Hi List >a wide view angle. >Straight lines get bend stronger when zooming out, which shows a >serious imperfection.
Some notes, stuff you probably already know: The curving visible on some wide angle lenses is due to the lens of course. The fact that the 4 x 5 (inch) negative did not show the effect is because it's wide angle lens did not need to be as wide an angle due to the negative size. A 28mm lens on a 35mm camera is the same as a 50mm lens on a 6 x 6 cm negative and drops even further for a massive 4 x 5 (inch) negative. I might be a bit out on the actual figures ... it's been a decade or two. Digital cameras still use optical lenses and these can be based on 35mm camera optics. Therefore curving of perspective lines can be visible at anything less than about 28mm focal length. To minimise them simply stand as far back from the object as you can and if it is a rectangle type subject then aim the camera parallel to the horizon and perpindicular to the object, wall or whatever ... stand directly in front and dont point the camera up or down or sideways. An excellent example of this is the Linhoff Technorama camera. It uses 6 x 6 cm film (called "120 film" mostly) but outputs a negative that is 18 x 6 cm (I think). It takes a massive 120 or so degrees of view and so is an extreme wide angle. But there is no curvature at all. It does this by using a wide angle lens design for a full plate (8 x 10 inch) camera. Beautiful results. The other issue is optical zoom lens imperfections. The thing is to realise what is being asked from the arrangements of glass elements in the lens. There are very robust lens element designs which give excellent sharpness over small zoom ranges ... say ... 35 to 80mm, 100 to 200mm, etc, focal lengths (in 35mm camera terms). There are patented lens arrangements that work well over larger zooming ranges but sooner or later, for most other lenses, at some point, there is going to be a position that simply can not be handled by any arrangement of shifting lenses. Even with the perfect zoom ranges, zoom lenses based on anything less than about 28mm for a 35mm camera, are going to show curvature. Neil Cooke ----- Original Message ----- From: "Arjo Rozendaal" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Wednesday, April 05, 2006 7:22 AM Subject: RE: tutorial images and wiki > Hi Frank, > > > > I agree with you about the floating viewwindow for camera matching but > > beware for a bug with the "fix aspect" button. Forgot when exactly it goes > > wrong but at some point the backdrop gets the wrong aspect ratio. I rather > > use a plane instead with the photo mapped to it. > > Yes I remember that you mentioned this. That's why I suggested to use a > rendersize and camera that matches the aspect ratio of the photo. > > > > > Perhaps it's old news to some, but I was exremely pleased when I > > found out: > > lens angle, aperture, and shutter speed are automatically > > recorded in a RAW > > file. Saves heapes of work and loads of guessing when using a > > zoom lens !! > > Yes this helps a lot to find a rough setting, but because of lens > imperfections it's not instantly perfect. Well that's what I found. When I > took this picture of the couch the camera had quite a wide view angle. > Straight lines get bend stronger when zooming out, which shows a serious > imperfection. CS2 has a nice filter to correct this bulging but I'm afraid > that such corrections do not improve correlation between the real life lens > and the calculated lens. > > The only time I saw a good picture when a friend of mine took a photo of one > of my paintings with a technical camera with 4 x5 inch negatives. With this > camera the painting was perfectly rectangular. > > Arjo. > > > > > Regards, > > > > Frank Bueters > > > > > > > > > Anyway it was no trouble to put the tutorial on my own space > > > for the mean time. > > > > > > www.arjorozendaal.com/tutorials/sofa.htm > > > > > > Arjo. > > > > > > > > > > > Way to go. Watch out for rampant egotists though. > > > > > > > > Neil Cooke. > > > > > > > > > > > > > > > > __________ NOD32 1.1470 (20060404) Informatie __________ > > > > > > Dit bericht is gecontroleerd door het NOD32 Antivirus Systeem. > > > http://www.nod32.nl > > > > > > > > > > >
