HVX Focusing Information

O

Opcode

Active member
I'm trying to get a handle on getting proper focus on the shoot that I'm on. So far, without an assistant, I'm zooming in and/or using the focus assist to get in focus and then reframing the shot. One of the issues I'm dealing with is having to shoot at or near wide open and often times I'm zoomed in pretty tight.

I am ready for some more advanced focusing methodologies.

1. I'd like to get an assistant to use a tape measure to mark some distances. Does anyone know where the focal point on the camera lies? I don't see any markings.

2. Can anyone point me to a suitable focus and hyperfocal distance tables that can be used with this lens? I like to be able to plan for focus better and figure out strategies for camera placement, zoom settings, and f-stops appropriately for a scene.
 
According to 2 DPs I've worked with, the usual focal plane for video is right at the front element of a video lens. A cine lens would be back at the CCDs. You can test this by turning on the inches or mm focal distance on the HVX then focusing on different objects and measuring. I tried and got spot on measurments.

Now to get focus and hyperfocal tables we need to know the dimensions of the exposed pixels and the circle of confusion of the image. If any one knows these numbers for the different record resolutions let us know. It would be useful info.
 
toddeastman said:
According to 2 DPs I've worked with, the usual focal plane for video is right at the front element of a video lens. A cine lens would be back at the CCDs.
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Do you mean that is how the lenses are marked up, because the focal plane should still be the CCD.

With the HVX however, I believe the CCD actually shifts in order to focus. The distance it moves is probably pretty minor though.

After playing with the HVX I would personally use the focus assist to find your focus at set points during rehersal. I would trust that more than a tape measure. I have seen 35mm cine lenses with unreliable distance markings, and always try to double check in the viewfinder or better still, a monitor if using video.
 
Because of the prism in the image chain, using the image plane distance doesn't work like it would on a film camera or even on single sensor imagers. Lenses designed for video have traditionally been marked from the front element since until recently, video meant having a prism in the image path. Lenses used for film have traditionally been marked from the gate as indicated by a marking that looks like a circle with a vertical line runing through it engraved on the camera body. The HVX seems to follow the Video convention of focusing from the front element. But, just like when preping any lens, I run tests on a focus chart and remark the lens accordingly. This is where I am really looking forward to the new Foxi from Bebob, I should be able to test focus and mark the Foxi based on the test and feel pretty confident that my results will be repeatable.
 
mmm said:
Do you mean that is how the lenses are marked up, because the focal plane should still be the CCD.
Click to expand...

I don't really know the answer but I believe that is the case. It has to be since all the light is supposed to converge at the CCD for sharp focus. All the tests and shoots I have done with video cameras with video lenses, measurements from the tip of the lens have produced spot-on focus. I have shot with a CineAlta with a Fuji HD video lens (i know....a sin) and the front of the lens technique never failed to give accurate results on the long lens settings. Now on our Varicam with the huge Cine lens, I'd better have a measurement back at the plane marker or there will be a problem.

It's a case of two people I respected highly giving me a tip and I wasn't in the situation to question it. Sad huh? :)
 
That's some great info guys...thanks. Personally, I prefer using an external monitor and zoom in to determine focus rather than using the focus assist in the viewfinder whenever possible. Unfortunately, I don't always have the luxury of having a monitor near me like the Marshall, especially when we are doing quick setups and takes. Often, in low light, with actors fidgeting around, it's hard to determine good focus. So, I always thought about giving measurement with tape a shot and see if it's any faster and more accurate. I'll have to test out measuring from the front of the lens.
 
According to the manual the feet/meters focus length is approximate only so you cannot use that for critical focus.

IMHO - the focus assist is far more reliable when combined with a zoom in and the peaking then using an external monitor - the external monitor will not display the assist nor the peaking
 
I think you may be right Smelni, using zoom with FA, even on the small lcd may be more accurate in many circumstances. However, I find it much harder to do that on moving subjects like actors (unless you get them to hold still for camera). Having a larger HD screen and zooming in a bit seems to work better for me I think, because I'm judging sharpeness over a larger image area rather than a small, tightly zoomed square. I'm still trying to determine which works best, so it's an ongoing test.
 
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