Canon EF 70-200mm f/2.8L USM Lens Focus Creep

[svc490]

Hi,

I am using the Canon EF 70-200mm f/2.8L USM Lens on a non-SLR camera in manual mode (no electrical connection).  In this application we set the zoom and focus on the lens and then leave it.  What we are seeing is that the lens drifts out of focus within 2-3 days.  Camera/lens is installed in an environmentally controlled enclosure and is not accessible.  It is installed on a stable platform (little to no vibration). We tried using a lens band on the focus ring and the focus still creeps.  We are also using several Sigma zoom lenses in this application and have never had a problem.  Only this lens does this.

Anyone had this experience or can provide some insight into what is going?  Thanks in advance for your help.

[RobertTheFat]

You do have the lens itself set to manual focus, right? You don't want its autofocus motors to think they have any role in the proceedings. Given the presumed lack of electrical connectivity, that shouldn't be an issue; but it's best to rule out all possibilities, however unlikely.

I'm a bit surprised to hear that there's a non-DSLR camera on which the lens can be used at all. Are you using some sort of adapter?

[svc490]

Thank you for the reply.  Yes, set to manual as a precaution though it shouldn't matter with no electrical connection.  We use a C-mount to CanonEF adapter.

[Waddizzle]

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@svc490 wrote:

Thank you for the reply.  Yes, set to manual as a precaution though it shouldn't matter with no electrical connection.  We use a C-mount to CanonEF adapter.

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How much is it changing, a little or a lot?  Can you post samples?

If you are using an adapter, how are you supporting the weight of the lens and camera?  Can you post an image of the setup?

[svc490]

Thank you for the reply.  Not sure how to quantify how much it is changing beyond enough to affect our application.  In our applilcation we set each camera/lens to a specific zoom and focus and then leave it.  For this install (16 cameras) we have 5 using this lens and they all focus creep, the others use Sigma lenses and there is no problems.

Both camera and lens are mounted to an enclosure plate via their tripod mounts (the tripod collar that comes with the lens). 

Sorry but unfortunately I cannot provide any images. 

[ebiggs1]

OK, here is the skinny.  The focus ring has a clutch mechanism and is not fixed to the focus system in the lens.  Making it stationary won't stop the focus from changing.  The zoom ring is fixed to the zoom mechanism.

How much that helps I don't know.  I have never done what you are doing but I never noticed my 70-200mm slipping focus. Perhaps using a camera that did electronically control the lens would work better.

The Siggy's are made the same way.  Why they hold and the Canon doesn't may be to how stiff the focus mechanism is.

[Tronhard]

This reminds me of a very similar issue discovered in the film Chasing Coral.  In that case they put a DSLRs in a waterproof box underwater and configured it to take repeated shots over a series of days in order to create a time lapse.  They too found that, despite setting the lens to manual, it drifted out of focus.  I might add that neither camera nor lens was a Canon unit.

I understand they resolved the issue but cannot recall if they explained how.  Worth watching the film though if you have Netflix...

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@svc490 wrote:

Hi,

I am using the Canon EF 70-200mm f/2.8L USM Lens on a non-SLR camera in manual mode (no electrical connection).  In this application we set the zoom and focus on the lens and then leave it.  What we are seeing is that the lens drifts out of focus within 2-3 days.  Camera/lens is installed in an environmentally controlled enclosure and is not accessible.  It is installed on a stable platform (little to no vibration). We tried using a lens band on the focus ring and the focus still creeps.  We are also using several Sigma zoom lenses in this application and have never had a problem.  Only this lens does this.

Anyone had this experience or can provide some insight into what is going?  Thanks in advance for your help.

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