.

 

You can definitely try another transfer to confirm. But, if you review the footage, you can see that the perfs stay perfectly registered and the frame moves laterally. It does so perfectly for both exposures. So, it sounds to me like the edges of the film itself were non-uniform and following the edges of the gate.

 

This is a natural and expected result of "edge guided" lateral centering. There's nothing much that can be done about it.

 

If you shoot in a locked position on a tripod, and the movement is noticeable, you will be able to "fix" it with motion stability software. You likely will not get a different result with a different camera.

 

This scan was probably done using a perforation only centering mechanism (in a computer). You would likely not see this problem as badly on an edge-guided setup such as a Spirit.

 

So just to make sure I understand correctly: This would still be an issue even if I change the gate/camera? I think the lab has a Scanity (can double check this…).

 

Thanks for all your help, it's a lot to take in and I appreciate that you're all so generous with your time and knowledge.

 

Will continue to do tests, but at the same time try to start getting some footage that useful for a personal project I'm planning to do. Let's hope I'll find a way to work around the "moving" or that it won't be a mayor issue in most footage.

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Well, problem is it's the only lab in Scandinavia still running so not sure where to send it…

 

Back to them, with the vimeo link - kindly ask them to join in the discussion.

 

Or ... much less fuss - be happy, the weave is so minimal that any post correction (if required) will leave next to zero artefacts.

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So just to make sure I understand correctly: This would still be an issue even if I change the gate/camera? I think the lab has a Scanity (can double check this…).

 

 

 

If the problem is that the edge of the film is "wavey", then correct... you would not be able to change this with any other camera or repair to this one.

 

However, I do not know enough about this camera to be sure of anything except that the film was definitely moving laterally back and forth in the camera. I can't be 100% sure why. But, again, I'm sure it's not the scan causing your problem. The perforations stay rock solid in the scan, but the frame still moves side to side. So, the frame actually moves side to side on the film for some reason and since it didn't break your test, clearly it's perfectly consistent lateral movement.

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Thanks for your reply. What is "Gate Weave"?

 

Even if the perfs look stable the whole frame is moving. You also see it clearly in this video after 03.25: https://vimeo.com/89728141

 

That looks much more severe and you can see the perfs moving a lot in that footage, even on the handheld stuff.

 

Freya

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That looks much more severe and you can see the perfs moving a lot in that footage, even on the handheld stuff.

 

Freya

 

The perfs do seem to move a bit on that footage as 3:25. However, the frame relative to those perfs is the majority of the movement. I think the channel the film runs through on this SR3's gate is just a bit too wide so the film is kinda swaying back and forth in it.

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I gather it's the SR3 model which had them fitted . Dom goes into some detail on the subject: http://www.cinematography.com/index.php?showtopic=621

 

From memory the registration pin on the SR isn't fully fitting as found on 35mm film cameras like the Mitchell.

 

That's a great thread! I think it pretty much answers the question about warn edge guides.

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I think it's worth noting this thread: and what Jeff Kreines says about SRs.

 

http://tig.colorist.org/wiki/Pin_Registration_for_Scanning

 

Thanks Brian, yes interesting stuff. I think this comment from Peter Swinson is also probably relevant:

 

"Many cameras do not use full fitting pins and rely on edge guidance. Pin scanning such film can provide worse weave than not pinning. In an ideal world there should be a scanner gate guidance system for every camera guidance system, to ensure that both camera and scanner guide the film at exactly the same points."

 

The first SR gate has fixed side rails that laterally guide the film at the top and bottom, one perf above and several perfs below the gate aperture, but at the gate aperture itself the film is not held. The film gap between the side guides is very accurately set, but as I understand it from talking to some industry veterans, if there is any weave in the film itself (due to age or storage or the tight coiling near the end of a roll) a scan or telecine that uses edge guiding at the gate, or perfs for lateral registration, will record that weave. A double exposure steady test will be solid though, because the actual camera registration is good, ie it can't be made any better. As Mr Swinson above mentioned, in an ideal world a scanner would replicate the camera's method of registration.

