Focusing and accuracy

[redlensandgreenbody]

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Hi! 

I have just started to shoot with M10 and I experienced one problem. 

I have astigmatism and don't wear glasses so my vision gets a little bit worse at night. I just came back from an evening walk with 35mm summilux pre-asph. I think I could focus as I can match two images in the RF patch. But then I started to wonder whether you have to be dead accurate when focusing an M. 
 

[evikne]

The accuracy you need depends on the depth of field (aperture + focal length + focus distance). A 35 mm lens at f/1.4 will need pretty accurate focusing at a close distance. And of course you and your subject must keep the same distance until you have taken the picture.

Some more practicing and testing will tell you whether your eyes are the problem, or maybe the lens needs some calibration.

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[jaapv]

Yes, you have to be dead accurate focusing an M and astigmatism can be a problem. Although you can use an ocular diopter to correct, that will only worsen the error when shooting in portrait orientation. Fortunately there is a solution:

 

http://walterleica.com/services/

[Jeff S]

Get glasses to correct astigmatism.  The Walter is somewhat clunky and will only correct your vision through the VF.  Photography depends on good vision even when your eye isn’t pressed to the finder.

I wear glasses to correct astigmatism, distance and glare (sunglasses), and still benefit from a +.5 diopter (due to aging eyes) for optimal viewing and focusing.  The M10 VF beautifully accommodates both (especially with flexible frames).

A good optician is your friend (and will have free trial diopters to use once your astigmatism is addressed).  The focus patch on the M is set at a virtual distance of 2m.  

Jeff

 

Edited January 17, 2019 by Jeff S

[adan]

Just for the record, and in no way meaning to belittle leoskkang's eyes (my own eyes are developing significant problems - like, Jeff, I get it). And to address his specific situation - focusing a 35mm Pre-ASPH.

The 35 pre-asph Summilux itself suffers from - severe astigmatism. It is part of what creates its signature "glow" at f/1.4. As well as other major optical problems - spherical aberration and coma. The pictures below show a pre-ASPH Summilux picture made at f/1.4 - full-frame, and cropped for details. (Sorry about the noise - M9 CCD at ISO 2500).

The astigmatism and coma are so severe they are visible even in the small whole image (area top right). The first crop shows that area in detail, and the streaks and blurs in the highlights that produce "wings" at 90° angles (—|— shapes) are classic astigmatism. With coma producing the bends in the longer wings.

BTW - just about all Leica-M 35mms (even the Summicron ASPH) show some coma and astigmatism wide-open - the only one that is virtually completely free of it is the 35 Summilux ASPH.

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Astigmatism and coma are always most severe the closer one gets to the corners, but in the center crop below, they are already starting to show just a few mms from the center of the image - see the triangular or "fanned out" highlight in the grape (or whatever it is) on the background plate.

But the primary purpose of the center crop is to show the effect of the spherical aberration, as it affects the focus point. There really isn't one. Each part of the lens, as one moves out from the center of the glass, is focusing the table at a different place. Thus there is a layering of "sharp butter" onto "fuzzy butter" and "sharp knife" onto "fuzzy knife" and so on. In effect it creates "artificial" depth of field, as no one focus plane is perfectly sharp, but a wider range of distances are equally "sort of" sharp.

The abberations all get stronger at close-focus distances. Which is why, in their wisdom, Leica never allowed the 35 Summilux pre-ASPH to focus closer than 1 meter.

Net result - at f/1.4, focus is not much of an issue, because of the lens characteristics, and at smaller apertures (where the 35 Lux pre gets very sharp), focus is not much of an issue with a 35, because "real" depth of field kicks in.

As I said, my eyes are weak. With my glasses off, I can't see anything critically sharp beyond about 26 inches /0.7 m. Nevertheless, I can often focus a 90mm f/2.8 or 75 f/2 at 3 meters, by sort of sensing the midpoint between where the (quite blurry) RF images start to merge, and where they start to separate again on the other side.

