usccharles
Well-known
my two newest lenses, 50 lux and 28 elmarit (both came six bit coded) are dead on in their focus, but my older lenses 75 lux and 35 lux both have bad backfocus, the former being older and more pominent its backfocus.
you think leica adjusts its newer lenses so it doesn't backfocus on the m8? or does focusing get worse as the lenses get older in general?
you think leica adjusts its newer lenses so it doesn't backfocus on the m8? or does focusing get worse as the lenses get older in general?
zeitz
Established
My very old mid-50s lenses, 50mm collapsible Summicron and 35mm 2.8 Summaron, along with a mid-60s 135mm Elmarit, all focus perfectly on my M8.
J. Borger
Well-known
none of my lenses back-focus on the M8 ........ nor the new ones nor the old ones 
harmsr
M5 Nut
Charles,
If anything, I think that the newer lenses are being rushed out of Leica and could use an improvement on their calibration.
I believe several points are happening:
On film we had more forgiveness than on a digital sensor for critical focus.
Leica is still using the same calibration standards it did with film, which is too loose for the M8 sensor. This also goes for the RF in the M8.
We also did not view everything from film at the same size we look at digital files with.
The instant confirmation of digital really is showing whether the focus is correct or not, vs. the question of us nailing the focus when we review the film print much later.
-----------------
I am very critical of focus and have had virtually every M lens calibrated to get them perfect.
--------------
However on the plus side, all the effort that I have put into the body and the lenses is well worth the end result now. It was a frustrating journey to get here.
Best,
Ray
If anything, I think that the newer lenses are being rushed out of Leica and could use an improvement on their calibration.
I believe several points are happening:
On film we had more forgiveness than on a digital sensor for critical focus.
Leica is still using the same calibration standards it did with film, which is too loose for the M8 sensor. This also goes for the RF in the M8.
We also did not view everything from film at the same size we look at digital files with.
The instant confirmation of digital really is showing whether the focus is correct or not, vs. the question of us nailing the focus when we review the film print much later.
-----------------
I am very critical of focus and have had virtually every M lens calibrated to get them perfect.
--------------
However on the plus side, all the effort that I have put into the body and the lenses is well worth the end result now. It was a frustrating journey to get here.
Best,
Ray
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usccharles
Well-known
harmsr said:
for some reason i felt like leica was recognizing that their old calibration methods with film RFs weren't as accurate on the M8, because the sensor gives no flex with critical focus as film did, and so they were adjusting for this varience by making their newer lenses focus more precisely with the M8's digital back.
i made this assumption because my newer lenses focus well, and my older lenses didn't. not scientific at all, but seeing that i guess other people don't have the same issues with older lenses as i currently do, that it may just be my camera that needs a overal calibration done.
:bang:
rxmd
May contain traces of nut
Why should film be more tolerant with regards to focusing than a sensor? Focusing distance is the same, and the rules for DOF are strictly geometric and independent of the medium, they work the same regardless if you record the image on film, a digital sensor, a focusing screen or a wad of toilet paper for that matterusccharles said:
Philipp
jaapv
RFF Sponsoring Member.
Philipp, the surface of a sensor is a plane that behaves like the perfect surface and is flat and two- dimensional,
a film has thickness, and is not perfectly flat, so three-dimensional. Thus the tolerances on film are wider than on a sensor. This has an effect on DOF as well. It is more defined on a sensor. A film produces a cone of light inside the fim, elliptic towards the edges with reflections and refraction inside the emulsion. A sensor has disks controlled mainly by the resolution and pixel size. Therefore DOF is more defined and steep on a sensor than on film.
a film has thickness, and is not perfectly flat, so three-dimensional. Thus the tolerances on film are wider than on a sensor. This has an effect on DOF as well. It is more defined on a sensor. A film produces a cone of light inside the fim, elliptic towards the edges with reflections and refraction inside the emulsion. A sensor has disks controlled mainly by the resolution and pixel size. Therefore DOF is more defined and steep on a sensor than on film.
