Yet another lens problem

[Farkle-Mpls]

Hello.

 

I have an FD 28mm/2.8 lens in otherwise good condition which is acting rather strangely. The F-stop as indicated on the band on the lens

body is consistently 0.5 stops lower than the aperture indicated in the viewfinder of my F-1N. This lens normally will allow F-stops between

2.8 and 22 to be selected. I can readily move the band around the lens, selecting F-stops in all ranges, including "A". I tested this lens on

my second F-1N body and the problem persists. Also, other lenses don't exhibit this behavior.

 

I'm not sure how long this has been happening but I had posted earlier that I thought my F-1N light meter was out-of-calibration because

my photos were all overexposed by 0.5 - 1.0 stops. I was shooting this lens at the time of my exposure tests.

 

I've never seen this before. Ideas? Is this a common problem?

 

Thank you!

[jack_fisher1]

If indeed it is the lens that is off, a competent service person could make an adjustment for you. The aperture mechanism is adjustable, but requires getting inside and removing the front elements to do it. Before tackling that problem, make sure the camera is properly calibrated, and your other lenses are OK. It is unusual to see a lens where the aperture has "slipped" off calibration.

[HenryUK]

There are two levers on the back of an FD lens.

 

The aperture lever which both signals the manually set aperture to the body and is used by the body to set the aperture, and

 

the stop-down lever which is used by the body to close the aperture to working value when the shutter is operated.

 

Is is possible that the aperture lever has been bent so it indicates the wrong value?

 

I would not think the lens is economically repairable, given the low prices on the secondhand market.

 

Henry

[User_1577653]

Carl,

 

I can't speak to whether this is a common problem or not, but I have a 100/2.0 FDn lens which seems to be

exhibiting similar behavior. I discussed it in this thread on the yahoo FD forum a while back if you read there:

http://tech.groups.yahoo.com/group/CanonFD/message/57391

 

Basically, what I noticed was that in manual mode the aperture blades are always stopped down 1/2 stop smaller

than what is indicated on the aperture ring. So at f/2.0 (should be full open) the aperture is actually stopped down to

what looks like f/2.5. At the f/2.5 setting the blades are stopped down to an f/2.8 opening, and so forth until you get

to the last aperture ring setting at which no change in opening is seen. The curious thing is that in aperture-

priority mode everything works as it is supposed to and the aperture DOES close down to the commanded setting.

In any event, you might want to look into the lens during an exposure and see what the aperture is actually doing.

Maybe you will find the aperture is like mine and not actually opening to the right stop.

 

Incidentally, I typically bracket my slide shots (+1/2 stop, 0 stop, and -1/2 stop). For this lens I have noticed that I

usually pick the image with the +1/2 stop exposure rather than the middle one, unlike most of my shots. This would

be consistent with the physical aperture being smaller by 1/2 stop from what I think I am telling the lens to do. So I

am pretty well convinced now that the problem is in the aperture mechanism and not somewhere else.

 

For the time being I have started to compensate for the 1/2 stop difference whenever using this lens, but eventually I

would like to get it serviced. Now if this were my 28/2.8 instead, I would be thinking along different lines and just

purchase a new one! :)