[bocaburger]

50 minutes ago, Jeff S said:

I wear glasses to correct astigmatism, distance and glare (sunglasses), and still benefit from a +.5 diopter (due to aging eyes) for optimal viewing and focusing.  The M10 VF beautifully accommodates both (especially with flexible frames).

Same, except I need a +1 and can't for the life of me see a whit of improvement with the M10 viewfinder over my M240.

[jaapv]

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But Andy, what does lens astigmatism have to do with it ? Good examples, though.

[adan]

Just an interesting coincidence - and that it, in part, makes worrying about "critical focus" with a 35 lux pre somewhat pointless. It is contributing to "fuzziness" over most of the image at f/1.4. Get the focus within about 10% of correct (1 foot at 10 feet) and that's as good as it gets.

[Jeff S]

14 minutes ago, bocaburger said:

Same, except I need a +1 and can't for the life of me see a whit of improvement with the M10 viewfinder over my M240.

Bigger opening, higher magnification and better eye relief.

But eye centering perhaps more critical.

Jeff

Edited January 17, 2019 by Jeff S

[TomB_tx]

I agree with Adan’s conclusion on focusing: I’ve worn glasses full time for 60 years with significant near sightedness and astigmatism, and nearly always wear glasses when focusing. Yet I find I can focus an M fairly well without them (if glasses fog over for example), while an SLR would be hopeless. But for critical focus my glasses are a must, and I do notice a much better hit rate with the M10 than with an M9.

[pico]

My optometrist told me during my last visit that cataracts are forming, but like prostate cancer it progresses so slowly that, "You probably be dead of old age before they become a problem."

I ain't ever gonna drink with her again.

 

[PhoebusXS]

If it affects that much, maybe you should wear glasses..

[250swb]

Presumably the OP can function in everyday life with his astigmatism so the first thing he can do to help himself is to understand depth-of-field and how the aperture used vastly affects what is in or out of focus. It isn't a complete substitute for focusing accurately on the subject, but if out for a walk understanding DOF will not only be a leg up towards sharp pictures but also give an understanding why critical focus can be hard to achieve if using wide apertures. 

When I first started being taught photography we were all given an eye test and still told to 'bracket focus' if in any doubt at all, because film is cheap but opportunities aren't. And the OP should also consider this, if in any doubt bracket focus, I still do it today if I know my lens suffers from focus shift so it's not a sloppy approach, just common sense.

I don't like viewfinder magnifiers, although I'm sure if I always needed one I'd soon get used to them. As the OP doesn't wear glasses they are easier to use than for people who wear glasses where the magnifier adds too much stand-off from the camera body, so I think in this case a dioptre is the way to go.

[jaapv]

13 hours ago, adan said:

Just an interesting coincidence - and that it, in part, makes worrying about "critical focus" with a 35 lux pre somewhat pointless. It is contributing to "fuzziness" over most of the image at f/1.4. Get the focus within about 10% of correct (1 foot at 10 feet) and that's as good as it gets.

I'm not sure whether a magnifier would solve the problem. Astigmatism is a complicated eye error, but can be compensated by a diopter lens - in one orientation only. I think that a diopter is basically the way to go, especially if one shoots in landscape orientation mostly. After all, you can focus with the camera horizontal and quickly turn it vertical as a workaround. The only other solution is to wear glasses, personally I don't like doing that. You lose contrast and they get dirty, etc.

Consult an optician, use his try-out lenses to determine the best diopter value.

[redlensandgreenbody]

14 hours ago, adan said:

Just for the record, and in no way meaning to belittle leoskkang's eyes (my own eyes are developing significant problems - like, Jeff, I get it). And to address his specific situation - focusing a 35mm Pre-ASPH.

The 35 pre-asph Summilux itself suffers from - severe astigmatism. It is part of what creates its signature "glow" at f/1.4. As well as other major optical problems - spherical aberration and coma. The pictures below show a pre-ASPH Summilux picture made at f/1.4 - full-frame, and cropped for details. (Sorry about the noise - M9 CCD at ISO 2500).

