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Help! Pulling focus with diopters


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#1 Satsuki Murashige

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Posted 28 May 2008 - 03:09 PM

Hi guys,

I'm pulling focus tomorrow on a HPX500 shoot. We have a shot where we need to start on a medium CU or a medium shot of an actor sleeping in bed, probably from straight above, camera to subject distance approximately 4-5'. We need to boom down as he snores and travel right up to his mouth, about 5" away from the front element of the lens. The shot needs to be in focus the whole time, and my stop will probably be around a T2.8 or T4.

The DP wants to use a 10mm Digiprime which close focuses to 20". The camera will be on a jib, and I'll be pulling remotely with a Preston. I'd like to know if this shot is possible if we use a diopter on the front of the Digiprime, and if so, would a +1 or +2 be sufficient to shift the miminum focus of the Digiprime to 5"? I plan to pull from the monitor, not the lens marks.

I'll be going to a camera prep in an hour or so, but the rental house probably won't have diopters in house to do a test with, they'd need to subrent them so I won't have them until the day of the shoot.

Any advice?
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#2 Satsuki Murashige

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Posted 28 May 2008 - 03:25 PM

Okay, the rental house DOES have diopters so I can test it out later today! I'll let you guys know what I find out.
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#3 Leo Anthony Vale

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Posted 28 May 2008 - 03:35 PM

The DP wants to use a 10mm Digiprime which close focuses to 20". The camera will be on a jib, and I'll be pulling remotely with a Preston. I'd like to know if this shot is possible if we use a diopter on the front of the Digiprime, and if so, would a +1 or +2 be sufficient to shift the miminum focus of the Digiprime to 5"? I plan to pull from the monitor, not the lens marks.


A dioptre is the reciprical of the focal length of the lens in meters. So a +1 is one meter, a +2 is 1/2 meter & a +1/2 diotre is 2 meters.

20" is about 1/2 meter. With a +2 on and the lens focused at 20", you should be focused at +4 dioptres,
about 10". But your focus with the digiprime at inf. will be +2 dioptres, 20".

It doesn't seem it will work with dioptres. You'll need a closer focusing lens.
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#4 Satsuki Murashige

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Posted 28 May 2008 - 04:23 PM

A dioptre is the reciprical of the focal length of the lens in meters. So a +1 is one meter, a +2 is 1/2 meter & a +1/2 diotre is 2 meters.

20" is about 1/2 meter. With a +2 on and the lens focused at 20", you should be focused at +4 dioptres,
about 10". But your focus with the digiprime at inf. will be +2 dioptres, 20".

Thanks for the quick reply, Leo! I guess I'm still confused about the relationship between the focal length and diopter because I don't understand how 20" is about 1/2 meter. Isn't 1/2 meter about 1'6"? Could you explain this further?

It doesn't seem it will work with dioptres. You'll need a closer focusing lens.

Okay, that's clear enough! I'll see if they have a macro lens. BTW, the 70mm Digiprime focuses to 13". Probably much too long a lens for the shot, but would that get me close enough? Just curious.

Thanks again, I really appreciate it.

* Another idea: What if we release the back focus ring and shift the FFD mid shot, sort of like using the macro ring of an ENG lens? Could that possibly work to get us the shot?

Edited by Satsuki Murashige, 28 May 2008 - 04:27 PM.

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#5 Satsuki Murashige

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Posted 29 May 2008 - 01:36 AM

Okay, so what I learned:

10mm @ T1.6 & inf. w/ +1 Diopter = focus @ 7'

10mm @ T1.6 & 20" w/ +1 Diopter = focus @ about 10"

10mm @ T5.6 & 20" w/ +1 Diopter = focus @ about 8"

Since the 10mm focused at 8" does not fill the frame with the mouth, we're going with the 14mm instead (cf=20"). This gives us the end frame we want but only a MCU (chest up) as our starting frame. At inf., the 14mm focuses to 5'.

