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Pressure Plate Issues with Arri 16S


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#1 Jon Hyde

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Posted 19 April 2008 - 12:21 AM

I just shot a short film with an Arri 16S.
I used fresh Kodak Vision 2 200T film in 400ft rolls, loaded into the 400ft mags.
I used a single torque motor, different mags.
I used the following lenses:

Schneider-Kreuznach/Arriflex Cine-Xenon lenses:
T2 16mm
T1.4 25mm
T2 50mm

And

T1.9 9mm Cooke-Kinetal
T4 150mm Cooke-Kinetal
F2.4 17mm to 70mm Berthiot Pan-Cinor

When I went to telecine the footage there is a bizarre breathing focus issue, like a bad consumer auto-focus on a video camera. It crosses several lens changes. Here are the main symptoms:

It is worse when the take first starts.
The center of the frame is badly out of focus (like someone wiped Vaseline down the center of the lens) while the far outside edges are in focus.
The issue is worse in some takes than in others.
Two people, myself as the DP and the Director checked focus and framing for each set up. Focus through the eye piece was good. And for several shots I used the ASC manual to measure the focus range with a tape measure (on a dolly shot to ensure I kept the main subject in focus the entire length of the dolly without pulling focus).

I did stop the camera after loading the first mag and I checked the film loops because the camera seemed to be running very noisy. But everything looked good and I ran a couple of feet to see how everything was running. It looked good. I figured it was a noisy Arri (I've seen many).

Now. I ran 2 100ft daylight rolls in the internal spools and they were flawless. As was the focus chart and registration chart tests.

What I think is that the torque motor was dragging or putting stress on the internal sprocket and as a result the film loop was creating pressure plate issues. The focus issues only happened with the 400 mags loaded. The two internal spools were perfect.

Could it be that the mag created this focus issue? Because the focus jumps in an out rapidly, and then once the motor is up to speed it settles into a generally blurry state like it was not focused... it has to do with the mag I think.

Could the pressure plate be stressed by the extra tension created by the magazine uptake spool?

Also, the battery was a 12v Bescor and I know the motor for the mag is an 8.4v standard Arri 16 motor. The main drive motor is a Tobin non-sync model. It is rated for 12v operation.
Could the 8.4v torque motor be failing and creating a drag situation which would affect gate and pressure plate operation?

I wouldn't think it was the lenses since the shots on the 100ft rolls with the same lenses are sharply focused.

Help! I have to figure this out so I can fix the problem! Any thoughts are much appreciated.
Has anyone seen this sort of quick focus breathing before with the Arri 16S?

THANKS!!!
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#2 Pete Von Tews

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Posted 19 April 2008 - 01:33 AM

Hi Jon,
What I would do is load up another 400' mag with some used/bad film, then fire up the arri, but take the side door off and see what's going on in there. I'd bet that will show you the problem.
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#3 Tim Carroll

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Posted 19 April 2008 - 09:40 AM

Jon,

Without seeing the camera it is impossible to be sure, but it sounds like you have a number of issues going on there. You should definitely not run the 8.4 volt torque motors with a 12 volt battery, that's a big No-No. Can cause different issues, not the least of which is burning up the torque motor.

Sounds like you have an issue with the pressure plate. With the 100 ft internal loads, the stress on the pressure plate may be lower, and with the 400 ft mags attached, and the torque motor running at the wrong voltage, the stress on the pressure plate is higher, and if the spring tension on the pressure plate is below spec. you're going to have some focus issues, it may not be as big an issue when running the 100 ft internal loads.

Your FFD may also be an issue. If the FFD is off, it won't matter how great the image looks in the viewfinder, it won't be great at the film plane.

I would definitely have someone look at the camera. If it hasn't been serviced in a few years, it needs an overhaul. You can read details of why an Arriflex 16S needs regular service and what the service does for the camera at the web page below:

Getting the most out of your Arriflex

Best,
-Tim
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#4 Jon Hyde

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Posted 19 April 2008 - 10:33 AM

Pete,

Thanks. And I did take the side door off and look at the loops, etc... to make sure the film was running through the camera OK. We did two 400 ft mags and had the same problem.

I think it's time to get the camera serviced.

I appreciate your feedback,

Thanks!

Jon
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#5 Jon Hyde

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Posted 19 April 2008 - 10:51 AM

Tim,

Thanks for the reply. I know you are the "go to guy" for the Arri S.
This is a camera owned by the school. It is not mine. To level the playing field we are not allowed to use our own equipment on student (graded) projects. There is another group in the class and it wouldn't be fair to allow me to use a superior camera when they don't have access to one.

