Olympus OM-1 Focus Problem

flavio81 · Jun 24, 2022

jdk01 said:
Ps - forgot to add that for me it’s a hobby only… no commercial interests …

Now i will give you another way to check mirror angle without the use of special equipment.

Go outside, with a lens with short depth of focus like a 50/1.4.

Focus on a subject at infinity, like a city landscape with buildings, using the center of the viewfinder. When the mirror angle is off, the uppermost part of the viewfinder image will likely be correctly in focus and the lower part of the viewfinder image will not (or viceversa).

When the mirror angle is correct, the whole viewfinder image will be correctly in focus, both at the top and at the bottom.

It's as simple as that!!

Bill Burk · Jun 24, 2022

You have a good OM-1 and the one with the problem.

Focus a telephoto lens close-up on a subject target. Hold the focus and switch bodies.

Adjust the mirror on the bad one until it agrees in focus.

jdk01 · Jun 25, 2022

flavio81 said:
Now i will give you another way to check mirror angle without the use of special equipment.

Go outside, with a lens with short depth of focus like a 50/1.4.

Focus on a subject at infinity, like a city landscape with buildings, using the center of the viewfinder. When the mirror angle is off, the uppermost part of the viewfinder image will likely be correctly in focus and the lower part of the viewfinder image will not (or viceversa).

When the mirror angle is correct, the whole viewfinder image will be correctly in focus, both at the top and at the bottom.

It's as simple as that!!

Thank you. To realign the mirror, I need to make the adjustment having removed the mirror box. My understanding is to implement the above, I will need to precisely lift the OM-1 mirror using the albeit ‘primitive’ rotary control, maintain this angle while I remove the lens, precisely mark the new angle within the mirror box, remove the mirror box, and precisely match the mirror angle to the mark. This may be possible to achieve and will be fun to try.

jdk01 · Jun 25, 2022

Bill Burk said:
You have a good OM-1 and the one with the problem.

Focus a telephoto lens close-up on a subject target. Hold the focus and switch bodies.

Adjust the mirror on the bad one until it agrees in focus.

Hi Bill, thank you…much appreciate your comment … unless I misunderstand, I think my previous reply is appropriate? ‘To realign the mirror, I need to make the adjustment having removed the mirror box. My understanding is to implement the above, I will need to precisely lift the OM-1 mirror using the albeit ‘primitive’ rotary control, maintain this angle while I remove the lens, precisely mark the new angle within the mirror box, remove the mirror box, and precisely match the mirror angle to the mark. This may be possible to achieve and will be fun to try. ‘

flavio81 · Jun 25, 2022

jdk01 said:
Thank you. To realign the mirror, I need to make the adjustment having removed the mirror box. My understanding is to implement the above, I will need to precisely lift the OM-1 mirror using the albeit ‘primitive’ rotary control, maintain this angle while I remove the lens, precisely mark the new angle within the mirror box, remove the mirror box, and precisely match the mirror angle to the mark. This may be possible to achieve and will be fun to try.

I'm sorry, i was just offering a method that works on almost all SLRs.

Almost every 35mm SLR out there can have its mirror angle adjusted from the outside. It surprises me that the OM-1 requires such a cumbersome procedure. Maybe you should double-check the service manual because I can't believe it would require such a painful procedure.

jdk01 · Jun 25, 2022

flavio81 said:
I'm sorry, i was just offering a method that works on almost all SLRs.

Almost every 35mm SLR out there can have its mirror angle adjusted from the outside. It surprises me that the OM-1 requires such a cumbersome procedure. Maybe you should double-check the service manual because I can't believe it would require such a painful procedure.

Hi, your help is appreciated! Thank you

Mamiya_Repair · Jun 25, 2022

flavio81 said:
I'm sorry, i was just offering a method that works on almost all SLRs.

Almost every 35mm SLR out there can have its mirror angle adjusted from the outside. It surprises me that the OM-1 requires such a cumbersome procedure. Maybe you should double-check the service manual because I can't believe it would require such a painful procedure.

The OM-1 does indeed require the mirror box to be removed to adjust mirror angle as is necessary on the OM1 through the OM4. I have attached a photo and in the middle is the mirror stop adjusting plate. You can see how the lock screw is loosened from the side of the mirror box.

Mamiya_Repair · Jun 25, 2022

jdk01 said:
Hi Bill, thank you…much appreciate your comment … unless I misunderstand, I think my previous reply is appropriate? ‘To realign the mirror, I need to make the adjustment having removed the mirror box. My understanding is to implement the above, I will need to precisely lift the OM-1 mirror using the albeit ‘primitive’ rotary control, maintain this angle while I remove the lens, precisely mark the new angle within the mirror box, remove the mirror box, and precisely match the mirror angle to the mark. This may be possible to achieve and will be fun to try. ‘

You won't be able to make an adjustment this way. Also, keep in mind that mirror position needs to be within 5 minutes of arc!

Mamiya_Repair · Jun 25, 2022

Mirror stop location

jdk01 · Jun 25, 2022

Mamiya_Repair said:
You won't be able to make an adjustment this way. Also, keep in mind that mirror position needs to be within 5 minutes of arc!

