I am looking to buy this lens soon and was wondering how sharp or unsharp my shots will be when using the DOF scale on this lens? Many of my other (non-Leica) lenses are off by 1/2 to 1 1/2 stops when using their scales, usually with the background being soft.

-- Steve Rasmussen (srasmuss@flash.net), June 02, 2001

Answers

The specification of depth of field is an arbitrary decision, based on average vision, average demands, and a particular print size.

What's really happening is that the image gets further and further out of focus as it drifts from the One True Plane of Focus, until finally you realize stuff isn't in focus anymore. That's, informally put, the end of depth of field.

Obviously you're pickier, or you make bigger prints than the standard is set for, or you're sitting too near the screen when showing slides, or you're looking too hard when it really doesn't matter :-) Whatever, but for you all depth of field scales are probably going to be off about the same amount.

-- Michael Darnton (mdarnton@hotmail.com), June 02, 2001.

I have always found that the DOF scales on lenses in general are--how to put it delicately? optimistic. So, I always use the scale at least at the next widest aperture.

-- Jay (infinitydt@aol.com), June 03, 2001.

As usual, Jay makes a good point. The DOF scale seems based on the assumption that DOF is equal in front and in back of the plane of focus and we know this not to be true. There is frequently more DOF beyond the plane of focus than in front. It is almost never 50/50.

Take Jay's advice. Go to the next f stop on the scale or, I think better, decide what you want in focus and choose the appropriate f stop that way.

One of the great street shooters once said that he left the lens on the 10 foot setting for 90% of his shots. This took him to infinity as well most of the time and focus was not as important as not missing the image.

Just musings.

Bob

-- Robert Burgess (bobburgess@earthlink.net), June 03, 2001.

After reading the above post, I rechecked a few lenses. Actually, my Leica lenses do reflect the greater DOF beyond the point of focus, compared to in front of it. The 50mm tabbed Summicron shows DOF from around 15' to infinity, and on the near side, to eight feet, at f/16. The same lens gives ten to 25 feet, vs. ten to six feet on the near side. So we have 15 feet out, but only four feet in. The 1969- 79 Cron shows the same thing. My old collapsible Cron gives 10 feet to 25, but on the near side, about six and a half feet to ten. 35mm Summicron, at f/16, six feet to 25, vs. 3'4" on the near side. Oddly, the 35 Lux gives closer to eight feet to infinity, plus just under four feet (maybe 3'9") to the focus mark. Obviously the same criteria were not used. I never thought to check this until the subject came up tonight.

I agree with those who say to stop down one more stop than the scales require. I project slides on a large, wide screen (I'm sort of an Ultra-Panavision/Imax wannabe). Of course, if extra stopping down for DOF brings the shutter speed so low that camera shake becomes more of a sharpness-limiting issue than DOF, then I go with the DOF scale, or even fudge a bit on DOF.

-- Bob Fleischman (RFXMAIL@prodigy.net), June 04, 2001.

Thanks, Bob. I never took the time to do such a complete check on the actual marks, not being one who uses them much.

It is good to know that Leica is looking out for us.

Regards,

Bob

-- Robert Burgess (bobburgess@earthlink.net), June 04, 2001.

Depth of field scales are based on an "acceptable" degree of unsharpness. Only one distance is really accurately focussed. The criterion is pretty much wishfull thinking, based on relatively unsharp films of the 1930's. There is some interesting info on focussing in the following web site of Harold Merklinger. http://fox.nstn.ca/~hmmerk/

I don't use his method, but in practice what I do is similar to what he recommends. If I want to focus a scene where important subjects are at different distances, I use a more stringent criterion for the long distances than the near distances. For example, if my aperture is f8, using the depth of field marks on the lens barrel I set my largest distance against the f4 mark, and the short distance against the f8 mark. Merklinger's reasoning is that you need more detail in the distance. It has worked for me.

-- john stockdale (jjss@bigpond.net.au), June 05, 2001.