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usccharles
Well-known
rxmd said:Why should film be more tolerant with regards to focusing than a sensor? Focusing distance is the same, and the rules for DOF are strictly geometric and independent of the medium, they work the same regardless if you record the image on film, a digital sensor, a focusing screen or a wad of toilet paper for that matter
Philipp
hi philipp,
thats not entirely true. its because film isn't completely flat like a digital sensor when a picture is taken. the film plane will have slight variences in curvature which will give soom 'room' for the critical focus point.
yes the rules of DOF ar strictly geometric, but the rules become a little different when you change from film (with alittle flex) to a digital (completely flat and secure in position to the lens). you would thus have much less tolerance on a digital back compared to a film back. thats atleast the reasoning i've read around here and it seems to make sense to me
usccharles
Well-known
jaapv said:
ok that was way smarter sounding than my explanation
thanks jaapv
jaapv
RFF Sponsoring Member.
I have a feeling, btw, that there is a possibility of the focussing mechanism/helix showing some wear on older lenses, leading to focussing errors. Having said that, the advent of asph and apo-lenses was only possible due to better manufacturing processes with smaller tolerances. there seems to be an ongoing process of improvement.
rxmd
May contain traces of nut
Hi Jaap & Charles,
Thickness is what Jaap alludes to when he talks about cones of light inside the film that we don't have in a digital sensor. However, there's two remarks to be made about this. Firstly, in a film camera the film shows the emulsion side towards the lens, so that the thickness of the film itself is actually irrelevant as long as it's constant and standardised across films, what's relevant is the thickness of the emulsion. Secondly, film manufacturers take great pains to avoid reflections etc. inside the film itself and inside the emulsion, which is why most films don't have a perfectly clear base, and why you have all sorts of flare protection layers inside the emulsion which get washed out when fixing (with a film like Lucky you get all sorts of weird flare effects). This is also why unexposed film is not transparent. Thirdly, the thickness of the emulsion is actually as close to zero as it gets; an ideal B&W film has exactly one layer of silver halide crystals, and these are very, very small in relation to the dimensions we are talking about. In particular, the crystals are a lot smaller than the acceptable circles of confusion that form the basis of any discussion about DOF (otherwise the whole concept of circles of confusion and DOF falls down and makes no sense). Fourthly, a sensor has a thickness, too, otherwise concepts like the Foveon sensor wouldn't work where a photon's colour is determined by its penetration depth. So film and sensors aren't fundamentally different in this respect.
Flatness is also alluded to in Jaap's post and forms the basis of Charles' post. The argument is, if I understand correctly, that if the film is less flat and bulges a little bit, then there is more room for the film to fall in the imagined plane of sharpness. However, this is just plain wrong. Focusing with any film camera is based on the assumption that the film is in a known location; focusing works by altering the lens geometry in such a way that the image is projected exactly onto the location of the recording medium. If the film isn't flat, this does not add any depth of field; on the contrary, because the film isn't where it's expected to be, it moves those areas of the negative that should be in focus out of focus. So if the film isn't flat, not only does DOF not get any bigger (in fact in practice DOF should be minimally affected, if at all), but also the focus is wrong. I don't see a gain in that. The best thing that could theoretically happen at this point is that areas that should be out of focus happen to be in-focus, because the cone of light from their projection is focused at a point in front of where the film plane should be, and now the film accidentally bulges into exactly this place. However, this is not only undesirable from the photographer's point of view, but it also does not add any depth of field either, it just results in an uneven distribution of sharpness across the frame. Camera manufacturers take great pains to stop the film from bulging and keep it flat. If the film isn't flat, it's a problem, not a source of added DOF. It's exactly the same as if saying that having a wobbly lens mount adds DOF, because the lens wobbles back and forth.
DOF has very little to do with what is happening behind the lens. It's just a way of thinking about how the human eye can be fooled into perceiving unsharp projections as sharp by keeping the unsharpness below a certain threshold. If the film moves back and forth behind the lens, this does not add any DOF. What is confusing in this respect is I think that when we talk about "depth" of field and about film bulging three-dimensionally in space, our mind assumes that both are connected with depth, and is thus fooled into thinking that they are somehow related.