I found out the camera will not be on a jib but handheld instead, so that will make things more challenging. Pulling focus from a monitor with the Preston is actually not too hard, even wide open (we tested with the subject moving toward the static camera, but we'll be shooting the other way around). It's a long pull of course, from inf. to min. focus with the diopter - the trick seems to be to pull only about 20 degrees on the focus knob until the subject gets to about 1'6" away from the lens, then crank the knob hard for the last 10" of travel. We'll be using a 24" JVC lcd monitor which is supposed to be great for checking critical focus. We were using the Panasonic 17" before which is not that great for this.
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#6 Leo Anthony Vale

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Posted 29 May 2008 - 02:55 PM

Thanks for the quick reply, Leo! I guess I'm still confused about the relationship between the focal length and diopter because I don't understand how 20" is about 1/2 meter. Isn't 1/2 meter about 1'6"? Could you explain this further?

One meter is a tad over 39". For a quick claculation in one's head, I rounded it up to 40", half of which is 20", which is 1'8". 1'6" would be 1/2 of of a yard.
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#7 David Auner aac

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Posted 29 May 2008 - 03:19 PM

Jee, why can't you folks get rid of that stupid imperial system. For good!

*runs for cover and hides behind the camera...

Sorry, couldn't resist! I'm really looking forward to your after action report, if you're willing to do one, Satsuki!

Cheers, Dave
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#8 Satsuki Murashige

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Posted 29 May 2008 - 11:54 PM

One meter is a tad over 39". For a quick claculation in one's head, I rounded it up to 40", half of which is 20", which is 1'8". 1'6" would be 1/2 of of a yard.

Oh, okay duh. I can't add! :)

The shoot went pretty well and we were out at 10 hours, but we went way over schedule on this one setup. We shot this first thing in the morning. Camera went on a dolly (I think it was a Fisher 11) with a jib offset over the bed. We used the +1 diopter in the matte box with the shade portion removed so the front element could go right up to the actor's face. We had a lot of problems getting a smooth boom down because the move necessitated a pan and tilt, so we tried various lenses and configurations until we decided to ditch the jib and use the dolly's arm to do a straight lock-off boom down. It was also hard to feather the move as it was a very fast move going from full up to full down on the dolly arm. We did multiple versions with and without tracking markers, so it took about 4 hours to finish the whole scene with all the coverage. It wasn't too hard to pull focus on though, the JVC 24" monitor was great for critical focus, and with the Preston I could sit at the monitor while pulling. I'm totally spoiled from pulling focus this way, don't know what I'll do when I get a big film job. If they put the final film online, I'll post a link.
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#9 Jamie Metzger

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Posted 30 May 2008 - 02:32 AM

Jesus!
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#10 Satsuki Murashige

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Posted 30 May 2008 - 03:33 AM

Jesus!

Yeah, well I didn't have to do any of that dolly move stuff, I pretty much just sat at the monitor and practiced my focus pull. The hardest thing I had to do was figure out how to take the shade off the matte box. :)

Day two tomorrow - if anything interesting happens, I'll let you guys know.

Edited by Satsuki Murashige, 30 May 2008 - 03:34 AM.

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#11 Jamie Metzger

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Posted 30 May 2008 - 04:01 AM

Yeah, well I didn't have to do any of that dolly move stuff, I pretty much just sat at the monitor and practiced my focus pull. The hardest thing I had to do was figure out how to take the shade off the matte box. :)

Day two tomorrow - if anything interesting happens, I'll let you guys know.


Sounds like one of those high pressure situations to learn the diopters and focus adjustments....sounds like you did just fine.
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#12 Jonathan Bowerbank

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Posted 30 May 2008 - 04:07 AM

Just be thankful you weren't using masterprimes on a Pro35 ;)
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#13 Satsuki Murashige

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Posted 31 May 2008 - 01:39 AM

Just be thankful you weren't using masterprimes on a Pro35 ;)

Yeah right. :lol: Well, if the director pulled his own focus on this shoot like on that Master Prime shoot, then I wouldn't have a problem with that either! That was extremely weird, BTW. Has anyone else worked with a director who likes pulling his own focus, yet is willing to pay union rates for a 1st AC? Whatever man, it's his show and I get paid the same either way.

