There are other ways of doing this, of course, such as carrying or memorising DOF tables (Google for DOFMaster), or using smartphone apps (whatever they might be)

Asking one of our esteemed moderators if it were possible to copy the thread across, I was told not, but it was suggested I might write something myself (

*yeah, thanks,*...)

**bruv**I'm not going to go into the ins-and-outs of hyperfocal distance and optical equations, because we can Google for that, or even read about it in a book (a paper one I mean), plus I'm certainly not qualified ... so “What is hyperfocal distance and why should I care what it is?” is a subject for another thread.

Right.

The gist of the idea is that, by remembering a few simple numbers and being able to perform some basic mental arithmetic, we can rapidly work out what the hyperfocal distance is for any lens focal length and f/stop combination.

I latched onto this because 1) my memory is a bit shot 2) I can't memorise all the hyperfocal distances for the few manual primes I use at all the f/stops and 3) I'm a bit of a sad sack

So ... it works like this:

For each focal length lens you use, there is a “K” number associated with it. (“K” is a conventional notation, it has no intrinsic meaning). The “K” number changes between camera formats, by the way, so the “K” number for a lens on a micro4/3 camera will be different from the “K” number of a lens with the same focal length, but used on a camera with a different sized sensor, such as APS-C or “full-frame”.

We can use this “K” number as the basis for doing a quick sum to establish hyperfocal distance in the field (or, indeed, the street), so long as we also know what f/stop we're using. As there's one “K” number per lens, it's a bit easier to memorise than a set of DOF tables. Probably.

As I'm a micro4/3 user, I'll work in micro4/3 numbers ... I'll explain about different sensor sizes later ... and let's forget zooms. And let's forget engraved DOF scales (because then all you have to do is set the infinity mark at twice the f/stop you're using and Robert's your Father's brother)

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