Very strange phenomenon

[Chris Fangio]

Hi there,

today I was filming my audio equipment with my XM2. Distance XM2 -> audio rack was 50cm. I zoomed in as much a spossible with manual focus. Picture sharp and clear. Then I zoomed out a little and the picture went blurry. Continued zooming out and the picture went sharp again. I retried but the effect was the same. There are always zoom-positions which are blurry. And I noticed that the picture is pumping as if the cam is trying to get the picture sharp. But hey - I was in manual mode!

The manual says that if your're using manual mode, you should zoom in to your object, get the focus right and then zoom out again.

My XM2 will be in service next week and now I'm very unsure, if this is also a defect.

I put up a Quicktime video (900kb) which can be found here:

http://www.wc-w.de/zoom.mov

This is me zoomin' in but the effect was the same when zooming out beginning with a sharp picture.


Any comments are highly appreciated.

Thanks in advance,
Chris

[Ken Tanaka]

You left the lens in auto focus mode.

Remember, switching the camera to "Manual" mode has no effect on the lens' operation whatsoever. You have to press the button on the lens.

[Chris Fangio]

Hi Ken,

no, that's what I meant mith "manual focus" ... I pressed the "focus a/m" button and the display showed "MF" for manual focus. That's why I think something went wrong.

Edit: I tried autofocus but it didn't manage to keep on focus, too. Maybe the details on the audio device were too high for auto mode.


Chris

[Ken Tanaka]

Chris,
If you're sure that the camera's "green box" switch was not set then you do, indeed, have a bug. That lens should be holding focus through the zoom using the procedure you described.

[Jeff Donald]

The minimum focus distance is 1 meter at the widest angle. The minimum focus distance increases as you zoom into the telephoto range. Move back several meters and try the same experiment.

[Chris Fangio]

I put a second video online I just recorded and used "char-recording" so you can see what I was doing. Distance was 20-30cm, so that might be the reason for this effect. But it remains somewhat strange.

www.wc-w.de/zoom2.mov


Thanks for your support,
Chris

[Jeff Donald]

All optics have a minimum focus distance. It can be decreased by adding extension tubes (not practical for video) or attaching close up filters or diopters. They are threaded like an ordinary filter and attach to the front of your lens. They can be purchased individually or in a set of 3. The set will contain 3 filters of varying power. Experimentation will show you what works best. Usually a little loss of quality is to be expected. Depending on the quality of filters the corners may get very soft. The center of the image usually stays sharp.

[Ken Tanaka]

Jeff's right about the minimum focus distance.

But I still vote for "bug". I just tried the same maneuver with my GL2 and had no trouble holding focus at just over 1 meter. If you can get good focus when you zoom-in, the focus will hold when you zoom-out and then start your shot with a slow (zoom) creeep in. The way your image's focus keeps waffling suggests to me that the auto-focus circuit has not been disabled (asssuming you're not manually trying to adjust it during the shot) despite the fact that MF is clearly engaged..

[Brian Maier]

Im having this same focus problem with my GL2, i will try and get a video of mine up today sometime.

I am also getting these wierd playback glitches. It will be playing fine then I will get a black bar along the top of my screen. It only lasts just long enough to notice it. It doesnt show up on my computer monitor just my NTSC monitor, at first i placed the blame on the GL2 but then i thought i might be my monitor but it only happens at certain points on the tape so not sure but it is pissing me off, i never had this much trouble with my cheapo Sony TRV8.

I just got this thing on friday and im starting to have second thoughts about it. ARGGGG...

Brian

[Jeff Donald]

Does it happen at the same point on the tape every time or does it vary? If it happens at the same place it is possibly a tape defect or it could have been recorded with a glitch. You might want to physically examine the tape for creases, wrinkles etc. Are you watching the camera master tape or an edited version?

[Brian Maier]

Well i checked the tape and there does appear to be a few very minor creases in the tape, so i guess that is somewhat comforting. At least it doesnt appear to be the camera. But on the other hand, i just bought 20 of these tapes so i hope the rest of them arent the same way.

[Brian Maier]

Here is a video of mine. Sorry for the poor lighting, but you can still see the focus shift. I cant get this to repeat everytime which leads me to believe that it may be something with the electronics in the camera. When i shot this the settings on the camera where: P-Box, auto, A/M Focus-MF

Well first before i blame the camera are my settings right?

www.redfusionfilms.com/focusproblem.mov

let me know what you think
Brian

[Jeff Donald]

I think you're zooming too fast in the low light for the auto focus to keep up. This is true for many cameras. Try the same setting with either more light or zoom slower.

[Rob Wilson]

Jeff, it appears he is experiencing this problem even when using MF base on his last post. You're right though, AF in low light does LOTS of hunting (which is why I almost never use it).

[Ken Tanaka]

Brian,
Are you absolutely certain that you have engaged Manual Focus? ("MF" is displayed in the viewfinder.) This looks like the same issue that Chris F. encountered. If you've really set MF then I'm led to believe that your auto-focus circuit is not disengaging. When correctly used, manual focus should set the lens' focus with absolutely no hunt or drift, regardless of crappy lighting.