M3 and 35mm SBLOO Viewfinder

[RayD28]

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Today I received a used 35mm viewfinder for my M3.  I have a 14-day return privilege.  

 

I put it on top of my M240 with a 35mm lens and took some test shots.  The tests shots were essentially framing a shot with a straight horizontal line (I used the rooftop of my neighbor's house) and aligning it the top viewfinder line.  

 

The subject distance was about 75 ft for the first test.  I took a shot using the M's internal viewfinder and took a second shot using the external viewfinder.  There was about a one foot difference between the two shots, so at 75 ft it's acceptable.  The subject distance for the second test was about 15 ft.  Here the SBLOO cutoff about six inches.  To me that is a lot but if it's consistent I can make it work.  Do these numbers seem acceptable given your experience?

 

Also, the top brightline sometimes disappeared.  It reappeared when I shifted my angle of view into the finder.  This happened when I was in full shade with the subjects in bright sun and not backlit.  Is this common?  

 

I plan to do some more formal testing, perhaps use a tripod.  I know rangefinder frame lines are close approximations of the actual frame so the same is true for an external viewfinder.  I just want to know if this particular viewfinder is a keeper or a dud.  

 

All advice and comments are appreciated.  

 

Ray

 

 

 

[Michael Geschlecht]

Hello Ray,

 

Welcome to the Forum.

 

Using a range/viewfinder camera is somewhat different than using a camera where the image coming thru the lens is used to compose & to focus.

 

With a range/viewfinder camera a person looks at the scene being photographed thru a window near the lens that is capturing the actual image.

 

Because of this small "displacement" the image being viewed by the person is sometimes somewhat different than the scene that the lens is actually capturing.

 

When you look thru the camera's range/viewfinder window it is important to look thru the center so that the frame lines on the perimeter of the viewfinder are equally distant from the dark sides of the viewfinder on all sides.

 

With an M3, which is the easiest Leitz/Leica range/viewfinder to look thru & to focus with: The outside frame, which is always present, represents the field of view of the 50mm lens. Which is approximately 2/3 the angle of coverage of a 35mm lens.

 

The SBLOO viewfinder, also sometimes referred to by its number 12010, shows the field of view of a 35mm lens which is approximately 1.5X the angle of coverage of the 50mm lens. 64 degrees as opposed to 45 degrees when measuring the angle diagonally.

 

Therefore the coverage of the SBLOO/12010 within the confines of its frame lines will be 1.5X the coverage of the M3 range/viewfinder within its permanent frame. Both top to bottom & left to right.

 

By the way, these are the angles of coverage when the lenses on the camera are focused to Infinity.

 

With either the range/viewfinder in the camera or a separate viewfinder (ie: SBLOO/12010): The camera captures a little MORE of the scene than the range/viewfinder or separate viewfinder "sees".

 

Explaining this takes a while.

 

When the lens is focused closer, say to 75 feet or 15 feet, then the lens elements move AWAY from the image capture surface (film or digital) and therefore effectively becomes a longer lens. Which means that its angle of coverage becomes SMALLER & therefore the amount of ADDITIONAL image captured on the film/sensor becomes GREATER. Because in Leitz/Leica cameras the frame lines do not change size as the lens is focused closer.

 

But: IN THE CAMERA all of the frame lines do move down & to the right as a lens is focused. This means that the image placement in the range/viewfinder is compensated for the changes in relationship when the lens is focused closer.

 

Altho the frames are not getting smaller to adjust for the smaller angle of coverage as the lens is being extended to focus closer.

 

In some add on viewfinders there are lines in the top left corner approximating how much of the scene is being excluded by thiis lens as it is extended.

 

To be continued.

 

Best Regards,

 

Michael

Edited May 6, 2018 by Michael Geschlecht

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[Michael Geschlecht]

Hello Ray,

 

I am back.

 

In some other viewfinders there are adjustment dials or levers that move the image to compensate for other distances.

 

So: When you are using the camera & separate finder: First compose the scene thru the separate viewfinder attached to the accessory shoe of the camera.

 

Your feet are good at doing this.

 

Then focus thru the range/viewfinder. An M3 has the best range/viewfinder to do this with. Please make sure that the 50mm frame is equally distant from the dark sides of the viewfinder on all sides, both before & after focusing. This is important because the frame will move as you focus.

 

Then re-compose in the SBLOO/12010 taking into account that as you focus closer the image becomes somewhat smaller & moves down & to the right. And then gently release the shutter.

 

This is actually much easier to do than it is to read what is written here about it.

 

You should end up with images on film that are a little MORE of what you were looking at & composing. The closer you focus. The more that you will capture that is outside of what you were looking at. Keeping in mind all of the above.

 

After all of the above, it is possible that the separate viewfinder is not correctly aligned. 

 

If you do all of the above & the separate viewfinder does not accurately (More or less.) show what it should. Let us know & we can go on from there.

 

Best Regards,

 

Michael

Edited May 6, 2018 by Michael Geschlecht

[RayD28]

Hello Ray,

 

I am back.

 

In some other viewfinders there are adjustment dials or levers that move the image to compensate for other distances.

 

So: When you are using the camera & separate finder: First compose the scene thru the separate viewfinder attached to the accessory shoe of the camera.

 

Your feet are good at doing this.

 

Then focus thru the range/viewfinder. An M3 has the best range/viewfinder to do this with. Please make sure that the 50mm frame is equally distant from the dark sides of the viewfinder on all sides, both before & after focusing. This is important because the frame will move as you focus.

 

Then re-compose in the SBLOO/12010 taking into account that as you focus closer the image becomes somewhat smaller & moves down & to the right. And then gently release the shutter.

 

This is actually much easier to do than it is to read what is written here about it.

 

You should end up with images on film that are a little MORE of what you were looking at & composing. The closer you focus. The more that you will capture that is outside of what you were looking at. Keeping in mind all of the above.

 

After all of the above, it is possible that the separate viewfinder is not correctly aligned. 

 

If you do all of the above & the separate viewfinder does not accurately (More or less.) show what it should. Let us know & we can go on from there.

 

Best Regards,

 

Michael

 

 

Michael, I knew the internal viewfinder on the M240 has parallax correction but I didn't think about the external viewfinder having no mechanism to make a correction.  Thanks for pointing this out.  Thanks also for explaining how focusing causes the lens elements to move so the internal viewfinder's frame lines compensate by moving.  I will take some test shots so I fully understand all of your explanation and tips. 

 

I deeply appreciate you taking the time to reply with such thorough posts.   

 

Ray