VX2100 Vignetting in Default Configuration

[Georg Liigand]

Hello everybody,

I received my new VX2100 about a week ago and am more than happy with it. There is just a small thing I noticed - in full or almost full zoom I get a slight vignetting effect although I haven't added any accessories and it has the factory lens hood installed which probably causes it. Not that it's a problem for me, but I'm simply wondering if it's normal with those cams.

Thanks!

[Dan Robinson]

I've had my 2100 for almost 2 years and have noticed this as well. It shows up more on a computer screen than on a monitor/TV.

[Richard Zlamany]

I think it is normal.

[Georg Liigand]

Yep, it certainly shows only in computer screen as TV crops the picture quite much. I'm also thinking it's nothing abnormal, but just thought I should ask.

[Tom Hardwick]

The VX2100 lens does indeed vignette the image, as does almost every other lens ever produced. The ones that don't have an aperture control ring that disables the widest two apertures, but this is a desperate measure to control a barely perceptable phenominum. It's not dependent on focal length BTW.

Hassleblad sell a 'grqaduated ND' filter that's one stop darker in the middle, fading out to clear glass at the outer diameter - and this is to counteract the vignetting that even their highly acclaimed (and expensive) lenses give.

Using the zebras clearly demopnstrates the vigentting that the VX/PD gives wide open, but it takes a trained eye to spot it in normal programme material. So this gets me thinking Georg - are you talking about vignetting of say one or two stops, or do you mean physically black corners to you image? If the latter then you have cause for complaint, as the hood (if fitted correctly) certainly doesn't impinge onto the image area at all.

[Georg Liigand]

Lots of good information, thanks Tom!

I double-checked and it's certainly not the lens hood causing the vignetting, but it happens just as well without the hood too. So it probably is the lens vignetting effect you told about and I guess it's normal. It does seem to be happening at the wider exposure settings and the little black in the corners is very very smooth, but noticeable in PC.

[Tom Hardwick]

I'm sure your camera has a fault then Georg. There should be NO black corners however you view your images. I wonder if the end-stops of the OIS have been set correctly? If you switch off Steadyshot does this problem go away? You've not stacked a couple of filters in front of your zoom, have you?

Remember that one day you might well be projecting your fiilms using a full-frame video projector. The visible vignetting won't look too good then. I'd have the camera checked out if I were you.

If you add a wide angle converter, switch on Steadyshot and wave the camera about, does the vignetting get worse?

tom.

[Georg Liigand]

Hi Tom,

I did more testing today and I think it was my own mistake - it's probably not real vignetting, but something that comes in low light. I did the testing in my room and I have very poor lighting here. I just pointed the desk lamp to the wall and then took the wall to my camera screen. The "vignetting"-like effect seems to go as soon as I put more lighting to the wall, even if exposure is locked. Maybe it has something to do with light entering the lens and the most gets in from the front of the lens and the sides stay a bit less illuminated resulting in the darker areas?

In good light there is none of that vignetting.

[J. Stephen McDonald]

Originally Posted by Georg Liigand

Hi Tom,

I did more testing today and I think it was my own mistake - it's probably not real vignetting, but something that comes in low light. I did the testing in my room and I have very poor lighting here. I just pointed the desk lamp to the wall and then took the wall to my camera screen. The "vignetting"-like effect seems to go as soon as I put more lighting to the wall, even if exposure is locked. Maybe it has something to do with light entering the lens and the most gets in from the front of the lens and the sides stay a bit less illuminated resulting in the darker areas?

In good light there is none of that vignetting.

It's a simple fact that in low light, the aperture opens wider. This allows the outer rim of the lens and any accessory mounted on it to be more likely to be inducted inside the image margins. A narrower aperture position would exclude those outer features from the optical image. Vignetting that occurs with a telextender or wide-angle lens is usually greater at a given zoom setting, when the light is lower.

[Tom Hardwick]

Not sure I go along with your theory Steve, as it would suggest that wider apertures change the field of view (i.e. the focal length). They don't.

But most cameras vignette the image in the extreme corners of the frame at full aperture - usually by a good couple of stops. Of course this gradual fading to under-exposure in the extreme corners is rarely noticed, but will be pretty obvious on plain, evenly lit walls in static shots.

The other time it's noticed is when you come to stitch a panorama in Photoshop from frames taken in progressive scan as you pan across a scene, but this a rather a specialist case.

tom.

[J. Stephen McDonald]

Originally Posted by Tom Hardwick

Not sure I go along with your theory Steve, as it would suggest that wider apertures change the field of view (i.e. the focal length). They don't.

tom.

