Pulling focus nudges the frame?

B

binba

Active member
Finally getting my GH2 rig together... after (too much) consideration, I chose a Berkey System rod base, Petroff follow focus, and Tokina ATX-Pro lenses. All serious pieces of gear.

I tested the follow focus today, the gears are smoother than butter, there's no noticeable play, and yet any focus pull causes the lens to move by 1mm or so. Basically the friction of the focus ring is more than the flex of the whole assembly - and the focus ring isn't that stiff. I was going to buy a lens support bridge anyway, but now it seems like I'll have to get one that zip-ties around the lens (like the Zacuto).
I've had this happen with Nikkor primes too.

I'm just putting this out there, because I wasn't able to find similar posts. Is this really a rare problem? Being unable to pull focus on locked-off shots is a pretty big problem...

Update: see a test I shot (go full screen at 1080p).
 
Last edited:
This is something I've noticed with my OM's. It is most likely some play in the adapter itself, I use a cheap OM to regular 4/3 adapter. Not all adapters are made equal and I have read that there can be a small amount of play with some.
 
Do you have a m4/3 lens with which you could test for the nudging? If it does too it isn´t the adapter that isn´t stiff but something else.
 
It seems like more than the adapter, it's the whole camera that's moving - so it's either the tripod mount surface or the rod base itself.

The only M4/3 lens I have is the teeny Lumix 14-42, so it obviously doesn't present those problems.

I wish I had moved on to PL glass already, so a DSLR becomes pretty negligible compared to the lens and the mount. Maybe next year :)
 
The camera body is not the sturdies thing. no second pin to lock on a plate, plastic body, small mount size...
With such light camera as the GH2, adapters should have a locking system (like the current PL mounts adapters) to hold everything together. I feel like we are going toward an era where the main piece of the rig is the lens and the camera is only an attachment at the end of it.
 
Hold on ... MTF wants 265 GBP for their adaptor and another 175 GBP for their lens support = 440 GBP which @ today's close @ $1.5542/BBP = $682.88 plus shipping and customs plus a FF and rails (another $500?) to help focus a camera that Adorama is selling (with a 14-42mm lens) today for $799 with free shipping (and was selling for $699 not long ago). I dunno, but a naive side of me sez that something here is not making complete sense.... mebee I jes don understan ... or maybe the accessory companies are paying the camera companies kickbacks to get the customers into the system - the razor model " a business model wherein one item is sold at a low price (or given away for free) in order to increase sales of a complementary good, such as supplies" (Wiki you know who). King Gillette would be proud.
 
@notharrylume

Are you implying that I am getting a kickback from MTF services?

If you look around at what I have posted you will see that I have had some issues with them, but they are fixing it for me. So yes I am a fan of a company that stands by their product and I recommend it. You really dont know what you are talking about, this is a pro product and behaves as such. This adapter is machined so well it hits infinity focus at the lens hard stop.

Take a look around the AF100 user section on this forum and you will see this adapter as standrad equipment for people in the field. They also make the most popular mount for the F3. This is pro level proven gear. So yes it costs a hell of a lot more then consumer gear.

I don't use a GH2 because its $699 I use it because it will give me the best image posable in a small DSLR format.

A cheap lens adapter will give you the same image but the OP was asking about focus shift which can be solved with the MTF product. If you are using an adapter that has any play in the mount this is going to be an issue.

If you know of another product that can solve his issue I am all ears.
 
@notharrylume

I understand your position and feel the same every time I look at accessories that are matching/more expensive than my camera. But I join @bitcrusher on the fact that yes this camera is dirt cheap, and has a great censor, but we are entering an era where your camera is a modular tool. The camera body is merely a sensor with a memory card to record the image. What you feed this censor makes all the difference. And in order to get a good image, you need precision tools that you can rely on.

Yes you can film with your GH2+stock lens, with the strap around your head and get great images (e.g. I shot this 1 week after buying the camera and shot without any tools http://goo.gl/yWW3c ). But then you wan to be more stable, get a grip. Even more stable! , go for a shoulder rig. Your glass isn't fast enough, get Nikon manual lens. now you can't really tell when it's in focus, get a monitor (my DP6 is more expensive than my camera as well) You need more control over your new manual lens, get a follow focus. Your follow is pushing on your cheap camera body, either get a lens adapter to hold the lens on your rig.

As technology goes at lightning speed nowadays, a little while from now, the GH2 is obsolete, you are migrating to a new camera body, wether it's GH3 or something different. Well, most if not all your accessories are going to fit this new camera. I can use my monitor on a RED or an Alexa without issue. This adapter would be a longer investment than the camera itself.

IMHO

PS: the cake is a lie.
 
Thanks for all the responses. I shot a test to demonstrate the problem and get a better look myself:
http://youtu.be/EH9n4Bandrc

1. Is this actually common with the GH2?? I've learned about lots of HDSLR problems, but never heard of "you often can't use a follow focus because it makes everything wobble", or "lens support is a MUST". (Lens supports for non-mammoth zooms are still kind of exotic).

