M8 backfocus

[KJB]

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You guys do understand that a lenses DOF is not symmetrical don't you? A rough rule of thumb is that 2/5 of the field of focus will be in front of whatever is at critical focus, and 3/5 will be behind that point. Its a fundamental rule of critical focus, and something we use in cinematography all the time. This means that focus will "fall off" faster in front of your mark, and 'fall off' less behind it. For whatever reason most stills guys never no this.

 

What this means is it's very easy to look at a photo and assume that the focus is off, based on the fact the the DOF is lopsided. When in fact this is an optical principle critical to the creation of DOF. Looking at all the examples posted here, it looks to me that this is actually what your seeing, and not miss calibration.

 

this is an excellent yet out of print book that covers all the nerdery of optics in a great degree:

Amazon.com: Optics and Focus for Camera Assistants, Art, Science and Zen: Books: Fritz Hershey

 

use this calculator to get an idea about what I'm talking about: Online Depth of Field Calculator

 

_mike

 

Talking subject out of focus, not lopsided. I would be perfectly happy with lopsided especially slightly to the front.

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[arthury]

I am not sure if the 45 deg test is workable for a longer lens such as the 90mm APO Asph Summicron-M. It is close to impossible to get the 45 deg right on a tripod at the closest focusing distance. I think that chart needs to be enlarged for a longer lens, too.

 

For this challenging lens, I would rather stick a newspaper flat on the wall and sit the camera 90 degrees to the wall, focus and shoot.

It should be sharp across; especially the center, where the focusing rectangle dot is located. Make sure the newspaper is perfectly flat.

 

For the fun side of things, here's one shot on tripod with the SF-20 on my M8 ... at f2.8.

 

Obviously, in a shooting environment, I think it's foolhardy to shoot at f2 in low light situation using this lens without tripod or support unless you can control your pulse or you bump up the ISO to near the max or the max. If that's so, you've lost quite a bit resoultion due to noise or your need to reduce noise.

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[pelikan1931]

is the M8 supposed to be fully tuned before getting into the market? or is it lens dependent, if so, does it mean that I have to send the camera+lens to Solms whenever I change lens?

 

or is it just particular to M8, because never heard of any complaints relating to M7/MP.

[khanosu]

The reason why you are hearing more complaints related to M8 compared to M7/MP probably is because M8 is digital and everyone can easily look at their images at a huge magnification of 26in by 39in (assuming 100 pixels/inch) on their monitors. At these huge magnifications even small inaccuracies in focus become magnified and readily apparent. I bet that if M7/MP owners routinely made 26in by 39in prints then they would be complaining as much as M8 owners.

 

Furrukh

[rvaubel]

The reason why you are hearing more complaints related to M8 compared to M7/MP probably is because M8 is digital and everyone can easily look at their images at a huge magnification of 26in by 39in (assuming 100 pixels/inch) on their monitors. At these huge magnifications even small inaccuracies in focus become magnified and readily apparent. I bet that if M7/MP owners routinely made 26in by 39in prints then they would be complaining as much as M8 owners.

 

Furrukh

 

Furrukh

 

This is so true. I am a bit compulsive about checking camera/lenses for backfocus problems. It is so much easier to do this check with a digital camera than a film camera. When I first got my RD1, I checked the rangefinder mechanism because of all the problems that I had read about. Well in the process, I find that about half of my lenses had focus problems that I never knew about. In fact, it turned out that a lot of my "favorite" lenses were the ones that were calibrated correctly. It made me wonder if proper lens calibration is the most important characteristic of a lens!

 

Poor Leica is now really under a microscope. And as a group, Leica owners are more likely to scrutinize every element of their camera more than other brands. Actually, now that I know what I know I have been subjecting my Canon 20D and its lenses to the same level of scrutiny.

 

Rex

[pelikan1931]

in my test for lens on R-D1s, I used to use bracket focus, ie I will take several shots, at front and back focus plane, as well the focus plane as indicated by the patch, because there are so many variables, I now know the patch can be as unreliable as the those green light in the autofucs machine.

 

perfection is such a difficult thing to achieve...

[lct]

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...the patch can be as unreliable as the those green light in the autofucs machine...

Not my experience i must say.

With a well aligned RF the patch is reliable fortunately.

[carstenw]

I just looked up the near setting. It looks a little more compicated than you would want to play with on your own. Incidentally, there was a distance setting gauge that went into the lens mount for setting up the rangefinder. This gauge had .7 meter, 1 meter and ten meter settings. The jig the camera went into had a target at a distance with reticles to focus on. There were three different reticles on the target, probably to simulate the 10m, .7m and 1m. mark. The Jig also had a magnifying eyepice to assure accurate focusing. The procedure was to set the 10m using the large roller then the distance setting plug is put in the 1m setting and a different graticle is used on the target. The near focus adjustment is then changed to align the graticle, 10m then checked again and the adjustments are made on both distances until a consistent focus is attained. Finally, the .7m is tested and the process of balancing the near with the far is started again.

 

Rob, how much of the complexity of this adjustment is due to the desire to nail it roughly the first time on Leica's behalf? In other words, given the willingness to use trial-and-error, does it sound reasonable to attempt it at home? Btw, how many pages of description and images are there in your book?