I did have a problem years ago with an East German 35mm SLR - the distance from the lens node to the focus screen was different than the distance from the node to the film plane. Easy to check - mount on tripod, focus at infinity, then pop the back open and check the focus with a piece of ground glass in the film plane. No adjustments so the repair was called new camera. Modern manufacturing tolerances and QC should eliminate this type of problem. Since the old eyes are not what they used to be, autofocus is a blessing.
Howard On Mar 30, 2012, at 9:05 AM, Dennis P wrote:
On Mar 30, 2012, at 5:03 AM, Peter Badcock wrote:Hi folks,I have just spent the past couple of months off and on re- calibrating the focus on my Mamiya C330f TLR. I finally succeeded but needed precision instruments/tools (vernier callipers +dial gauge) to do this to what I consider an acceptable precision.Due to the small tolerances required (usually better than 0.1mm), I can't help but think there are many cameras out there (both analog and digital) which are also not optimally calibrated either (for focus) due to being bumped, poor design or poor original manufacturing.My lens is an 80mm f2.8, but if you have say an f1.4 or lower aperture, your depth of focus will be really tiny (like <0.1mm if you use 120 film or smaller) and your system could easily get knocked out of alignment.What are your experiences with fixing focus issues and why aren't more people noticing these kind of problems.thanks PeterI think probably most people aren't experiencing any problems. If you are talking about your lens focus being less than 0.1mm off the film plane then that is probably beyond people's ability to focus accurately regardless whether the lens is that out of calibration. Also there is a small amount of film curvature or lack of flatness especially in 120 that is probably greater than the tolerance you are talking about.I know from experience with lots of tests with my Rolleiflexes that even taking off the WLF and focusing with a loupe on the focus screen it is very easy to miss focus by an inch or more from a distance of 10 feet. People often have the impression that those Rollei lenses aren't very sharp at 2.8 but I think a lot of it is the difficulty of focusing correctly enough for wide open. Once you stop the lens down a stop or two the small degree of miss focus is a moot point because the image looks sharp.I have noticed a couple of times the focus screen is off a bit with my Pentax 67 and I have corrected it by adjusting the tightness of the screws in the corners of the screen. I think the screen being off by half a mm is probably enough to make a person think the Pentax lenses just aren't that sharp, which is probably the conclusion most people come to with any system that has slight out of adjustment problems.Anyway that is my opinion. Dennis
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