I feel like people's standards for acceptable focus must vary quite a bit. I've spent quite a bit of time with various rangefinders, focus targets, and carefully measured distances and it's puzzling to me when I see people assert that it's just never an issue. Either I've had a statistically unlikely run of bad luck with rangefinder calibration, or most people are generally ok with a few cm of front or back focus. Estimating focus shift helps somewhat, I guess.
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Are you able to consistently nail focus your subject's eyes at F2.8 on a rangefinder with a 50mm lens?
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Focus confirm can indeed be useful, but many versions don't show very roughly what is focused, so will confirm focus for a bit of grass in the foreground, or the background next to the flower being photographed.... This sort of issue is particularly common in macro photography. AFAIK even the best focus indicators only show which AF point is focused, Plenty good enough for BIF, or most portraiture, but not in every case. Focus Peaking is more specific but less accurate (magnified view is best when there is time).
Another time my AF has issues is in low light.
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Odd thing to say. Ground glass shows you what is focused.
On my 5x4 if I check with a loupe yes the ground glass does show whats focused (though it's not a focus confirm indicator). Without the loupe it's only possible to see areas that are close to focus, perhaps close enough for a contact printed snapshot style image, but certainly not 'focus nailed' (hardly anyone does snapshots with a 5x4).
On A DSLR - which is typical for AF systems with focus confirm - only very roughly, which is why many SLRs pre AF had microprisms & split type focus indicators.
Focus confirm on some of my cameras is simply a green hexagon showing the AF system has found something in focus. IIRC a friends Nikon shows which sensors have detected focus similar to many of my mirrorless bodies in AF. (Mirrorless cameras don't have ground glass)
Rangefinders typically use 2 images that have to overlay correctly. This requires the focus linkage of the lens to move the rangefinder mechanism correctly. Some of my LTM lenses fail to operate the rangefinder at all & without the rangefinder the viewfinder tells nothing about focus - remember it doesn't see through the lens.
I think most competent rangefinder users are pretty quickly aware of focus shift etc, and equally quickly learn how to compensate as needed. The ones who don't are those who then publish lengthy screeds/ blog posts/ youtube videos full of questionable measurements and assertions, while not addressing that SLR lenses (for example) also can suffer from focus shift (fact of life with some designs). And in an awful lot of environments where you might be using a rangefinder, you might be dealing with subject matter that will quickly evade your useful depth of field at 2.8 unless you have a clue about what the lens is doing (and how you can use that in your favour) anyway.
How do you tell it what you want the focus on? Love my F4 but it can’t tell when I want to focus off center.
This significantly bothers my daughter…
But for the original question: depends on light, angles and most of all, how long you get to futz around focusing before the subject wanders off.
Surely there’s a focus lock on an F4?
Why do I get the feeling that the obvious "focus & recompose" is not the correct answer?
Adorable!Standards vary, but this was 3/3 (for my standards)...
(50mm, probably @f2 or @f1.5)
As mentioned by @BrianShaw, focusing a 50mm f0.95 lens is as easy/hard as f8 lens on a rangefinder camera. Rate of properly focuses shots will vary, of course, but if you consistently miss focus with 50mm lens @f2.8, there might be something wrong with the lens or camera.
I don't know if I am that competent to know for focus shift on an RF, but I find myself at least nailing focus better than an SLR. Regardless of model, I seem to back focus on my SLRs quite a bit. On the OM4t I wonder if it was because of the diopter setting set for when I dont wear glasses vs me wearing glasses, but at the same time I've done the same on a Minolta SRT plenty of times...
And I wondered if the PEN FT's increased DOF helped mask my focusing error.
And I wondered if the PEN FT's increased DOF helped mask my focusing error.
Because some people find various assistance features helpful?
Both system can be out of calibration and different people find this or that system easier to use.
With SLR it’s easier to establish how much (if at all) focus shifts with smaller apertures. It’s also easier to check the field curvature.
A 50mm lens sees 40 degree AOV along the long dimension of the frame, so it is readily possible that if one focuses on the eyes with the rangefinder, then shifts the camera to recompose the frame, there is as much as a 15 degree shift off the point of focus. Focus-recompose could result in almost 3.5% error or 1.8" at a shooting distance of 4.5', and if added to error inherent to the DOF zone at f/2.8 it could compound the issue (vs. neutralize the issue of focus error..additive rather than cancelling)
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I’ve not had any problem with rangefinders focus (Zeiss ikon primarily) but do struggle with slr focusing from time to time.
True...& also has nothing to do with rangefinderfocusing....
it's also easier to miss with an SLR in low light or with slower lenses....
I agree with the calculation, but how did you arrive at the 15 degree figure? Are you counting edge-to-edge movement of the subject (I think that would be wrong because the focus error will be symmetrical), or centre to edge? If we assume the latter, I think the error is less than 1%.
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Half the FOV is 20 degrees, so shifting the eyes from center (target of rangefinder image) to off-center...maybe up to 15 degrees.
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You're quite right, but my reply was to @Paul Howell who in the quoted post was talking of focus confirm on his Nikon F4 - which is a SLR
It seems to me that a great many posts here are talking of focus on cameras that are not rangefinders. Despite the title it's drifted into more general focus.
no kidding.....
You are completely right. I’ve just measured it using my M6 with a 50mm lens. Forgive me for questioning your logic, it just sparked my curiosity.
But does anyone here take this into account in practice? Although I’ve always been aware that there is scope for focussing error in that way, it has generally seemed the least of my worries when trying to get a picture. Something else to bear in mind, I guess.
It might be worth mentioning that the DOF at 4.5 ft - assuming a circle of confusion of 0.03mm, which is archaic but widely used - would be +/- 1.6 inch at f/2 with a 50mm lens. That’s very close to the error caused by (quite extreme) re-framing after focussing.
Yes. And no.
1. I know that most of my lenses are not that good at edges wide open so I try to avoid using wide apertures when I need critical sharpness on the edges.
2. I also know that most of my lenses don't have perfectly flat field of focus. Most of them* have "inward" field curvature (edges are focused closer than the center) so the effect of "trigonometric error" (where you would have to focus closer after recompose than what rangefinder would indicate) and field curvature work in opposite directions (where you would have to focus further away for the edges to be in optimum focus).
* it's shorter focal lengths that are harder to correct for this aberration and those are also the same that suffer more from "trigonometric error".
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