Measuring focus for crane/jib work

Satsuki Murashige · March 8, 2008

Hey guys,

So I've recently had a chance to pull focus with a Jimmy Jib at 25' extension. It was an F900 shoot with the Pro35 and Zeiss Superspeeds. We ended up using a 35mm lens wide open on the jib to capture swooping shots of a theater audience and focus was critical. You can see the finished product here:

http://www.ethosedit.com/sony/Buzz_Preview_Mix_022108a.mov

The shot that finds the girl and follows her as she stands up, walks down the aisle and exits toward camera was the hardest shot for me technically (also since we shot all the rehearsals) but I'm pleased to say they had good takes of every shot that were spot-on sharp.

What's bothering me though is that with HD, I could sit by the video tech's tent and grab quick eye focus marks from the big HD monitor as the jib op. was practicing his moves, which were never the same from take to take as he was tweaking the movement. In fact, I got so used to this that I rarely pulled out my measuring tape on the whole shoot. But if I had to pull strictly based on estimating distances, I would have been screwed.

So my question is: what tricks do you focus pullers use to grab marks for big jib/crane shots on a film job?

Chris Keth · March 9, 2008

My solution would be this. Use a laser rangefinder and tape a tennisball to the top of the camera where the film plane is. Then you stand at the subject and measure from subject to camera. For closer things that get more critical, you can run a tape since it should be more practical to do.

Satsuki Murashige · March 10, 2008

My solution would be this. Use a laser rangefinder and tape a tennisball to the top of the camera where the film plane is. Then you stand at the subject and measure from subject to camera.

Thanks Chris. I've since purchased a Disto, so I'll give it a try on my next gig. BTW, why do you recommend a tennis ball as opposed to a flat target plate? Is it so you can take off-axis readings if you need to?

I guess with longer lenses and shallower depth, you probably could tell critical focus from the video tap in a pinch, though I wouldn't rely on it. Interestingly, I've found that the Zeiss Superspeeds "pop" in and out of focus more visibly than newer Zeiss and Cooke glass. I haven't shot with Ultra Primes or Master Primes yet but this seemed to be the case with the Ultra 16s, DigiPrimes, and S4s. There could have been other factors at play I guess, but I'm wondering if this generally jibes with anyone else's impressions.

Chris Keth · March 10, 2008

That's exactly my thought, that something round would give less chance of error on off axis measurements. Probably a little flag of tape at the right place would be fine as well.

Let me know how you like the disto. I've been considering one if I can find one on ebay or something cheap enough for me.

Satsuki Murashige · March 11, 2008

That's exactly my thought, that something round would give less chance of error on off axis measurements. Probably a little flag of tape at the right place would be fine as well.

Let me know how you like the disto. I've been considering one if I can find one on ebay or something cheap enough for me.

The Disto works pretty well, I got the A5 model which ran me $450. :ph34r: It's the one with the optical viewfinder so you can use it for day exteriors. I bought it for a steadicam shoot which basically paid for itself so I didn't feel too guilty about spending so much. If you decide to get one, laserstreet.com has a deal where you can get a free Pelican case with it as well as the soft case. I did a lot of research but wasn't able to find one cheaper. On the other hand, you might be able to rent the meter out from a local camera rental house to make it pay for itself when you're not using it.

The Disto can be a little slow (like up to 5 seconds) to give you readings in bright light which might be an issue. The viewfinder is also puny, but it works. It's great for steadicam at distances over 10' when you can't use a soft tape, and also for quickly measuring hallways and corridors if you're doing a shot that requires holding someone in focus as they walk up or down. I'm sure you'll be able to find all sorts of uses for it.

I've also had a chance to play with the Hilti PD32 which is their equivalent model (at the same price). The Hilti is quite a bit smaller, seemed easier to use, and had a better viewfinder, but you can't store as many readings (I think the Disto can retain up to 20 vs. 4 for the Hilti). This hasn't really been an issue for me so far, as I've only need up to four at one time - after that, I start to forget what the hell I've measured! The PD32 has been discontinued as far as I can tell, so you might be able to find a deal for one of those on ebay.

Zac Halberd · March 12, 2008

Dude, love the video you posted. Probably the cheesiest adverts I've ever seen. But your sharps were spot on. Good question as well. I've worked with other focus pullers that use distos, and they've come in really handy (although sometimes they could get lazy with one). I just can't afford one.

I remember this one guy shot a disto through a double pane window in a recording studio and bounced it off a mirror to get his reading. He was sharp! Well impressed.

The tennis ball idea is great. I'm using that one. I'll give you the credit Chris. Thnx

Chris Keth · March 13, 2008

Dude, love the video you posted. Probably the cheesiest adverts I've ever seen. But your sharps were spot on. Good question as well. I've worked with other focus pullers that use distos, and they've come in really handy (although sometimes they could get lazy with one). I just can't afford one.

I remember this one guy shot a disto through a double pane window in a recording studio and bounced it off a mirror to get his reading. He was sharp! Well impressed.

The tennis ball idea is great. I'm using that one. I'll give you the credit Chris. Thnx

I'm kind of thinking a ping pong ball might be better. You would be able to see the laser on it better and it's smaller, lighter, and less obtrusive.

Jonathan Bowerbank · April 19, 2008

It's so hard to hold that laser still, aiming for a ping pong ball that's even 10' away would give me a nervous breakdown. Perhaps a french that's clipped on and oriented so it's placed at the focal plane would be easier to measure.

Joe Christofori · April 24, 2008

It's so hard to hold that laser still, aiming for a ping pong ball that's even 10' away would give me a nervous breakdown. Perhaps a french that's clipped on and oriented so it's placed at the focal plane would be easier to measure.

Yeah If possible, I try to tape a piece of showcard to the bottom of the remote head,

score it half way through then bend to a 90 degree angle and tape it underneath parallel to the film plane (obviously) cut another piece at the corner of the show card to make a brace, so its not all floppy, that should give you a good target for a Hilti or Disto.

Edited April 24, 2008 by Joe Christofori