This Arri is pretty beat-up. I did use my lenses, the ones listed above. The school's camera comes with the Angie standard mount zoom lens.

I used their body, mags, torque motor and battery. I'd never put a 12v battery on my camera, but my battery has finally died and needs to be re-cored. Since I had to deal with the school's camera anyway, I haven't gotten it done yet. Running their camera on my battery was not an option and I wasn't going to put my mags and motor on their camera. It was a catch-22.

I would agree that I think there are many things going on with this camera. I want to narrow it down the best I can so I can answer the questions the professor is going to ask. Being that I was the DP on the shoot and doubled as the cam-op, my classmates are looking to me for answers and I am going to stand up and take responsibility. Their grade shouldn't suffer; the camera was my responsibility.

Other than doing dailies, which on a film with a total of 780ft of film doesn't make a lot of sense, I can't see how I could have known that this was going to happen, especially when the focus and registration tests looked great. But really when we are looking at re-shooting, that doesn't give one much consolation.

I do plan on saving up some money (being a full-time student means I am poor most of the time) and sending my Arri to you for a total overhaul. I want to ensure that when I get into my senior classes (in two more semesters) and I can shoot with anything I want (most students rent cameras) I want to use my Arri for my projects.

Thanks a bunch Tim. I really appreciate you taking the time to respond in such detail.

Best regards,

Jon
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#6 Tim Carroll

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Posted 19 April 2008 - 11:22 AM

Jon,

If you don't mind my asking, which school are you attending. I service the cameras for a number of universities here in the States, including some in Southern California.

Best,
-Tim
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#7 Mike Lary

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Posted 19 April 2008 - 11:47 AM

Tim. I have a problem that might be related. I don't mean to hijack the thread - maybe similar culprits are at work with both cameras. Any advice you have would be greatly appreciated.

I just bought an SB with a Tobin motor and 400 foot mag with torque motor. The previous owner said she used it without any problems. The external battery doesn't have any markings on it, but the AC charger says 12v output (I don't know if that means the battery is 12v as well).

What's happening is this:
-Camera runs sync at all motor speeds fine when running spool to spool.
-When running core to spool, it also runs fine, but only at one speed (regardless of what the motor is set to). It appears to be running at about 24fps, judging by the speed of the dial, and the sync alert light doesn't come on, so it appears to be running sync.
-If I try to run core to core, the take-up side never fails to pull the film taut and it jerks on the base of the pressure plate, and sprockets start tearing. If I take out the core and run to a take-up spool, it runs smoothly.
-I can run core to core with both motors set in reverse without any problem, so it seems to be the take-up side causing the problem somehow.

Do you know what would cause this?
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#8 Tim Carroll

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Posted 19 April 2008 - 12:03 PM

Mike,

Some of what you are observing doesn't add up, so I would again really need to see the camera and mag and torque motor. I would suspect a couple of things. First, you are running an 8.4 volt torque motor on 12 volts, and as I mentioned above, that is a big No-No.

The other thing it sounds like is that your friction adjustment on your torque motor/magazine combo is out of spec. The torque motor/magazine combo is not direct drive, if it were, it would rip the film to pieces. The drive goes through a friction clutch to each spindle. These friction clutches must be adjusted to the proper friction so they slip somewhat yet still pull the film properly. If the friction is set too high on the take up spindle (when running in forward) or the feed spindle (when running in reverse), it will rip the film or tear the sprocket holes. If the friction on either spindle is set too low, the film will not take up properly.

Best,
-Tim
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#9 Mike Lary

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Posted 19 April 2008 - 01:16 PM

Thanks, Tim. I guess I'll just run from spools for now because I'm shooting in less than two weeks. Maybe I can get the camera serviced after that and see about getting a proper battery. I appreciate your help.
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#10 Jon Hyde

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Posted 20 April 2008 - 06:40 PM

Hey there everyone!

I've done a Flash animation with several frame-by-frame progressions at both 24fps and 3fps to show what this bizarre breathing focus issue looks like.
These are straight frame captures from Vegas, no manipulation other than importing them into Flash.

Perhaps after looking at these you can tell me what is going on.

Remember, this is NOT a zoom lens. It is a PRIME lens and no one is touching the focus ring.

