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-   -   image stableizer, zebra stripes and auto focus (https://www.dvinfo.net/forum/sony-vx2100-pd170-pdx10-companion/26445-image-stableizer-zebra-stripes-auto-focus.html)

Adi Head May 24th, 2004 01:18 AM

image stableizer, zebra stripes and auto focus
 
questions regarding the pd150:

1. does IMAGE STABLEIZER function, when turned ON, affect the image quality in any way?

2. do you use the zebra stripes function to set exposure?

3. i know that in most cameras the AUTO FOCUS mechanism has to set itself every once in a while, causing the picture to momentarily come out of focus and back into focus. does this happen with the pd150 AUTO FOCUS function as well?

thanks

Tom Hardwick May 24th, 2004 06:26 AM

1) What you and I can have bought Adi, is a mechanical device that vibrates (in almost complete silence) a vari-angle prism in sync with and opposite to the shake you're applying to the camera body. In real time the camera is detecting the shake, calculating its speed and direction, applying electrical currents to the linear motors that move the element, overcoming the inertia of the element, accelerating it in compensation, decelerating it
to a stop and setting it off in a completely new direction. It does this to bend the light that is rapidly (oh yes) travelling on its way from the front element to the chips. It does it just-in-time.

There must be losses, but the quality level of DV footage isn't good enough to detect it. As I've said before Sony's Optical Steadyshot is the closest you'll get to real magic for the next few years.

I leave my almost totally transparent Sony SS on permanently.
When people ask me why I don't rate it as totally transparent, I point to this one tiny failing: with a powerful wide-angle attachment you can have no vignetting with the camera stationary yet can see the vignetted corners float into view when the camera's shaken. Not visible with TV masling of course.

If you're using a rock-solid tripod then turn the SSSS off, that way you'll save battery power and delete another variable.

2) Yes - use the zebras to guide you when setting the exposure manually. Click to auto - see what zebras the camera likes. Then switch to manual and fine-tune from there.

3) No. It will only refocus if the subject matter changes.

tom.

Adi Head May 24th, 2004 06:58 AM

thanks tom.

Mike Rehmus May 24th, 2004 10:11 AM

I have to comment about a couple of things.

1. OIS does cause an artifact that is normally masked when hand-holding the camera but at times is painfully apparent when the camera is moved on a tripod.

Because the OIS does counteract motion from any source, it thinks a pan or tilt while on a tripod, are motions to counteract. and does so. The result is a video image that trails the field of view by some amount, depending on the speed of the motion. Within a small range of speeds that seem to correspond exactly with the motion I want, the generated artifact is apparent and can cause a problem.

The artifact is this. You start to move the camera and the captured image doesn't follow. OK, so who will know? But, you stop at the other end according to the image you see in the viewfinder and the image captured by the camera does not. OOPS. You just overpanned or over tilted.

This is not necessarily apparent to a viewer of the resulting video.

2 Because the camera is very susceptible to RFI and I spend a fair amount of time in situations that can cause RFI, I tend to keep the OIS off.

So when will you find RFI strong enough to effect the OIS (or more)? A photographer's stobe will do it. As will many radio transmitters including Police and Fire radios, hand-held radio transmiters, RC transmitters, etc.

The RFI can cause a rapid shift of the image as the OIS slams into its limits, sometimes many times and at high speed. The camera will actually vibrate quite strongly when this happens. You also, with an on-camera microphone, will pick up the mechanical noise of this event.

Sony replaced my first PD150 because of this. The new unit is just as susceptible.

3. OIS is the cause of the dancing fairy lights you will see if you shoot a scene (normally at night) where lights or highlights are present in the field of view and the camera is not held steady. What you see is a second copy of all the lights in the scene but spaced away from the 'real' light source. As you move the camera, the phantom lights dance around. The only way to stop the dance (not the phantom images) is to turn OIS off.

The phantom images are caused by reflections off the OIS optical elements which are really variable wedges.

4. Auto focus isn't exactly the rock-solid focus we wish it were. In difficult shooting situations, like in very dim light, it will hunt quite badly. And at extreme telephoto, it takes a long time to focus even in good light with reasonably decent subjects in the field of view.

I have also had it hunt while taping a normal scene that was of low or medium contrast.

I leave auto focus and OIS off unless I specifically want those functions.

The zebra stripes work very well for setting exposure. Much better than the auto function.

You want just a bit of zebra on a caucasian skin, less as skin gets darker (only experience will help you here), a fair amount on green grass or medium blue sky or an 18% gray card.

K. Forman May 24th, 2004 10:50 AM

Sounds like a cool new way simulate drunkeness with a cam! Thanks for the idea Mike!

As far as auto focus goes, I have found it to be more of a nuissance than a help. There is always something more interesting that the cam wants to focus on, regardless of what you want. Someone here said it the best- *Let the camera decide what it likes, then lock it down, and shoot it manually from there.

As far as the image stabalizer, I am overly critical of my footage anyways, so when I see additional artifacting, I want to eliminate it. I use a tripod or a mono pod, so I don't need it. If I were to start doing more handheld, I would get a steady cam and avoid the extra blemishes.

The zebra stripes are the neatest thing since sliced bread, and I work with them. When set properly, it really does help your exposure look better.

* Not an exact quote, but you get the idea?

Adi Head May 24th, 2004 04:18 PM

from my short experience using the pd150, i found it rather hard to manually focus during a shot when not shooting zoomed in. when setting focus prior to shooting, there's no problem. i just zoom in - focus - zoom out to the desired frame and shoot. but trying to focus while shooting is really hard. also, probably one of the most unprofessional things about the pd150 is it's manual focus ring, which really frustrates me.

i'll try using the zebra stripes.

thanks.

Mike Rehmus May 24th, 2004 06:07 PM

There is where the momentary auto focus button may help. But the proper way to focus is to zoom in and focus, then set the zoom to taste as you mentioned. Neither the viewfinder or the LCD have enough resolution to allow focusing anywhere in the zoom range but all the way in or close to it.

Glen Elliott May 25th, 2004 12:57 PM

I'm too much of a chicken to shoot without Auto Focus- it's the ONLY auto function I use. Granted using the push auto button would help but knowing me I'd think I have the focus locked then go back in post to see it's a hair out of focus! Shooting event videography (weddings) tends to be very fast paced and can throw you some curve balls due to the uncontrolled environment. Auto focus is a nice saftey blanket- besides I've yet to have a problem with it thus far. If it's so dark it's having trouble locking focus it's too dark for the footage to be usable anyway.

Auto focus on an XL-1s on the other hand...that's another story. It's constantly fading and relocking even with well lit subjects and no camera movement. It's terrible.

K. Forman May 25th, 2004 01:28 PM

"It's constantly fading and relocking even with well lit subjects and no camera movement"

It's almost like they have attention deficit disorder, eh?

Mike Rehmus May 25th, 2004 05:44 PM

<<<-- Originally posted by Glen Elliott : If it's so dark it's having trouble locking focus it's too dark for the footage to be usable anyway.
-->>>

I frequently have to shoot in environments lit only by candles. Not a great image but it is an image. And that's what the bride wanted even after being warned. In those situations the AF turns into a Hunter

Glen Elliott May 25th, 2004 06:17 PM

Ouch- and I thought simple reception environments were tough.


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