Vignetting with wide-angle lesn on Toyogreenspun.com : LUSENET : Large format photography : One Thread
I have recently purchased a Toyo 45 AII after having a Tachihara for a number of years. When using my 75mm and 90mm lenses, I get some severe vignetting at the top of the photo (bottom of the viewing screen). The initial set-up of the camera prior to shooting is done according to the Toyo instructions...red indent at top of lens board carrier. Vignetting occurs with or without filters. Lens boards are drilled at the factory. Is this a common problem with TOYO ( I never had the problem with the Tachihara)? Is there a quick check to insure that lenses are centered? Will tilts cause vignetting? Thanks
-- John Wiemer (firstname.lastname@example.org), December 26, 1997
Hi John. Your question puzzled me for a while, but I think I've figured it out. I too have a 45AII but have not experienced this problem with my 90mm lens. Therefore, the explanation must be due to the only difference between your camera and mine, namely, the lensboards. Since you were a Tachihara user, you've undoubtedly retained your Linhof lensboards and bought a Linhof-to-Toyo adapter. I use the Toyo 110mm lensboards, in which the holes are drilled dead center. I looked in my Nikkor catalogue, and they show the 3 drilled Linhof lensboards with the holes noticeably off center, especially for the No. 0 and No. 1 shutters (and here the No. 0 is the relevant one). In particular, your 90mm lens is lower than mine is when the red dot is at the recommended position, and that explains the vignetting you see. (I also checked my Toyo catalogue, and it appears that the Linhof-to-Toyo adapter is almost perfectly centered and so does not compensate for this discrepancy.) The recommendation regarding the red dot assumes a centered lens, so you should ignore that recommendation. Maybe the simplest way to determine the correct position of the red dot is to mount your lens with the smallest image circle, probably your 75, and rotate the back to a vertical composition. Lower the lens until you see vignetting and note the position of the red dot. Now raise the lens until you see vignetting and again note the position of the red dot. The average of these two positions will be your neutral position for shooting. (For folding the camera, you should probably use the Toyo recommendation.) This also suggests that you will have more front fall but less front rise than the Toyo specs. Interesting.
Finally, re your last question: Yes, tilts can cause vignetting. The easiest way to see this for yourself is to experiment with front swings, which being on-axis don't require refocussing. Focus on something in the center of your frame, then watch it move as you swing the lens (it should remain reasonably in focus). The same is obviously true of tilts but harder to demonstrate because of the lack of axis tilts on the Toyo.
I hope this helps.......Stewart
-- Stewart Ethier (email@example.com), December 30, 1997.