Prime lenses, rack focus...alert

Shooter

Shooter

Veteran
Link to test shot.

http://vimeo.com/19021498


I have been setting up my AF102 as a production rig which is how I use any camera in what I do.

This means baseplate, rods, follow focus , matte box, on boards etc...

With the AF102 I will be using my own Nikkor set and PL lenses (rentals) in a production configuration.

While doing this set up , I discovered a little issue!

With old lenses (such as Nikkors) and worth checking with any other non cine style lens...

As amazing as the images are .. you need to be aware that you can get an image shift when focusing these lenses. ie racking focus.

The issue is not the adapter mount, or the rings (in my case) ...it is mostly in the focus mechanics of an older lens not designed for "rack focussing". A follow focus or a hand rack direct on the lens can display the issue.

It can be partly attributed to wear.

Test: Lock off your head and legs on a subject...do the focus pull.

Comments anyone please. ( Check your lenses your self)
 
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It's just the still lenses breathing, common with any non-cine lenses. They breathe because in stills there's nothing it needs to capture while you focus. It's something to be aware of for sure, but something we'll see more and more as these cheaper cameras come out and people use all kinds of stills on them. Any Cine Lenses should not have this breathing issue at least for the most part. You'll find the mechanics of the PL lenses a whole different league.
 
From experience, some old canon FD lenses(zooms especially) do this wobble when changing focus directions. I think it's due to being so old and worn. I try to avoid buying lenses that look like they've been dropped or bumped(dents and scuffs) because of this.
 
astigmatic said:
From experience, some old canon FD lenses(zooms especially) do this wobble when changing focus directions. I think it's due to being so old and worn. I try to avoid buying lenses that look like they've been dropped or bumped(dents and scuffs) because of this.
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He's talking about the image appearing to slightly change size as you rack focus. It's called breathing. You get more breathing in still lenses and less to little to none in cinema lenses. What you're referring to is something different that could be fixed. You can't do anything about breathing in a still lens other than slowing your rack focus down enough to make the breathing less apparent.
 
Mike@AF said:
He's talking about the image appearing to slightly change size as you rack focus. It's called breathing. You get more breathing in still lenses and less to little to none in cinema lenses. What you're referring to is something different that could be fixed. You can't do anything about breathing in a still lens other than slowing your rack focus down enough to make the breathing less apparent.
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This effect is not "breathing".

It is an image shift in the direction of the focus rack. Rack counter clockwise and it shifts left ( and vice versa).

I have not observed it shift up or down but believe that I could induce that. ( Will test)

It is absolutely the "slack" and "wear" in a lens that is not usually observed in movement of the focus ring. eg.a still photo is taken after the focus is made.

The operator and the AC need to be aware of it.

It is subtle but enough to ruin a shot.
 
Shooter said:
This effect is not "breathing".

It is an image shift in the direction of the focus rack. Rack counter clockwise and it shifts left ( and vice versa).

I have not observed it shift up or down but believe that I could induce that. ( Will test)

It is absolutely the "slack" and "wear" in a lens that is not usually observed in movement of the focus ring. eg.a still photo is taken after the focus is made.

The operator and the AC need to be aware of it.

It is subtle but enough to ruin a shot.
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Then I'm confused about what you're referring to. It sounds like a mount-related issue. I notice a slight physical shift in my lenses when I rack focus and it's because of the mount type. With PL mount you don't get that. With m4/3 and Nikon mount you do get that. Try moving the lens by hand once it's mounted. You notice a slight shift in it. As far as I know there's no way to "fix" that, but if someone can point out a way I'm all ears.
 
I have that exact same problem with some of my nikon primes. I actually sold a mint 50mm 1.4 for this very reason. The image shift when changing focus direction was just too much.
 
oh yeah, to add. I dont' think I've ever had an L series Canon FD do this. They're much better built than the regular fd lenses. Also, I have not seen this happen with any of my Contax Zeiss lenses. Another reason to buy quality, even when going vintage.
 
Isn't this the 'issue' that led Optitek to develop their positive locking mount for Nikon lenses used on the RED? Any time I've used still lens glass on adapters I've seen this - and it's always been because of slight (micro slight - almost imperceptible) movement between lens and mount adapter.
Still lenses and their mounts just were not designed for the stress of a follow focus - place another point in the PL cine lens column.
 
I've experienced this as well with my Nikkor 35mm 1.4. Let me add that it is not just old as in 'worn' lenses. Though the 35mm 1.4 is an AIS (old design), it was brand new from B&H and exhibited this issue.

It's really subtle though.
 
Taylor Rudd said:
My only lens that has this problem is the 50mm f/1.4 AI-S
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This is the same lens I have this problem on. It came back from a rental a couple years back and was never the same. It still works great I just try to avoid racking with it. And if I do have to rack with it I only do one rack one direction. That can work if before you start you go beyond the first mark, then turn around and go the direction you intend to do the pull up to the first mark. Think rotating caster wheels on a dollie and sometimes you have to go past the starting point and go back up to it so the wheels spin the direction you intend to move.
 
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I get this issue on my 7D. If I use my canon 50mm 1.8, I get some jerkiness while focusing. This is a cheap $100 lens. It's incredibly sharp, but is built like crap. When I use my L series glass, the problem is gone. This issue is simply due to cheap construction or lens wear. This is a non-issue for stills. A reminder that we are using gear outside of the application for which it was built.
 
I believe others are confirming the fact that the image can "shift" when racking focus.
Yes , I also think it is the glass and the mechanical connection to the focus ring. There is most likely some sort of helical thread in that mechanism ( that could wear)

In my case it is definitely not the mount.

Those that have had their lenses dampened... can you test to see if it is a total solution? (I will get my lens technician to check mine and offer an opinion on that - will report back )

I would be really keen to hear if any of the RP Lens cine conversions exhibit this?

I am going to check my entire lens set today. I will record and post a test that exhibits the issue later.
 
It's not a mount related issue, it's literally the lens mechanics and the fact that they're old.

It's a loose barrel and yes, it does happen. Especially with Nikons.

The new Zeiss lenses do not have this, unless they've been damaged.
 
I've experienced both phenomena, the image shifting due to the adapter being torqued by the follow focus (on my 5D) and then exactly what Shooter is talking about. I had a old Nikkor 24 f2.8 AI that did this, bought a newer manual focus AIS 24 and the problem is gone. My 20 year old 16mm does it also. You can have it mounted on a NIkon even and see the effect. I'd be surprised to see a MF Nikkor new out of the box do it. The engineering and lack of plastic that went in to those lenses were top notch.
 
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