Tom, a wider aperture may not change the focal length, but it will allow a larger diameter of the optical image to pass through. When the swath of light that is used for the image, angles inward through the lens, if a wider portion passes through the aperture, it is more likely to include the edge of the lens rim or add-ons in what strikes the CCD. This can be demonstrated by putting a telextender on the lens, then manually lowering the exposure setting a bit and zooming back to the point where vignetting begins. If you then manually increase the exposure setting to a proper level, you can see the vignetting increase, as the aperture widens. You could demonstrate the same thing by using an ND filter to widen the aperture while on auto exposure. Of course, in doing these things, you need to be sure that the increased vignetting isn't due primarily to the presence of the add-ons.

[Tom Hardwick]

Hi Steve. You say: "Tom, a wider aperture may not change the focal length, but it will allow a larger diameter of the optical image to pass through."

This isn't really optical engineering speak IMHO. When you open the aperture by individual stops from f/11, you let in twice the light. So moving from f/11 to f/8 lets in twice the light. Moving to f/5.6 lets in 4 times the light and so on.

That's all it does. It doesn't allow the lens to 'see more' of the object it's looking at, and it doesn't affect the image circle at the film plane. What it will do is alter the dof and affect the sharpness and the flare levels of the image.

Often lenses vignette the image if we've used too many stacked filters, say. At wide apertures this vignetting might well go un-noticed as the offending filter ring will be so out of focus, but at very small apertures the ring will become a lot sharper in the image, and the vignetting will appear worse.

Some cameras alter their set focal length as they're focused from infinity to macro, and this can indeed alter the field of view.

tom.

[J. Stephen McDonald]

Originally Posted by Tom Hardwick

Hi Steve. You say: "Tom, a wider aperture may not change the focal length, but it will allow a larger diameter of the optical image to pass through."

This isn't really optical engineering speak IMHO. When you open the aperture by individual stops from f/11, you let in twice the light. So moving from f/11 to f/8 lets in twice the light. Moving to f/5.6 lets in 4 times the light and so on.

That's all it does. It doesn't allow the lens to 'see more' of the object it's looking at, and it doesn't affect the image circle at the film plane.

tom.

Tom, I think our differences on this are based more on nomenclature and different ways of describing things, than they are on lens function. True, a wider aperture can't cast a wider image of the subject that's outside the end of the lens. Only a change in the focal point will alter the width of the subject's image that reaches the CCD. From this point on, I suspect we aren't talking about exactly the same thing. However, the tests I described show increased vignetting with a wider aperture, under some circumstances. I'm going to do all these exercises again (much more carefully) and see if I can find a flaw in my observations and reasoning. I won't stick to this position if I can convince myself there's another explanation for what I'm seeing.

I've also seen changes in image quality (improvements sometimes), by using ND filters. But the reasons I've assumed for some of the changes don't follow standard lens theory, as professed by some experts. I think it's a mistake to assume that experts are always right about every aspect of their subjects. Only by postulating ideas that may be proven wrong, can you chisel out a bit of hidden fact.

[J. Stephen McDonald]

Tom, I hashed over all this in my sleep and then dragged myself out of bed at 5:00am, as I had to resolve it. After playing with several of my old camcorders, I have concluded that you were right about aperture width not affecting the amount of vignetting. What I had been seeing, to give me the mistaken impression that a wider aperture increased vignetting, was this:
With a narrower aperture and reduced exposure, the dark, vignetted corners were faded and less visible. When the aperture was widened and exposure increased, the contrast and visibility of the vignettes increased, leading me to think they were becoming larger. In fact, they stayed the same size and just their visibility was changing. It seems that the corners lose contrast a bit more than the center of the image, when exposure is lowered. So there, I've learned something. The complexity of these lenses is great and after learning more about them, one can appreciate the precision work that went into engineering them.

I was further rewarded in this little examination by discovering that my Canon A1 Digital and L1 both still work flawlessly-----no ruptured capacitors yet, even after sitting in cases for many years. Too bad these models weren't given better CCD and battery systems, as they would have been champs in their time. If I could put the CCD and its processer from my Sony TR700 into either of them, I'd still find situations to use them. Of course, the fundamental L1 is still present in its DV and HDV descendants. At the time of their introduction, in '90 and '91, Canon was using good lenses and mediocre CCDs in their camcorders, while at the same time, Sony was putting great CCDs and crappy lenses in their consumer models. If they'd combined the strong points of both brands, the result would have been just what we wanted. Naturally, they didn't do this, as customers who get just what they want, don't buy new camcorders the next year.

[Tom Hardwick]

Good to read your revelations Steve. I remember waiting till video 'got better' and I bought into a TR2000 Hi-8. Verses the competition available at the time the Sony's VAP OIS was miles ahead, and that kept me buying Sony (TRV900, VX2000). I did buy a Panasonic MX300 while my TRV900 was away for repair, but although it gives good results, it's the TRV900 I remember with fondness.

I'd change your last line. Customers who get just what they want stick with the brand when they replace their camcorder, upgrade to HiDef, recommend it to others and enthuse constantly. That's why the VX/PD series has done so exceedingly well.

tom.