Philipp
jaapv said:
Sorry, I think you are both wrong. I think we need to distinguish between two different geometrical aspects in which films and sensors may or may not differ, and that's (a) flatness and (b) thickness.usccharles said:
Thickness is what Jaap alludes to when he talks about cones of light inside the film that we don't have in a digital sensor. However, there's two remarks to be made about this. Firstly, in a film camera the film shows the emulsion side towards the lens, so that the thickness of the film itself is actually irrelevant as long as it's constant and standardised across films, what's relevant is the thickness of the emulsion. Secondly, film manufacturers take great pains to avoid reflections etc. inside the film itself and inside the emulsion, which is why most films don't have a perfectly clear base, and why you have all sorts of flare protection layers inside the emulsion which get washed out when fixing (with a film like Lucky you get all sorts of weird flare effects). This is also why unexposed film is not transparent. Thirdly, the thickness of the emulsion is actually as close to zero as it gets; an ideal B&W film has exactly one layer of silver halide crystals, and these are very, very small in relation to the dimensions we are talking about. In particular, the crystals are a lot smaller than the acceptable circles of confusion that form the basis of any discussion about DOF (otherwise the whole concept of circles of confusion and DOF falls down and makes no sense). Fourthly, a sensor has a thickness, too, otherwise concepts like the Foveon sensor wouldn't work where a photon's colour is determined by its penetration depth. So film and sensors aren't fundamentally different in this respect.
Flatness is also alluded to in Jaap's post and forms the basis of Charles' post. The argument is, if I understand correctly, that if the film is less flat and bulges a little bit, then there is more room for the film to fall in the imagined plane of sharpness. However, this is just plain wrong. Focusing with any film camera is based on the assumption that the film is in a known location; focusing works by altering the lens geometry in such a way that the image is projected exactly onto the location of the recording medium. If the film isn't flat, this does not add any depth of field; on the contrary, because the film isn't where it's expected to be, it moves those areas of the negative that should be in focus out of focus. So if the film isn't flat, not only does DOF not get any bigger (in fact in practice DOF should be minimally affected, if at all), but also the focus is wrong. I don't see a gain in that. The best thing that could theoretically happen at this point is that areas that should be out of focus happen to be in-focus, because the cone of light from their projection is focused at a point in front of where the film plane should be, and now the film accidentally bulges into exactly this place. However, this is not only undesirable from the photographer's point of view, but it also does not add any depth of field either, it just results in an uneven distribution of sharpness across the frame. Camera manufacturers take great pains to stop the film from bulging and keep it flat. If the film isn't flat, it's a problem, not a source of added DOF. It's exactly the same as if saying that having a wobbly lens mount adds DOF, because the lens wobbles back and forth.
DOF has very little to do with what is happening behind the lens. It's just a way of thinking about how the human eye can be fooled into perceiving unsharp projections as sharp by keeping the unsharpness below a certain threshold. If the film moves back and forth behind the lens, this does not add any DOF. What is confusing in this respect is I think that when we talk about "depth" of field and about film bulging three-dimensionally in space, our mind assumes that both are connected with depth, and is thus fooled into thinking that they are somehow related.
Philipp
ferider
Veteran
usccharles said:
The 75 lux and the 135/2.8 are the two Leitz lenses with the most
shallow DOF. DOF gets more shallow with the M8's crop factor (measuring
DOF for constant COC at same print size). On the M8 the 75 lux is
equivalent to a 90/1.4 on, for example, an M3. Both lenses are
much harder to focus than for example the Noctilux.
Also Leitz lenses come sometimes not perfectly adjusted from manufacture.
On a digital camera this is immediately apparent since testing
is easy.
Jorge once did a test on his M8, with all new lenses, some were good,
some had front- and some had back focus.
It used to be standard practice to have lens/body combinations
adjusted to each other, right after purchase. I have a 90/2 Summicron
that is perfect on one of my M bodies, and very slightly off at infinity
on 2 other M bodies. The 3 bodies and the lens were CLA'ed by either
Don or Sherry.
IMO, this is just part of RF usage and has nothing to do with old or new,
film or digital.
Roland.
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jaapv
RFF Sponsoring Member.
