Zoom in,focus, zoom out. Am I still in focus?

B

BWyldeck

Well-known member
Which cameras can actually perform this operation correctly? (where the image that was in focus on the long end, remains in focus when it's wide) Can the cheap/mid range cameras do it?
Z1
Ex-1
Ex-3
Dvx-100
Hvx-200
Canon Xlh-1

It was my understanding that only the big boys could do this. Is it called a par-focal lens?

I'd mainly like to confirm if the Sony ex-3 can or can not perform this function?
 
Yes, I think it´s called parafocal lens.
Don´t know about the cameras you´ve named, but JVC GY-HD250 with stock Fujinon lens does that, but only if the backfocus is set right (if that´s any help, hope it is :D ).
 
I believe the HVX200 can do this as well, at least, that's what I saw our camera guy doing every time he said "Getting critical focus" :)
 
Pretty sure on Barry Greens HVX bootcamp video he explains that the HVX does not have this function since it is an electronic focus. I know a lot of camera operators do this, but I'm now wondering if they are all mistaken. I'm an editor, and i seem to constantly view rushes that have background in focus and foreground slightly soft - particularly on the ex3's. I've read a few forums that have in-conclusively suggested that these cheaper cameras do not have parfocal lenses and therefore do not perform this operation. Today, in edit, I was viewing rushes where a shot would zoom in, grab focus, and the zoom out and be soft. I know that the standard viewfinder on these camera is to small to be able to see critical focus (on wide), and since the standard lens holds fairly deep focus on the wide end, it is pretty hard to tell on that tiny, low-res viewfinder. A lot of the images look fine, unltil you notice that the background is slightly sharper than the foreground (I'm mainly referring to interview/vox pop shots).
I would really like to get to the bottom of this.
 
BWyldeck said:
How do you set the back focus? Does the ex3 have back focus?
Click to expand...

Back focus is a setting that needs to be correct in order to be able to zoom in, focus, zoom out and stay in focus.
It´s set by a ring on the bottom of the lens (or on the camera, not quite shure and it´s a shame since I use it daily :D ).

This setting moves part of the lens further or closer (or at least does some movement in the lens or camera or whatever :) ) in order to make the lens able to focus as mentioned above.
Get it wrong, and your picture will soften quite badly when zooming out or in.
You have to do this everytime you change the lens. Or even when humidity changes (but we´re not playing it this precise :D).
This is how it looks like, exactly on the camera I´ve mentioned (the JVC) http://www.youtube.com/watch?v=GHsZFY5_s6g

About the EX3 backfocus, this is what I´ve found:
http://www.dvinfo.net/forum/sony-xdcam-ex-cinealta/136299-ex3-back-focus-issue.html
So it seems like it does have backfocus.
 
Last edited:
Daniel thank you. Very helpful info here. But as for the camera in question, still no real answers here.
 
Most info regarding the EX3 i found, was in the thread I posted :(
Owner seemed to have problems with setting the backfocus right. But that also means, yes EX3 can do what you´ve asked for ;)
 
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