Have a look at my back focus clip at DVinfo.net

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Old March 23rd, 2008, 11:00 AM   #1
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Have a look at my back focus clip

Ok,to Ex owners with back focus problems,how obvious is it if your back focus is off ?
Are you able to see it on the cam lcd or do you need a big monitor to see it ?
I think mine is ok,i've also checked it by connecting the cam to a 40 inch HD lcd.
I've posted a vimeo clip,could someone who has seen a bad back focus have a look and let me know.

Thanks. Paul
The link is below.

http://www.vimeo.com/815100
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Old March 23rd, 2008, 11:18 AM   #2
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I get the vimeo message that this clip is protected and private.
Cant watch it.
On my cameras I could see it on the LCD at first. When it got better I could still see it with the expanded focus function on fullscreen on monitors.
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Old March 23rd, 2008, 11:27 AM   #3
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OOps,it's public now,i just changed it and checked the link from here.

paul.
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Old March 23rd, 2008, 11:32 AM   #4
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Paul,
it looks pretty soft to me - I think your backfocus is off as well.
What were your camera settings? The castle in the background and the tree in front of it definitely are getting out of focus... But as the file is pretty much compressed its a little hard to judge.

cu,
gerald
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Old March 23rd, 2008, 11:38 AM   #5
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Thanks for looking at it .
So how do i fix the back focus ?
I know i need a backfocus chart but how big does it have to be and how far away from the cam ?

Thanks,Paul.
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Old March 23rd, 2008, 11:41 AM   #6
 
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looks fine to me, paul, if you're shooting with DETAIL off.
If detail is on...that may be another story.
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Old March 23rd, 2008, 11:50 AM   #7
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Hi Bill. Thanks for replying.
Yes detail was off,with standard PP. I'd only just got the cam and hadn't got to PP's at that point. I'm now using your PP with the detail on and it does look sharper than that clip.
I'll do the test again and put another clip on vimeo.
What is the absolute best way to check for back focus problems ?
Is the adjustment something that all of us will have to do at some point with this cam or are there just a few unlucky owners ?

Regarding the chart,how big does it need to be ? A4 ? And how far away ?
Where would i get a chart from,there's a few online for download ? Preston media for one ?

Thanks,Paul.
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Old March 23rd, 2008, 12:03 PM   #8
 
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I'll refer you here.....
http://www.dvinfo.net/conf/showthread.php?t=110220

DSC Labs makes some very nice test charts, but, they're pricey. Obviously, the bigger they are, the better. I always use a star chart for focus issues.

One more note: Backfocus issues can crop up with the ND filters selected. I suggest you check with and without the use of the built in ND filter wheel.
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Old March 23rd, 2008, 12:59 PM   #9
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I just found an interesting article about EX1 back focus.

http://provideocoalition.com/index.p...ing_explained/

Interesting part about using faster shutter speeds instead of using the built in ND filters.

And i just downloaded the same back focus chart from the link below

http://www.creativevideo.co.uk/publi....php?article=2

Paul.
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Old March 23rd, 2008, 01:25 PM   #10
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I think you have to do two backfocus adjustments

I am even more convinced now that there are two backfocus LUT's built into the EX1 - one for ND1/2 (ND on) and one for "ND Clear" (ND off).

I had a friend's camera and it had terrible backfocus when the filters were engaged, but perfect backfocus without the ND's.

We did a backfocus correction in both modes (re-doing the auto back focus with ND off and with ND 1) - and there was a marked improvement in the "ND on" backfocus and no degradation of the "ND off" backfocus.

For those having trouble with ND 1/2 backfocus, try doing the backfocus adjustment twice - once with ND 1 and once with ND off.
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Old March 23rd, 2008, 01:31 PM   #11
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MM,that's contradicting what that review is saying,the focus is either correct with filter on or filter off,not both.

Paul.
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Old March 23rd, 2008, 01:33 PM   #12
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Has anyone done a back focus yet and made a right mess of it,ie made it worse ?
I'm not sure if mine needs doing,it's certainly not bad.
Do i want to risk it ?

Paul.
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Old March 23rd, 2008, 01:37 PM   #13
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Hi, Eric

I know how to adjust back focus the old fashioned way, but of course, that knowledge does not work w/ the EX-1.

Any chance I could get some instruction?

I apologize if this was already posted. I read through this thread rather quickly.

Jac
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Old March 23rd, 2008, 01:40 PM   #14
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Quote:
Originally Posted by Paul Kellett View Post
MM,that's contradicting what that review is saying,the focus is either correct with filter on or filter off,not both.

Paul.
Yes, that's true. But my results were different.
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Old March 23rd, 2008, 01:41 PM   #15
 
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Someone published, a while back, some white papers together with a patent for adjusting back focus by making some of the elements in a zoom lens adjustable, not actually the rear flange, as is the conventional approach. There is some computational power needed for the adjustment algorithms to do their thing and move the adjustable elements. If you hose your system, it's only because you weren't set up properly. I have done the process 3 times, the second time it failed. But, I'm sure it was because I had too small of a target. I repeated the process, immediately, and all was well.

On the basis of optics, I don't see how the same backfocus adjustment will work with and without the ND filter. Inserting a plano-parallel piece of glass in a converging optical path WILL shift the focal point. It would make a lot of sense to me to have two memory locations for with and without the ND filter.

Last edited by Bill Ravens; March 23rd, 2008 at 02:18 PM.
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