Thanks,

Jon

LINK HERE:

http://www.jonhyde.com/arri16s.html
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#11 Tim Carroll

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Posted 20 April 2008 - 07:21 PM

Jon,

When I checked, only one set of clips was up, are the others coming soon?

Again, without looking at the camera I am only guessing, but here's my hunch. Are you sure you had the proper loops above and below the gate? That's my first thought. When using the 400 ft magazine it is sometimes tricky to set the loops properly without the two metal spools as reference points.

But seeing the footage reminded me of some footage I saw years ago where the latch that holds the pressure plate assembly closed, that latch was not latched properly. That latch holds the back plate of the pressure plate assembly firmly in position, a spring rides on that back plate, and that spring presses the pressure plate against the film, holding it to the gate. Without the back plate held firmly, the spring pressure from the pressure plate was not keeping the film tight up against the gate, which caused the film to float, and therefore the FFD was way off, and therefore everything was out of focus.

I would say it was probably one or the other of those two things, especially if some of the footage (the stuff shot with the 100 ft metal spools) looked fine. If the FFD was off on the camera, none of the footage would look fine. And I'd venture to guess that of the two, the pressure plate assembly latch is the most likely culprit.

Best,
-Tim
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#12 Jon Hyde

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Posted 21 April 2008 - 12:21 AM

Tim,

Thanks for the feedback. I had to run out and am going to put the other two video samples up in a few.

When I put the first 400ft mag in place, the loudness took me by surprise. It didn't feel right.
I immediately turned the camera off and took the side door off to check the loop. The loop was perfect according to the loop mark guidelines provided inside the camera. I checked the door, it was latched, and I checked the inside of the compartment for shredded film; a good sign that something is wrong.

Door was closed and no shredded film was present so I put the side door back on and started it back up again. It still sounded off so I turned it off again (realizing that I am only 3ft into a 400ft roll) and checked again. Everything was still good. So I decided to run a few feet of film with the door off to check and see that everything was OK. Both the Director and the AD were standing next to me.

The loops held, the door stayed latched and everything looked good. I figured we had a "noisy Arri". Some I've seen sound like a blender, others more like a muffled weed-whacker.

I definitely think it's the pressure plate. The more I look at the footage, there is another issue with the focus looking good on the far outside edges of the negative and more off in the center. Which tells me the film was moving across the gate "bowed" and not flat. I think the added tension, perhaps because the angle the film enters the feed and uptake sprockets is different when using the 400ft mag, that the film was pushing the pressure plate past its tolerance. And perhaps the springs in this older, well used Arri are less than factory spec now; good enough to hold the pressure of the internal 100ft roll which is timed with the sprockets and comes in at a different angle, putting more film across the sprockets before the loop than with the mag.

I'll put up some samples for you to view with the strange focus on edge but not in the center thing.

And as always I really appreciate you taking the time to share your knowledge of these cameras.

Best regards,

Jon
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#13 Tim Carroll

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Posted 21 April 2008 - 09:35 AM

Jon,

A few things, then I'm going to have to let this go as time is money for me. Without seeing the camera, there is little else I can tell you.

If the camera was threaded properly, with the proper size loops top and bottom, and you were using a camera with a buckle switch (that little lever switch that the lower loop passes as it comes out below the pressure plate and heads up to the take-up side of the sprocket), and there were no ripped sprocket holes, then the torque motor and the 400 ft magazine would have had nothing to do with the blurred footage. Had the magazine/torque motor been pulling too hard on the film, it would have ripped sprocket holes or tripped the buckle switch (which would have stopped the camera). Had the magazine/torque motor been not pulling hard enough, you would have just gotten loose take-up or possibly film spaghetti in the magazine.

As far as your focus being off in the center and good on the sides of the frame, at least in the one frame you enlarged and split into five sections, the girl in the center is in a very different focal plane than what is on the sides of that frame. She is proportionally much closer to the camera than the door jam or the bookshelf. It would be much more telling if you had a shot of a focus chart or something were the whole image was in the same plane.

It does appear that the pressure plate has some issues, but without seeing the camera I really can't tell anything for sure. What doesn't make sense is that the 100 ft rolls looked good. A pressure plate issue would be worse with the 100 ft rolls because the film coming off a 100 ft roll has a "tighter memory" than that coming off a 400 ft roll. In other words, the film will have a tighter curl if you just laid it down on a table top. This would make a weak pressure plate spring even worse, as the film from the 100 ft roll would be pushing away from the gate harder because of its "tighter memory" than the film from the 400 ft roll. It would be interesting to see some of the footage from the 100 ft roll.

