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Focus Pulling


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#1 Samuel_Kim

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Posted 28 December 2017 - 01:41 AM

Hello, been following this forum for quite a while and there is so much information that it is hard to find/follow the information I need, so apologies for the repetitive question if it's already been asked. A while back I was pulling focus on a steadicam (75mm, T4, push in) commercial and we had rehearsals and I had marks all ready but for some reason, when we came to about 4' The shot always ended up a little soft. I finally got one take that was on point but it seems to me I keep having issues when it comes to pulling focus when I push-in. Is there any solution, advice or tips to nailing focus each and every time? Thanks for all your answers in advance!


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#2 evanwalsh

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Posted 28 December 2017 - 12:45 PM

75mm @ T4 and 4' away gives you about 1.5" of depth (according to pCam). Assuming for less in reality, that shot didn't give you a lot of wiggle room in terms of focus.

 

A few things are at play here.

 

Even though you had your marks all set, the Steadicam could have been an inch or more past the mark you had made for 4' by the time you got there on the wheel. Even when you get all the marks and rehearsals you want, an early or late steadi op or dolly grip can make all your marks go out the window and you just have to handle it on the fly and/or ask for another take.

 

The index marks on the lens themselves become increasingly further apart as you approach close focus and they're all slightly different for each lens in terms of the º of rotation on the focus rings.

 

It comes with a bit of practice and adjusting to each lens and wireless follow focus system to get the feel for how much you need to ramp the speed of your turns depending on which direction the camera/talent is moving. If you're pulling at a constant speed throughout the range that may have been the root of the issue you're having as you would need to start turning a bit faster the closer you get.

 

For example, Preston's intention with the pre-marked rings on the FIZ 3 is to even out the rotations of the focus scale so that every lens feels more or less the same on the wheel. Where as if you were using a bartech or other single channel system (Preston, Arri etc.) you would be subject to the normal ramping of the scale.

 

Push in's can also be a bit tricky simply because the closer you get the less depth you have, a long focal length + talent not hitting marks or moving in and out can increase the difficultly to these shots. Lets say 75mm @ T4, pushing in from 10' to 2'6", you go from 9" of depth to .5" of depth.


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