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Sunday, 04 September 2022


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"Circle of Confusion?" That's been a major consideration throughout my life. Is it a photographic term as well?

Just a subjective comment out of left field about the emotional (not technical) importance of focus.

I recently found some 1979 negatives of the woman who had been my first grade teacher and who taught me how to read. About five or six years after I took the photograph she died of breast cancer. When I scanned the negatives, I found that I had missed critical focus on her face. But the picture is now precious to me, because with her gone, there will be no new photographs of her made. Of course, this is not an artistic concept more of an emotional response. But aren't our artistic choices about inducing an emotional response in the viewers of our pictures? In this case, it turns out that critical focus was not an important part of that emotional response

Hey, I love my Voigtländer APO-Lanthar 90mm f/3.5 SL (admittedly half a stop faster than f/4 ...) for being compact, sharp and close focussing!
Merklinger's explanation of the hinge line in lens tilt helped me tremendously using Nikon's 24 and 85 mm PC-E lenses.

The rule of thumb I learned with manual focus lenses was to assume that the depth of field scales were about two stops optimistic, e.g., you should set the aperture at f8 and use the f4 dof marks.
I’m finding the dof scales on autofocus lenses to be fairly useless. Often the only mark on the lens is ‘f32’. Determining a hyperfocal distance involves a lot of trial and error.
On my Canon R5, if you set the lens on manual focus, the display in the viewfinder shows a scale with the focus distance highlighted. How hard would it be to show the depth of field for your chosen f-stop with shading on the distance scale? It would sure make things a lot easier.

For those interested in a lot of technical stuff about photography, all in one place, check out the website "Cambridge in Color." Includes, among millions of other things, a DOF calculator.

I recently saw a wonderful exhibition of woodland pictures by Joe Cornish and Simon Baxter. Some of the prints were several feet wide. You could go in close and the detail was amazing. I wonder how many owners of their 50+ mp cameras make prints large enough to use that resolution and worry about dof to match. Not many I bet.

OK, you explained the title of this post. Are you going to explain "Thing One and Thing Two"?
I remember! And I'm 68.

[I honestly didn't even remember consciously. But...The Cat in the Hat. Makes sense. I'm of your generation. --Mike]

I have an app called DoF which shows all the relevant parameters of DoF as sliders. It hasn't really been all that helpful, but it shows in an obvious visual way the effect of changing any parameter, e.g., change the aperture and watch the field of focus change.

The German term Schärfentiefe, (sharpness depth), seems to be interchangeable with Tiefenschärfe, which gives some idea of how the parameters are interconnected. Well, to me, anyway.

I remember a feature of the original Canon Elan, whereby you auto-focussed (if that's a verb) on a near object followed by auto-focussing on a far object, then the camera would choose the appropriate focussing distance and aperture to take the final shot. This was years ago and I only used it once or twice so my description of the process is probably not accurate. With cameras loaded with computing power these days, you'd think they'd revive this, given that they have so many other dubious features.

Another feature that would be nice would be for the camera to "set" focussing distance permanently (until you turned it off). It's so easy to set a hyperfocal distance with a focus-by-wire lens in manual focus mode, only to inadvertently knock it off focus by brushing against the focus ring. Since it's focus by wire anywhere, it should be trivial to "freeze" focus distance.

And another thing. Why can't I set focus distance to infinity? I think some models of Olympus cameras do something like this for astrophotography, but it should be commonplace.

Cameras are loaded with computing power these days, let's use it for something useful and convenient.

Luke: Schärfentiefe and Tiefenschärfe are not interchangeable in German. No way. However, many people do confuse the two.

You got Schärfentiefe correctly translated. Tiefenschärfe is an "Unwort" and can not really be translated. Unless you think ice cream and cream ice is the same thing.

Small world department. Canada's DND had a few research sites around the country and I worked one summer at the one near Valcartier QC, north of Quebec City, in 1974. A friend here in town had a summer job at the one near Dartmouth about 10 years later and knew Harold there. I sent him this link. I met this fellow socially through the local Ottawa car rally scene and it turns out that he also knew Harold in the car rally world in Nova Scotia. My friend used to do some hobby photography and may own that book; he's looking for it.

Mr. Almqvist: Thanks for that.
But Zeiss use Tiefenschärfe on their website:


Maybe they mean something different. My German is such that I drove along the Mosel River for a couple of days before I figured out that Einbahnstrasse was not the name of a street, but a warning of One Way Street.

About circle of confusion. My friend, David Jacobson, analyzed lots of published DOF data from many manufacturers. Every one except Zeiss had about the same diameter circle on film. Zeiss used a slightly smaller one. If I remember correctly, these were 0.03 mm for most, with Zeiss using 0.025 mm. Of course, these are arbitrarily chosen numbers for all the reasons Mike enumerates about print size, photographer's intention, etc. etc.

Luke: Yes, you are correct. Zeiss use the term Tiefenschärfe on their website for scientific instruments. If they are correct is another matter. ;-)

On their consumer web site for Batis lenses https://www.zeiss.com/consumer-products/int/photography/batis/batis-2818.html, selecting the German version and using the search function, they say: "1 Ergebnisse für tiefenschärfe". They do, however show: "22 Ergebnisse für schärfentiefe".

The German language often uses long words made up of two or more simple words. The positioning of the parts in relation to oneanother is of significance for the meaning of the long word and there are rules governing this. Neither German nor English is my mother tongue so I better do not get into this subject.

You may find this interesting http://timmermann.tv/technik/schaerfentiefe.php

As the source of the comment that was apparently the proximate excuse for the welcome refresher on focus and DOF, I wanted to say: Thank You, Mike!

It wasn't that long ago that I was in the habit of walking city streets with a film rangefinder, hyperfocusing by feel. How quickly changes in subjects, styles and equipment, not to mention less shooting overall, can dull skills and affect one's mind-set (hopefully to be replaced by more relevant ones).

Re the side discussion on lens diffraction: I stumbled onto an article that is refreshingly focused (pun unintended) on goals and practicalities:


I'm now inspired to look for that deliberate TOP series on the basics of photography from a few years ago, and in particular on framing and perspective.

Again, Thank you, Mike (again)!

My search for "perspective" in the TOP archives actually turned up two articles by Ctein on diffraction, covering what it is and why we shouldn't worry about it, respectively.



Will nominate as a "small, high-quality f/4 lens" the lovely Olympus M.Zuiko 12-45/4. With today's excellent IBIS it allows handholding in light that would once have me grabbing for an f/1.4 somethingorother. No optical gotchas and nicely priced.

Wish to also note the not-small M.Zuiko 12-100/4, working proof a gaudy 8X zoom range isn't a necessarily a parlor trick, but can be a viable one-lens option for all kinds of pursuits.

The f/4 prime I have for m4/3 is, frankly, large.

Re the Ctein articles on diffraction:

As is often the case on TOP, the post is just the tip of the iceberg; there's arguably more value and entertainment in the ensuing conversation, so don't miss!

In essence, one of those finely written articles tells us that we needn't pay any attention to the other finely written article, which also strikes me as very TOP. ;)

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