Lens won't hold focus when zooming at DVinfo.net

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Sony VX2100 / PD170 / PDX10 Companion
Topics also include Sony's TRV950, VX2000, PD150 & DSR250 family.


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Old March 6th, 2002, 08:19 PM   #1
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Lens won't hold focus when zooming

Is the zoom lens not a true zoom but a vari focus? On all other cameras with zooms (pro cams),I have always zoomed in tight for focus then made sure backfocus was adjusted so I woud hold focus throughout the zoom range.

Not so with the 2000, I have to refocus at every focal length... makes zooming during shots a racj focus manuever.. then add that to trying to focus using the color viewfinder.

Of course, there is no back focus adjustment on the camera. I know this is a new lens, but at least my 1000 acted like a real zoom lens.

Is it my camera? I have read quite a few forums on the 2000 and haven't seen a complaint about focus.

tia, rob
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Old April 2nd, 2003, 11:14 AM   #2
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no backfocus on PD150?

I just realized this problem with the sony PD150/vx2000, and I'm wondering if anyone has a definitive answer on the subject. Is there no backfocus on the pd150? What is the best way to ensure focus when zooming? Does sony think that AF is sufficient and therefore no attention is paid to backfocus? I've also heard that if one does not zoom to full tele and manually setting focus, focus is maintained when zooming back.
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Old April 2nd, 2003, 01:08 PM   #3
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If you zoom into your subject then focus, then zoom back, it should still be in focus and keep focus throughout the zoom range. Is this not happening?

John.
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Old April 2nd, 2003, 02:33 PM   #4
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Yes, that is how I've always focused with the PD150, but it has come to my attention that some people has experienced a loss of focus when zooming out from full tele after having focused manually or pressing "push auto". The backfocus seems to be almost non-existent or at best unreliable. The advice I've been given is to find focus whenever I zoom to compose a new frame. Some even say that the problem only affects some individual cameras, and not every unit of the same make.

I've found similar, but few, discussions on the web on this topic, but none give a final conclusion as to what the problem really is.

From the web:

http://www.nikonlinks.com/ruether/posts_html/backfocus%20and%20focus-shift%20with%20zooming.html

http://www.nikonlinks.com/ruether/posts_html/incorrect%20backfocus%20in%20%20zooms....html

even the XL1 is said to have a similar issue:

http://dvinfo.net/canon/articles/article30.php


All in all, the PD150 is not really a proffesional camcorder (even though it is used by broadcasters all over the world), and perhaps sony has implemented some solutions of lesser quality to save money in production; thinking that the AF will do the job in most circumstances.
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Old April 2nd, 2003, 04:24 PM   #5
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I wonder if you could try a little experiment...


1 Switch to manual focus

2 Zoom full tele then focus on an object

3 Slowly zoom back

4 Stop at the point where you suspect focus is lost and make a note of the zoom scale in the viewfinder (24 clicks)

5 At that zoom position see if you can get better focus

6 Report your findings here
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Old April 3rd, 2003, 11:46 AM   #6
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I have a friend who bought an XL1 new, and it would lose focus when zooming back. He sent it to the service center, and they recalibrated the lens to the camera and all is well.

I've also got a DSR250, which has the same lens as the PD150, apparently. There is no back focus issue with it.

So, I would say if there is a problem, the camera should be sent to a Sony service center. The early VX1000's had that problem, but VX2000's and PD150's don't, unless they are defective, I think.
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Old April 3rd, 2003, 01:35 PM   #7
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Getting back to Rob's initial post; that indeed is a problem. I recently loaned out my camera, and when I got it back, it exhibited a very unusual problem; it would not focus manually. I tried everything I could think of to get it into manual mode, but no luck. I would zoom into something at ten feet (for example) and the camera would focus on the object. Then I would pan over to something at four feet, and the camera would focus on that object. All this while everything was in manual mode. I was about to call the person who I loaned the camera to, and tell him the camera was going to the Sony repair center and be prepared for a big bill, but I decided to try one last drastic measure first: I pressed the reset button to restore everything to the factor settings. And lo and behold, that did the trick. The camera focuses normally now, but I am still curious as to what he did to cause the problem. I would suggest Rob gives this a try before sending the camera in for repair.

Open the lcd screen. Look in the lower right hand corner where all the menu buttons are located. There you will find a very tiny recessed button labled "reset." Use a pin or some other small pointed object to press this button. The camera will burp, and you will be returned to the factory presets on everything. This means you will need to set your clock, calendar, custom presets, audio (48K), track set ups, DVCAM mode, etc, etc. This is obviously a drastic measure, but it may save an expensive repair bill.

Remember the lenses on these cameras don't work like a true lens: you have a look up table that it uses to calculate the proper focus, so there really is no back focus in the classic sense. You can't adjust back focus if there is no back focus adjustment. And there are a few isolated instances where you may not be able to get the lens to work exactly the way a real lens would. That's the trade off with a lower priced camera. But certainly it should track normally for most situations.

Let us know what happens if you use the "reset" button, Rob.
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Old April 3rd, 2003, 04:51 PM   #8
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There truly is a back focus adjustment on the VX-2000/PD150 according to Sony. Because a Sony tech screwed mine up and the camera had to go back to be adjusted. They had removed the lens and forgot to check the back focus. We mortals just cannot get to it without some disassembly. I guess that is the reverse of 'Some Assembly Required.'
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