new backfocus thread-solution

[fotografr]

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i would like to contact don

 

 

Melissah--It's Don Goldberg, dagcam@chorus.net

 

He's the best.

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[JHAG]

Melissah--It's Don Goldberg, dagcam@chorus.net

 

He's the best.

 

He's got everything I sent in his hands right now.

[badpets]

After applying the the method of "adjusting roller cam" in M8 body, it does allow me to focus accurately with my Noctilux 50mm and Summicron 35mm at high speed. However, the focus shift emerges again at lower speed, that's aperture 5.6 - 11.

 

Do you think so called "body&lens calibration" done at Solm will resolve this kind of issue? In other words, enabling the focus to be accurate at all speed?

 

Thank you.

[Jamie Roberts]

Wow--I've never heard of focus shift from f5.6 to 11... does the point of focus shift beyond the DOF?!!

 

Are you sure you're not just seeing a loss of sharpness due to diffraction? Even Leica isn't immune to that

[JHAG]

According to Don (DAG), whith whom I've spoken of this extensively,

you always have to accept a compromise, and DOF won't compensate

entirely focus shift, which will go beyond.

[badpets]

it was focus shift at high speed before i made the roller cam adjustment. now it's the other way around. i'm not joking.

 

the funnier thing is that if i tune to infinity and focus on the moon now, the viewfinder shows a split moon. but the focus is spot on from 5.6 - 1.0.

 

that's why i was asking the question.

 

 

Wow--I've never heard of focus shift from f5.6 to 11... does the point of focus shift beyond the DOF?!!

 

Are you sure you're not just seeing a loss of sharpness due to diffraction? Even Leica isn't immune to that

[badpets]

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i think you understand what i'm experiencing now. so the answer is that focus shift will exist no matter what we do.

 

PS. sorry, but what does DAG stand for?

 

 

 

According to Don (DAG), whith whom I've spoken of this extensively,

you always have to accept a compromise, and DOF won't compensate

entirely focus shift, which will go beyond.

[blakley]

PS. sorry, but what does DAG stand for?

 

Don A. Goldberg

[badpets]

i see. thanks

 

Don A. Goldberg

[gdi]

it was focus shift at high speed before i made the roller cam adjustment. now it's the other way around. i'm not joking.

 

the funnier thing is that if i tune to infinity and focus on the moon now, the viewfinder shows a split moon. but the focus is spot on from 5.6 - 1.0.

 

that's why i was asking the question.

 

I have found this a problem as well - did you find a solution ?

 

Thanks

[JHAG]

I found the solution : DAG.

[badpets]

tuning the roller cam nearly drove me crazy, so i have given up finding the "perfect" solution. i have tuned the cam back to its factory position which i feel is best because it will let me use all my lenses again without serious focus shift. actually the factory setting makes all lenses quite spot on wide open (1.0 - 2.0); it only focus shifts when the speed steps down (2.0 - 16). so i figured out it's better to make a little mental adjustment than rendering some lenses completely unusable due to making a particular lens perfect by adjusting the cam.

 

i also did a little research on the web and found that RF technology can never be 100% precise anyways. some say SLR is precise, but i doubt about it too cuz i tried a canon SLR (such as EOS-1D) and it's not even sharp compared to leica m8's images despite its full frame sensor gives larger images.

 

anyway, it's my personal experience. i'd love to hear difference experience.

 

I have found this a problem as well - did you find a solution ?

 

Thanks

[badpets]

DAG doesn't travel around the world to answer all the questions. do you have his personal contact? can you give it to me?

 

I found the solution : DAG.

[markgay]

As backfocus problems manifested themselves during the digital era due to the tighter tolerance of digital sensors vs film...it's really a 'digital' issue, that must apply to all cameras.

 

What's the difference between rangefinders and autofocus DSLRs as regards backfocus. Where do we look for the weakness - lens construction, focus system, occular accommodation or pure sensor vs film tolerance?

[badpets]

very good point. to0 many variables. i think leica made it up by making excellent lenses.

