Grandagon N 65mm f/4.5

[tom north]

I have a 65 mm f/4.5 Grandagon N on a Horseman SB612. I am surprised and perplexed that the negs I've shot so far (all at infinity) have not been very sharp. I've been focusing the camera on the ground glass and have noticed that the focus has not been at the infinity mark. I then tried shooting some objects at 10-15 ft, again focusing on the ground glass. The negs turned out very sharp. I suspect that the ground glass is off so I ran some tests using the focus ring only. I am running more tests but my problem is that the focus ring goes from 30' to infinity. Question #1-Has anyone had any experience with recalibrating the focal distance on a ground glass? Question #2-What distance is infinity set at on these lenses?

Thanks

Tom

[Steve Barber]

I am not familiar with your camera, but that lens should be sharp on anything from about 26.5 feet or further when focused at infinity. In other words, the markings are not what they should be if the closest focus shown is 30 feet. Perhaps the mount is not correct for that lens?

As to focusing on the ground glass; if a focused image on a ground glass produces a sharp negative at one distance, you should be OK when you focus on the ground glass at any other distance. You should not have a problem just because you focused at a different distance.

[tom north]

Steve,

Sorry. I failed to mention that there is a normal focus scale on the lens, i.e., 1.5', 3', 7', 15', 30', infinity.

Tom

[Steve Barber]

Tom,

Yes, but, for that lens, infinity should be at something less than 30 feet, not at something more than that.

If I understand correctly, your camera has a film back that must be removed to use a ground glass back for precise focusing. For convenience, the lens is mounted in a helical mount and you should be able to focus approximately, close enough, by setting the distance to the subject on the focus ring without having to use the ground glass back. For this to work, both the film back and the ground glass back have to be correctly registered so the film plane and the ground glass plane are exactly the same distance from the back of the camera when either is in place. If you can focus using the ground glass back and get a correctly focused negative, then the backs are correctly registered and the ground glass is not the problem.

If, however--as seems to be the case from the markings--the focusing ring does not have markings corresponding to the distance to a subject that is in focus on the ground glass, then your problem is with the helical mount. Either the mount is not correct for that lens or the lens is not correctly positioned in it. Because the marking for infinity is not correct for the lens you describe, I think the problem is that you do not have the correct mount. The only other alternative, that both the film back and the ground glass back are exactly the same wrong distance from the camera back is, I think, unlikely and, even if they were, you would still have the problem of the incorrect markings.

Steve