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A simple tip for improving focus sharpness

dannh

Member
About a year ago I attended one of the Leica M9 roadshow workshops and there were a few good tips shared. One of the tips in particular has helped me increase the number of sharp, in focus shots I take, which is always something we're striving to do with rangefinders.


For this tip, think about depth of field and where your focus point lies within the in focus portion of your shot. As you can see in the diagram below, in front of your focus point, you only have 1/3 of your depth of field, whereas behind your focus point you have 2/3 of your depth of field. This is probably old news to many of you, but even after many years of a photography hobby, somehow I had never understood this concept.





So here's where the tip comes....

When focusing, you can approach your focus point from either direction; from the minimum focus distance, or from infinity. Go pull out your M camera and look at the top of the lens with the depth of field markers. You can either rotate it clockwise or counterclockwise to arrive at the point where your subject is in focus.

Now, think about the diagram above. The trick is to always approach the point of focus from the rear, or from infinity, because you're more likely to have the portion of your subject in focus that you desire. If you're a little off, it's probably ok because you've got twice as much depth of field on that side of your focus point.

Give it a try, and feel free to discuss this one. I'm open to hearing if any of you have similar tricks or a variation of this tip to share. Overall I've found that if I approach the focus from infinity rather than hunting back and forth for focus, I have a better chance of of a sharp in-focus subject. Obviously this is critical when shooting the lovely Leica glass wide open!

Diagram credit and more about depth of field:
http://www.dumetier.com/photography/depth.html
 

dannh

Member
To add to this, I've gotten in the habit of always throwing my lens focus to infinity after I'm done with a shot, or when setting it down. This way, when I go to pick up the camera or bring it to my eye, it's already in position. Then it's just extend finger, pull focus tab until subject is in focus, and click! This also helps eliminate much of the "hunting" for focus.
 
OK, as for your first post, the 1/3 - 2/3 rule is approximately true for far enough distances, and can be useful to know. As for its application to RF focussing, I´m a bit doubtful. In fact, if the DOF is measured instead in terms of lens displacement (same as rotation angle of the focussing ring), it is perfectly symmetrical, as can indeed be seen from the DOF markers you mention; they´re all symmetrically placed around the index mark. So the demand on focussing in terms of turning the ring is just as ´tight´ from the infinity end as from the close end.

As for your second post, I agree wholeheartedly; it makes life far easier, and most old Leica shooters have this habit since years. And that´s quite enough to make it a good tip....
 

dannh

Member
Per, you're certainly correct about the lens displacement distance going from either direction. Physically turning the lens from either directions gives no advantage.

But I believe the advantage is achieved because of the human error we can all make when we *think* an object is in focus, but isn't quite. If I've erred by focusing slightly behind the subject, wouldn't this be more desirable than erring in front of the subject, because there's twice as much wiggle behind than in front?

I'm still learning a lot about they physics of photography, so by all means educate me where I'm wrong. :)
 

Godfrey

Well-known member
... But I believe the advantage is achieved because of the human error we can all make when we *think* an object is in focus, but isn't quite. If I've erred by focusing slightly behind the subject, wouldn't this be more desirable than erring in front of the subject, because there's twice as much wiggle behind than in front? ...
It doesn't really make any difference. If you want a particular plane of focus to be sharply focused, it is what needs to be in focus. The same amount of distance in front of and to the rear of that plane will be in focus no matter which way you approach it.

If you are looking for which error in focus plane ("too close" or "too far") might be more tolerable, that will change depending upon what the scene you're shooting contains. For example, if there is a lot of significant detail behind the subject plane and you focus a little farther away than you ought, that detail will be better focused at the expense of the subject ... whether this is more or less distracting is up to the particular scene. Similarly, if there is significant detail in front of the subject which is out of focus, that might be more or less distracting depending on what's important in the scene.

The important thing to realize is that whatever the focus zone might be, the sharpest plane of focus in that 'acceptably sharp' focus zone is approximately 1/3 of the way in from the near edge.*

With that fact in mind, look carefully at your scenes and subjects to understand where, for a given scene, the best placement of the focus plane might be. Then use whatever means to achieve that works best for you.

