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Archive 2013 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?

  
 
turnstyle
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p.1 #1 · p.1 #1 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


Hi all,

I've read a number of conflicting comments regarding this.

Some people say Focus Shift only impacts Leica Rangefinders, and has no meaning on non-Leica mirrorless bodies (EVF focusing).

Other people say that Focus Shift can still apply if (for example) you focus wide and change aperture.

Just wondering if anybody here can help clarify this?

Thanks, -Scott



Nov 26, 2013 at 08:10 AM
ISO1600
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p.1 #2 · p.1 #2 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


If you focus at your shooting aperture, then no.


Nov 26, 2013 at 08:13 AM
eSchwab
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p.1 #3 · p.1 #3 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


Focus shift happens in a lot of fast lenses like the Canon 50mm 1.2. As you stop the lens down, the part that you thought was the most in focus stays the same while things behind it start to get sharper. So technically if you shot it wide open and focused on the eyes, they would be kind sharp. If you stop down to 5.6 the eyes are still kinda sharp, but the actual focus point was behind it and now the ears are much sharper making it look like the focus has moved back. It can effect any lens on any type of body. The only way you can bypass it is if you have a lens that you can stop down and focus.


Nov 26, 2013 at 08:13 AM
turnstyle
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p.1 #4 · p.1 #4 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


Thanks!

And the reason it's a bigger deal for rangefinder shooters is that they can't see the change in the rangegfinder -- and it's less of a big deal (though still annoying) if you can see it in an EVF.

That about right?



Nov 26, 2013 at 08:17 AM
Michael Gordon
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p.1 #5 · p.1 #5 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


Focus shift is classic on the ZE Zeiss 50/1.4 Planar. Only an issue at intermediate apertures as increased dof trumps the focus shift at some point. Dr. Nasse at Zeiss explanis it as a a result of change in spherical aberration when stopping down with this lens.
Nice to use Live view if circumstances permit--one trick with Canon is to use Movie mode and focus at aperture as it will stop down the cam.



Nov 26, 2013 at 09:04 AM
carstenw
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p.1 #6 · p.1 #6 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


turnstyle wrote:
Thanks!

And the reason it's a bigger deal for rangefinder shooters is that they can't see the change in the rangegfinder -- and it's less of a big deal (though still annoying) if you can see it in an EVF.

That about right?


I don't know why it would be annoying if you can see it. I would think that it is irrelevant if you can see it, since you just focus until sharp where you want.

It negatively affects rangefinders (since the focus cam on the lens cannot be calibrated for all apertures on a focus-shifting lens), and cameras with auto-aperture (since you typically focus wide open, manually or automatically, and the camera stops down the lens after focusing). Some cameras may know about some lenses, and are able to compensate for it. I believe that the Leica S system has information in each lens for optimal focus.

When you use dumb adapters for manual focus lenses, it is almost never an issue, since the aperture is at its set value, so you see what you need to see to focus properly.



Nov 26, 2013 at 09:25 AM
LightShow
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p.1 #7 · p.1 #7 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


Seeing it happen with live view makes it a non issue, when you can't see it as with RF or auto stop down cameras you can miss it and ruin the shot, more so with RF's.


Nov 26, 2013 at 09:29 AM
turnstyle
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p.1 #8 · p.1 #8 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


carstenw wrote:
I don't know why it would be annoying if you can see it.


If you want to focus wide and then step down to get DOF where you want it.



Nov 26, 2013 at 09:30 AM
Steve Spencer
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p.1 #9 · p.1 #9 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


If you use the aperture ring on a lens and stop down to the aperture you intend to use, then focus shift should will not lead to out of focus images. It does not, however, mean nothing. The usual cause for focus shift as Michael pointed out is quite a bit of spherical aberrations. So a lens with focus shift probably has that sort of aberrations, which means it will have a loss of contrast wide open that will resolve as you stop down. It also tends to have it worst effects at closer shooting distances. So it is a good guess that a lens with focus shift will be kind of soft wide open and especially so at close distances. It is not all bad, however, because under corrected spherical aberrations also can add a softness to the bokeh behind the focal plane, so many of the lenses that have focus shift and high spherical aberrations also have very pleasant bokeh.

One thing to look for in lens design is a lens with a floating element design. This design tends to reduce focus shift quite a bit and they tend to perform much better at close range (in fact Nikon calls this sort of design close range correction). It does have a drawback for lenses that use an adapter, however. Lenses with floating element design tend to be finicky about adapter and are particularly sensitive to adapters that are too thin. Even a good lens with a floating element design and a thin adapters will tend to show chromatic aberrations that would not typically be seen and may lose sharpness as well.



Nov 26, 2013 at 09:32 AM
turnstyle
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p.1 #10 · p.1 #10 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


LightShow wrote:
Seeing it happen with live view makes it a non issue, when you can't see it as with RF or auto stop down cameras you can miss it and ruin the shot, more so with RF's.


fwiw, this sort of "it's a non issue" language is what confused me.

Because it is still an issue, insofar as the focus distance is still changing. I wasn't sure if it was just something about how the lens communicated with the rangefinder.

It's *less* of an issue if you can see it in an EVF -- but if you want to focus wide and the step down, it seems like it's still somewhat of an issue.

thx!



Nov 26, 2013 at 09:34 AM
ken.vs.ryu
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p.1 #11 · p.1 #11 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


The af lenses focus wide open, then stop down as the shutter is pressed.


Nov 26, 2013 at 09:37 AM
carstenw
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p.1 #12 · p.1 #12 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


turnstyle wrote:
If you want to focus wide and then step down to get DOF where you want it.


Right. Don't do that Set your aperture, then focus.



