Recomposing & keeping focus.

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Fujiowski

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I have a question regarding recomposing and keeping focus using a rangefinder camera. I have a FUJI GA645 which I can use in total automatic mode. I can use the center finder to lock focus and then when pressing a button move that subject to the left in the frame.

However, when I use my FUJI GSW690 and GW690 they are totally manual and I would like to know if it's possible to recompose while keeping focus or is that not possible?

What I mean is I'd like to use the center finder to focus on a person and then move the camera to the right so that the person is to the left in the photo. If that's not possible I can just keep the person in the center of the frame for the shot.
 
I mean I focus on the main subject then change the framing.
It is the normal procedure.
For both focus and exposure
 
Use an SLR, ideally with a nice bright viewfinder and wide aperture lens. Then you can see immediately and obviously whether any part of the image is in focus or not. Rangefinders are basically hard work with any moving, off-centre subject. (I may be drummed out of RFF for this).
 
It's not possible to lock focus on one person or object and shift the camera's viewpoint to something or someone that is a different distance away and retain focus on both. Is that what you want to do? Even your camera w/ autofocus can't do that. Your best bet is to stop the lens down as much as possible to cover the focal distance with depth of field. If both persons or objects are the same distance away then no refocus is necessary if you reframe a shot.
 
Malcolm M said:
Use an SLR, ideally with a nice bright viewfinder and wide aperture lens. Then you can see immediately and obviously whether any part of the image is in focus or not. Rangefinders are basically hard work with any moving, off-centre subject. (I may be drummed out of RFF for this).
Click to expand...

Yep, this is a problem with rangefinders. It is even a problem with SLRs and with TLRs. I was advised by the maker of high-quality focus screens to not put a split image focusing screen in a Rolleiflex if I was going to be doing large aperture close focus shots. The 'ground glass' of the screen was coarser than on the 'no split' screen, making it harder to do precise focus away from the central focus aid. I assume that SLR screens can have this issue.

I remember my first DSLR's focus screen was not good for showing if things were in focus or not. Pentax K10d, APS-C format, known to have a large viewfinder for the format but still darn small screen. I put in a different screen that showed focus much better.

OP, the solution is twofold- to pay attention and to learn your depth of field in various situations. Pay attention to what you do in reframing. If you lean back and forth after focusing, step one way or another, etc., you'll need to either refocus or you'll need to think about keeping the camera in one spot. Focus, then hold the camera stationary except for rotation and tilt while moving your body. If you do need to move the camera from the last focus position, think about the movements keeping the camera the same distance from the focus point. Sort of like imagining a string of specific length and if you move the camera you need to keep the string taut; if, say, you move left or right, you may need to also move forward a slight amount as you swing on the string.

And then understand depth of field and how it will cover for precise focusing errors. All of the above keeping the camera in the same spot is relative. If you have four feet of depth of field and you are shooting a person from 20 feet away, it would probably be hard to lose focus. But if you are shooting a flower at three feet at a wide aperture you probably don't have much room to move before losing focus (and probably you should use an SLR if this is a typical shooting situation).

Learn to zone focus a rangefinder if the situation allows- depth of field, speed of motion of subject, etc.
 
If I understand your question, you're concerned about recomposing after focusing, then when hitting the shutter button the camera will try focusing again, but not on your intended subject. The "AF" button on the top of the camera, does it turn off the AF? If so, then try focusing on the subject, recompose, then turn off AF with the top button and then take the shot. It would be a 2-button press, a bit ungainly perhaps, but may work for you.

~Joe
 
I'm not familiar with the cameras mentioned but....

For AF cameras you can usually just hold the shutter release button while recomposing and it will hold focus until you finish pressing it. With manual focus cameras just recompose and fire shutter after focusing.
 
You need to understand how dof is affected on recompose. Focus in the middle and then turning left or right might affect. Larger aperture is, size of the negative and closer the distance - more likely to have less in focus after recompose.
Use dof online calculator to see how really shallow dof could be.
 
Fujiowski said:
I have a question regarding recomposing and keeping focus using a rangefinder camera. I have a FUJI GA645 which I can use in total automatic mode. I can use the center finder to lock focus and then when pressing a button move that subject to the left in the frame.

However, when I use my FUJI GSW690 and GW690 they are totally manual and I would like to know if it's possible to recompose while keeping focus or is that not possible?

