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shooting s16 on unmodified 16mm mags with Arri SRII


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#1 Luke Randall

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Posted 10 December 2015 - 06:36 PM

Anyone run in to trouble doing this?

 

I've heard of people doing it without issues or scratches but not the inverse... as yet.


Edited by Luke Randall, 10 December 2015 - 06:44 PM.

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#2 Gregg MacPherson

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Posted 10 December 2015 - 07:18 PM

  

Inverse is a tricky word there.

Proposition...Unmodified mags => No scratches
Inverse proposition...Modified mags => Scratches.

I think you just mean a simple negation...Unmodified mags => Scratches.

 

Anyway,  hard to prove that something never happens.  And if it happens rarely,  how often does it have to happen before you should worry? 

 


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#3 Luke Randall

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Posted 10 December 2015 - 07:22 PM

Ha thanks Greg, I guess I could have been worded that better.

 

 

What I meant was, does anyone have an informed opinion on the risk -- if any -- of shooting s16 on unmodified srII mags?

 

Cheers


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#4 Gregg MacPherson

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Posted 10 December 2015 - 07:29 PM

Just me having fun.  It would be nice to have all the real data,  so you knew how often it actually happened (scratches from unmodified mags).

 

Have you carefully scratch tested the unmodified mags you want to use?


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#5 Luke Randall

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Posted 10 December 2015 - 07:40 PM

Just me having fun.  It would be nice to have all the real data,  so you knew how often it actually happened (scratches from unmodified mags).

 

Have you carefully scratch tested the unmodified mags you want to use?

 

No. I have two s16 mag's, I want to get a third so I can have a backup mag/low light (500t) mag on set. There are a lot of unmodified mags going cheap on ebay.

 

Plenty of people say they shoot s16 on regular mags without issue, but there also must be reasonable motivation for modding the mags in the first place.


Edited by Luke Randall, 10 December 2015 - 07:41 PM.

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#6 Dom Jaeger

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Posted 10 December 2015 - 08:41 PM

I recall being told that when the first S16 SR conversions were done the mags were not altered, and in most cases there was no scratching, but with the amount of 16mm being shot professionally even a small percentage of footage getting damaged was a big deal, so mags started to get converted too. Certainly if unconverted mags are not being regularly serviced the risk of scratching will increase. It's mainly a case of turning down one shoulder of the film rollers in a lathe, although when I was at Panavision Sydney in the 90s we were modifying parts of the film guide too.
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#7 Luke Randall

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Posted 10 December 2015 - 08:44 PM

Cool thanks for the info Dom and hi from a fellow Aussie.

 

I lived in Melbourne for 8 years before moving to L.A. Great city, I miss it!


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#8 Tim Carroll

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Posted 11 December 2015 - 09:34 AM

Scratching does occur, and you need to turn down the rollers as well as cut back the film guides.  Will every un-converted mag scratch every roll of film?  Definitely not.  But do you want to take a chance that the one spectacular take you got on that one shot, ends up being scratched when you process and scan the film?  Probably not.


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#9 Mark Dunn

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Posted 11 December 2015 - 10:54 AM

 

 There are a lot of unmodified mags going cheap on ebay.

 

 

Now you know why.


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#10 Luke Randall

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Posted 11 December 2015 - 02:42 PM

Now you know why.

 

Ha, maybe. I'm not sure even s16 SR mags have much market value at the moment. I picked up a SRII s16 with ccd tap, 2 mags, 3 batteries for $1500.

 

Hopefully the prices will encourage more people to use film. You can barely get a couple days rental on an alexa for that price.

 

 

Scratching does occur, and you need to turn down the rollers as well as cut back the film guides.  Will every un-converted mag scratch every roll of film?  Definitely not.  But do you want to take a chance that the one spectacular take you got on that one shot, ends up being scratched when you process and scan the film?  Probably not.

 

Indeed, I do not. I'll either have to get one modded or rent an extra mag. Cheers


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#11 JD Hartman

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Posted 12 December 2015 - 07:14 AM

I recall being told that when the first S16 SR conversions were done the mags were not altered, and in most cases there was no scratching, but with the amount of 16mm being shot professionally even a small percentage of footage getting damaged was a big deal, so mags started to get converted too. Certainly if unconverted mags are not being regularly serviced the risk of scratching will increase. It's mainly a case of turning down one shoulder of the film rollers in a lathe, although when I was at Panavision Sydney in the 90s we were modifying parts of the film guide too.