 

As backfocus problems manifested themselves during the digital era due to the tighter tolerance of digital sensors vs film...it's really a 'digital' issue, that must apply to all cameras.

 

What's the difference between rangefinders and autofocus DSLRs as regards backfocus. Where do we look for the weakness - lens construction, focus system, occular accommodation or pure sensor vs film tolerance?

[wlaidlaw]

As backfocus problems manifested themselves during the digital era due to the tighter tolerance of digital sensors vs film...it's really a 'digital' issue, that must apply to all cameras.

 

What's the difference between rangefinders and autofocus DSLRs as regards backfocus. Where do we look for the weakness - lens construction, focus system, occular accommodation or pure sensor vs film tolerance?

 

Markgay,

 

SLR or DSLR lenses can be out of adjustment but the more likely problem with an SLR is that the focusing screen is not in the same focus plane as the imaging medium (for manual focus cameras) so that an image which looks sharp on the screen is not sharp on the imaging medium, film or sensor. This seems particularly to be a problem on those cameras where you can easily change the focusing screen like the Contax RTS series. If you keep taking the screen in and out, the register can vary quite a bit with I would guess, tiny particles of dirt getting between the screen and its housing or even wear.

 

With autofocus where the focus is detected in the camera body, the issue is essentially the same. the sharpness is wholly dependent upon the autofocus sensor/detector being exactly in the same focus plane as the imaging medium. In addition, the collimation of the focus detectors is, on better cameras, adjustable. The advantage of this system is that there are no mechanical moving parts and normally, unless the camera is dropped, once in good adjustment, such an autofocus system, will stay in adjustment. Where the focus is mechanically transmitted to the lens as for example in older Nikon AF lenses, wear may occur in this mechanism.

 

Finally of course if the focus detection system is in the lens, you can, just like a rangefinder, get a back focus issue, as what may seem sharp to the lens, is calculated for a different lens to imaging medium than is actually the case . Some of the Canon zoom telephoto lenses are well known to suffer from this issue.

 

Wilson

[pklein]

In addition to what Wilson discussed, add the effect of the anti-aliasing filter, or in the M8's case, the lack of it. An AA filter "chops off" the sharp focus peak of a really good lens, turning it into a broader zone of focus where everything is good enough, but not quite stellar. Exactly where the peak is, within this zone above which the AA filter cuts off, doesn't really matter.

 

With the M8, the sharp peak is still there, so if it is slightly off what you focused on, you notice it. So it's not so much the rangefinder that's at issue, it's a camera that is often used with very good, fast lenses and has no anti-aliasing filter.

 

To put it another way:

 

- "Good enough" next to "good enough" looks OK.

- "Good enough" next to "even better" means "good enough" may no longer look good enough.

- If you have "even better," it had better be exactly where you intended.

 

--Peter

[JHAG]

Don Goldberg did a real fine job on all my lenses, which are now spot on.

To me, tweaking the cam could do when just shooting one or two lenses.

Beyond, it's a no go.

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Look here: Leica M

[dalippe]

Recently I've started having back-focus problems on lenses that I believe to be correctly calibrated. As I'm going on vacation on Sunday and don't have time to have the RF properly fixed, I'm willing to give the DIY adjustment a try as a temporary fix. I've just tried gauging infinity focus on the moon, and I believe that with my 75mm lux set to infinity, I am just short of getting coincident images (although I'm not entirely convinced....I'll try to tomorrow to find a vertical on the horizon to test with).

 

My question: does this go in the right direction? In other words, would coming short of coincidence (rather than overshooting) lead to back-focus or front-focus? If the latter, perhaps I'll be able to convince myself I was actually seeing overshooting

 

Thanks.

 

David

[barjohn]

I'm not sure which direction gives you what; however, you really need a distant subject like the moon or a star. I find that even far distant objects don't seem to provide as good a reference.

 

Alternatively, I have used a close object and calibrated for focus being right on and then checked infinity against the moon or a star afterwards. This is easy to do if you use a ruler on a wall and stand off to an oblique angle and focus and shoot and adjust until the focus is correct then check infinity to make sure you didn't miss. Keep your adjustments really small. Good luck!