New Leica M3 user with focus question.

[bendee]

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Hello all!

I've just purchased my first Leica (M3 DS) having only ever been a digital user. I also purchased the following mighty lens:

Summicron-M 50mm F/2 Type V Chrome   

A weighty beast to be sure!

 

Please forgive me if this is a really obvious question about the rangefinder focus.

 

I'm guessing the pinpoint digital sharpness factor becomes far less important with film. It's hard for me to explain but I'm wanting to know that if the images are lined up (the ghost and the real) inside the rangefinder does everything within the vicinity come into focus too? I know this has to also do with depth of field and f-stop as indicated on the first ring of the lens (the one nearest the body).

If I focus an object or person within the rangefinder then adjust the camera position so said object is in the left or right of the frame, does it remain in focus?

Any tips advice at all will be fantastic!

Cheers,

Ben

 

[jaapv]

I think you are missing something here: The rangefinder patch shows you where the plane of focus is located, nothing else.

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[stunsworth]

If I focus an object or person within the rangefinder then adjust the camera position so said object is in the left or right of the frame, does it remain in focus?

Any tips advice at all will be fantastic! 

 

 

In theory there will be minor differences in the distance between the two locations (edge of frame and centre), but in practice I've used that trick a lot and always had acceptable results. If you're doing that with the lens stopped down the depth of field will mask any differences.

[stunsworth]

Ignore my last post. If you focus on something and then swing the camera to the left or right the object will remain in focus as the distance between camera and object hasn't changed.

[bendee]

Ah thankyou!

Yes I'm so used to spot focussing on an eyeball (or even lash!) that planes of focus are a whole new idea - albeit logical. I've never really bothered with depth of field so it's a bit of a learning curve. One that I'm really looking forward to.

Think I'll be F8-ing for a while!

[UliWer]

 

 

If I focus an object or person within the rangefinder then adjust the camera position so said object is in the left or right of the frame, does it remain in focus?

Any tips advice at all will be fantastic!

 

 

The focussing patch of the rangefinder is in the middle of the frame. When you change the camera's position after focussing you may try to imagine a triangle: 

 

Is your position on equal length with the two positions before and after changing the framing, your focussing will be right even after the camera's shift.

 

Though such a situation with equal lengthes for two different framings will be the exception. Much more often the distances between the object you first focussed on and the framing after the camera's shift will differ, especially on short distances - like a triangle with a short and a long length (scalene triangle).  So you have to compensate: give your focus a little bit more or less distance than you see in the rangefinder.

 

To tell the truth: a rangefinder camera is not ideal for focussing on objects which are not in the middle of the frame.  

[spydrxx]

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Just to add fuel to the fire, theoretically everything within the plane of focus should be in perfect focus, BUT, at least in some cases, as related to lens design, the plane might not be a straight line but rather a slight curve as one moves from the center toward the edges....at least that is what I have interpreted from past readings of Puts. For those more mathematically inclined than me - perhaps somebody could elaborate.

[250swb]

You have a row of wedding guests 20 foot long, you are the photographer standing ten feet from the central person and focusing your rangefinder on them. If you swing the camera to the end of the row that person is 14 feet away from you, so they will be out of focus but the central person will still be in focus (if they are still in the frame, all the usual provisos apply around optics, worked it out in my head, etc.). 

[Rus]

What you are describing is, as far as I can see, the technique of focus and recompose. In theory, there may be slight drifts of focus but in practice this shouldn't cause significant problems. For some lenses that have more pronounced field curvature in the shape of a central bulge, I sometimes deliberately focus slightly behind the object/person before recomposing. 

[Ko.Fe.]

Lets convert it to digital lingvo. RF patch (two images) equals to central AF point. This is it, the rest is geometry and DoF.

If you focus by cAF and recompose it is not the same distance. At f2 and close, DoF might be affected. Use online DOF calculator to learn more.

And ruler to measure long side C of triangle (side A - camera to cAF, side B - cAF to the point which needs to be in focus).

You don't need film camera to learn about this, if you have digital camera with equal to 135 film format sensor, a.k.a. FF and 50mm lens for it with f2 and less.

 

On practice, yes, if close I use f8, greater distance is - more DoF it is. 

[tranquilo67]

What you are describing is, as far as I can see, the technique of focus and recompose. In theory, there may be slight drifts of focus but in practice this shouldn't cause significant problems. For some lenses that have more pronounced field curvature in the shape of a central bulge, I sometimes deliberately focus slightly behind the object/person before recomposing. 

 

That's my understanding also.

 

And that happens not only in film and not only in rangefinder. In a SLR or even in a DSLR if you focus manually (or autofocus and lock the focus) when you recompose there can be a minimal difference in focus.

 

In my case, I do love to focus manually and, once I've focused, I'm not concerned about AF when I will recompose.

 

Hope that helps

Edited May 21, 2018 by tranquilo67