2. For now, I improvised a lens support out of a Noga arm. Merely bracing the lens didn't help, I had to nudge it hard, you can almost see how the lenses are forced upwards. That can't be good for the M4/3 mount either.

3. Looking at it, I'm thinking it's not the common problem of the lens mount, it looks like the whole camera is moved (by a mere nudge of the FF drive gear, geesh). Play it at 1080p and look at :38 and :40, for example.

This leads me to believe the problem is either the rod base surface, the GH2 tripod mount, or the camera body itself.

3.1 The rod base is by Berkey Systems, specially designed for the GH1/2. The mounting surface has protruding rubber panels so they flex, but my EX1 was way more stable on this teeny mount (which is not designed for it). Berkey has so far been excellent, I'll contact Brian to see what he has to say.

3.2 I've seen some posts about the protruding tripod thread, again, is this something you guys had to contend with?

4. I should note that the focus rings on these Tokinas are not the smoothest in the world, but really not that stiff. The Petroff follow focus is brand new, introduces no extra friction, and otherwise works great.

5. Thanks for the heads out on the MTF adapter, I've been looking for a something like that for a while. I know 'pro' prices but $600 is problematic. (Plus it's 1,100% more expensive than other decent but non-mountable mounts.) It's a matter of having convinced my boss this is a worthwhile low-cost system, and then finding out about this pretty big problem.
 
I have the same issue. I'm using a gini rig and baseplate, some lenses are worse than others. But it is annoying. There has to be a way to keep it steady without any movement when pulling focus, I just haven't found a cheap way yet.
 
This is a real issue and particularly with stills lenses. (I reported it in the AF100 Forum within days of the camera being released - with test footage)

http://www.dvxuser.com/V6/showthread.php?235813-Prime-lenses-rack-focus...alert&highlight=technician

It maybe a combination of everything you are looking at .. camera mount fixture, rods, lens support etc...but in the end ...the main culprit is that still lenses are not actually constructed and engineered as solidly as a cine lens.

They are not engineered for focus pulls and zooms ( stills guys dont need that) and the internals are kept light weight for AF and motorized zooming control.
Often plastic components.

The thing is...this stuff wears and the tolerances allow the play you are observing.

I had some of my Nikkors "fixed" to resolve this issue.

BTW - those bolt on ff rings as shown are not perfect diameters. They are slightly eliptical and therefore focus rotation creates different leverage on them at different points.
fixed (custom fit) gear rings will improve the issue/
 
Last edited:
I had made the case to my boss for getting 'real' (PL-mounted) cine glass, one day it will hopefully happen. For now... I think the best way to go is to anchor the lens at both ends. At the front a lens support bridge - I'm going with the Cavision for the price and adjustability. The Zacuto support would be ideal if you use the zip gear, but I think swapping lenses gets just too cumbersome at this point (oh yeah, and the price again).

At the back, I finally found an affordable mountable M4/3 adapter. I'm sure the build quality is not as good as the $650 MTF, but the basic fact it can be mounted should help a lot.

It might take a while for the adapter to ship, but I'll report when it does.
 
binba said:
At the back, I finally found an affordable mountable M4/3 adapter. I'm sure the build quality is not as good as the $650 MTF, but the basic fact it can be mounted should help a lot.

It might take a while for the adapter to ship, but I'll report when it does.
Click to expand...
I've bought several adapters from him before (his office is near mine!). Good seller but products are so-so. I don't know why but it's always the m43 adapters that are dodgy. My NEX ones work great with very little room to nudge (if any). I've learned now I shouldn't skim on such basic items.
 
I don't care if it's $30 or $60 if the quality was better, it's just the only M4/3 adapter in the world with a mount - that and the MTF. I talked to 16x9 Inc. in Burbank a month ago, they said they were working on more adapters but I haven't seen any released. Until I found it, I was actually looking into drilling and tapping an existing lens adapter, I just hope to avoid that.
 
When I started building my rig a year ago, I noticed this nudging problem during focus pulls. The camera body, being made of plastic, is the main source of nudging and flexing. Without a second point of attachment, there is no way to stabilize the lens.

I spent a lot of time brainstorming with DIY solutions, and came up with a very elegant way to solve this problem. Basically, I mounted the camera on a quick release plate like this:
http://www.amazon.com/dp/B004T16MKS...e=asn&creative=395109&creativeASIN=B004T16MKS

I made a spacer that is sandwiched between the plate and the camera. Then I attached a 1/4" nut at the bottom of the lens adapter with a hose clamp. I drilled holes on the hose clamp to allow access to the lens release button on the adapter, as well as a hole for access to the nut. I can now fix the lens adapter to the Benro plate with a 1/4" screw.

This way, I created a two-point attachment for the camera. One screw on the bottom of the camera. One screw on the adapter. It is now rock solid during focus pulls. The lens adapter becomes semi-permanently attached to my GH2. With the Benro quick release plate, I can quickly take the camera body off my rig to change battery.

I will upload a photo when I have my camera with me.
 
You must log in or register to reply here.
Back
Top