Leica S3 focusing at longer distances and infinity

[epines]

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I recently got a new S3, and I love it. After briefly having an 007, I definitely feel the AF accuracy is better in the S3, along with all the other improvements. I find the AF to be very accurate. I shoot portrait and conceptual work, so I'm always working at distances of around 3 to 20 feet. 

However, I'm seeing that it's sometimes inconsistent at greater distances -- say, 100 feet away and more. I realize the camera is most accurate when focusing on subjects with contrast and internal definition. But I'm getting some misfocused shots even with subjects that should be easy to focus, for example, a tall tree against a blue sky, lit from the side, about 150 feet away. 

Is this a known issue with the S system? I'm hesitant to send the camera back to the dealer, in case I got one that's worse at closer distances. And I'm hesitant to send the body to Leica, in case whatever service they performed altered the the focus accuracy at close distances. (It's also very expensive to ship from the US to Europe right now.)

The odd thing is, sometimes the focus on these distant subjects is dead-on and tack-sharp. It seems to be hit and miss. The 70mm and 45mm lenses seem to be doing better than the 35mm. Of course, the desired focal point is smaller with the 35mm, due to the wider view, so perhaps that gives the camera more trouble. (All three lenses have great accuracy at closer distances, as I mentioned.)

Note: I'm talking about AF with the mirror down. Focusing via live view is very accurate in all instances. Maybe the smart thing is to just use a tripod and live view for focusing on longer distances? I'd like to be able to trust the camera when handheld in all circumstances.

Any input is appreciated. Thanks.

[mgrayson3]

Ethan,

Infinity and near-infinity focus has always been a weak spot on the S series. For each lens, I find exactly *where* on the infinity symbol marks true infinity, and I visually check that before shooting anything very far away. 150 feet wide open is a tough one. Pressing the focus a few times, or focusing on something near and then refocusing at distance helps. If time permits, take 3 or 4 images while refocusing. If time REALLY permits, use magnified focus peaking under live view. I know we love the camera for its OVF, but for some pics I just have to check the magnified view.

I've found the S3 better at this than the earlier versions. Infinity focus on the S(006) was pretty useless but, again, I knew where that was on the lens barrel.

Matt

I just tried this with the 120/2.5 wide open in fading light. First is focused on building 1/2 mile away. It is pretty good, but slightly soft. This is a 2000 pixel wide crop.

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Next, I focused on some trees in the 100'-150' range. Pretty perfect.

Then back to the distant building. This time spot on. Any residual softness is due to heat waves.

And this is magnified focus peaking, and is indistinguishable from the previous.

 

 

Edited July 29, 2022 by mgrayson3

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[epines]

Matt -- really appreciate this. It's good to know that what I'm seeing isn't an anomaly unique to my S3 body. I can live with this, given how great the S3 and the system are overall. I'll do what you did with finding true infinity for each lens. The truth is, if I'm ever shooting at those distances, I'm probably on a tripod since it's some kind of landscape photo. And on a tripod, AF in live view works perfectly. I don't even think magnification and focus peaking are necessary.

Thanks

e

 

[mgrayson3]

I’m afraid that with the resolution of the S3 and the shallow DoF of these lenses wide open (especially the longer ones) that the lens barrel technique isn’t sufficient. At f/8, perhaps.

M

[helged]

With S3 & for landscape photography, I (almost) always use manual focus in live view with magnification. And using tripod, clearly.

Due to field curvature, focusing about 1/4 or 1/3 off the image centre may work better than using a focus point at the centre. This can be the case even at f8. Here I assume that the landscape is far away. If there is a 3-dimensionality in the image, I pick the part of the image that should be in focus.

You may also use the dof scale in the top window (keeping the shutter half pressed while moving the focus ring), but I have mixed experiences with this method. 

If hand hold, I 'trust' the cameras AF, taking multiple photos at slightly different focus distance as @mgrayson3 mentions above. And preferably keeping the shutter speed away from (about) 1/60 sec, since this speed is prone to vibration unsharpness from mirror and shutter movements (so a speed of 1/250 sec or shorter or, if possible, using some additional support at slower speeds).

Enjoy shooting! 

Edited July 29, 2022 by helged

[epines]

14 hours ago, helged said:

Due to field curvature, focusing about 1/4 or 1/3 off the image centre may work better than using a focus point at the centre. This can be the case even at f8. Here I assume that the landscape is far away. If there is a 3-dimensionality in the image, I pick the part of the image that should be in focus.

