Auto Focus + Letus EX + HVX: Why the heck not?!

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ozzymandius

Active member
It seems that Auto Focus CAN be a benefit with the Letus Extreme and HVX (and I imagine any camera with any 35mm adapter). I did some searches and did not see this covered, so I am posting this to see if anyone else is already doing this. And if not, why not.

Basically, we discovered today that leaving Auto Focus ON, with our Nikon prime lenses and HVX, acts better than a human focus puller for certain types of shots. As long as the subject stays within the depth of focus of the Nikon lens, using auto focus on the HVX keeps them in sharp focus. No need for a focus puller or for the camera operator to act as his own focus puller. Just put the HVX into auto focus mode and forget about it! The only reason we never tried this before is because all the info we found on the net said not to use auto focus with a 35mm adapter. But that seems to be wrong advice (at least some of the time).

I am not suggesting that you don't need a follow focus, as complex shots demand that. But a lot of tripod and some handheld shots can be better handled without a focus puller and simply using the auto focus. We are going to do more tests to see just how far we can push this. But just wondering - anyone else using auto focus with their 35mm adapters?
 
This makes no sense. The HVX's lens has to be precisely focused onto the ground glass -- regardless of what the subject in front of the Nikon lens is doing. You should focus on the ground glass and then never touch the HVX's focus again -- tape it down or whatever you need to do.

Can't see how autofocus would improve anything, unless you hadn't established good focus on the ground glass in the first place?
 
Right. That's what we've been doing for the past few months - keeping the HVX's focus ring taped down and focussed on the GG. But by chance we took off the tape and put in auto focus and it seems to hold focus on the subject within a certain range of movement. Of course we are only looking at the camera's LCD right now. Later we'll see how it looks on an HD monitor. Maybe the GG grain will show up?
 
ozzymandius said:
But by chance we took off the tape and put in auto focus and it seems to hold focus on the subject within a certain range of movement.
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But how would that negates the need for focus pulling? Focus control is now done by the SLR lens, which has no autofocus.
 
Huy Vu said:
But how would that negates the need for focus pulling? Focus control is now done by the SLR lens, which has no autofocus.
Click to expand...

What we saw is that the subject can be slightly out of focus on the SLR lens, and the HVX's autofocussing lens can bring the subject automatically into focus. Of course by doing that, one is no longer precisely focussed on the plane of the ground glass, as Barry mentions. That might produce some detrimental side effect (like seeing ground glass grain), that we don't yet see when viewing the camera's LCD. We will test this out in a few days with an HD monitor to see what it looks like.
 
I'm just going to say NO!
If the SLR lens is not in focus with the subject, then apart from changing the focus distance on the slr itself, the only way to get the subject 'in focus' would be to change the backfocus - that being the distance between the focussing screen (ground 'glass') and the slr lens mount. Changing the video cameras focus DOES NOT do this.
 
Indeed, this pretty much explains itself. The image first enters the SLR lens, and if it's not in focus in the SLR lens, it's never going to be in focus. It's telecine, just make sure to have proper focus on the GG and then think in terms of the SLR lens.
 
Having the auto focus make a unfocused image in focus?

Makes me wonder if perhaps you where just paying more attention to focusing the nikon.

Perhaps the backfocus of your camera is not correct and by using the autofocus the camera finally focused properly on the ground glas.

One thing it will never do is focus your prime, It is a bit like suggesting auto exposure will create more light when you ran out.
 
Charles Lowthian said:
oh i thought that was gain. great to know that. cheers :grin:
Click to expand...


Gain is only for more grain or "film look" and the A, B switch is for shooting A or B roll. :Drogar-BigGrin(DBG)?!?!?


And to really spoil this thread with some actual facts: Back focus on handycams with electronic lenses is done by servo adjustment, a factory set average does the adjustment.

So if you zoom in, focus and zoom out it is not lens mechanics that correct the backfocus but electronics set to an average they figured would work best for this lens. On a few of the handycams I noticed backfocus is pretty horrible unless you use the autofocus.


anyway.....
 
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