And for me, this is something I need to better understand - how to translate 5 minutes of arc into a relatively imprecise sub-mm change in the mirror adjustment. What level of adjustment is actually possible and practical …

jdk01 · Jun 26, 2022

A quick estimate on the 'back of a match box' cover suggests to me that based on:

1. the mirror adjustment can travel a straight line of 5mm vertically (yes, I realise it is an arc, but the vertical distance travelled is 5mm approx.)

2. the mirror therefore can travel a straight line of 5mm vertically (yes, I realise it is an arc, but the vertical distance travelled is 5mm approx.)

3. based on a right angled triangle, a 30mm (hypotenuse) length mirror starting position of a 45 degree angle -> adjacent and opposite lengths of 21mm approx.

So... the 5mm vertical change to the mirror -> changes the 45 degree mirror angle by approx. 12 degree 58' or approx. 778' (arc minutes). This is calculated again by using right angles triangle - opposite is now = 16.21mm (21.21mm-5mm), hypotenuse = 30mm.

In other words, achieving tolerance of 5 arc minutes (mentioned by mamiyrepair - great cameras by the way - used to sell the 645 is the 1970s) requires the mirror vertical adjustment to be within .03mm (calculated by (5mm * (5'/778')). With such a physically small 'primitive' adjustment system, I am uncertain how this may be achieved even if you have the best auto-collimator in the world to help you. But it is clearly possible, or else we would have another adjustment system.

Perhaps there is a tool? Perhaps my maths are incorrect? I would love to get to the answer, but am aware that this topic may have naturally come to the end. Thank you to everyone for your help! And please correct my 'school boy' maths .... I was never very good at such things....

Bill Burk · Jun 26, 2022

I tried twisting the mirror lockup a bit to cause your problem. Focused something in the (infinity) distance. The lens showed 1.5m when it was obviously up too high.

Mirror up too high allows focus past infinity (Seemingly. You really don’t focus properly because with mirror too high appearance of focus sharpness arrives before lens is truly focused at infinity).

I don’t remember the error in your focus, but if you cannot focus at infinity (the other issue where sharp infinity doesn’t appear in finder even when lens reaches end of travel). If this is your problem you could fix it with a little shim glued where the mirror touches the rest.

Bill Burk · Jun 26, 2022

I think you mentioned the first problem- you think you are focusing past infinity and you turn back to see sharpness in the finder when the lens scale indicates a closer distance.

Is that so? Then you may need to lower the stop, which looks like a job where the mirror box needs to come out.

Does mirror lockup work properly?

Mamiya_Repair · Jun 26, 2022

jdk01 said:
In other words, achieving tolerance of 5 arc minutes (mentioned by mamiyrepair - great cameras by the way - used to sell the 645 is the 1970s) requires the mirror vertical adjustment to be within .03mm (calculated by (5mm * (5'/778')). With such a physically small 'primitive' adjustment system, I am uncertain how this may be achieved even if you have the best auto-collimator in the world to help you. But it is clearly possible, or else we would have another adjustment system.

Using an auto-collimator is indeed the way to adjust mirror angle. I use this tool many times a week to adjust mirror angles on Mamiya 645 cameras (plastic mirror stop that breaks). My collimator is just a standard Pearl 6810 and the reticle is marked with 30 second increments up to 15 minutes of arc. Getting the mirror angle to within 30 seconds is trivial although in reality if you are within manufacturers tolerance of 5 minutes plus or minus you would not be able to see any change on the focus screen.

jdk01 · Jun 27, 2022

Bill Burk said:
I think you mentioned the first problem- you think you are focusing past infinity and you turn back to see sharpness in the finder when the lens scale indicates a closer distance.

Is that so? Then you may need to lower the stop, which looks like a job where the mirror box needs to come out.

Does mirror lockup work properly?

Hi, the mirror stop does work…. Thank you…

jdk01 · Jun 27, 2022

Mamiya_Repair said:
Using an auto-collimator is indeed the way to adjust mirror angle. I use this tool many times a week to adjust mirror angles on Mamiya 645 cameras (plastic mirror stop that breaks). My collimator is just a standard Pearl 6810 and the reticle is marked with 30 second increments up to 15 minutes of arc. Getting the mirror angle to within 30 seconds is trivial although in reality if you are within manufacturers tolerance of 5 minutes plus or minus you would not be able to see any change on the focus screen.

It does look I will have to buy one. I suspect this may take some time, but perhaps the used market will offer one at some point, although competition will be significant. Unfortunately a new one is so much money - and may be more precise than I would need. My next step is to find photos of the proposed setup, to make sure I have all the other accessories eg. Something to mount the camera and mirror box to ensure the correct angle… thank you …

flavio81 · Jun 28, 2022

jdk01 said:
It does look I will have to buy one. I suspect this may take some time, but perhaps the used market will offer one at some point, although competition will be significant. Unfortunately a new one is so much money - and may be more precise than I would need. My next step is to find photos of the proposed setup, to make sure I have all the other accessories eg. Something to mount the camera and mirror box to ensure the correct angle… thank you …

If the adjustment is on the "up" direction you might get away by putting something (i.e. electrician tape) to act as a shim so the mirror sits higher.

jdk01 · Jun 29, 2022

Thank you.

Olympus OM-1 Focus Problem

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