What I mean is I'd like to use the center finder to focus on a person and then move the camera to the right so that the person is to the left in the photo. If that's not possible I can just keep the person in the center of the frame for the shot.
Click to expand...

The short answer to your question is yes. When you focus on the person and then move the camera to recompose, the focal distance remains as it was with a manual-focus rangefinder.

The exception would be if YOU move or your SUBJECT moves between the time you focus and the time you trip the shutter. Then the subject might or might not still be in focus, depending on something called 'depth of field' (DOF).

Focus is about distance, in the simplest form. When you focus on a person X feet or meters away, and then recompose, the focus is still set to X distance. If you move or they move, focus is still set to X, but the subject may not be X distance away any more.

As others have noted, this can be complicated by the fact that focus is a subject that has many characteristics. When you focus at a certain distance, objects in front of or in back of that distance may be in focus or not, depending on this like your lens focal length, the size of your aperture, and other things.

I hope you find this helpful.
 
I may be confused regarding what you want but I'll give it a try.

In short, yes. You can focus and then change the composition without affecting the focus...or exposure.

These cameras are fully manual cameras. You set the focus and you set the exposure. If you focus on a person and set the exposure then you can move that person (or object) around in your viewfinder to your heart's content without changing anything but the composition. Unlike auto-focus cameras, these cameras will not refocus until you manually make the adjustment. Likewise with the exposure.

And it makes no difference whether it is a rangefinder you are using or an SLR...or a TLR...or anything else. As long as that camera's settings are manual they cannot change until you do it.

Of course, if you take a step forwards or backwards or move sideways then you may change the distance between the camera and your subject enough to need to refocus. (This is where depth of field comes into play.) But if you stand in one place and only recompose in your viewfinder then you will still be properly focused on that person.

I hope that helped??

BTW - I love working with my Fuji GA645. Wonderful camera and awesome lens.
 
Technically, most good modern lenses have a nearly flat focal plane, which means that when you recompose after focusing in the middle, you get backfocus. It's called cosine error. Forum member ferider has explained it here: https://www.rangefinderforum.com/forums/showthread.php?t=148485
with this diagram:


In practice, and evidenced by people here who don't believe there's a problem, you need to have pretty thin depth of field, a wide lens and rather extreme recomposing to notice. Just do your own tests, theoretical reasoning won't help much figuring out the practical limits because we usually don't have data about how flat the focal plane of a lens is. A lens with focal plane curved such that the camera is in the middle of the circle would eliminate cosine error. Focal plane curved away from the camera makes it worse.
 
retinax said:
Technically, most good modern lenses have a nearly flat focal plane, which means that when you recompose after focusing in the middle, you get backfocus. It's called cosine error. Forum member ferider has explained it here: https://www.rangefinderforum.com/forums/archive/index.php/t-148485.html
with this diagram:

In practice, and evidenced by people here who don't believe there's a problem, you need to have pretty thin depth of field, a wide lens and rather extreme recomposing to notice. Just do your own tests, theoretical reasoning won't help much figuring out the practical limits because we usually don't have data about how flat the focal plane of a lens is. A lens with focal plane curved such that the camera is in the middle of the circle would eliminate cosine error. Focal plane curved away from the camera makes it worse.
Click to expand...

All true, but as you said, the DOF would have to be pretty thin.
 
"... Focal plane curved away from the camera makes it worse..."

I'm trying to get my head around this. We don't see much data about field curvature. If I remember correctly, when I have seen it, for example large aperture older lenses, it has been concave (towards the lens) which would mean that the edges of the frame are focused on more distant parts of the subject, which would make matters worse in the case of the example diagram above. Does this seem correct? Are there lenses that would improve the situation?
 
Did anyone read what the OP is asking. Never saw so many confusing and complicated answers. The OP isn't asking how to focus the GA645 but a totally manual RF camera.

If you focus a RF manual camera on a subject (which is in the middle of the focusing frame) and then move the focusing frame so the subject is now at the edge of the frame - no you do not to to re-focus or do anything besides take the picture.
 
You have to be aware of the hyperfocal distance for what ever aperture you are using for your lens, and film size, and then consider the distance to your subject. Then you can use depth of field to maintain focus while recomposing. There are many handy charts on the interwebnets.
 
Can a mod maybe change the thread title to include GW and GSW690 and/or move this to the Medium Format RF subforum? Most useful for OP would be input from users of these specific cameras, maybe someone has experimented to see if cosine error is significant of not with these lenses.
 
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