line curves on edges of Z1U lens...mystery

[Nicholas Natteau]

Just quick question about something that has me puzzled:

When I checked out the Sony Z1U video camera in the store, everything was perfect. I aimed the video camera at a door frame so that the frame was on the edge of the lens. Amazingly, the vertical frame of the door did not curve.

But on the Z1U I purchased and brought home with me, I do see straight vertical lines curving towards the edge of the lens.

I'm sure it's just a setting to tweak in the camera.

Suggestions welcome!

- Nicholas

[Douglas Spotted Eagle]

Haven't seen anything like it, but could you post a pic? Email it to me if you don't have a posting location, I'll host it on a private page. I'd like to see what this looks like.

[Nicholas Natteau]

post

[Ben De Rydt]

I guess that what you are seeing is barrel distortion. Zoom in and it will be gone.

Barrel distortion is an optic phenomenon. It is a function of the focal distance of the lense. Wide angle lenses show barrel distortion, telephoto lenses do not. Since the Z1 has a fairly wide angle lens at wide open(32 mm in 35 mm equivalent terms) it will show some barrel distortion.

[Nicholas Natteau]

Thanks for your reply.

What puzzles me is that on the Z1U that I played with at Rule Broadcast Systems in Watertown, MA, there was no barrel distortion at all, not even when the lens was zoomed out all the way.

That's why I'm wondering if there is a setting somewhere in the Z1U menu that minimizes or eliminates barrel distortion.

- Nicholas

[Douglas Spotted Eagle]

Nope...there is no setting, which is why I'd like to see a shot of yours and compare with my cameras. It would be good to start a repository of potential "problems" with the camera if there are any.

[Bill Pryor]

Could be a lack of quality control in the lens, or they could be using two different lens suppliers. Or the lens manufacturer could be using different suppliers for its glass, or could be lacking in good quality control. I've seen variation in two different identical lenses before.

[Patrick Williams]

On my FX1 I notice it on some shots I took of some tall buildings, but again only when zoomed out completely. I'm fairly sure that it is not a problem at all, but rather the beginning of a fisheye effect because of the wide angle lens. Because the picture is wider horizontally the effect is noticed on the left and right. If I zoom in just slightly, the vertical lines become perfectly straight, due to a slightly longer lens.

[Derek Serra]

"Could be a lack of quality control in the lens, or they could be using two different lens suppliers. Or the lens manufacturer could be using different suppliers for its glass, or could be lacking in good quality control."

Somewhat unlikely, as these are all Carl Zeiss lenses - and Zeiss are particularly fussy about components, quality control, etc. That said, if you're not happy, take the camera back and ask to try another.

[Barry Green]

It's likely just barrel distortion... the DVX has the exact same wide-angle focal length, and exhibits mild barrel distortion at full wide.

You might see a tiny little bit more barrel distortion on the Sony because the chips are a little bit wider, meaning that they'll see more of the edge of the circle of illumination.

Barrel distortion usually only becomes an issue if you have straight vertical edges on the sides of your frame (or straight horizontal edges at the top and bottom). For a quick check, zoom all the way out and then frame a doorway or something, such that the sides of the doorway are all the way at the edges of your frame. You should see barrel distortion... it's just the way these wide-angle lenses are.

[Bill Pryor]

Zeiss also makes cheap lenses. The cheaper the lens, basically, the more distortion it is going to have. You're not going to get a $10,000 lens on a $5,000 camera. The fact that, so far, one lens is distorting and the other isn't implies a lower quality control than we'd all like to see. I think it's appropriate to send the camera back if you can manage to get a test shot from the guy whose camera doesn't do it. Otherwise, the manufacturer can say, "Whaddya expect for $5K?" But, if you can prove that that is not the norm, then you can prove a quality control issue. Just my opinion.

The comment about distortion due to the 16:9 chips is probably accurate. In my experience, my old Nikon 8.5-127mm ED (a $15,000 lens in today's market) was excellent edge-to-edge on the BVW300 camera that I bought it for. When I retired the old 300 and got a DSR500WS, the lens is still distortion-free in 4:3 mode, but in 16:9 I get some barrel distortion out on the edges when zoomed back the last few millimeters. But that's not a defect--the lens was made in 1988 and designed for 4:3 cameras.

I'm guessing that there are going to be a few of the Z1 cameras with great lenses that are practically distortion-free, and others that aren't; and that probably falls within the manfuacturer's specs. You're not going to get the same level of quality control on a $5K camera's components you get on a $40K camera. Still, I think it's worth sending it back and demanding another. The squeaky wheel gets the grease, as they say.

[Ignacio Rodriguez]

> What puzzles me is that on the Z1U that I played with
> at Rule Broadcast Systems in Watertown, MA, there was
> no barrel distortion at all, not even when the lens was
> zoomed out all the way.

Could it be that in the store the camera was set to SD 4:3 mode, or was viewed on a TV that cropped the left and right edges? The barrel distortion at the wide end of the lens has been mentiones by several reviewers.

[Nicholas Natteau]

No, the camera was not connected to a monitor and it was in HDV 16x9 mode. In fact I'm going back to the store today to tes out another Z1U camera. If it occurs on another one then I'll know it's just the Z1U lens that is built that way.

[Ben De Rydt]

I bet there won't be any difference. The amount of barrel distortion of a lens is a primary design parameter that won't be changed by variations in the production process.

There are two extreme categories in the case of wide angle lenses: true rectilinear lenses and fisheye lenses. Rectilinear lenses are designed to show an imaged rectangle as a true rectangle. Special optics inside the lens will stretch the corners of the image more than the middle part. Fisheye lenses don't bother with these corrections at all. They give the typical bulbous look. They are cheaper than rectilinear lenses.

It is possible to correct an image from a fisheye lens to the equivalent of an image taken with rectilinear lens. This tutorial on photo.net ( http://www.photo.net/learn/fisheye/ ) will show you how. Take a look at the final result of the tutorial. The important thing to notice is that the person on the left is really stretched out. This shows that true rectilinearity comes at a price.

A lens designer will have to balance the amount of barrel distortion against the unnatural stretch a rectilinear lens gives. So, in reality, all lenses will live somewhere between the true rectilinear and fisheye types. Some will have more barrel distortion than others, but one thing is for shure: the wider the lens, the more either barrel distortion or rectilinear stretch will be visible.

[Filip Kovcin]

my ideas:)

1. maybe you can change your camera to that first camera you tested in the shop

2. check the doors in the shop :) maybe there are barrel proof (just kidding)

but, seriously - definitelly there ARE differences in the lenses in the same cameras. i didn't saw that barrel distorsions, but i do saw different focal lenghts on two cameras - one manufacturer, same model, same year of production. both brand new. both at the same zoom lever position etc. and the difference was not "just a touch" it was very visible. in terms of 35mm focal lenghts it was at least like 25 to 23mm difference.

i know that this cannot help you, but i can bet that this was somehow normal in this price range - the producers must leave something better for those who will buy their 100.000$ cameras.

filip