Philipp - in order not to waste bandwidth, you might refer to this post by me, which shows that, although we may disagree on certain aspects of the differences between sensors and film - and believe me, as a user of both I really see them (btw, I was talking about the thickness of emulsion, and yes, the Foveon sensor is a case apart) - we certainly agree about most of the theoretical aspects of DOF.
http://www.rangefinderforum.com/forums/showthread.php?t=26541
That is not the point. It is a major headache of film and camera manufacturers that film will not be flat. Vacuum devices have been used to ensure flatness, but normal cameras don't have these. As a result it is theoretically impossible to achieve the ideal focussing plane on film, making, to exaggerate, your photographs unsharp in some areas anyway, regardless of focussing accuracy. A sensor gets magnitudes closer to that ideal.
http://www.rangefinderforum.com/forums/showthread.php?t=26541
That is where you are wrong. Technical Pan, for instance, which is as close to an ideal film as you can get, has an average emulsion thickness of 0.01 mm, which is 1/3rd of the ( too large in this age) COC. Most consumer films, particularly the faster ones, have a considerably larger emulsion thicknesses.rxmd said:
rxmd said:
That is not the point. It is a major headache of film and camera manufacturers that film will not be flat. Vacuum devices have been used to ensure flatness, but normal cameras don't have these. As a result it is theoretically impossible to achieve the ideal focussing plane on film, making, to exaggerate, your photographs unsharp in some areas anyway, regardless of focussing accuracy. A sensor gets magnitudes closer to that ideal.
rxmd
May contain traces of nut
Hi Jaap.
Philipp
Well, that's 10 µm, or rather thin; that's also the order of magnitude of sensor thicknesses - (though upon googling I find data only for back-illuminated sensors for astrophotography applications, which are ground and etched down to 10-20 µm for extra thinness to give more sensitivity to short wavelengths). Also I'm not sure about how much of an ideal film Technical Pan really is in the context of this discussion; I remember that Ilford's Delta crystals and Kodak's T crystals work on the basis of having extra flat silver halide crystals (in German they're even called Flachkristallfilme, or flat-crystal films). It would be interesting to have more actual data on emulsion thicknesses for a number of real-world films; on googling I find nothing substantial. Also in the context of circles of confusion a thickness of 10 or 20 µm seems still rather small to me, because they are projected in a conical shape from the lens, so that their dimension in the directions of the film plane have different significance from their dimension in the direction of the normal of the film plane. Otherwise it would be impossible to take sharp pictures with slide film.jaapv said:
I agree that flatness is much better for sensors. (On the other hand, they have other issues, such as reflections in the various protective glass, UV filter and microlens layers, which you don't have with film.)jaapv said:
Philipp
usccharles
Well-known
are you guys speaking english??
i remember a quote from the greatest movie ever made, Days of Thunder:
"a screw here, a screw there, I just don't know!"
"but how can that be??"
"I don't know, I'm am idiot! but what difference does it make? they told me to get in a car and drive and i can drive!"
heehee, god i need to go to sleep
i remember a quote from the greatest movie ever made, Days of Thunder:
"a screw here, a screw there, I just don't know!"
"but how can that be??"
"I don't know, I'm am idiot! but what difference does it make? they told me to get in a car and drive and i can drive!"
heehee, god i need to go to sleep
Ben Z
Veteran
None of my lenses, Canon EF's, ancient Nikkors and Takumars, even my Leitz 400mm Telyt and M-series 135 T-E lenshead on short helical mount, backfocuses on my 20D. But I've heard of people having back (or front) focus problems on DSLR's too. Sometimes it's a lens, sometimes the body, but always a fault of maladjustment somewhere, not an innate characteristic of sensor vs film. So I suspect that's the case with M8 also. If it back or front focuses it's either the register, the rangefinder, or the lens collimation that's off. There's another issue, that is focus shift as the lens is stopped down, which is a different phenomenon entirely, and is a characteristic of a lens that can't be adjusted away. The problem with such a lens on a rangefinder (film or digital) is that the photographer has no inkling it's happening because the focusing is by facsimile not visual sharpness.
jaapv
RFF Sponsoring Member.
Quite right, Benson. Some time ago I was active on FM's canon Forum. Every second thread was a complaint about backfocus.