Helged, thanks for the input. Regarding focusing about 1/4 or 1/3 off the center due to field curvature, tell me if I'm correct in my interpretation of your thinking here: When you stop down, the far part of the field curvature (in the center), which is now behind your initial point of focus, will bend inward / towards you to match the initial point of focus. And the nearer part of the field curvature (toward the edges of the frame), which is now in front of your initial point of focus, will bend outward / away from you to also match the initial point of focus. The far and near parts of the field curvature both flatten to approximately meet your initial focus point 1/4 to 1/3 away from center. Does that sound correct?

I find that these lenses flatten out very nicely once you stop down. My 45mm and 70mm are sharp across the image even wide open, and the 35mm gets there pretty quickly with stopping down. So I feel like field curvature isn't too much of an issue.

 

 

[helged]

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1 hour ago, epines said:

Helged, thanks for the input. Regarding focusing about 1/4 or 1/3 off the center due to field curvature, tell me if I'm correct in my interpretation of your thinking here: When you stop down, the far part of the field curvature (in the center), which is now behind your initial point of focus, will bend inward / towards you to match the initial point of focus. And the nearer part of the field curvature (toward the edges of the frame), which is now in front of your initial point of focus, will bend outward / away from you to also match the initial point of focus. The far and near parts of the field curvature both flatten to approximately meet your initial focus point 1/4 to 1/3 away from center. Does that sound correct?

I find that these lenses flatten out very nicely once you stop down. My 45mm and 70mm are sharp across the image even wide open, and the 35mm gets there pretty quickly with stopping down. So I feel like field curvature isn't too much of an issue.

Essentially, yes. Field curvature could have any shape; it can be wavy, convex, concave, etc. If the objective is to get as much of the scene in focus as possible (and assuming that the scene is flat - like a distant landscape), you generally/typically maximise the sharpness across the image by moving the focus point a little off the image centre. I don't claim that this is the best method for all lenses, but it works more often than not (based on my experience). By using live view with max magnification, you can check this by focussing at a distant landscape, distant city lights, etc., starting with the focus point in the image centre, then moving the focus point towards the corners, etc. Typically you have to refocus a little when moving around in the image. A compromise is often to put the focus point a little off centre. Things may change when lenses are stepped down. This effect cannot be easily tested by using the camera's af, but it can be seen in live view.

[jip]

I've always felt the S2 and S006 (have no personal experience with S007 and S3) focus way better at eyes, and details up close, than they do at or near infinity. 

Focussing at infinity is for me always hit or miss with the S-E 006 when using autofocus, instead I rely on the split/micro prism focus screen I had installed years ago by Leica. 

It's the number one reason I'd get a S007 or S3, to get live view and use live view for tack sharp focus when doing landscapes from tripod etc.

Edited August 3, 2022 by jip

[Stuart Richardson]

I think you are right. I will say, however, that they work better if you can find a flat object at a distance. I think the S AF sensor is often tricked if you point at a horizon. Rather than focusing on the horizon line, it will often focus on things in the foreground (but still in the AF patch). On the other hand, if you focus on something like a skyscraper or the moon, I think it is very accurate. Most of the AF problems in the S system are because of the large AF patch area, more so than the lack of accuracy of the sensor itself. Unfortunately, most distance compositions make it hard to fill the AF patch completely with something at the right distance. I find it works better in mountainous compositions, rather than grasslands etc. Once you are aware of this, you can be a bit better about catching it before it becomes a problem. Another good idea in that situation is, as said above, to learn your real infinity markers on the lens, and just take a quick glance at the lens to see where it is actually focusing.

Furthermore, I think S wide angle lenses have this problem a bit worse, as I think the designers tried to correct a bit for field curvature by adjusting the focus a bit closer to the camera. So I would often find that with the 35mm and 45mm lenses that they would often focus closer in than I intended. So if I point at mountains in the distance it would focus at 30m instead of infinity. Often this can be covered by DOF, but since the S is so sharp and high resolution, the comparative softness at infinity can be readily visible. So with those lenses I often checked focus pretty carefully.

Edited August 3, 2022 by Stuart Richardson

[helged]

Just to add another point to the discussion of focusing at infinity/far away: If one uses live view with magnification on S007 or S3, one will see that only a tiny bit of rotation of the focus ring may change the focus dramatically. Once the lens is correctly focussed, the details are just fantastic. A little off, and things are far from perfect. I have quite some examples of the latter with mountains several km away...

[epines]

Thanks, Stuart and Helged. Agreed. AF at distances is definitely better if you can find a flat object. The camera's accuracy is actually spot-on; it just seems to get confused in certain circumstances. And the resolution of the lenses is really impressive, even when focusing on distant objects. You know when it's 100% in focus. The clarity is amazing. The lenses are the best I've ever used, and I've used many in the MF world. (Tech-camera lenses are also incredible, but we're talking about f-stops of f/8 and f/11 with those; with the S lenses, it's there at f/2.5 and f/2.8.)