And finally, if all film from 100 ft rolls looks great, and all film from 400 ft rolls looks out of focus, then you've got a weak pressure plate spring and your FFD is long. Therefore, the "tighter memory" of the 100 ft film would push the weak pressure plate spring back from the gate which would make the film fall into the longer FFD, whereas the 400 ft film, with the "weaker memory" would not push the pressure plate back as far and the film would fall short of the longer FFD, and therefore the film would be out of focus. Again, all guesses without seeing the camera.

Best,
-Tim
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#14 Sam Wells

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Posted 21 April 2008 - 10:33 AM

In my one experience with the Arri S latch not being fully closed (100' spool fwiw) the first few frames were sharp then it went out and stayed out - a bit more subtle than this and it didn't breath as I recall. I think the last frame or two got a bit sharper.

This looks like the pressure plate was hardly or not even touching the film.

Is it possible that whoever loaded actually secured the latch w/ the spools and not with the mag load(s) ?

-Sam
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#15 Jon Hyde

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Posted 21 April 2008 - 10:42 AM

[quote name='Tim Carroll' date='Apr 21 2008, 07:35 AM' post='228465']
A few things, then I'm going to have to let this go as time is money for me. Without seeing the camera, there is little else I can tell you.

As far as your focus being off in the center and good on the sides of the frame, at least in the one frame you enlarged and split into five sections, the girl in the center is in a very different focal plane than what is on the sides of that frame. She is proportionally much closer to the camera than the door jam or the bookshelf. It would be much more telling if you had a shot of a focus chart or something were the whole image was in the same plane.

And finally, if all film from 100 ft rolls looks great, and all film from 400 ft rolls looks out of focus, then you've got a weak pressure plate spring and your FFD is long. Therefore, the "tighter memory" of the 100 ft film would push the weak pressure plate spring back from the gate which would make the film fall into the longer FFD, whereas the 400 ft film, with the "weaker memory" would not push the pressure plate back as far and the film would fall short of the longer FFD, and therefore the film would be out of focus.
____________________________________________________________

Tim,

I completely understand about your time and believe me I appreciate every second you've generously offered. If it is any consolation you've definitely acquired at least one new customer out of this. So I hope you will not consider this a complete loss of your time.

I can look through the frames to see if I can find a better example of the same-plane focus issue. My thing as I said above is that this shot was composed using the ASC Manual and I've never known those charts to steer you wrong. I double check everything. I'm methodical that way. The math was right. Everything from 3ft in front of the camera to the door should have been in focus, same plane or not. I do agree that a less complex image would be much easier to diagnose.

I understand what you are saying about the roll memory. I was looking at the problem strictly from the standpoint of area of film across the sprocket and the angle of deflection and the tensile strength of the film. I fall back on my standard physics rules (I studied physics and my father is an engineer) so without your expert knowledge I'd be running around looking at the wrong thing. Again, I really appreciate your help.

The most important part of this for me is eliminating the different common variables until the ones which make the most sense remain. I want to know what happened so I can make sure it doesn't happen again. And I want to be sure that it wasn't operator error. For if it was, I am the sort of guy who will step up and take responsibility for it. But then it really becomes important to understand what when wrong so I can be sure to never let it happen again. Mechanical or operator. I never want to see film like this again.

Thanks a bunch and have a great day,

Jon
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#16 Tim Carroll

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Posted 21 April 2008 - 01:00 PM

My thing as I said above is that this shot was composed using the ASC Manual and I've never known those charts to steer you wrong. I double check everything. I'm methodical that way. The math was right. Everything from 3ft in front of the camera to the door should have been in focus, same plane or not. I do agree that a less complex image would be much easier to diagnose.


Jon,

Am a bit confused by what you are talking about with the ASC Manual? Keep in mind, if you are using the lenses you listed above, they are all forty or more years old. The distance scales on those lenses were never that accurate when brand new, and now after all these years and who knows when they were collimated last, the distance scales can be completely meaningless. If you set up your shots by some mathematical formula from the ASC manual where you calculated the depth of field when the lens was set a a particular distance, that could be where the problem lies. Without lenses with very accurate distance scales (which none of the lenses you listed would I consider accurate) you can't use the tables and calculations in the ASC manual.

The other thing to keep in mind is depth of focus. I looks like some of your bad footage was shot with a fairly wide angle lens. A wide angle lens has a VERY SHALLOW depth of focus. So the film floating just a little bit at the gate will throw the wide angle footage out of focus. If all the bad footage was when you were shooting wide angle, and the good footage was when you were shooting normal or telephoto, then a weak pressure plate spring would be the culprit, and it would have nothing to do with internal spools or external mags.

