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Out of focus despite showing in focus using peaking

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Olly Lawer
Out of focus despite showing in focus using peaking
on Dec 15, 2011 at 11:51:15 pm

Hi,

I sometimes hire a 2nd EX1 for shoots from a local TV Station. I thought I was imaging it, or it was user error, but the 2nd EX1 is definitely out of focus, even though at the shoot, I clearly see peaking on everything I am shooting. I usually use the 2nd camera for a static wide shot.

Looking at the footage in the edit, I am disappointed that it seems slightly out focus. I have raised it with them before to which they told me they had no other complaints and would check the back focus...

Is there something else it could be?

Olly Lawer


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Bob Cole
Re: Out of focus despite showing in focus using peaking
on Dec 19, 2011 at 12:03:10 am

Hi Olly,

I suspect you have to adjust the back focus. A back focus problem is indicated when you focus at tele, zoom out, and find the image is soft.

There is a special automated procedure for this, but it is deliberately made rather inaccessible. I think you can mess the camera up by doing this so be warned! Take a look at this web page from the excellent and generous Don Greening: http://reeltimevideoworks.com/blog/pmw-ex1r-flangeback-adjust/

My personal experience: After putting the camera through the automated flange-back adjustment procedure, I still found it very difficult, even with a large star chart (16x24"), to verify correct back focus. The peaking does tend to indicate falsely that all is well; and even with a large monitor, I find it very tough to verify perfect adjustment by looking at a star chart. At some point, the radiating "rays" of a star chart blend together, and how can you tell whether they're blending at the correct point or not?

The most effective quick test I have discovered is to set the camera up inside, using ND2 and high shutter to give you a wide aperture, aim at some trees outside through a traditional window with muntins. Focus at tele on an intersection of muntins. Slowly zoom out, observing the tree branches in the distance. They should not be in focus; peaking will confirm this.

Good luck.

Bob C


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Bob Mark
Re: Out of focus despite showing in focus using peaking
on Dec 29, 2011 at 6:45:01 pm

There are actually three focus modes. Full Manual, Manual Focus, and Auto Focus. In Manual Focus mode there is the option (in the cam menu) to add a MF Assist function. Perhaps that was on, and it slightly over or undershot the scene. I have seen it do weird things in low light.

Bob


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Olly Lawer
Re: Out of focus despite showing in focus using peaking
on Jan 2, 2012 at 11:18:25 am

Thanks for your feedback. Yeah, I did check it was full manual and all the settings were on full manual, but thanks for the suggestion.

I've let them know, so hopefully it will be fixed next time.

Interesting what you say about low light - it was a very low lit scene, but I have noticed it in normal light conditions too. Annoying.

Olly Lawer


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Bob Cole
Re: Out of focus despite showing in focus using peaking
on Jan 2, 2012 at 11:52:15 am

If the camera's back focus needs adjustment, even the greater depth of focus that a short focal length gives you may not make the image sharp. As for peaking giving you a false indication of focus, I suspect that the resolving power on edges at wide angle is not fine enough for the peaking function to work conclusively.

I'd be very curious to know, from the other EX1/EX1R users out there, how many have had an issue with back focus (aka "flange adjustment"). I had a problem, but quickly fixed it before testing extensively, so I don't really know the answer to this question: if a camera has a back focus issue (defined as "at telephoto, it's in focus, and at wide angles, it is out of focus"), is it EVER possible to overcome it by using a smaller aperture?

Bob C


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