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How do you recompose with a rangefinder?

fahim mohammed

fahim mohammed

Well-known member
I seem to get many misses when I recompose using a rf as opposed
to my nikon. realise the plane of focus etc.,

How do you folks do it?

Thanks.

Edit: changed the title to convey more info to searchers. CU.
 
Last edited by a moderator:
Asher Kelman

Asher Kelman

OPF Owner/Editor-in-Chief
Hi Fahim,

The rules of optics are the same for your Nikon DSLR and any rangefinder, even a Leica! DOF is narrow and precarious with wider apertures and longer focal length. Swinging a lens from one point of focus, therefore will be wrong after recomposing if the target one chooses is on the same flat plane as the intended final composition. Let's do this by imagining.

In short, imagine a large sphere with it's surface the plane of focus of a tiny camera lens in the center. Any angle the lens is swung to will maintain the focus of any object anywhere on that curved surface.​

With any camera, the plane of focus, (after adjustment), is a fixed distance orthogonal to a line coming out of the axis of the lens. If the camera is shifted a tad without changing the angle one is pointing the camera, the plane will shift to that side but plane of focus and the DOF will remain the same! Everything in the center that was in focus should remain in focus with a well corrected lens.

So where's the problem? It's when the camera is pointed at a new angle. The plane of focus is now moved away from its original position. If one had focused on the top of a building and now we reframe on the center of the structure, the distance from the camera to the new center is much shorter. This means the plane of focus is now thrown behind the front of the building!

With a rangefinder, I presume you refer to a Mamiya 7, Leica or similar. Here we have to align the lighter, often green/yellow tinted floating) image of the subject with the larger bright clear image in the viewfinder. Using a wider lens, such as 50mm at say f8, focus on the top of a person's head and they are across the street, recomposing might matter little.
We only escaped from problems here because the lens is stopped down and therefore depth of focus is deeper and buffers recomposing change and anyway shorter lenses have deeper focus anyway.​

Now if we do this with the lens open to f4.0, for example, the DOF is markedly decreased. At 2.0 it would be much thinner and at 1.2, just mm! Then should we choose a longer lens the situation is even worse.

To maintain focus when one arcs the camera from one position to another, one has to focus on a target the same distance from the camera: For example, I might choose a high contrast object, (such as a spoon), on a table at the same distance from the camera but a different angle from my proposed target, the eyes of a person in less than perfect light. Swinging the camera beck to the face to recompose will result in perfect focus!

The Canon 5D, suffers unreliable focus in poor light. However, with my technic of using a target in the arc from the front of the lens, focus is almost always perfect.

I hope this helps even without formulae or diagrams.

Asher
 
M

Mike Shimwell

New member
Great description Asher, just need practice.

Hi Fahim

As Asher said, the problem is the same as focus recompose with your Nikon, but you only have a centre focus spot so you tend to recompose by a greater amount and so get bigger issues. The only solutions are to

1. Use Asher's approach and focus on something the same distance as the target will be when the camera is pointed where you want it.

2. Focus and then shorten the distance a bit(!)

3. Use a small aperture to get more dof

4. Scale focus - using a tape measure if necessary (difficult with children and dogs

5. Always frame with the target in the centre of the fov - crop later if necessary

6. Adopt a HCB near enough is good enough approach

7. By a small sensor camera to give even more dof.

Have fun

Mike
 
B

Bob Sumitro

New member
Hi Fahim,

What Asher and Mike said. And I'd like to add my own experience.

I'm new to rangefinder world, got my first rf (Leica M6 classic) in december last year, and I had the same problem as you do. Using canon dslr 30d, I seldom focus and recompose, I simply picked the outer focus point except in low light condition where using outer focus point usually result AF focus hunt. When I use my FM2, every now and then I focus and recompose, but most of the time though (since it's a manual camera hence no focus point) I do not do it. The focus screen is adequate to do it without focus and recompose.

Now, when I received my M6 I was surprised with how different it is from SLR, and I have to learn to work differently. That small focus patch is just, well really small :) I have the 0.72 finder.

So the way I do focus and recompose when I shoot RF (wide open and when the subject is at close distance) is to place the subject in the middle, focus using the focus patch and then I move slighty sideways or up and down a bit, to place the subject where I want but I do not swing the camera in an arc. I got more keeper with this technique.

But often times, I simply use small aperture. At f/5.6 or smaller, I simply look at the dof scale on the lens (to estimate how much dof I'll get) and focus and recompose by swinging the camera and hoping that the dof will take care of it :)

Bob
 
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