Just some thoughts,
-Tim
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#17 Jon Hyde

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Posted 21 April 2008 - 01:05 PM

Sam,

Thanks for this input. I wish I could say that it was something simple (and embarrassing) the door for the film gate not being closed or secured well. But this is something I know to look for and part of my film loading inspection is to ensure it is latched securely.

I also do the following:

1) Make sure the film is properly threaded through the sprockets (disengaging the pressure roller assembly)
2) The film is properly fit into the registration pin (pin in open position by turning motor inching knob)
3) The pull-down claw is in the very top position and the perf on the film fits over it easily (fitting into the registration pin at the same time)
4) That the film loop matches the markings inside the camera body
5) That the uptake loop of film is threaded through the uptake sprocket correctly
6) That the pressure roller assembly is re-engaged.
7) That the mag or internal spools are tightened (using the tension thumb screws).

I then run a few feet of film with the door open by pressing the internal manual power switch. I also ensure that the manual override for the buckle switch is in the correct "off" position.

The threading procedure is the same for both internal and external spools. It's actually easier to load the loop from a pre-loaded magazine than using internal 100 spools because you don't have to thread the uptake spool. You just tighten the mag tension knobs.

I'm pretty sure the camera has a pressure plate problem. Why it is acting the way it is doesn't make a lot of sense but hey... it's a strange world I guess.

But sincerely, thanks for making the effort to help. It is much appreciated.

Regards,

Jon
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#18 Jon Hyde

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Posted 21 April 2008 - 01:43 PM

Tim,

THANKS!!! No one has told me that the 16mm distance scales in the ASC manual are not accurate with these lenses.
So that might be part of the problem. We are taught to use these charts when in doubt about where the focus should be.
Mainly when doing a dolly shot or when trying to limit/extend DOF. We have learned to figure the points where focus will drop so we can plan to pull focus if needed. I carry a 100ft tape measure around when shooting. WONDERFUL!!!

I realize the 16mm doesn't allow for limitation of DOF like 35mm does. Likewise I know that wide lenses work against limiting DOF whereas long lenses can be used to compress images in the foreground/background. And of course the lower the t/f stop - the larger the iris, the less DOF.

But you are right. Once I checked my camera reports all focus issues are with the 25 and 16mm lenses. Not the 50, 150 or the two zooms (Pan-cinor and Angie).
So only the lower (wider) lenses created this issue.

And I never put the 9mm Cooke on because we never needed a shot that wide (and the parallax is pretty severe).

So. This is a good thing to know. And you are right. I didn't use any short lenses with the daylight spools. I either had the zoom or the telephoto on.

HAHA! I feel much better. Finally something that makes sense. THANK YOU! Now I am going to see about testing the camera to make sure.

At least it wasn't anything I could have foreseen. And that's what's been driving me nuts! I'm type A that way (if you haven't noticed).

Thanks again!

Jon
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#19 Tim Carroll

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Posted 21 April 2008 - 01:58 PM

Jon,

I apologize if you already know all of this, but just to point out the difference between Depth of Field and Depth of Focus. A wide angle lens has a big Depth of Field, which deals with things in front of the lens where the Depth of Field is what is in focus from that which is closest to the camera to that which is furthest from the camera. The greater the distance between what is in focus close and what is in focus far, the greater the Depth of Field.

A wide angle lens has a very small Depth of Focus, which is the point behind the lens where the light rays coming through the lens come into perfect focus. Ideally, this is exactly at the film plane. If the film plane is slightly ahead or slightly behind, again we are talking thousandths of a millimeter (less than one tenth the diameter of a human hair), with a wide angle lens, then the image will be out of focus. So for a wide angle lens, the FFD has to be dead on. Conversely, on telephoto lenses, the Depth of Focus is rather large, so the FFD of the camera can be off and still produce good images if you are shooting with a telephoto lens.

Best,
-Tim
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#20 Tim Carroll

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Posted 21 April 2008 - 02:00 PM

And I never put the 9mm Cooke on because we never needed a shot that wide (and the parallax is pretty severe).


Jon,

Can you clarify this? I use a Cooke Kinetal 9mm on an Arriflex 16S all the time, happen to love the look of that lens, not sure what you mean by the "parallax is pretty severe".

Thanks,
-Tim
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