My OM-1 photos are out of focus. A ruler shows 3cm difference at 1m when compared with another OM-1. The focus also extends beyond infinity when looking at objects 100m+ away. I have checked the distance to the film rails and it is within tolerance 46.00 +/- 0.2. The mirror is at 45 degrees. Focus screen is correctly located. Multiple lens do not correct the problem. Through my view finder I can achieve focus, although it is incorrect for the film plane. The visible shims in the prism area sit above the focus screen and so cannot affect the focus screen positioning. My eyesight is good. No problem with testing similar and same focus screen using 2nd OM-1. Is the answer to adjust the location of the focus screen? Somehow? I note in the camera repair guide something about 5.53+/-0.05 between the 'l-pin' and measuring stage, but not even sure how this is relevant and indeed what is an 'l-pin'. Any advice appreciated. Thank you!
Olympus OM-1 Focus Problem
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Is the tab broken off the screen and the screen installed upside down?
Hi Randy, thank you for your reply. The tab is intact…and the focus screen works well in a second OM-1. I am working on the basis that the answer may lie with the ‘l-pin location’, but I am struggling to know what that actually means given the lack of related documentation. There may be another reason . Kind Regards, Julian
That seems too large. Assuming the OP is using a 50mm lens to quote a focus difference of 3 cm at 1 meter:
the extension to focus at 1000mm (950mm lens to subject) is approx 52.78mm,
the extension to focus at 1030mm (980mm lens to subject is approx 52.68mm.
So the offset would be just 0.1mm. That is a fairly small number and difficult to measure critical quantities such as the distance between flange and the film rails to that accuracy. I would try to focus with a ground glass or focusing screen on the film rails of both cameras to confirm the size of the offset.
Is the 45-degree angle of the mirror correct? A slight angle-error could cause a .1 mm offset.
Unfortunately, I don't remember how to adjust mirror angle.
Unfortunately, I don't remember how to adjust mirror angle.
Regarding the "I pin", you are probably referring to the "L pin" which is the mirror pivot. I don't think that is going to be your issue as that part rarely needs adjustment and it requires the mirror box to be removed and a special fixture to adjust. First thing to do with focus issues is check focus at the film plane with a ground glass at an infinity object. Then check at the viewfinder. If there is an error and the focus screen is intact and seated properly, I would suspect the mirror angle. To check the angle, a 45 degree fixture is used along with an autocollimator. It does not take much of an error to effect focus at the fresnel.
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That's where you need to start. Camera on a tripod, shutter on B, GG taped across the film rails (it's easy to mistake the raised part that's not the film rails), lens focused to infinity on something that's a fair distance away, and a loupe. I've used a magnifying glass or a camera lens in place of a loupe, worked fine.
Thank you. I will try this. Just a question re: a) l-pin adjustment fixture and b) auto-collimeter + c) 45 degree fixture… do you have any recommendations at the lower end of the price scale suitable for the OM-1?
Thank you… I will try this!
Thank for checking this I mistakenly calculated for a 3 decimeter difference.
Sorry, one additional question... does the bottom surface of the ground glass (I am using a number 13 focus screen) sit on the surface of the film rails or does the focus screen need to sit into the shutter curtain area such that the upper surface of the focus screen is parallel to the surface of the rails? I hope this makes sense.... Thank you.
Hi, An update for anyone who is interested.
I reduced the size of my type 13 fresnel screen and placed it into the gap between film rails and shutter curtain. The focus was almost correct when then looking back through the focus screen with a loupe (from rear of camera towards the lens) towards any object 100cm away. The positioning of the focus screen became the main source of error. Although the upper surface of the screen was intended to be inline with the film rails, I could not guarantee this and it did move so slightly during the checking process thus affecting the focus. At infinity the focus seemed correct for the object, again subject to errors caused by the micro movements of the focus screen.
So, this would suggest that the continuing issue I am having with the mirror focus is either the angle of the mirror and/or the positioning of the focus screen in the retaining tray. I have rechecked the mirror angle and it seems to be 45 - but there could still be sub-1-degree margin of error. I think I have to rediscover math to work out the impact on focus of a one degree error in the mirror angle to understand more and to determine whether this is causing the extent of focusing error I am witnessing.
Thank you.
so… you look back into what would normally be the underside of the focus screen if it were placed into the carry tray? So the distance to the upper side of the focus screen when sitting in the carry tray is actually the same distance to the rails? Thank you ….
The focus screen has a matte surface on one side. That's where the image is formed that your eye focuses on. On the Olympus OM-1, I believe when installed in the normal place, the matte side is up, away from the lens. (I looked at one to check.) In many cameras, the matte surface goes on the underside. But that's not relevant to the film rails. When you put the focusing screen on the rails, you're trying to check whether the image is in focus where the film would be. So you need to put the matte surface on the film rails, regardless of which way it is oriented under the prism.
How are you checking the mirror angle?
If the mirror angle is off, you will have off focusing too.
I'm not versed in OM-1 service, and don't have any incentive to attempt the service of those glorified machines designed by the Devil himself, but here are some resources to help you:
Service manual, pg. 144:
So, the adjustment is by washers, so the focusing screen position is changed.
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Hi, thank you. I am checking the adjustment through the use of lasers. These are not autocollimators given the expense. But I may have to buy one. Mirror adjustment is achieved by adjusting the height of the mirror resting place by raising or lowering a spring. The difficulty is that this mechanical movement of the spring seems lacking ie, does not to allow for the arc sec angle accuracy that may be expected/wanted today. My experience with OM-1 is such that there is a knack to achieving a goal and I suspect this is no different.
Mirror angle is not likely what is causing your issue unless the camera has been subjected to some type of trauma. In fact, mirror angle on the OM series is not simple to correct- the mirror box needs to be removed to reach the adjustment lock screw and it is sealed in place, a clue that Olympus feels this is not a common adjustment. Also, the manual that is often linked to is for the early OM-1 and the mirror angle stop mechanism was changed soon after production. And, adjustment is made not by raising or lowering a spring, but by changing the position of the spring stop. The spring is used as a shock absorber. I have attached a photo of how I check mirror angle on cameras - it shows a forty five degree fixture resting on the film rails of a camera body and an autocollimator squirting an image to the mirror.
Attachments
Hi, thank you. Yes, I agree with your explanation. Mine was imperfect. It is the adjustment of the spring stop. Your approach seem good! Did you design or buy your 45 degree fixture and/or autocollimeter. My mirror is off angle… just deciding the best way to return it …
You really will need a 45 degree fixture and an autocollimator to adjust the mirror. I have had my test equipment for many years, it is mostly factory repair tooling.
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