PMW200 Back Focus Issue

[Shaun Roemich]

Caveat: I come from the broadcast world and have over a decade of setting backfocus of true broadcast lenses from Betacam SP/SX/DigiBeta to DSR300 DVCams up to my recently disposed of JVC GY-HD200ub cameras with Fujiunon zooms. I understand the process.

So, I have repeatedly used the Auto Flangeback Adjust function on my 2 month old PMW200 with Siemens Star charts up to 20" x 30".

Wide open to f2.8, when I focus on an object at full telephoto and start to creep back in zoom, the focus point CHANGES to a point in front of the "tacked up" focus point.

At this point, this camera is very nearly unusable to me.

I'm setting AFB with a clean, well lit high contrast target of adequate size at EXACTLY 10' from front of lens on a clean featureless wall.

Help!

Addendum: this is with the lens "clicked" into MF manual focus, non-servo focus mode.

[Warren Kawamoto]

I always thought distance was measured from the plane of the image sensor to the subject, not from the front of the lens to the subject. Am I wrong?

[Chris Medico]

Unfortunately there are no other settings you can try so if the ABF routine isn't correcting the problem then the camera needs a trip to Sony for a repair.

That is a servo driven lens so there could be a problem with its calibration. That has to be done at a service center.

[Shaun Roemich]

Warren: the 10 foot reference was for the Auto Flange Back adjustment. I don't use physical measurements for focus while shooting - I use the zoom-tack-up and/or Peaking/Expanded Focus methods.

Any further than 10 feet, the Back Focus chart becomes quite small at the wide angle view while performing the AFB adjustment so I want to work as CLOSE as I can to provide an adequate chart size but far enough away to actually be able to perform the adjustment.

The ONLY thing I just noticed is that in the END of the manual (not where it tells you how to perform the procedure, which I follow to a T) it suggests that the camera should be in 59.94i mode. I've been performing it at 29.97P or 23.98P. I'll double check that later today.

For your information, here is the page that details the procedure:

[Alister Chapman]

My experience with the auto flange back routine is that it doesnt work well with a seimens chart and you want to be at least 10ft from the target. I tend to use a brick wall or wall with a patterned wall paper. The chart that does work very well is the DSC Fiddle sticks chart. The problem with a Siemens chart is that the last bit of focus depends on the very smallest part of the chart, so the most critical thing is done with the least optimum setup and the nature of the chart can introduce image artefacts that can fool the camera into thinking its in focus. The cameras focus detection circuits are contrast based so easily confused.

[Jonathan Goff]

Allister, I have 3 PMW-200's and some days the back focus is good and some days it is way off. I have performed the AFB adjust many times, but within a few days it is out again. Is this a common problem that you have seen with with the 200's?

[Bill Rankin]

I have the same problem on occasion...what I do is shift from manual focus to auto focus and then back to manual focus again and it seems to solve the problem for the moment.

[Shaun Roemich]

Update:

Had a MASSIVE failure last week while in Mexico. Needed to go find a wall mural of black on white to get the routine to work AT ALL... it kept timing out.

Brick wall didn't work.

When it looks good, it's great but this is getting silly...

ADDENDUM:
On the UPSIDE, the back focus is now as accurate as it has ever been...

Just need to carry a spare 10' x 20' WALL MURAL with me everywhere...

[Shaun Roemich]

Originally Posted by Bill Rankin

I have the same problem on occasion...what I do is shift from manual focus to auto focus and then back to manual focus again and it seems to solve the problem for the moment.

Tried that as well... didn't work for me.

[Kevin Lewis]

I will be curious to see what becomes of this situation. I plan on purchasing this camera next month. I am a little concerned because I've read about this problem before. And by the way Shaun, I just purchased a pair of Dracst led's, in part, based on your recommendation in a previous thread. They should arrive next week, just in time for a scheduled shoot.

[Shaun Roemich]

I have shoots for the next two months before I have a chance to send it away so I'm HOPING I can continue to find ways of addressing this issue.

May need to get some HUGE Fiddlehead targets...

Hope you enjoy the Dracasts, Kevin.

[Jack Zhang]

Originally Posted by Shaun Roemich

Update:

Had a MASSIVE failure last week while in Mexico. Needed to go find a wall mural of black on white to get the routine to work AT ALL... it kept timing out.

Brick wall didn't work.

When it looks good, it's great but this is getting silly...

ADDENDUM:
On the UPSIDE, the back focus is now as accurate as it has ever been...

Just need to carry a spare 10' x 20' WALL MURAL with me everywhere...

Yup, my EX1R had one massive backfocus failure in it's lifetime and it hasn't happened again. It probably is that some machines will experience one failure and then come right back after a full power-down.

[James Kuhn]

Greetings to all...I also have a PMW-200 with F/W v. 1.2 loaded. I thought this corrected the Back Focus issue? I performed the AFB routine after updating the F/W and everything seemed to work fine, but should AFB be performed on a regular basis? Is it something that should be done before each shoot? Like W/B?

I've reviewed several threads from users concerned about PMW-200 Back Focus, but I haven't seen anything from Sony acknowledging the issue, nor have I seen any Sony response with technical feedback? Is this a systemic issue?

Being relatively new to video I don't have a great deal of experience in maintaining video cameras. Is this just something you live with when operating a 'fixed lens' video camera?

Best regards,

J.

[Shaun Roemich]

Flange Back adjustment should only be done when back focus has "gone out".

In the "Old Days" this was usually when a camera (or more specifically the lens...) was bumped or when temperature changes may have caused different metals to expand and contract, changing the minute distances between mounting points of lens and camera.

The new Sony lenses have a "lookup table" that micro adjusts flange back on the fly, depending on what focal length you are shooting at. This adds a new level of complexity.

If your lens will focus at all focal distances at all focal lengths AND holds focus when zooming out from a telephoto position, you are fine. In fact, you can ONLY make things worse if you try to back focus when everything is working properly...

I've had BOTH kinds of "failures" with the PMW200:
- no focus available to me past 15 - 20 feet at a wide angle lens position
- focus point "wander" as I zoom out after tacking up focus at extreme telephoto (well, as "extreme" as one gets with a 14x wide angle lens, but you get my point...)

[James Kuhn]

Shaun Roemich...thank you for your response.

Regards,

J.