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Preston F/I calibration issues


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#1 Satsuki Murashige

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Posted 16 March 2010 - 12:20 AM

Hey all,

So recently I had an issue on set with the Preston F/I unit, the Red camera, and a set of Zeiss Standard Speeds T2.1 which had their near-focus stop pins pulled to enable macro focusing. The issue was that the lenses were able to rotate beyond 360 degrees (more like beyond 720 degrees), and the auto calibration was not be able to find the end stops or map the full focus range. After calibration when the lens finally hit the near stop, I would be stuck with like a 1" to 2' focus range. Pushing the calibrate button again during the procedure just caused the process to reset and start over with the same result.

I wasn't sure if there was a way to manually set end stops like with the Bartech, but I didn't have time to figure it out. So what we ended up doing was tricking the Preston by calibrating with a non-macro lens (50mm T2.1), then slipping that lens out and inserting our other macro lenses as called for (16, 24, 32mm). To complicate things even further, the lenses were the DP's personal set, and the 24mm lens was so stiff and gritty that it would cause the motor to stop working. Recalibrating or resetting changed nothing. It took us awhile to identify and sort out all the separate issues and just stop using the 24mm.

Anyway, I have to assume I'm not the first AC to encounter this macro lens issue, so how do you guys deal with this? Am I missing something really obvious? Right now, I'm thinking "just rent a Bartech!"

A separate issue I had was with getting power out of the Red camera. The rental house provided us with (2) D-tap to 2-pin lemo power cables and (1) 4-pin XLR to 2-pin lemo cable. There also should have been a Red auxiliary to 2-pin lemo, but it wasn't included (no camera prep day, duh!).

The two D-tap cables both stopped working several hours into the first day, and the Steadicam op was forced to wear a battery belt for the rest of the job (he's a friend, luckily). We were running the D-tap into an ET battery plate which had a Camwave transmitter attached to it, but no battery (we ran the camera off a second camera battery on the back of the sled).

When we switched to handheld mode, the battery went back on the Camwave, but the power issue persisted so we just switched to the regular follow focus for that.

*The only thing I can think of is that maybe the D-tap was not providing enough power with the wireless transmitter on it and without a battery, but it still occurred when we put a battery on. Maybe the Camwave was drawing too much power? Should have tested that...

The rental house said we must have fried the D-tap cables by plugging in the D-tap in reverse, but I tested afterward to see if that was even possible and it was not. After the job, the rental house tested the cables and said they were fine, but they were not able to recreate the problem. So now, everyone is stumped. Does anyone have any ideas?

Edited by Satsuki Murashige, 16 March 2010 - 12:25 AM.

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#2 Matt Irwin

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Posted 13 July 2010 - 11:48 PM

Hey Sats-

I'm on a feature right now with that exact camera/lens combo, and two of our lenses have been de-pinned as well. We initially had a FIZ II with standard PCS motors and it couldn't deal with the 720+ deg. rotation. That problem along with another issue with the MDR required a swap-- we got handed a C-Motion from the rental house..... which is a terrible pile of junk and didn't work with the macro 2.1's either.

After 5 days we found the solution: beg and plead to get a Preston III and never look back.
The digital focus mapping is the only way to get those "macro" lenses to work on a wireless because you can limit the the range to MARKED minimum instead of HARD minimum. Once you have a lens file made, you barely have to think about it during a lens change. If you need the macro range, switch to a normal follow focus, or create a separate lens map that includes it (haven't done that but it seems that the III can handle it). I guess a Bartech would work too, but their motors don't have enough torque to deal with the one stiff-as-sh*t lens in every set of Zeiss T2.1s.

Regarding the power issue-- There was probably not enough juice to go around in that setup. The Camwave's hunger runs deep. ("So deep, so deep")
I've found P-Tap to be much more reliable with most Reds because their aux ports don't always send clean power to the FIZ. They will read out fine with a volt meter, but you will see the status lights on the FIZ flicker and will then have all sorts of weird problems with calibration and motor fluttering.

I realize your post is months old, but I hope this is helpful.
Cheers,
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#3 Brad Grimmett

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Posted 16 July 2010 - 06:53 AM

The issue was that the lenses were able to rotate beyond 360 degrees (more like beyond 720 degrees), and the auto calibration was not be able to find the end stops or map the full focus range. After calibration when the lens finally hit the near stop, I would be stuck with like a 1" to 2' focus range. Pushing the calibrate button again during the procedure just caused the process to reset and start over with the same result.

I think the trick that would have worked for you would have been to stop the calibration with your hand at the point you needed it. You just need to grab the lens and stop it and it will think it's the end of the lens. I haven't dealt with this exact issue, but that may be a good fix in the future.

The two D-tap cables both stopped working several hours into the first day, and the Steadicam op was forced to wear a battery belt for the rest of the job (he's a friend, luckily). We were running the D-tap into an ET battery plate which had a Camwave transmitter attached to it, but no battery (we ran the camera off a second camera battery on the back of the sled).

Why wasn't he powering the Preston off his rig? It sounds like you were using the Red, and I've had power issues with that camera in the past. Powering the Preston off your rig is standard with steadicam, so I'm confused why it had to power off the camera.
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