 

If there is wear to the gate side rails the lateral registration will be compromised, which shows up quite clearly on a double exposure steady test. Certain deformations of the film can create repeatable errors, but a loose gate will create random weaving that is impossible to exactly repeat on a separate pass.

 

I don't know why Arri chose to use fixed side rails on the SR after having a sprung side rail on the 16S and 16BL lines, I suspect it was to do with how the SR coaxial magazines mated, but certainly the SR3 Advanced gate design is less problematic. Back when SR2s and 3s were industry workhorses we (or the clients) used to steady test them before each big rental. Over the years some SR2s showed up laterally unsteady and we'd fit new rails and everything would be OK. It never seemed a huge issue but then we meticulously maintained the cameras. We always projected the steady tests and disregarded any overall jitter or movement, only watching for movement between the double exposures. This is how I was trained anyway, under technicians from Panavision and Arri.

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Thanks Brian, yes interesting stuff. I think this comment from Peter Swinson is also probably relevant:

 

"Many cameras do not use full fitting pins and rely on edge guidance. Pin scanning such film can provide worse weave than not pinning. In an ideal world there should be a scanner gate guidance system for every camera guidance system, to ensure that both camera and scanner guide the film at exactly the same points."

 

The first SR gate has fixed side rails that laterally guide the film at the top and bottom, one perf above and several perfs below the gate aperture, but at the gate aperture itself the film is not held. The film gap between the side guides is very accurately set, but as I understand it from talking to some industry veterans, if there is any weave in the film itself (due to age or storage or the tight coiling near the end of a roll) a scan or telecine that uses edge guiding at the gate, or perfs for lateral registration, will record that weave. A double exposure steady test will be solid though, because the actual camera registration is good, ie it can't be made any better. As Mr Swinson above mentioned, in an ideal world a scanner would replicate the camera's method of registration.

 

If there is wear to the gate side rails the lateral registration will be compromised, which shows up quite clearly on a double exposure steady test. Certain deformations of the film can create repeatable errors, but a loose gate will create random weaving that is impossible to exactly repeat on a separate pass.

 

I don't know why Arri chose to use fixed side rails on the SR after having a sprung side rail on the 16S and 16BL lines, I suspect it was to do with how the SR coaxial magazines mated, but certainly the SR3 Advanced gate design is less problematic. Back when SR2s and 3s were industry workhorses we (or the clients) used to steady test them before each big rental. Over the years some SR2s showed up laterally unsteady and we'd fit new rails and everything would be OK. It never seemed a huge issue but then we meticulously maintained the cameras. We always projected the steady tests and disregarded any overall jitter or movement, only watching for movement between the double exposures. This is how I was trained anyway, under technicians from Panavision and Arri.

 

Thanks once again for your time. Just out of curiosity- around how much was it in those days to change the rails?

 

I hope I'll find a "old" service technician in Stockholm that was around during these cameras glory days. Even if the camera seems to be in good shape now it would feel secure to have someone to turn to if problems arise. Here in Stockholm the video/tv-scene and film scene is really segregated so I don't have that many connections on the film-side.

 

Great to have this forum!

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Thanks for your reply. What is "Gate Weave"?

 

Even if the perfs look stable the whole frame is moving. You also see it clearly in this video after 03.25: https://vimeo.com/89728141

That test shot is on a locked off tripod but the frame is still moving. I mostly shot my test handheld and then it's not as noticeable.

The first picture steadiness test is shoot on an expired Kodak 7207 250D and everything else on a fresh Kodak 7219 500T, so it shouldn't be a problem caused by the film.

 

Looking forward to hear any thoughts.

 

 

Sounds like it would be worthwhile doing another test using stock from a different film batch.

 

As you see in the quote above I've shoot with two different stocks. I think Dom is right and that this should be considered normal for Sr2´s (if I've understood him correctly).

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