FDN 35-105/3.5 focusing, please helpgreenspun.com : LUSENET : Canon FD : One Thread
Hi, this is my first entry on this list.
I bought couple months a go a very good (mint+ ?) FDN 35-105/3.5. For some reason I didn't find out earlier than now (haven't had time to use it much yet) but it seems to have some slight problem with focusing (checked with two bodies, T70 and T90).
At 105mm it focuses right from 1.5m to infinity. Also 70 and 50mm seem to be quite fine (judget on the finder view) but when zoomed to 35mm it seems to be impossible to focus to infinity.
Also, if I at 105mm focus e.g. to 2.5 meters (which is approximately the truth) and zoom to 35mm I have to refocus so that the focusing ring shows 4 meters (instead of 2.5m)
Is this normal or should I have the lens serviced?
Servicing might cost here some 200USD worth of local money so I wouldn't like to do it if it does not really help. I haven't shown the lens yet to service personnel (by phone they asked me to take photos first to check, which I have done but the roll is still in the camera so I don't know the results yet).
I have myself 'oiled' my 85/1.8 and feel somehow confident to repair the 35-105 even if it must be more complex. Does anyone have any service information for this? I heard it is possible to do some adjustments.
Could someone please check also the following: With the lens removed from the camera, zoom to 105 (focused to infinity). Then look at the back of the lens. You should see the aperture blades half closed like normally. When you now slowly zoom to 35mm look at the movement of the aperture blades. In my lens they move towards the front of the lens until at about 50mm the movement stops and the aperture blades seem to come back very slightly when turned to 35mm. Does your lens do the same?
thanks for help Vesa-Pekka
-- Vesa-Pekka (email@example.com), April 28, 1999
When focused to infinity at 35mm it is a bit difficult to say on the matte area if it is really correctly focused or not but the microprism and the other focusing system (don't remember now the name in English language) tell it is not focused right. It is not even close to right according to them.
I also dropped the lens from 1m (3 feet) on my shoe (I immediatly punished myself, I don't usually drop lenses) without any problems I could see/feel but they may have caused something though.
-- vesa-pekka (firstname.lastname@example.org), April 28, 1999.
I have a 28-85 f4 that did the same thing. A fellow I work with used to be a Canon repairman adjusted the lens for me. He said that the screws along side the barrel near the mount hold one of optical elements in place and by loosening them and moving the element you can adjust the infinity focus. He says also that the parfocality (whether the lens stays in focus during a zoom) can be affected by this adjustment so it is a tradeoff.
I understand this is usually done on an optical bench with a collimator but that it can be done outside with a distant object. I suspect there is a bit of skill and knowledge needed to perform this adjustment. Most any camera repair facility should be able to perform this operation. Personally, I think the only danger is loosening the wrong screws or allowing something to shift too far and you won't be able to recover. I have done similar things myself but have usually triumphed in the end and learned something too.
-- Duane Kucheran (email@example.com), April 28, 1999.