* a note on hyperfocal focusing: The hyperfocal distance setting is that point, for a given format, focal length and lens opening, for which the far edge of the acceptably sharp focus zone first reaches infinity. A lot of people seem to misconstrue this as saying that "everything from the near distance to infinity is sharp" where "sharp" implied "equally sharp". That's not true: If you're focused at the hyperfocal setting, THAT is the sharpest plane of focus, and things in the scene which lie at that distance are sharper than things further away or nearer. So when you're shooting landscape photos, you don't necessarily always want to use the hyperfocal setting if you're trying to get ultra sharp detailing of the trees in the distance. In this case, you'd be better off losing a bit of sharpness in the near field so that tree branches and such are better defined in the distance.

Resetting the lens to infinity (or close to it) is one good habit, at least at the beginning, if you're typically shooting a relatively distant subject and want the camera to be as ready as possible for the next shot. I take this another step: when I'm out shooting and using manual focus, after I work on a particular subject, I always re-set the focus to be where I expect the next shot might be. The goal is always to have the camera ready ... re-set focus as close to the right point that you can make a quick capture without having to work to move the focus to the right point.

When I'm walking and looking about, I'm constantly calibrating what focus zone and primary subject distance I think might pop up at any moment, so I don't set the camera to infinity, I set it to the right focus distance for the expected subject I am looking to capture.
 
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dannh

Member
Godfrey, you've helped clear up a few misunderstandings on my part, thank you. I enjoyed your website as well. I always enjoy learning from someone with many many more hours experience than I.

I guess one of my struggles is that I always want to oversimplify photography. I look for simple rules and tips that I can apply during that small window of time when I'm about to take a shot, where time speeds way up because I don't want to miss that critical moment. I'm learning that instead of oversimplifying things with rules, the better approach is to spend a lot of time practicing and learning, as well as taking the time before the shot even presents itself to prepare myself and my gear.
 

Millsart

New member
One important thing to remember is that in reality no one factor really makes or breaks a photograph being sharp or unsharp, rather it is a combination of factors. One might have a lens that slightly backfocuses and by taking that 1/3-2/3 principle into account more shots of acceptable critical focus could be achieved, but then on the other hand, a front focusing lens might end up with a very low keeper ratio because if your focusing slightly past your subject on purpose, with a lens that front focuses your then at or even out of the DOF for acceptable focus.

On top of that sometimes the slightest lean in our out can also throw your focus off a bit. I know that as a habit, I find myself leaning back a little when I view the full viewfinder image after focusing on the center patch. Just a habit I do as I slightly recompose but with a fast lens, that 1" lean can sometimes be enough to shift my focus from eye to tip of nose.

As such, I think the only good "rule" is that there are no rules and to each his own. Everyone is going to have some lens or a RF that is going to differ from another shooters, and also our own body mechanics and habits.

In the end one really just needs to learn their camera and given focal lengths for a given subject distance and learn, for example, that if you've shooting a subject at 6 feet with your Zeiss 50 f1.5 at f.5 but which is calibrated for f2.8 where to focus.

Nothing wrong with theory of course but there are just so many variables that trying to use any one size fits all rules of thumb that some lens/distances are going to be hindered as much as others are helped.

But all and all, thats a little bit of the fun of RF photography. Its not an exact science nor a 100% assurance that all you have to do is press a button and get a perfectly exposed, perfectly focused photo. I've got cameras that darn near come close to giving me that and they are great for paid work but don't give me near the same satisfaction of getting a perfectly focused and exposed photo where I feel I can take the credit rather than the camera
 

fotografz

Well-known member
I've been using the "Back To Infinity" technique for 40 years ... a photojournalist taught me to do that for faster focusing in spontaneous street conditions. It served me well when I started shooting weddings with a M. It is a speed technique as much as anything, but can help with accuracy also ... like with the 50/0.95 and 75 Lux.

Sorry, but I do not understand the statement: "... as can be seen by the DOF markers, they're all symmetrically placed around the index mark." Really? While the numbers are placed symmetrically, the actual indicators grow narrower and narrower as they approach the index mark don't they?

