Long End of the Zoom
 

Uh oh... just noticed today, for the first time in the 7 months I've owned my PD170 that when zoomed in all the way, there is a weird circle - like i'm seeing the iris or something. I set the exposure to 2.4 so that it wouldn't change and the circle is still happening.
What's going on? Is something misaligned?

post .jpg

lens hood?

leslie

If you point towards a white wall in medium light conditions, zoomed right in, aperture wide, you may see a slight darker greying of the image in a circular pattern into the corners.

I think that may be normal trait and means that have to be lived within. As mentioned above, post a frame grab, because what you have may be exceptional.

Dave - remove all filters and the lens hood and try again, you may well have a camera fault. Is the vignetting still there? Remember that at maximum aperture the corners of the PD170's frame are all under exposed by 1.5 stops, but this is normal vignetting and all cameras suffer in the same way.

Generally it's not noticeable (normal programme content) but when shooting test charts or frame filling signs it will be. Easy to test out using your zebras - and it comes as a surprise to a lot of people.

To remove vignetted corners stop down two stops. To f/3.4 at wide and f/4.5 at tele.

tom.

I was very surprised when I noticed the same thing on my new VX2100. Its one of the few things that has made me wish I sprung for the PD170 -- being able to stop down to f3.4 or so and turn up the gain if need be. In my case, I rarely need to go to full telephoto, so if I'm in a low light situation I can force the aperture to f2.4 with a little gain and zoom back out, and not notice the vignetting at 5x zoom or so. But I definitely see it at f2.4 and full zoom, or at f1.6 and ~3x zoom.

Also keep in mind how you're viewing the final footage -- if its on a conventional TV, then the corners are partially cropped, but if your material is being viewed on a digital screen then everything gets viewed.

Yes Terence, the PD170 does allow you the freedom to have evenly exposed footage corner to corner in the frame but in my view the +12dB of gain-up needed to effect this is not a fair trade. I'd rather have footage shot wide open and 0dB gain any day.

tom.

I took off my sunshade and UV filter and the problem is still there.

I looked at some stuff I shot this past summer, bright daylight stuff exposed from f8-f11 with the built in number 2 ND filter. I didn't notice any vignetting.
The footage that I noticed this problem in was pretty contrasty and shot around f4, I think.

Are there certain things, certain lighting conditions that have to be preent in order for the vignetting to occur?

Thanks a lot.

~~Dave

Vignetting is an optical-mechanical issue. All lenses vignette to some degree. Usually this is seen when the aperature is wide-open and the scene has smoothly lit areas (like the sky, a white wall, etc.).

You can remove the effect in Post or just avoid if you can, the settings at which it becomes objectionable.

how
 

I know this is a little late. I haven't been doing much full-screen stuff in the conditions where this problem occurred since I last posted on this thread. Now, however, I realized that I may need to do just that. How can I remove this problem in Post (I'm using Premiere Pro 2.0)?

Thanks.

~~Dave

In post I'd apply a feather-edged circle to the centre of the frame, then reduce the exposure within that circle. In fact Hassleblad sell just such an ND filter - it gets gradually darker towards the centre (1 stop down) and their instructions suggest using it for open aperture and the next stop down.

Your VX/PD will easily show you how much your lens vignettes the image. Turn on the 100 zebras and select maximum aperture but with zero gain up. Allow the shutter speed to vary to give you correct exposure of a plain white sheet of paper that fills the screen.

You'll notice that the zebras only occur in the center of the frame at max aperture. As you close down by a half stop the zebra area expands, so that when you're 1.5 stops down (wherever you are in the zoom range) zebras evenly cover the frame.

This is showing you that anything you shoot wide open under-exposes the edges of the frame by 1.5 stops. Not usually a problem, though it will be if you try and stitch still frames together to make a panorama.

As Mike says, this 'problem' isn't unique to Sony. All lenses suffer from it, even if you buy expensive Hassleblad Zeiss optics.

tom.

I have it on my camera also. Was setting up for lens shading adjustments on the F350 and saw this on the luminance scope with aperture wide open. At F4.5 the line goes flat, indicating even exposure across the frame. At wide open, the scope will show a drop off in luminance at the edges of the frame.

-gb-

How is it removed in Post?

two posts above yours Russ.

oops, sorry.