Today was a crazy focus pulling day. I guess expectations were raised after yesterday because I got almost no rehearsals for blocking or focus today. Some crazy "wing it" type, shallow dof, no marks, wildly gyrating handheld camera setups. I had to rack to various subjects and objects as the DP panned, tilted, whipped, and dollied. It just got crazier and crazier throughout the day until crew and clients who were watching my monitor were giggling because the camera at times just seemed totally out of control, "Irreversible" style.

I got into "the zone" focus-wise, where the Preston hand unit seemed to be an extension of my brain and I didn't have to think about which way to turn the knob. I just thought "closer" or further", turned the knob by feel and managed to get things in focus 80-90% of the time. Then, about 2/3 through the day, I suddenly lost the "zone" and started to screw up, turning the knob the wrong way when I wanted to go the other. I don't know why this happened but it totally messed with my game. I had to start asking for eye marks and sometimes had to look down at the ring during a take to make sure I was going to pull in the right direction. I got over it and pushed through, but I never really got back into the zone which made me lose some confidence. Has this happened to anyone else?

We had a few shots where the director handheld the diopter and a magnifying glass in front of the camera lens and waved them around. Many of our shots were on the 40mm @ T1.6 today. We also had some shots on the 70mm, which has almost no dof. Luckily, out sound man/video tech helped me out A LOT. We were moving and setting up the camera cart with the download station/battery charging station (laptop, two firewire drives, Duel Adapter), four monitors (camera->waveform->my 24" JVC->client 17" Pany->8" on-board Pany), all of our cases, my Cinebag, and all of our computer bags, two cameras (HPX500 and HVX200), and two tripods. He also had his own sound cart and equipment to wrangle. We had two locations, one company move, up and down elevators all day. Anyway, it was a fun, tough job. On to the next gig!
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#14 Satsuki Murashige

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Posted 31 May 2008 - 01:56 AM

Here's the director's blog for those who are interested: http://cephalonosa.blogspot.com/

He told me that he might put some footage up on the site at some point but the main release is for DVD (for the medical professional community) and won't be finished for a while.
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#15 Jonathan Bowerbank

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Posted 01 June 2008 - 02:02 AM

Yeah right. :lol: Well, if the director pulled his own focus on this shoot like on that Master Prime shoot, then I wouldn't have a problem with that either! That was extremely weird, BTW. Has anyone else worked with a director who likes pulling his own focus, yet is willing to pay union rates for a 1st AC? Whatever man, it's his show and I get paid the same either way.


Yeah, it was definitely weird...plus his focus pulls from soft to sharp were quite poor and unnatural, especially since there really wasn't that much movement of either the actor or the camera to motivate it. But anyway

I love those shoots where there's a lot of frantic handheld and they just tell you to focus on whomever. Had a 75mm Zeiss super on a Pro35 once in a club scene, handheld. I had to dance with the cam op and just watch the onboard since I didn't have the luxury of a Preston. But it's a blast.
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#16 Sam Wells

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Posted 03 June 2008 - 12:40 PM

Hi Satsuki, I pulled focus off a videotap monitor on dozens of Kenworthy snorkel jobs back in the past, yes you can get into the "zone"

B&W monitor no shadow mask.

Easier with "hard light" DP's than "soft light" DP's B)

-Sam
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#17 Satsuki Murashige

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Posted 03 June 2008 - 03:44 PM

Easier with "hard light" DP's than "soft light" DP's B)

Agreed. :) Although, some actors' faces just always seem out of focus to me. I think it's mainly in faces with light colored hair and perfect skin. There's just very little contrast there for the eye to grab onto. I've come to really enjoy working with wrinkly, pimply faces since it makes my life easier!
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