The astigmatism and coma are so severe they are visible even in the small whole image (area top right). The first crop shows that area in detail, and the streaks and blurs in the highlights that produce "wings" at 90° angles (—|— shapes) are classic astigmatism. With coma producing the bends in the longer wings.

BTW - just about all Leica-M 35mms (even the Summicron ASPH) show some coma and astigmatism wide-open - the only one that is virtually completely free of it is the 35 Summilux ASPH.

Welcome, dear visitor! As registered member you'd see an image here…

Simply register for free here – We are always happy to welcome new members!

Astigmatism and coma are always most severe the closer one gets to the corners, but in the center crop below, they are already starting to show just a few mms from the center of the image - see the triangular or "fanned out" highlight in the grape (or whatever it is) on the background plate.

But the primary purpose of the center crop is to show the effect of the spherical aberration, as it affects the focus point. There really isn't one. Each part of the lens, as one moves out from the center of the glass, is focusing the table at a different place. Thus there is a layering of "sharp butter" onto "fuzzy butter" and "sharp knife" onto "fuzzy knife" and so on. In effect it creates "artificial" depth of field, as no one focus plane is perfectly sharp, but a wider range of distances are equally "sort of" sharp.

The abberations all get stronger at close-focus distances. Which is why, in their wisdom, Leica never allowed the 35 Summilux pre-ASPH to focus closer than 1 meter.

Net result - at f/1.4, focus is not much of an issue, because of the lens characteristics, and at smaller apertures (where the 35 Lux pre gets very sharp), focus is not much of an issue with a 35, because "real" depth of field kicks in.

As I said, my eyes are weak. With my glasses off, I can't see anything critically sharp beyond about 26 inches /0.7 m. Nevertheless, I can often focus a 90mm f/2.8 or 75 f/2 at 3 meters, by sort of sensing the midpoint between where the (quite blurry) RF images start to merge, and where they start to separate again on the other side.

Adan,

Wow. Thanks for your explanation with the examples! 

[redlensandgreenbody]

Thanks all for the comments.

 

I guess I need to bracket focus when needed. I am thinking of getting an summicron 50mm. For this I would definitely need to wear glasses? When shooting cron/lux 50 wide open how long is the DOF at about 2-3m? Would really really slight misalignment of two images in the RF patch be able to compensated within the thickness of cron/lux 50 DOF? 

I do have a pair of glasses and I wear them when I am driving. With 35mm I don't like to wear them as I cannot fully see the frame lines. Would it be better to wear glasses and shoot 35mm not seeing the frame lines and train enough to imagine FOV of 35mm? 

[jaapv]

You need to be able to see sharp at 2 meters for optimal focusing.

[mdemeyer]

3 hours ago, leoskkang said:

Thanks all for the comments.

 

I guess I need to bracket focus when needed. I am thinking of getting an summicron 50mm. For this I would definitely need to wear glasses? When shooting cron/lux 50 wide open how long is the DOF at about 2-3m? Would really really slight misalignment of two images in the RF patch be able to compensated within the thickness of cron/lux 50 DOF? 

I do have a pair of glasses and I wear them when I am driving. With 35mm I don't like to wear them as I cannot fully see the frame lines. Would it be better to wear glasses and shoot 35mm not seeing the frame lines and train enough to imagine FOV of 35mm? 

To the last question, I’d say “Yes”.  I don’t find it difficult to estimate the image coverage but need sharp vision on the RF patch to focus. 

[Jeff S]

6 hours ago, leoskkang said:

I do have a pair of glasses and I wear them when I am driving. With 35mm I don't like to wear them as I cannot fully see the frame lines. Would it be better to wear glasses and shoot 35mm not seeing the frame lines and train enough to imagine FOV of 35mm? 

Presumably your glasses correct for astigmatism.  If so, thin and flexible frames should allow you to press close to the VF to see the 35mm frame lines well (at least mine do).  28mm lines are a different story, but practice can make this inconsequential.