1/3 to 2/3 DOF is only an approx. indicator, and an average rule of thumb mostly for average distance focusing: using a M35mm lens set to f/11 and critically focused at 8', the DOF distance covers from 5' to 30' ... so, approx. 25' total is in reasonable focus with 8' falling roughly 1/3 into that total plane of focus (25' X.33 =8.2'). Same lens set closer to 3.2' critical focus: f/11 provides DOF distance from 2.5' to 4', or 1.5' total plane of reasonable focus with 3.2' falling roughly 1/2 into that plane of focus ( 3.2' X.50 = 1.6'). So a more reasonable rough rule of thumb for DOF is 1/3 into a scene when at distance, and 1/2 in when closer.

The following depends on how one tends to shoot ... consistently closer up, or at more normal distances:

... Using "infinity reset" as a speed technique can be attributed to the fact that greater distances can be covered with less focus throw from infinity. The amount of focus adjustment to go from infinity to 6' with a M35mm lens is less than from 2.5' to 6' ... and involves a more natural hand action (presupposing one holds the lens cradled in the left hand and uses the forefinger/thumb to drive the focus adjustment) ... the forefinger is already in position to do this from infinity, and is not in position if driving the focus preset to the closest focus distance.

Presetting to an approximate distance is fine when there is time and things aren't in spontaneous flux ... where it can then lead to hunting. Resetting to infinity after a series of shots develops a natural muscle memory action of always moving in one direction.

My 2¢ :)

-Marc
 

Terry

New member
The other easy tip to focus faster was taught to me by Guy and Jack. It works on all lenses with a focus tab. Having that tab at the bottom will always be at the same focus distance. I forget exactly what that distance is and can't check it (no longer have any lenses) but it is a good way to work quickly regardless of focal length.
 

fotografz

Well-known member
The other easy tip to focus faster was taught to me by Guy and Jack. It works on all lenses with a focus tab. Having that tab at the bottom will always be at the same focus distance. I forget exactly what that distance is and can't check it (no longer have any lenses) but it is a good way to work quickly regardless of focal length.
It's about 4' or 5' on the 35/1.4 ASPH ... which is a good distance. It's more on a 50mm.

-Marc
 

johnnygoesdigital

New member
My guess is that Per's reference to symmetry probably relates to the placement of indicators on either side of the index mark as they are evenly spaced left and right.
Being able to accurately gauge close distances without the viewfinder seems key to either technique.
 

fotografz

Well-known member
My guess is that Per's reference to symmetry probably relates to the placement of indicators on either side of the index mark as they are evenly spaced left and right.
Being able to accurately gauge close distances without the viewfinder seems key to either technique.
Got it, thanks.

It is the relationship of those evenly spaced indicators on either side of the center, to the uneven distance markers which grow wider apart as you approach the closest focusing distance, that determines DOF.

-Marc
 

jlm

Workshop Member
if you focus from the back and don't quite get there due to error, doesn't that place your object in front, and therefore in the 1/3 range, not the 2/3 range?
 

Godfrey

Well-known member
Godfrey, you've helped clear up a few misunderstandings on my part, thank you. I enjoyed your website as well. I always enjoy learning from someone with many many more hours experience than I.
You're welcome. And thanks for visiting and viewing my website! :)

... I'm learning that instead of oversimplifying things with rules, the better approach is to spend a lot of time practicing and learning, as well as taking the time before the shot even presents itself to prepare myself and my gear.
That sounds like you're on the right track! When you see well enough, and the muscle memory of what to do in various situations is there, and your equipment is all ready, you'll find that the hectic anxiety of the moment of shooting disappears. At that point the camera disappears and your attention is on the scene, you can calmly make decisions without conscious thought.

It's a great place to get to.
 

robsteve

Subscriber
On a side note, starting from infinity is also a tip for manual focusing on a SLR as well. Ted Grant had mentioned this years ago in regards to focusing wide angles on Leica SLRs.

Robert
 

silverlight99

New member
Very helpful thread, thx everyone. The best recent addition for me was an MS Optical 1.15 which allowed me to dial in a diopter adjustment so I no longer have to wear glasses while shooting. I've probably had a 100% increase in usable shots. Also now focusing from the direction of infinity per above :D
 
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