 

Are the roller steel or Aluminum?  Is the part of the roller being turned down in contact with the film?  Or does it need to be reduced in size so it doesn't contact the film at all?  If the former and they are steel, then it's likely that the roller would need to be ground (on a cylindrical grinder) to size, not turned on a lathe to achieve an acceptable finish.  If they are Aluminum, you should be able to achieve an acceptable finish on a lathe.


Edited by JD Hartman, 12 December 2015 - 07:20 AM.

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#12 aapo lettinen

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Posted 12 December 2015 - 07:44 AM

You will lathe the soundtrack area of the roller's contact surface away but leave just a little narrow bit of it to support the film edge, i think it's half or quarter of a mm or something like that
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#13 Dom Jaeger

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Posted 12 December 2015 - 08:04 AM

Are the roller steel or aluminium?


Neither, they are a type of thermoplastic.
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#14 JD Hartman

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Posted 12 December 2015 - 08:39 AM

You will lathe the soundtrack area of the roller's contact surface away but leave just a little narrow bit of it to support the film edge, i think it's half or quarter of a mm or something like that

 

Machinists don't "lathe" anything, we turn down material to a desired diameter.  Not knowing the type of plastic, might be difficult to get a smooth finish.  Most plastics are thermoplastic, acrylics as cast.


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#15 Dom Jaeger

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Posted 12 December 2015 - 02:32 PM

Machinists don't "lathe" anything, we turn down material to a desired diameter.


Sure, just like cinematographers don't "lens" a project, they capture images with the desired characteristics.. ;)

Language is a fluid thing, sometimes technical accuracy is important, other times not so much. It's also worth remembering that this is an international forum, and English is not everyone's first language.

I don't know exactly what type of thermoplastic Arri used for the rollers, but they turn down just fine.
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#16 JD Hartman

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Posted 12 December 2015 - 03:06 PM

Sure, just like cinematographers don't "lens" a project, they capture images with the desired characteristics.. ;)

Language is a fluid thing, sometimes technical accuracy is important, other times not so much. It's also worth remembering that this is an international forum, and English is not everyone's first language.

I don't know exactly what type of thermoplastic Arri used for the rollers, but they turn down just fine.

 

Well as a member of a professional machining forum with many international members, I can say that none of the machinists from abroad "lathe" anything either.  A lathe is a specific machine, not an operation.


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#17 aapo lettinen

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Posted 12 December 2015 - 07:34 PM

Should I use the term machining for that, in Finnish it is normal to specify also the work process if it is known (eg do you use lathe or milling machine for removing the metal or in this case plastic, and if you use multiple tools for the job it is usually said that you are machining the material. So, in Finnish you would definitely "lathe the soundtrack area away". I have used metal lathe and milling machine so I know the process quite well but don't know all the pro terminology for all the processes)
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#18 aapo lettinen

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Posted 12 December 2015 - 07:40 PM

That said, I think it is very important in this case to specify which kind of tools one would need to modify the rollers so one would understand the amount of work needed and could then find out which kind of place could do the actual mod and order the service more easily

Edited by aapo lettinen, 12 December 2015 - 07:41 PM.

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#19 JD Hartman

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Posted 13 December 2015 - 09:01 AM

What tools would depend on how the roller was to be held in the lathe, if both end were to be turned in one operation or turned down one end at a time with then the roller being flipped.  Then there are tools and tooling.....will it be held in a four jaw chuck or collet and live center?  Will they need right and left hand turning tools?   These details are superfluous to the customer,  all you need to do is bring the rollers to a machine shop with an accurately dimensioned drawing of the modified roller.  How they accomplish the operation is their business.  Most machine shops would not want you telling them what to do anymore than a heart surgeon would want you telling them how do perform your transplant.

 

Conversely, telling them, "leave just a little narrow bit of it to support the film edge, i think it's half or quarter of a mm or something like that", would have them decline the job.


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#20 aapo lettinen

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Posted 13 December 2015 - 12:23 PM

Conversely, telling them, "leave just a little narrow bit of it to support the film edge, i think it's half or quarter of a mm or something like that", would have them decline the job.

I calculated it SHOULD be around 0.5 - 0.6mm but I hoped someone like Dom could tell the exact width of the support edge, it is very difficult to find it from the web.  

I have some old footage shot with SR3 which I could use to measure the dimensions of the SR3adv gate and determine the width available but that would be unnecessary because someone already knows the exact dimensions and could just bring them up  <_<   

 

The point was that one will need a metal lathe for the work, whether if letting a pro machinist to do the job or by trying to do it by yourself (that is entirely possible though the end result may be not absolutely perfect) . first it is of course necessary to find out the exact width of the edge but after that it is very straightforward unless the guides have to also be modified 


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