Here’s a simple exercise (ideally if your distance prescription also provides good viewing at 2m... mine luckily does).  Take your camera to any local optician that has a set of trial diopters (I did).  Put your glasses on and place diopters in front of the VF to determine optimal viewing and focusing (my optician was kind enough to tape them in place).  You may or may not benefit from an added diopter. Then take your glasses off and try again to find best diopter strength. Then you can judge the possible trade off between clear focus patch alignment (with glasses) vs getting your eye closer for frame line viewing (without glasses).

Personal circumstances vary.  The best way to ‘see’ what works is to test for yourself.  Good DOF technique is wise for any photographer, but why cheat yourself by not simultaneously getting optimal viewing... if you can.

Jeff

Edited January 18, 2019 by Jeff S

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[redlensandgreenbody]

21 hours ago, adan said:

Just for the record, and in no way meaning to belittle leoskkang's eyes (my own eyes are developing significant problems - like, Jeff, I get it). And to address his specific situation - focusing a 35mm Pre-ASPH.

The 35 pre-asph Summilux itself suffers from - severe astigmatism. It is part of what creates its signature "glow" at f/1.4. As well as other major optical problems - spherical aberration and coma. The pictures below show a pre-ASPH Summilux picture made at f/1.4 - full-frame, and cropped for details. (Sorry about the noise - M9 CCD at ISO 2500).

The astigmatism and coma are so severe they are visible even in the small whole image (area top right). The first crop shows that area in detail, and the streaks and blurs in the highlights that produce "wings" at 90° angles (—|— shapes) are classic astigmatism. With coma producing the bends in the longer wings.

BTW - just about all Leica-M 35mms (even the Summicron ASPH) show some coma and astigmatism wide-open - the only one that is virtually completely free of it is the 35 Summilux ASPH.

Welcome, dear visitor! As registered member you'd see an image here…

Simply register for free here – We are always happy to welcome new members!

Astigmatism and coma are always most severe the closer one gets to the corners, but in the center crop below, they are already starting to show just a few mms from the center of the image - see the triangular or "fanned out" highlight in the grape (or whatever it is) on the background plate.

But the primary purpose of the center crop is to show the effect of the spherical aberration, as it affects the focus point. There really isn't one. Each part of the lens, as one moves out from the center of the glass, is focusing the table at a different place. Thus there is a layering of "sharp butter" onto "fuzzy butter" and "sharp knife" onto "fuzzy knife" and so on. In effect it creates "artificial" depth of field, as no one focus plane is perfectly sharp, but a wider range of distances are equally "sort of" sharp.

The abberations all get stronger at close-focus distances. Which is why, in their wisdom, Leica never allowed the 35 Summilux pre-ASPH to focus closer than 1 meter.

Net result - at f/1.4, focus is not much of an issue, because of the lens characteristics, and at smaller apertures (where the 35 Lux pre gets very sharp), focus is not much of an issue with a 35, because "real" depth of field kicks in.

As I said, my eyes are weak. With my glasses off, I can't see anything critically sharp beyond about 26 inches /0.7 m. Nevertheless, I can often focus a 90mm f/2.8 or 75 f/2 at 3 meters, by sort of sensing the midpoint between where the (quite blurry) RF images start to merge, and where they start to separate again on the other side.

You said: 'I can often focus a 90mm f/2.8 or 75 f/2 at 3 meters, by sort of sensing the midpoint between where the (quite blurry) RF images start to merge, and where they start to separate again on the other side' 

The way I focus with my cron35asph and lux35pre-asph is similar to yours. I focus my looking at the clarity of an image shown in the RF patch. But what I worried is when using this method when shooting wide open with cron35asph or elmar-M 50 (which I want to buy later). For example, if I am shooting a coca-cola bottle at about 3-4m I cannot clearly see the logo but I can see the clearest point while matching two images in the RF patch. Is is ok to focus like this with cron35asph and 50mm lens? I want to shoot 50mm without glasses (if possible). With 50mm wide open at f2 or f1.4, would a slight misalignment in the RF patch make any difference with regards to focus?