Nov 26, 2013 at 09:38 AM
turnstyle
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p.1 #13 · p.1 #13 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


Steve Spencer wrote:
If you use the aperture ring on a lens and stop down to the aperture you intend to use, then focus shift should will not lead to out of focus images. It does not, however, mean nothing. The usual cause for focus shift as Michael pointed out is quite a bit of spherical aberrations. So a lens with focus shift probably has that sort of aberrations, which means it will have a loss of contrast wide open that will resolve as you stop down. It also tends to have it worst effects at closer shooting distances. So it is
...Show more

Thanks for that.

But don't rangefinder shooters complain that focus shift often results in *missed* focus?

Regarding your comments, let's imagine I'm shooting toward a ruler -- I'm wide open -- and I'm focused on 1 meter. For the corresponding narrow DOF, roughly 1/3 in front of 1 meter will be in focus, and 2/3 behind it.

So, focus shift means that if I step down, 1 meter will remain in focus, but the increase in DOF will not maintain that ration of focus around 1 meter.

That more like it?



Nov 26, 2013 at 09:40 AM
Steve Spencer
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p.1 #14 · p.1 #14 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


turnstyle wrote:
Thanks for that.

But don't rangefinder shooters complain that focus shift often results in *missed* focus?

Regarding your comments, let's imagine I'm shooting toward a ruler -- I'm wide open -- and I'm focused on 1 meter. For the corresponding narrow DOF, roughly 1/3 in front of 1 meter will be in focus, and 2/3 behind it.

So, focus shift means that if I step down, 1 meter will remain in focus, but the increase in DOF will not maintain that ration of focus around 1 meter.

That more like it?


For rangefinder shooting focus shift can be a real problem because using the range finder patch will not work properly at narrower apertures with a lens with focus shift, at least as I understand it. That is why it leads to missed focus. With regard to your example that is much too simplistic, IMO. As I understand it based on the severity of focus shift the 1 meter can move totally out of focus and is not always covered by the increased DOF. It is not simply a matter of the way the DOF spreads out as you stop down, but rather the sharpest point of focus moves and depending on how much it moves (and how picky you are about calling things in focus) the focus point can be no longer in focus.



Nov 26, 2013 at 09:58 AM
carstenw
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p.1 #15 · p.1 #15 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


turnstyle wrote:
Regarding your comments, let's imagine I'm shooting toward a ruler -- I'm wide open -- and I'm focused on 1 meter. For the corresponding narrow DOF, roughly 1/3 in front of 1 meter will be in focus, and 2/3 behind it.

So, focus shift means that if I step down, 1 meter will remain in focus, but the increase in DOF will not maintain that ration of focus around 1 meter.

That more like it?


No, you might focus accurately at 1m at f/1.4, but if you then change nothing else (specifically don't move the camera, nor turn the focus ring), but stop down to f/2, the DoF might have increased, but the point of best focus may have moved to 1.1m, outside the new, larger depth of field.



Nov 26, 2013 at 10:15 AM
waterden
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p.1 #16 · p.1 #16 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


These are all great explanations of how and why focus shift occurs but the question asked was whether it occurs on mirrorless. The answer, as ISO1600 pointed out at the beginning of this thread, is no provided you are focusing at the required aperture. Since the NEX and, presumably the A7 and the other brands also, will boost brightness in the EVF / LCD screen at whatever aperture you use you have all the visual DOF benefits of stopping down without the increasing difficulty of focusing in diminished light. That's it. This differs from range finders, as described above, and also from SLRs which focus wide open and only shut the aperture down when the shutter is tripped. Thus, very fast lenses will often shift focus on SLRs when focusing at short distances unless shooting wide open. It will not be an issue forinfinity or long distance focusing. So MLCs are best for very fast lenses as I understand it.


Nov 26, 2013 at 10:30 AM
turnstyle
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p.1 #17 · p.1 #17 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


I have been defining "focus shift" as whether "the optimal focus distance changes if you change aperture" -- so, at least using that definition, focusing at the 'final' aperture doesn't really apply, if you see what I mean.

What do fast AF lenses do? They focus wide, and stop down -- so does that mean they are designs that shouldn't have any focus shift? Or do they somehow have some additional 'compensation' for the final focus?



Nov 26, 2013 at 10:49 AM
carstenw
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p.1 #18 · p.1 #18 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


They typically have compensation. Try to turn off AF and focus manually. I believe that the current Canon 50L is famous for this.

Waterden, I specifically avoided saying this, because I don't know if it is true for all systems, and all modes. I could imagine that in some modes the camera focuses the lens wide open and then stops down. This is of course only with native lenses.



Nov 26, 2013 at 11:31 AM
douglasf13
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p.1 #19 · p.1 #19 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


It depends on the mirrorless camera. My NEXs focus at shooting aperture, until you get to low light, and then they focus wide open and stop down at capture. My Fujis always seemed to focus wide open. My RX1 always focuses at shooting aperture in all light. That's three different ways of doing it.


Nov 26, 2013 at 11:52 AM
RustyBug
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p.1 #20 · p.1 #20 · Does Focus Shift mean anything on mirrorless (non-Leica) bodies?


Does it really matter if there is a mirror or not ... the optical projection from a given lens/aperture is the same whether you have or don't have a mirror to contend with.

If stopping down induces a focus shift to the optical projection on an SLR, it is going to produce a focus shift on a mirrorless (i.e. same distance to the film plane) ... it is the optical projection of the lens, not the camera. Having an SLR vs. RF vs. Liveview vs. stopping down only impacts your ability to detect/view any induced shift.

How one might go about contending with it differently via stopped down viewing, live viewing, auto aperture, rangefinder (i.e. not viewing) may vary depending upon the options available for the camera of choice ... but that doesn't change whether or not it does occur just because you mount to a different camera.



Nov 26, 2013 at 11:59 AM
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